Final Report Summary - TRISOFC (Durable Solid Oxide Fuel Cell Tri-generation System for Low Carbon Buildings)
Executive Summary:
The project aims to develop a low temperature solid oxide fuel cell (LT-SOFC) tri-generation system for low carbon buildings.
The LT_SOFC will waste up to a half of the primary energy supplied as heat, and so by exploiting the waste heat for domestic heating and cooling (tri-generation) will improve the performance of the fuel cell in comparison to conventional SOFCs and increase its commercial value. The project integrates a LT-SOFC with a fibre membrane liquid desiccant dehumidification and cooling system to enable the system to produce electricity, heat and cooling.
The consortium has made significant advances in materials technology that will contribute to improved SOFC performance and other conversion technologies such as solar photovoltaics. Power density of almost 800mW/cm2 at 550C and improved performance over conventional FCs at 550C.
The LT-SOFC cell and stack design as well as of the entire generator system for a low cost application has been optimised.
Design of a complete SOFC power system capable of meeting the varying power demands of a low carbon building over a comfortable life space has been achieved.
A 2-cell 6cm x 6cm planar-type SOFC produced around 12W at 530C and in the best case we produced over 2.0 OCV and generated nearly 20W.
Good repeatable single cell performance was achieved at 1.1OCV and 9W at 540C.
Work was carried out investigating thin membrane stacks (~0.5mm thickness) and results showed output of over 2.0 OCV and 18W.
100W stack has been developed with 15 6cm x 6cm membranes in a stack, producing 100W and 12.0OCV at 550C.
Improvement of materials and design for membrane desiccant technology:
The consortium has developed two types of membrane desiccant systems; a combined desiccant and cooling system and a separate desiccant and cooling system. It was found that the combined system was more difficult to optimise as the three parts could not be operated independently, and the complexity of the arrangement caused some leakage to both the supply air stream and to the surroundings of the unit.
Integration of LT-SOFC and desiccant components into an application under challenging constraints including system efficiency, lifetime and cost targets to meet market requirement;
The consortium has successfully proved the concept of a SOFC tri-generation system using a conventional (micro-tubular) SOFC. Delays in development of the LT-SOFC stack meant that the consortium could not deliver a 1-1.5kWe LT-SOFC within the project timeline.
System testing both in the lab and in field-trials under real-life context to improve the whole-system design and the understanding of degradation mechanisms of LT-SOFC stacks.
The consortium has demonstrated performance in the lab and in field trials under real-life context.
An environmental assessment has shown that the LT-SOFC tri-generation system is environmentally advantageous in terms of reducing carbon emissions based on a range of environments. In a UK energy system context the tri-generation system generates up
to 51% annual CO2 emission reductions compared to the base case. The system was only environmentally unsuitable in France and Norway, which contained substantial nuclear and renewable energy supplies.
An economic assessment concluded that at current costs, only a small number of countries would benefit from the installation of a LT-SOFC system. However, component parts, such as LT-SOFC single component technology, membrane separation and open cycle cooling, balance of plant, control and monitoring systems could all be marketed independently of the overall system.
Project Context and Objectives:
Summary description of project context and objectives
Due to the increasing concern over the provision of future energy and global warming, there is a significant interest in the development of alternative clean energy sources and efficient power generators. According to the World Business Council for Sustainable Development, buildings consume 40% of the world’s primary energy using for cooling, heat and power, and most of it is from electricity generated at centralised power stations, where at present up to 70% of available energy is lost. The overall system efficiency is low leading to high waste of energy resources resulting in considerable CO2 emissions and unnecessarily high running costs. Reducing the energy consumption of buildings can make a substantial contribution towards attaining the European Union’s 20/20/20 targets and at least 80% reduction in its carbon dioxide emissions in 2050. But this will only be achieved by moving from conventional centralised power generation systems to onsite highly-efficient clean micro-generation technology.
One of the more promising possibilities for this future energy generation is the solid oxide fuel cell (SOFC), which uses the hydrogen from the gas stream to generate electricity through chemical reactions in the anodes, and the only by-product is water vapour and a modest amount of carbon dioxide. This is more efficient than simply combusting the fuel. The technical assessment demonstrated that if the CHP (combined heat and power) technology is used with SOFC, the total system efficiency can be as high as 90%. CFCL (Ceramic Fuel Cell Ltd, Australia) reported that the SOFC residential market is 17,000 kW per year, thus a big market potential. Even a moderate size city such as Stockholm has a plan to construct green residences incorporating 6000 units (5 kW) fuel cell CHP units.
Unfortunately, although the technical assessment for the SOFC micro-generation system shows a promising future for high energy efficiency with a potential big market, the durability and lifetime of the SOFC system has yet to be solved. These problems arise from fuels, such as natural gas (methane), the widely available fuel in residential buildings, also containing sulfur. Sulfur poisoning and carbon deposition from methane are two major issues inhibiting application of conventional SOFCs with Ni-YSZ (yttrium stabilized zirconia) as anodes. High operating temperature is a further considerable challenge. To achieve a better performance, the conventional SOFCs using YSZ are usually operated around 1000 ºC, but this can only be achieved at technical complexity and consequently cost that inhibits commercialization. A breakthrough on low temperature SOFC (LT-SOFC) materials has been made by the applicant in KTH, based on ceria-carbonate two- or multi-phase nanocomposite, showing an excellent tolerance to the sulphur poisoning and carbon deposition, reaching a high power density of 1.2 W/cm2 at temperature as low as 500 °C. Furthermore, the invented materials have provided feasibility for manufacturing LT-SOFC stacks below 400 €/kWe, compared to more than 1000 €/kWe of the conventional SOFC stacks. Some of these exciting research achievements were recently highlighted by Materials Views and Nature Nanotechnology.
Desiccant system, in the context of HVAC (Heating, Ventilation, and Air Conditioning) applications of indoor environmental comfort, are used primarily where simultaneous maintenance of temperature and humidity control is an important benefit to the user. This technology is often used in tri-generation, also called CCHP (combined cooling, heat and power), where the desiccant system is driven by the heat by-product. If the waste heat from SOFCs is used to drive the desiccant unit, then a tri-generation system will result, supplying not only the power and heat as the conventional CHP technology to the buildings, but also cooling and humidity controlling. According to the extensive work carried out by applicant in NOTT, this desiccant unit could increase the total system efficiency by 13-16%. So, the overall aim of this project is to develop a low-cost durable LT-SOFC tri-generation prototype, based on the breakthroughs in LT-SOFC and the desiccant technologies already made by applicants involved in this project. The proposed system could be used for residential and commercial buildings (e.g. school buildings/offices), providing cooling, heat and power for the living space. It will be tested under real-life context using a unique zero-carbon modular home as part of the Creative Energy Homes at the University of Nottingham. The environmental sustainability of the prototype will be assessed by means of Life Cycle Assessments studies, and the result obtained will be disseminated to industry and research as proof-of-concept of fuel cell systems for stationary applications for sustainable low carbon buildings.
Despite SOFC technology lagging PEMFC and MCFC by a number of years it presents a significant opportunity for many applications, including buildings, due to its fuel flexibility. More stimulus is needed to advance SOFC technology, particularly in Europe, and a low carbon building application will provide this. TriSOFC aims to define, develop and deliver LT-SOFC tri-generation technology in low carbon buildings for early market application. The project will be carried out as an integration of material, nanotechnology, device fabrications and stack, unit constructions to system integrations, field-trials and public demonstration joining closely to the marketing explorations.
TriSOFC aims to design, optimise and build a 1.5 kW low-cost durable LT-SOFC tri-generation prototype, based on the integration of a novel LT-SOFC stack and a desiccant unit. Additional components of the system are a fuel processor to generate reformate gas when natural gas utilized as fuel and other equipment for the electrical, mechanical and control balance of plant (BoP). All these components will be constituents of an entire fuel cell tri-generation prototype system to supply cooling, heat and power, which will first be tested in the lab and, after further optimisation and miniaturisation, under real-life context in the Creative Energy Homes platform built at the University of Nottingham. TriSOFC is primarily aiming at the low carbon building platform using natural gas but will also integrate with other available resources (e.g. alcohol, propane, renewable biomass liquid fuel and biodiesel) with simple modifications. Natural gas was chosen as the fuel due to its widely availability in current residential and commercial buildings compared to hydrogen and other fuel resources. Other renewable fuels will also widely suitable for North European regions, e.g. fuels made from biomass resources. The design of the tri-generation system will be primarily driven by the high efficiency, low-cost and long–term duration. It will open opportunities for exploitation in other sustainable low carbon applications.
Project objectives of the period
The main technical objectives of the period are listed below:
• Improvement of materials for LT-SOFC technology with respect to power density and minimising degradation of cell performance;
• Optimisation of LT-SOFC cell and stack design as well as of the entire generator system for a low cost application; Design of a complete SOFC power system (i.e. including balance of plant and control system) capable of meeting the varying power demands of a low carbon building over a comfortable life space;
• Improvement of materials and design for membrane desiccant technology;
• Integration of LT-SOFC and desiccant components into an application under challenging constraints including system efficiency, lifetime and cost targets to meet market requirement;
• System testing both in the lab and in field-trials under real-life context to improve the whole-system design and the understanding of degradation mechanisms of LT-SOFC stacks.
• Environmental sustainability assessment by Life Cycle Assessments studies carried out according to the International Life Cycle Data System (ILCD) handbook requirements;
• Evaluate the prototype system to international standards and finish the risk assessment, defining the requirements in the applications in sustainable buildings and developing recommended practice for the tri-generation concept.
• Economic assessment and investigation of spin-off opportunities into other market sectors, especially residential building applications;
• Dissemination of information to industry and research via a regularly updated website as well as publications and presentations at relevant conferences;
• Development of exploitation routes for bringing the new technology to market;
• Strengthening of the European position in this technological field.
Achievements of the period
• Improvement of materials for LT-SOFC technology with respect to power density and minimising degradation of cell performance;
The consortium has made significant advances in materials technology that will contribute to improved SOFC performance and other conversion technologies such as solar photovoltaics. Power density of almost 800mW/cm2 at 550C and improved performance over conventional FCs at 550C.
• Optimisation of LT-SOFC cell and stack design as well as of the entire generator system for a low cost application; Design of a complete SOFC power system (i.e. including balance of plant and control system) capable of meeting the varying power demands of a low carbon building over a comfortable life space;
A 2-cell 6cm x 6cm planar-type SOFC produced around 12W at 530C and in the best case we produced over 2.0 OCV and generated nearly 20W.
Good repeatable single cell performance was achieved at 1.1OCV and 9W at 540C.
Work was carried out investigating thin membrane stacks (~0.5mm thickness) and results showed output of over 2.0 OCV and 18W.
100W stack has been developed with 15 6cm x 6cm membranes in a stack, producing 100W and 12.0OCV at 550C.
• Improvement of materials and design for membrane desiccant technology;
The consortium has developed two types of membrane desiccant systems; a combined desiccant and cooling system and a separate desiccant and cooling system. It was found that the combined system was more difficult to optimise as the three parts could not be operated independently, and the complexity of the arrangement caused some leakage to both the supply air stream and to the surroundings of the unit.
• Integration of LT-SOFC and desiccant components into an application under challenging constraints including system efficiency, lifetime and cost targets to meet market requirement;
The consortium has successfully proved the concept of a SOFC tri-generation system using a conventional SOFC. Delays in development of the LT-SOFC stack meant that the consortium could not deliver a 1-1.5kWe LT-SOFC within the project timeline.
• System testing both in the lab and in field-trials under real-life context to improve the whole-system design and the understanding of degradation mechanisms of LT-SOFC stacks.
The consortium has demonstrated performance in the lab and in field trials under real-life context.
• Environmental sustainability assessment by Life Cycle Assessments studies carried out according to the International Life Cycle Data System (ILCD) handbook requirements;
The consortium has shown that the LT-SOFC tri-generation system is environmentally advantageous in terms of reducing carbon emissions based on a range of environments from UK, Portuguese and Hong Kong climates.
• Evaluate the prototype system to international standards and finish the risk assessment, defining the requirements in the applications in sustainable buildings and developing recommended practice for the tri-generation concept.
The risk assessment and international standards evaluations have shown that the market for the LT-SOFC tri-generation system is wide and highlighted factors that needed to be considered in order to commercialise the system, which include reductions in first cost, major improvements in reliability and durability as well as evaluating incentives (feed-in tariffs, subsidies, etc) for the take-up of renewable and low carbon technologies.
• Economic assessment and investigation of spin-off opportunities into other market sectors, especially residential building applications;
The economic assessment concluded that at current costs, only a small number of countries would benefit from the installation of a LT-SOFC system. However, component parts, such as LT-SOFC single component technology, membrane separation and open cycle cooling, balance of plant, control and monitoring systems could all be marketed independently of the overall system.
• Dissemination of information to industry and research via a regularly updated website as well as publications and presentations at relevant conferences;
A website has been set up since the beginning of the project and is regularly updated with information and news. The consortium is engaged in many scientific, engineering, business and industrial activities and has published over 100 journal and conference papers.
• Development of exploitation routes for bringing the new technology to market;
The consortium has engaged with the fuel cell and hydrogen community to understand better the current market and future trends. Ibrahim Pamuk of Vestel Industries is leading efforts to engage with businesses in the power generation and domestic/commercial building industries
• Strengthening of the European position in this technological field.
The major breakthroughs in nano-scale composite materials development will put the European Union at the forefront of technological development, not only in terms of SOFC technology but other conversion technologies.
Description of S & T results/foregrounds
Work packages and tasks of the period
WP1 Project management and co-ordination
WP2 Desiccant unit development
WT2.1 Heat and mass transfer
WT2.2 Working fluid and membrane evaluation
WT2.3 Heating/cooling unit design and test
WT2.4 Heat storage investigation
WP3 LT-SOFC component and single cell fabrication
WT3.1 Material engineering and production
WT3.2 Cell component/MEA development
WT3.3 MEA and single cell fabrication
Task 3.4: Scale up
Task 3.5: Testing and evaluation
Task 3.6: Development of carbonate free nanocomposite cell:
WP4 LT SOFC stack development
WT4.1 Stack construction and development
Task 4.2: Flat-tubular/group type stack
Task 4.3: Planar type stack
Task 4.4: Micro-tubular type stack:
WT4.5 Modelling
Task 4.6: Testing and evaluation
WP5 Tri-generation system integration
WT5.1 Reformer development for natural gas and bio-fuel
WT5.2 Thermal management system
WT5.3 Power management system
WT5.4 Electronic control system
WT5.5 Tri-generation system design
WP6 Prototype system testing
WT6.1 Laboratory test of the components
WT6.2 Assemble of the prototype
WT6.3 Testing and modification of the prototype
WT6.4 Analysis of the testing results
WP7 Field trials of the prototype system
WT7.1 Prototype system installation and commission
WT7.2 Prototype system testing under real-life context
WT7.3 Thermal management analysis
WP8 Economic and environmental assessments
WT8.1 International standard evaluation
WT8.2 Economic evaluation
WT8.3 Environmental sustainability assessment
WT8.4 Risk assessment
WP9 Dissemination activities
WT9.1 project website
WT9.2 Dissemination activities
The deliverables for the period
D2.1 Working fluid and membrane evaluation
D2.2 Desiccant cooling/heating unit
D2.3 Desiccant heat storage unit
D3.1 LT-SOFC material and production report
D3.2 Component, MEA and single cell fabrication
D3.3 Progress report of on carbonate free nanocomposite fuel cell testing
D3.4 Report on performance and durability of carbonate free fuel cell
D4.1 Device construction report
D4.2 Report planar stack
D4.3 Report on micro-tubular type stack
D4.4 Carbonate free Device/stack modelling and performance testing results
D5.1 Reformer development report
D5.2 Thermal management system
D5.3 Power management system
D5.4 Electronic control system
D5.5 Tri-generation system design report
D6.1 Main component pro-testing results
D6.2 Prototype detail construction data
D6.3 Prototype testing and evaluation report
D7.1 Prototype installation and commission report
D7.2 Prototype testing and analysis results
D7.3 Prototype demonstration
D8.1 International standard evaluation report
D8.2 Economic assessment results
D8.3 Environmental assessment results
D8.4 Risk assessment report
D9.1 Project website
D9.2 Dissemination activity reports
Project Results:
Modifications to the original DoW were requested to take account of one partner withdrawing from the project due to bankruptcy and technical challenges in developing single component materials and stacks within the framework of the project. A summary of the amendments requested and granted is provided below:
Modification 1: The consortium proposes that some funds are transferred from KTH budget to UBHAM budget to enable them to carry out tri-generation systems integration (WP5) and prototype systems testing (WP6). The plan is to buy a SOFC suitable for tri-generation integration and testing with the funds and enable the UBHAM partners to contribute to its development. In the original DoW, UBHAM played a minor role in WP5, but with the abandoning of plans to develop microtubular stacks, the personnel will contribute more time and resources in these work packages. We propose that 8,550Euro is transferred from KTH to UBHAM direct costs budget to enable them to fund the acquisition of an off the shelf fuel cell and ancillary equipment required to set up the system, as suggested in the mid-term review report.
Modification 2: The original DoW allocated 17 person months to prototype systems testing, but the consortium does not intend to request an extension to the project and so we request that some of the person months are re-allocated to WP3 and WP4, so that UBHAM can continue to investigate the application of carbonate free nanocomposite materials in microtubular fuel cells. If we can show a breakthrough in materials development and processing in this particular application then the consortium will have achieved a significant outcome and the application of the single component system will have much wider potential. We request that the personnel allocation of 17 months in WP6 should be reduced to 11PMs, with the remainder increasing allocation to 12PMs in WP3 and 12PMs in WP4. An additional work task has been added to the DoW, WT3.6 to enable us to develop the single later nanocomposite materials and membranes, and two further deliverables are proposed, D3.3 “Progress report of on carbonate free nanocomposite fuel cell testing” and D3.4 “Report on performance and durability of carbonate free single cell”. D3.3 will become a stop/go point in the project and if no progress is made then the project officer will be able to terminate the contract.
Modification 3: KTH do not have the capability to mass produce materials and manufacture large scale planar-type membranes, so we propose that some of the person months allocated to KTH should be reallocated to UBHAM, to enable them to carry out more work that was set out in the original DoW. In the first amendment, the personnel allocation for KTH was increased from 40PMs to 69.5PMs when all tasks were reallocated from GETT to KTH. As KTH are unable to carry out some of these tasks, we propose that KTH personnel allocation is reduced from 69.5PMs to 63.5PMs. In parallel, UBHAM personnel allocation will be increased from 42PMs to 48PMs.
Modification 4: The original target for the development of a 1-layer LT-SOFC was for 1-1.5kWe but delays in the work plan have meant that this outcome is unlikely to be successfully realised. The consortium is proposing that to meet realistic objectives within the timeline, we ‘prove the concept’ by building a small planar LT-SOFC fuel cell stack. An additional deliverable D4.4 “Carbonate free Device/stack modelling and performance testing results” has been added to the DoW.
Modification 5: The development of a LT-SOFC tri-generation system requires the development of a LT-SOFC stack, but the stack will require a great deal of research and development to reach the point of integration with other systems. Therefore, we propose to obtain a conventional SOFC that is capable of tri-generation capability. The mid-term review report recommended that the consortium purchase an off-the-shelf SOFC to enable us to carry out prototype development, integration and field trials. One unit has been identified as a 200We/1kWh SOFC manufactured by Adelan Ltd, UK. We propose that some of the resources re-allocated to UBHAM and resources available to NOTT will be used to purchase the unit, as recommended in the mid-term review report. The plan is for the unit to be installed and set up in UBHAM laboratories and its performance monitored for up to 100hours. NOTT and UBHAM will collaborate to develop the CHP/tri-generation system. On completion of fuel cell performance testing, the system will be transported to NOTT to be integrated in the tri-generation system. The system will then be monitored over a range of operating conditions at NOTT. The total cost of the unit is estimated to be around 13K Euro, and the costs will be split approximately 60:40 between NOTT and UBHAM.
Modification 6: It will not be possible within the timeframe of the project to carry out field trials with either the LT-SOFC stack or the integrated SOFC highlighted in Amendment 6, so we propose to install the tri-generation system in one of the creative energy houses at NOTT. Field trials will be carried out over about 6 months and should be concluded by month 36 of the project.
Modification 7: Following the recommendations of the mid-term review we have amended the DoW part B to include an exploitation plan and engagement strategy with the European and World-wide fuel cell and hydrogen community. Please refer to the document for further details.
Modification 8: IDMEC ceased to exist after 31st December 2015 and it was merged (personnel, equipment, installations) with the existing INEGI. From this date on, all rights and obligations of IDMEC in this project will be transferred to INEGI. The amendment requests that IDMEC is terminated from the consortium and that INEGI is added to the consortium as a beneficiary.
Work Package 2: Desiccant unit development
D2.1. Working fluid and membrane evaluation
Introduction
Up to a half of all energy consumption and up to a third of carbon dioxide emissions in the developed world are from buildings and almost a half of this is due to heating in winter in cold climates and cooling in summer in hot and humid climates. A combination of energy efficiency measures within buildings and efficient building services systems could dramatically reduce energy consumption and carbon dioxide emissions in the building sector. Combined heat and power (CHP) and combined cooling, heating and power (CCHP), also known as Trigeneration, could reduce carbon dioxide emissions in domestic and non-domestic buildings by exploiting waste heat for heating in winter and cooling in summer, improving the overall efficiency of the power generation system, replacing conventional heating and cooling plant and more fully utilising the waste heat.
The low temperature solid oxide fuel cell being developed through this project, wastes up to a half of the primary energy supplied as heat, and so the exploitation of this heat will improve the performance of the fuel cell in comparison to conventional solid oxide fuel cells.
Waste heat can be stored sensibly in conventional tanks as hot water, stored as latent heat using ice or other phase change materials (PCMs), or chemically, as binary systems that absorb or desorb the heat of absorption/desorption. Partner 4 is carrying out analysis of the options for storing the waste heat from the fuel cell.
Modelling work is an essential task for the design, building, testing and optimisation of the liquid desiccant air conditioning unit for the TriSOFC system. Modelling work has been used to identify the important operating parameters of the desiccant unit, to facilitate optimisation, to predict the performance of the unit under variable conditions and to assist in sizing of a unit suitable for the application. Two stages of modelling work have been conducted for the desiccant unit. A preliminary 1-D model was used to obtain initial estimates and to select a suitable working fluid, then a more comprehensive 2-D model was developed for specific unit sizing and fabrication.
One-dimensional modelling
Preliminary modelling work has been carried out for the desiccant dehumidification system. The performance of a desiccant air conditioning system is strongly related to the quantity of water condensed from the humid air to the desiccant solution in the dehumidifier. In the literature there are numerous validated models predicting this quantity, however it should be stated that the majority of these correlations are only valid to the specific desiccant unit and solutions for which the correlations were obtained. Therefore, a simplified model to estimate the preliminary performance of the novel cellulose fibre packed bed system based on fundamental equations would be valuable at this stage of modelling work.
The preliminary modelling task has called upon the work of (Gandhidasan 2004; Gandhidasan 2005). Gandhidasan describes a relatively simple model for the preliminary design of a liquid desiccant air conditioning system, using dimensionless vapour pressure and temperature difference ratios. These ratios are used to derive an expression to determine the mass of water vapour condensed from the air to the solution in the liquid desiccant dehumidifier shown and for the mass of water vaporised from the desiccant solution to the scavenging air stream in the regenerator, both in terms of known operating parameters. The model has been validated by well-regarded experimental data presented in the literature provided by Fumo and Goswami (2002) with very good agreement.
Basic working principle
In the dehumidifier mass transfer (dehumidification) occurs due to differences in vapour pressures. The cool concentrated desiccant solution exhibits a vapour pressure which is lower than that of the water vapour present in the humid air, therefore the moisture moves from the air to the solution. In addition to this in summer it is expected that the temperature of the humid air that enters the desiccant dehumidifier is higher than the desiccant solution temperature, therefore sensible heat transfer will also occur. The greater the cooling of the desiccant solution prior to entering the dehumidifier, the greater the heat and mass transfer, and thus the greater cooling output. Following dehumidification, the weak desiccant solutions needs to be regenerated i.e. re-concentrated. This takes place in the regenerator. Prior to entering the regenerator the desiccant is heated first in the desiccant to desiccant heat exchanger (also used to pre-cool the desiccant flowing to the dehumidifier), then using an external source e.g. the fuel cell. In the regenerator, the heated weak desiccant solution will have a vapour pressure higher than that of the scavenging air stream, thus the water vapour present in the solution will transfer to this air stream, thus re-concentrating the desiccant solution ready for dehumidification in the dehumidifier.
The modelling work was carried out using Engineering Equation Solver (EES), a general equation solving program that can numerically solve thousands of coupled non-linear algebraic and differential equations. Air and water property routines are inbuilt functions in EES, making calculations involving psychrometric functions much easier. Once the model had been developed, and adjusted such that the output results were in good agreement with the experimental and theoretical results presented by Gandhidasan (2004) and Fumo, parametric analyses were carried out. Parametric analysis for the dehumidifier and regenerator has looked at the variation of mass condensed/evaporated in the dehumidifier/regenerator respectively with:
• Cooling water temperature
• Regeneration temperature
• Fluid flow rates (air and desiccant)
• Fluid flow rate ratios
• Heat exchanger effectiveness
• Different desiccant solutions – LiCl, CaCl2 and CHKO2
Furthermore a parametric analysis of the inlet operating conditions of the desiccant unit was investigated; this was to see the effect environmental conditions had on performance. In this analysis, the following were assessed in terms of cooling output:
• Air inlet temperature
• Air inlet relative humidity
The parametric analysis has been used to identify the parameters that have the greatest influence on performance. It has also shown the optimum environmental conditions for which the system should be operated in. The initial stage of preliminary modelling results is split into two sections: dehumidifier and regenerator.
Summary of initial modelling results
The moisture removal rate of the process supply air is strongly controlled - assuming constant mass flow rate, by desiccant temperature and cooling water temperature. The air inlet conditions have a large influence on performance in terms of cooling output. The unit will generally perform better in a hot and more humid climate such as southern China, or the Middle East as opposed to drier cooler climates such as the UK. The Potassium Formate desiccant solutions shows the highest cooling performance for the given conditions, and with its lower environmental impact compared to LiCl and CaCl2, is a suitable solution for the desiccant unit in the TriSOFC system.
As the regeneration heat source temperature increases, the mass of water vapour vaporised from the weak desiccant solution increases. Although too high a desiccant concentration is not always required, a higher regeneration temperature could mean a lower desiccant and air flow rates are required (beneficial to COP) in order to yield a similar outlet concentration and for the mass balance between dehumidifier and regenerator to be satisfied.
Although basic, this modelling has helped understand the fundamentals of the liquid desiccant system, namely the interactions observed in the parametric analysis. The current model does however have its limitations and is not particularly robust; for example it does not include the heat and mass exchanger effectiveness of the cellulose fibre membrane, geometry of the contactor or desiccant carry-over. Furthermore, there have been some issues encountered with the described model such as assessing the variation of desiccant concentration and mass flux condensed/vaporised. However the above model has provided a valuable quick evaluation tool for operational performance of liquid desiccant dehumidification systems.
This initial modelling work will be essential for the development of a more comprehensive 2D component based model and future intended experimental work.
The next stage of modelling will aim to develop a model in order to obtain more accurate, specific results for the novel cellulose fibre based liquid desiccant air condition unit, operating with a potassium formate solution. Following the development of the more comprehensive desiccant contactor model, the aim will be to develop a system model, linking the dehumidifier and regenerator models together, including a desiccant to desiccant heat exchanger. This work will enable parametric analyses to be carried out to determine the optimum operating strategies for improved system COP, as this will be crucial to the fuel cell tri-generation systems overall performance.
Summary of the recommendations from previous reviews
The mid-term review highlighted severe delays in the project and acknowledged the difficulties arising from the novel character of the materials and recipes used in developing the LT-SOFC fuel cell, the withdrawal of GETT Fuel Cells from the project due to bankruptcy and inadequate coordination and co-operation between partners. The consortium has agreed to submit an amendment to the DoW that would address some of the delays and enable the project to reach a successful conclusion.
Work progress and achievements during the period
WP2: 1-D and 2-D modelling of the desiccant dehumidification and cooling system. Analysis of individual components and the whole system have been developed and tested against published data. Computer simulations developed for the modelling were modified to analyse the geometry of the individual heat/mass exchangers and to evaluate and compare different working fluids. It was concluded that Potassium Formate offered the best combination of thermophysical properties, dehumidification and regeneration performance and health and safety considerations.
A desiccant dehumidifier and cooler has been designed, commissioned and built. It will combine a regenerator, a dehumidifier and cooler and an intercooler in one unit. The unit has been tested in laboratory conditions at the University of Nottingham and has demonstrated cooling output of 1.8kWh for a heat input of around 1.5kWh giving an average COP of 1.2.
Investigation of phase change materials (PCMs) for storing heat from the SOFC and was found that for a fuel cell operating 21 hours per day, the PCMs could store enough energy to maintain indoor temperatures at approximately 20ºC for winter heating conditions in Porto. However, for the situation on Nottingham, the PCMs could only store enough energy to maintain indoor temperatures at 16ºC, and so back-up heating would be required. It was concluded that desiccant storage offered a better solution to storage and thermal management.
A SOFC with a heat output of 1.5kW would be suitable for use directly in a dwelling in winter. Therefore, there would be no need for winter storage. However, the heat demand from a desiccant cooler in would be higher than its maximum output, so storage of heat or the storage of coolth is required. A thermal storage system has been designed to store desiccant solution suitable for the heat output of the fuel cell and the cooling requirements of a dwelling in Nottingham.
WP3: This work package focuses on the optimising the functional nanocomposite materials, ceria-based two or multi-phase materials, to fabricate LT-SOFC components and MEAs. Fabrication protocols with different MEA structures will be considered during developing the program. Various methods will be combined for fabricating single cell. Three types of single cells will be fabricated: the conventional planar type cell, the flat-tubular with completed single cell technology developed by GETT/KTH and the micro-tubular type cell developed by IVF. This amendment proposes that the consortium concentrates on the planar and micro-tubular fuel cells. GETT were tasked with developing and scaling up the stack, but their expertise in flat tubular stacks has been lost to the consortium as well as causing delays in cell development. In the remainder of the project, it is proposed that KTH/VSS develop the planar single cells and UBHAM/IVF develop the micro-tubular single cells. The testing will be performed to components and single cells to evaluate the different process condition and modify the fabrication procedure. Based on the optimization process, the fabrication sizes will be scaled-up to meet applications of LT-SOFC stacks in the tri-generation system.
Materials
The research activities on single-layer fuel cells (SLFCs) or “Three in One” fuel cell have opened new doors for keeping ahead with two major areas of focus: improvement of SLFC performances by contributing new materials, and scientific understanding of the SLFC nature and science as well as technological developments. The successful developments of design and synthesized new materials composed of the ionic ceria based materials and the semiconductors, e.g. mixed transition metal oxides, LiNiCu based-oxide etc., perovskite oxides as well as layered structured metal oxides, combining ionic and semiconducting properties for SLFCs as given below:
■ Ion conducting materials:
Doped and co-doped ceria, e.g. SDC (Sm3+ doped CeO2), ceria-composites, with or without carbonates were prepared.
■ Semiconducting materials:
1) Various transition element oxides, Ni, Cu, Co, Fe, Mn etc;
2) Perovskite oxides, BaSrCoFe, LaSrCo, LaSrCoFe, LaSrMn, LaSrMnFe, LSCT, SmSrCo, SrFeMo, BaSrFeMo etc (novel perovskite cathode material) and BaCaCoFe composite cathode were synthesized.
3) Layered structured materials: LiMOx (M=Ni, Cu, Co, Fe, Mn, Mo), thousands designs and recipes were tested with extensive efforts.
D3.1: The main objective of the TriSOFC project is to develop a low temperature (500-600C) solid oxide fuel cell suitable for use in domestic dwellings. The ambitious target of producing a low cost (<400euro/kWe), durable (>40,000 hours) system is being delivered by teams across the European Union with expertise in fuel cells and trigeneration systems. The first year of the project has been targeted at the basic science of developing the novel single component nano-composite material, fabricating and testing single fuel cell elements, developing scale-up methods and investigating novel working fluids, membranes and storage methods for the trigeneration system. Single component materials have been developed by KTH (LiNiCuZn) and tests on pellets have shown improved performance compared to two and three component systems. The maximum performance achieved in this period was
OCV = 0.95 V, I = 1016 mA/cm2 at 230 mV @ 550ºC
Compared to a three component pellet with performance of
OCV= 0.95 V, I = 875 mA/cm2 at 180 mV @ 550ºC
D3.2: Nano-composite materials have been developed by KTH with single component characteristics. Tests have been carried out and good results have been obtained. At an operational temperature of 500-550C the OCV achieved was 0.95V and the current density was 1016 mA/cm2 at 230 mV. A 6cm x 6cm x 1mm thickness fuel cell has been developed with a maximum power output of 16W.
Micro-tubular cells have been fabricated by UBHAM by extrusion. Test results show performance comparable with KTH (OCV = 0.9V I = 0.8A P = 0.22W. Durability is poor (150-200 min). Micro-tubes thin walled and off-centered. An Investigation into the extrusion of thicker walls to improve performance and durability is to be carried out. New extrusion dies and barrels have been commissioned. Iso-static pressing was to be investigated but the equipment has not been delivered, and so the work has been delayed.
D3.3: KTH is continuing its efforts for electrolyte free fuel cell recipes which are internationally recognized by fuel cell experts which are success of this project. An article has been accepted for publication in Journal of Power Sources as given below. FP7 TriSOFC project contribution has been acknowledged in this work. Another paper was submitted in 5th World Hydrogen Technologies Convention (WHTC 2013)-Shanghai Conference. Our research work was selected for oral presentation in the conference where we have successfully presented the work for advanced fuel cell technology. The work has been published in the International Journal of Hydrogen Energy. The abstract of this work is given below. KTH has got an achievement making joint efforts with its strategic partners and an electrolyte with high conductivity for fuel cell application is generated recently as explained below. By preparing the composite electrodes a very high device performance is achieved. ‘‘Scaled up low-temperature SOFCs with MgZnSDC composite electrolytes for applications’’, in this study, a new type of the Mg0.4Zn0.6O/Ce0.8Sm0.2O2-δ (MZSDC) composite electrolyte was synthesized using one step co-precipitation method. Recently world record results have been achieved in the experiments with OCV = 1.19 V for EFFC with repeated results by KTH.
At UBHAM, all as-prepared micro-tubular LT-SOFC single cells are tested in the UBHAM lab. Besides of the tubes itself, the influences of temperature, flow rate, cell sealing conditions are also investigated. The durability of some selected tubes was also checked for up to 100 hours operation at 550C. Due to the poor durability of the tubes with current Nanocomposite materials, all testing are still conducted with H2.The experimental results demonstrated the power performance is highly sensitive to the tube structure, although the testing conditions do have some influence. The power performance of tubular LT-SOFCs can be potentially improved by the optimal structure, but the durability is still a big challenge at the moment and this can hopefully be addressed by the new generation of Nanocomposite material which was recently confirmed by KTH.
D3.4: The research and development activities have been done on our recent research breakthrough based on the single-layer fuel cells (SLFCs) or “Three in One” fuel cells from new functional semiconductor-ionic materials, technologies for device and stack demonstrations. We have succeeded in the targets according to the project deliverables as below:
1. New materials have been scaled up for production at kgs level thus guaranteed extensive uses for the project (WP3)
2. Scaling up of 6x6 cm2 cells fabricated and about 2000 of 6x6 cm2 engineering fuel cells with new materials and new invention of the single layer fuel cell (SLFC) devices instead of the conventional anode/electrolyte/cathode structure. (WP3)
3. Each 6x6 cm2 SLFC reached at 8-10W (Targeted at min 5W) below 550C. (WP3)
Scaling up production of the core material and single cells have been performed; Nanocomposite single component materials have been developed by KTH. A variety of single cells have been fabricated with different combinations of semiconductors and ionic conductors. Tests have been carried out and good results have been obtained by KTH. Carbonate-free new single component materials with better performances have been successfully developed and subjected for scaling up productions in kgs. The single-component nanocomposite free electrolyte-free fuel cells (EFFCs) have been scaled up for engineering large size 6x6 cm2 fabrications by investment for purchasing combined with the hot-pressing machine.
At an operational temperature of 500-550C the OCV achieved was 0.95V and the current density was 1016 mA/cm2 at 230 mV. A 6cm x 6cm x 1mm thickness fuel cell has been developed with a maximum power output of 16W.
Micro-tubular cells have been fabricated by UBHAM by extrusion. Structure analysis demonstrated the networking distribution of the semiconductor phases and ionic conductive phases in pellets; Single-component micro-tubular SOFCs, with ID 1.5-1.6 mm and OD 2.3-3.2 mm, were extruded and tested. The OCV reached 1.0 V. The maximum power density obtained was 260 mW cm-2 at 550C. The durability tests of 15 hours was performed and the current dropped from 0.52 A to 0.22 A at 0.5 V;
WP4: A planer-type stack is to be developed by KTH/IVF/GETT. The withdrawal of GETT from the project due to financial difficulties and problems with producing stable and durable materials has delayed this work task. 6cm x 6cm membranes have been tested in a two cell stack. Output of 12W at 550C has been demonstrated. KTH reported durability of over 100hours.
VSS/GETT has carried out mathematical modelling of a SOFC planar stack. A three component (anode/cathode/electrolyte) was analysed and its results compared to work carried out on a fuel cell obtained by VSS.
Dr. Zhu from KTH established a joint lab with a strategic partner matching local finance to develop cells and stack. It involves metal bipolar plate, soft mica sealing materials and single layer engineering and big amount of numbers for large size cells fabrications. The single cell tests have achieved great successes with one cell delivering 10W (6x6 cm2) in average at 500-600C; based on the single cell measurements, we started construction of two and five cells short stacks. We have achieved the two cell stack OCVs at 2.2 V (reached perfect expected value) and the power outputs between 3-4 watts at temperature 380-500C. Though we have not enabled to measure our stack at desired temperature 550-600C as designed power outputs at 20W, these results are the first world record on such extremely low temperature SOFC stack data. It proved our single-component electrolyte free fuel cell (EFFC) has taken away the electrolyte bottleneck with great low temperature breakthroughs. In the latter development, improved the two cell stack power outputs at 12W at around 500C using the bipolar plates with improved gas distribution channels and sealing-free stack design.
Due to integration of new resources for both invested machine/facilities and team/manpower takes time, our stack developments have just started. Initial results are promising but not reached the expected power outputs. To overcome the current technical problems, our new solutions with new efforts will be soon restarted. For a time being we will overcome the current technical challenges and present more successful results in next term period.
D4.4: By modelling, according to former planar type stack design studies and experiences two type of stack were designed, verified by performing flow simulations and manufactured. Planar type LT-SOFC stacks fabricated from 6x6 cm2 cells were tested based on 2-5 cells installation, and the optimal stack with 4 cells has been operated in accumulating for 100 hours, subjecting 10 thermal cycling from operational temperature shut-down to room temperature. A 100W stack was successfully demonstrated using 15 pieces of 6x6 cm2 SLFC cells. In parallel, we also co-developed 1000W conventional SOFC stack using NiO-YSZ anode supported thin film YSZ incorporated by GDC buffer layer and LSCF cathode, we reached at 1020W at 700C. The conventional 250We micro-tubular SOFC stack was also tested with industrial propane for ca. 130 hours, including 19 thermal cycles
from room temperature to operating temperature (ca. 700C), 1 forced stop and 1 severe sulfur poisoning. These joint efforts from Partner 2, 3 and 6 also effectively supported new material stack developments.
WP5: Results of this work showed that bi-metallic Ru-Ni containing ceria-alumina supported catalysts were more stable than mono-metallic catalysts containing only Ni or Ru, in the reforming reaction of kerosene. A reforming catalyst was developed and produced based on 500-600C range. And using numerical studies reforming reactor design was done based on 500-600C range and 100W output power with assumed fuel utilization.
In our studies direct decomposition, steam reforming and autothermal reforming of methane, used to obtain hydrogen rich gas mixture were examined. In this conversion process the catalysts containing “Ni”, “Fe” and “Ru” metals were prepared by using commercial alumina as carrier. Methane conversion was examined by experiments and the gas mixture which came into effect as experimental result was analysed by the help of Agilent branded gas chromatography device and the volumetric percentages of hydrogen which went out were compared. In the conversion experiments of methane with steam reforming and autothermal reforming the effect of parameters such as temperature, gas feeding velocity and the amount of steam to “H2 “ quantity was examined. The coking period was associated with the decrease of hydrogen quantity in the gas mixture going out during direct decomposition, steam reforming and autothermal reforming of methane experiments. It was observed that the coking periods differed according to conversion methods and depending on the experimental conditions in three methods investigated.
WP6:
Because of delays in developing a planar type LT SOFC stack for integration with the tri-generation system, the consortium applied for an amendment to the description of work. This entailed developing the LT SOFC membranes and stack in parallel with proving the concept of a tri-generation SOFC. In order to prove the concept, the consortium obtained a commercially available SOFC based on micro-tubular membrane technology developed by Adelan Ltd (UK). The SOFC had a performance of 250W electrical output and approximately 1000W waste heat output. This was assessed as appropriate for domestic scale applications where low power constant output electricity was required and where a large quantity of heat could provide heating and cooling to the building.
The micro-SOFC units was totally tested at UBHAM for approximately 130 hours, including 19 thermal cycles from room temperature to operating temperature (@ 700C), with one forced stop and one severe event of sulphur poisoning at around 80 hours. High purity propane gas (99.5%) was used for approximately 66 hours for the first 8 cycles, and then BBQ propane gas was used from the 9th thermal cycle until the end. Results showed stable voltage output of 12.3-12.4V and a maximum power output of 250We. Sulphur poisoning at 80 hours caused a rapid fall-off in output, but power output recovered to 140W after about , but demonstrated recovery of over half of the original performance after about 90 hours.
Following fuel cell performance tests at UBHAM, the unit was transported to NOTT for integration with the desiccant unit. A second desiccant dehumidification and cooling unit was designed, constructed and tested following the identification of problems with the original design and comments from the mid-term reviewers that work should be done to reduce the size of the unit. The first version combined the regenerator, dehumidifier and intercooler into one unit. The second version separated the three processes so that they could be operated independently.
Results show increased dehumidifier performance with increasing inlet air temperature, relative humidity, air volumetric flow and desiccant solution volumetric flow. A maximum moisture removal rate and cooling output achieved were 0.3203 g/s and 954 W respectively. Over the testing conditions presented, the latent (dehumidifier) effectiveness was in the range of 30 – 40%. Unlike the IDCS, the SDCS dehumidifier component tests have been conducted within the environmental chamber. As a result, the water and desiccant fluids were at ambient temperature, this had an impact on the moisture absorption capacity of the desiccant solution and the cooling output.
Dehumidifier performance will need to be balanced by the available regeneration capacity obtainable from the SOFC CHP system during tri-generation system integration. Next, the regenerator component analysis is presented.
Results show increased regenerator performance with lower inlet air temperature and relative humidity, increased air volumetric flow and desiccant solution volumetric flow. Regenerator performance is also improved with increasing hot water volumetric flow in the heating circuit and hot water flow temperature. A maximum moisture addition rate of 0.4331g/s was achieved, with a regenerator thermal input of 1588 W. During tri-generation system integration, the performance of the regenerator will be largely dictated by the available thermal energy from the SOFC CHP system. To ensure balanced SDCS operation, this will inform the permissible moisture removal rate that the dehumidifier should be operated at.
WP7:
Technical and commercial issues have meant the 1.5kWe building installed (BlueGEN) SOFC CHP system was not available for tri-generation system integration. However, using collected empirical SOFC and SDCS data, a theoretical tri-generation system integration analysis has been completed. The tri-generation system performance has been evaluated at a 1.5kWe and 2.0kWe capacity. The two cases generate a cooling output of 332W and 649W respectively. The highest tri-generation efficiency of 71.1% is achieved at a 2.0kWe capacity; however the electrical efficiency is lower than the 1.5kWe case. As a result, the 1.5kWe case produces the greatest cost and emission savings of 61% and 69% respectively. The inclusion of liquid desiccant air conditioning technology provides an efficiency increase of up to 28% compared to SOFC electrical operation only. The performance of the novel tri-generation system is competitive with other systems of this capacity reported in the literature. The results demonstrate effective pairing of SOFC and liquid desiccant air conditioning technology in a tri-generation system application. The theoretical tri-generation system integration analysis has achieved the thesis technical objective of a 1.5kWe system operating at an electrical efficiency of 45% or more. The encouraging performance is primarily due to the high electrical efficiency of the SOFC and the reasonable thermal COP of the liquid desiccant system. Technical and commercial issues with the SOFC highlight the real challenge of fuel cell deployment in the built environment.
Following the failure of the 1.5kWe SOFC, a 250We micro-tubular SOFC had to be acquired. The novel tri-generation system concept has been proven experimentally using the micro-tubular SOFC. The experimental results demonstrate regeneration of the potassium formate solution using the thermal output from the SOFC in the first of its kind tri-generation system. Optimisation has shown that a 2.2L.min-1 regenerator desiccant volumetric flow facilitates best performance. The novel system can generate 150.4W of electrical power, 442.6W of heat output and 278.6W of cooling. Due to its low temperature regeneration requirement, potassium formate at a 0.65–0.7 mass concentration is an appropriate desiccant solution for a SOFC tri-generation system. When integrated with the micro-tubular SOFC, the SDCS demonstrates a COPth of 0.62 an encouraging value for a waste heat driven cooling system of this capacity. Instantaneous tri-generation system efficiency is low at approximately 25%. This is primarily due to the low capacity and poor performance of the micro-tubular SOFC. Sulphur poisoning has caused a 40% reduction in micro-tubular SOFC electrical output to 150W. Insufficient WHR means only 450W of thermal energy is available for regeneration purposes, and thus the cooling output is low. However, it has been suggested that if these issues are addressed, the novel system can provide higher overall efficiency. A daily tri-generation performance analysis is presented which serves to demonstrate the novel system operating in a building application. In such a scenario, 527W of cooling is produced and a daily tri-generation efficiency of 37.91% is presented. This is an encouraging value for a tri-generation system of this capacity. Compared to a base case scenario, the novel tri-generation system generates a cost and emission reduction of 56% and 42% respectively, demonstrating the potential of the novel tri-generation system in applications that require simultaneous, electrical power, heating and dehumidification/cooling.
The difference in performance seen between the two tri-generation systems presented demonstrates the significance of (a) the performance of the SOFC component and (b) the requirement of optimal pairing of components, in the development of an efficient and effective tri-generation system. The micro-tubular SOFC was acquired at short notice to replace the 1.5kWe BlueGEN SOFC. As seen in the low thermal output, it is not the ideal match for the developed SDCS. However, the novel tri-generation concept has been successfully demonstrated. Both tri-generation system analyses presented have considered balanced liquid desiccant system operation. This is a stipulation other tri-generation systems employing liquid desiccant technology reported in the literature have not reported and demonstrates the strength and rigour of the work presented.
The aim of the prototype development is to design, develop and test an efficient and effective tri-generation system based on SOFC and liquid desiccant air conditioning technology. This chapter has demonstrated a clear contribution to new knowledge with the development and evaluation of two SOFC liquid desiccant tri-generation systems and as a result it is proposed that the thesis aim has been completed.
Based upon the experimental work, three general conclusions are provided with respect to the design, development and testing of an efficient and effective tri-generation system based on SOFC and liquid desiccant air conditioning technology for building applications.
• SOFC and liquid desiccant is an effective technological pairing. The inclusion of liquid desiccant can bring significant improvement to system performance, particularly in applications requiring simultaneous electrical power, heating and dehumidification / cooling.
• Overall tri-generation system performance is more influenced by the SOFC component than the liquid desiccant. Appropriate matching of component capacity is necessary.
• The novel tri-generation system concept has been demonstrated experimentally. Future work needs to focus on improving the current unreliability and sensitivity of fuel cell technology.
WP8: In our economic assessment (WT8.2) we demonstrated that the novel tri-generation system was viable only in certain cases. The tri-generation system has a lower annual operating cost than the base case, however, the high capital cost of the SOFC and requirement of stack replacement means that the tri-generation system NPC is only favourable when FiT is considered. However, with anticipated SOFC capital cost reductions the economic performance is predicted to improve. The current tri-generation system does not have a SPBP of less than five years, and is thus not immediately attractive to investors. Furthermore, with the possibility of future withdrawal of government support, a move mirroring the Japanese market towards smaller electrical capacity domestic fuel cells may be required to achieve/maintain economic viability. The economic performance of the tri-generation system is sensitive to natural gas and electrical unit cost. The future economic feasibility of the system will therefore be dependent upon future energy prices, which can be highly volatile. Currently, the tri-generation system is only economically viable in Denmark due its high unit cost of electricity.
The environmental assessment (WP8.3) has demonstrated that the novel tri-generation system is viable across a large range of operational values. Within a UK energy system context, annual CO2 emission reductions of up to 51% compared to the equivalent base case system have been demonstrated. The environmental performance of the tri-generation system is more sensitive to changes in the natural gas emission factor than the base case system. The CO2 emissions of the tri-generation system are insensitive with respect to electricity emission factor. However, electricity emission factor does affect the relative performance of the tri-generation system with respect to the equivalent base case system. The tri-generation system is environmental superior when the electricity emission factor is greater than 0.23kgCO2.kWh-1. As a result, the tri-generation system is not currently viable in France and Norway. Australia and China demonstrate the greatest environmental benefit from adopting the novel tri-generation system. With a transition to hydrogen-fed fuel cells, the novel tri-generation system will be highly competitive in almost all scenarios.
This chapter has provided a detailed economic and environmental assessment of the novel tri-generation system. The following general conclusions, with respect to the chapter aims set out in section 1.1 are as follows:
(1) The system is currently only economically viable with government support. SOFC capital cost and stack replacement are the largest inhibitors to economic viability. Environmental performance is closely linked to electrical emission factor, and thus performance is heavily country dependent.
(2) The countries, in which the system is environmentally viable, are in general the counties in which the system is not economically feasible. This is primarily due to the play off between cheap electrical generation from fossil fuels and more expensive cleaner electrical generation from renewables or nuclear.
(3) The economic feasibility of the novel tri-generation system will improve with predicted SOFC capital cost reductions and the transition to clean hydrogen production.
Although the SDCS has been developed with the aim of integration alongside a SOFC into a complete tri-generation system, the SDCS shows significant potential for integration with other CHP prime mover technologies such as ICE or SE. Due to the lower capital cost of ICE and SE technology (roughly ten times that of SOFC) and cheaper maintenance/part replacements, the economic performance of an ICE/SE based liquid desiccant tri-generation system can be expected to be much better than the current SOFC based system. However, the environmental performance of the SOFC based system will remain favourable compared to alternative options due to high electrical conversion efficiency and the provision for zero carbon energy conversion with the transition to a pure hydrogen fuel feed.
This chapter has demonstrated that the novel tri-generation system is, in certain cases, economically viable.
From the risk register it was observed that the most serious risks were that of first cost and unreliability. A second order risk that could affect commercialisation is changes to incentives for adopting low carbon technologies. Many countries and regions have adopted policies that provide financial incentives to promote renewable and low carbon technologies, but others do not have incentives or do not have consistent long term policies, and so at current cost projections, the most likely places to take up the TriSOFC system are those offering incentives.
Many countries around the world operate feed-in-tariffs, including most members of the European Union, China, Malaysia, Japan, Brazil and Argentina and a small number of countries in Africa (mainly solar and hydro related), whilst some states or regions within countries operate a feed-in-tariff regime, including the USA and Australia. It can be observed that many countries and regions in the world would be suitable for installation of the TriSOFC system, including southern European Countries such as Greece, Turkey, Portugal and Spain, as well as tropical countries such as Malaysia, Southern China and Japan.
Reductions in first cost is a major priority and the consortium is well placed to scale-up manufacture, adopt mass production methods and reduce the cost of membranes, stacks and BoP. Reliability and durability are major concerns of potential customers, not only with respect to the TriSOFC prototype, but most SOFCs. Further work will focus on producing repeatable, reliable and durable fuel cells.
Other factors come into play when comparing existing and competitive systems, such as space taken up by plant and machinery, which could otherwise be used for occupants. In domestic dwellings, anything larger than a washing machine or fridge would reduce space available for other appliances and reduce useable space. In commercial buildings, this would mean less room for lettable space and may require investment in strengthening building structures to take the extra weight. Most of the other risks identified are easily mitigated at the design stage and so should not present risks either technically, economically or environmentally.
The case will be made that the overall system has advantages over existing and competitive technologies over and above issues about space.
WP9:
Website:
A website has been created and is used to disseminate information to the general public and others outside the consortium and EU commission. www.trisofcv.com In addition, we have set up a drop-box system where we can share confidential information between partners, such as minutes of meetings, presentations and progress reports. www.dropbox.com.
Dissemination:
The consortium has been very active in promoting and disseminating results from the research and development emerging from the project. Many significant results and discoveries have been unearthed as a result of the project and this report highlights these achievements. We have also taken on board comments by the mid-term reviewers, who recommended that we should engage more with the international fuel cell and hydrogen community, therefore we highlight these activities as well as reports on publications and conference participation. The following section lists the activities undertaken by each consortium member, but many of the activities were either engaged in jointly with other members, or materials and content were shared between members.
We report over 25 journal papers, over 30 conferences and over 20 Fuel cell and hydrogen community related activities.
Potential Impact:
Environmental Impact
In this section, an environmental assessment of the novel tri-generation system operating within a UK energy system context is presented. The environmental assessment compares the 1.5kWe and 2.0kWe tri-generation system with an equivalent base case system comprising grid electricity, natural gas fired boiler and electrically driven VCS. The evaluation metric used in the environmental assessment is the annual CO2 emission. This is determined through the multiplication of the annual natural gas and electrical demand by their respective emission factors and summing the result. The emission factors of natural gas and electricity are varied, in a reasonable range, to carry out a sensitivity analysis of the environmental performance. The assumptions used in the environmental assessment are the same as those presented in the economic assessment in section 1.2.2. The emission factors used are based on a UK energy system context, and are as follows:
▪ Average natural gas emission factor: 0.184 kg CO2.kWh-1 (EST, 2014)
▪ Average electricity emission factor: 0.555 kg CO2.kWh-1 (AMEE, 2014)
We compared CO2 annual emissions for the cases of a SOFC with 1.5kWe and 2.0kWe output, and found that tri-generation systems produce a respective 51.3% and 50.2% reduction in annual CO2 emissions compared to the equivalent base case system.
We assessed annual CO2 emissions of the 1.5kWe and 2.0kWe tri-generation systems and equivalent base case systems with respect to natural gas emission factor. Over the investigated natural gas emission factor range of 0.05 to 0.3kgCO2.kWh-1 the tri-generation system always has a lower annual CO2 emission. Both the tri-generation and base case system have a natural gas requirement. However, the greater proportionate natural gas demand in the tri-generation system means its annual CO2 emission reductions are more sensitive to changes in the natural gas emission factor. Consequently, as the natural gas emission factor is increased, the relative reduction in annual CO2 emissions compared to the equivalent base case system is diminished. The 2.0kWe tri-generation system is more sensitive to changes in the natural gas emission factor than the 1.5kWe tri-generation system due to a lower electrical efficiency.
We showed that annual CO2 emissions of the 1.5kWe and 2.0kWe tri-generation systems and equivalent base case systems with respect to electrical emission factor. The tri-generation system has no electrical demand, and thus only the base case system is affected by the electrical emission factor. The tri-generation system has a lower annual CO2 emission compared to the equivalent base case system when the electrical emission factor is greater than 0.2363kgCO2.kWh-1 for the 1.5kWe case and 0.2305kgCO2.kWh-1 for the 2.0kWe case.
We showed that annual CO2 emissions of the 1.5kWe and 2.0kWe equivalent case system in a range of different counties using published electrical emission factor data. The annual CO2 emissions of the respective tri-generation systems (horizontal lines) were plotted to indicate the countries in which the novel system is currently environmentally viable. The 1.5kWe and 2.0kWe tri-generation system is feasible in all the countries investigated except France and Norway as these countries have an average electrical emission factor of less than 0.1kgCO2.kWh-1. France and Norway have an energy system that is largely characterised by the use of nuclear and renewables. As a result, the average electrical emission factor is low. We showed that the 1.5kWe and 2.0kWe tri-generation system is most environmentally viable in Australia and China. Australia and China generate a large proportion of their electricity from coal, which has a high emission factor per kWh of electricity generated, and thus strengthens the environmental benefit of adopting the novel tri-generation system. Based on the data presented, Denmark is currently the only country investigated where the novel tri-generation system is both economically and environmentally viable. Interestingly, the countries where the tri-generation system is not economically feasible due to a low electrical unit cost are in general the countries in which the system is most environmentally feasible i.e. Australia and China. This is primarily due to cheap electrical generation from easily accessible, more polluting fossil fuels such as low grade coal.
Environmental assessment conclusions
The environmental assessment is based on annual CO2 emissions of the novel tri-generation system compared to an equivalent base case system. Sensitivity analysis has been used to assess the impact natural gas emission factor, electricity emission factor and country of operation has on environmental performance.
The environmental assessment has demonstrated that the tri-generation system is environmentally viable in almost all scenarios. In a UK energy system context the tri-generation system generates up to 51% annual CO2 emission reductions compared to the base case. Over the investigated natural gas emission factor range, the tri-generation system is always superior. The tri-generation system’s environmental performance is not directly influenced by changes in the electrical emission factor, however the base case is. As a result, changes in the electrical emission factor have a marked impact on the relative performance of the tri-generation system with respect to the base case system. The tri-generation system is environmentally viable when the electricity emission factor is greater than 0.23kg CO2.kWh-1. France and Norway have a large nuclear and renewable (hydro-electric) energy capacity. As a result, their electricity emission factor is low, and thus the tri-generation system does not provide an environmental benefit in such a setting. Countries such as Australia and China demonstrate the greatest environmental benefit from adopting the novel tri-generation system. However, the move to a hydrogen economy and with it the transition from the use of hydrocarbon to pure hydrogen-fed fuel cells in the next 30 years provides the potential for highly efficient, zero carbon energy conversion. With such a transition the novel tri-generation system would be highly competitive in almost all scenarios. This is discussed further in section 9.4.
This section has provided an economic and environmental assessment of the novel tri-generation system operating in a UK economic and energy system context. The assessment has used the BlueGEN SOFC tri-generation system performance data. The tri-generation system has been compared to a base case system comprised of grid electricity, natural gas fired boiler and electrically driven VCS. Sensitivity analysis has been used to assess the performance of the tri-generation system across a range of operating scenarios.
The economic assessment has demonstrated that the novel tri-generation system is viable only in certain cases. The tri-generation system has a lower annual operating cost than the base case, however, the high capital cost of the SOFC and requirement of stack replacement means that the tri-generation system NPC is only favourable when FiT is considered. However, with anticipated SOFC capital cost reductions the economic performance is predicted to improve. The current tri-generation system does not have a SPBP of less than five years, and is thus not immediately attractive to investors. Furthermore, with the possibility of future withdrawal of government support, a move mirroring the Japanese market towards smaller electrical capacity domestic fuel cells may be required to achieve/maintain economic viability. The economic performance of the tri-generation system is sensitive to natural gas and electrical unit cost. The future economic feasibility of the system will therefore be dependent upon future energy prices, which can be highly volatile. Currently, the tri-generation system is only economically viable in Denmark due its high unit cost of electricity.
The environmental assessment has demonstrated that the novel tri-generation system is viable across a large range of operational values. Within a UK energy system context, annual CO2 emission reductions of up to 51% compared to the equivalent base case system have been demonstrated. The environmental performance of the tri-generation system is more sensitive to changes in the natural gas emission factor than the base case system. The CO2 emissions of the tri-generation system are insensitive with respect to electricity emission factor. However, electricity emission factor does affect the relative performance of the tri-generation system with respect to the equivalent base case system. The tri-generation system is environmental superior when the electricity emission factor is greater than 0.23kgCO2.kWh-1. As a result, the tri-generation system is not currently viable in France and Norway. Australia and China demonstrate the greatest environmental benefit from adopting the novel tri-generation system. With a transition to hydrogen-fed fuel cells, the novel tri-generation system will be highly competitive in almost all scenarios.
This section has provided a detailed economic and environmental assessment of the novel tri-generation system. The following general conclusions, with respect to the chapter aims set out in section 1.1 are as follows:
(1) The system is currently only economically viable with government support. SOFC capital cost and stack replacement are the largest inhibitors to economic viability. Environmental performance is closely linked to electrical emission factor, and thus performance is heavily country dependent.
(2) The countries, in which the system is environmentally viable, are in general the counties in which the system is not economically feasible. This is primarily due to the play off between cheap electrical generation from fossil fuels and more expensive cleaner electrical generation from renewables or nuclear.
(3) The economic and environmental feasibility of the novel tri-generation system will improve with predicted SOFC capital cost reductions and the transition to clean hydrogen production.
Although the SDCS has been developed with the aim of integration alongside a SOFC into a complete tri-generation system, the SDCS shows significant potential for integration with other CHP prime mover technologies such as ICE or SE. Due to the lower capital cost of ICE and SE technology (roughly ten times that of SOFC) and cheaper maintenance/part replacements, the economic performance of an ICE/SE based liquid desiccant tri-generation system can be expected to be much better than the current SOFC based system. However, the environmental performance of the SOFC based system will remain favourable compared to alternative options due to high electrical conversion efficiency and the provision for zero carbon energy conversion with the transition to a pure hydrogen fuel feed.
Economic Impact
Introduction
The economic and environmental assessments uses the BlueGEN SOFC tri-generation system performance data presented in section WP07 reports operating at a 1.5kWe and 2.0kWe capacity. These data, as opposed to the simulation data and laboratory testing data, are used because the system demonstrates good performance and is based upon commercially available components which have long-term stable performance, accurate costing figures and qualify for government support.
The aim of the economic and environmental assessment is to establish:
1. Whether the proposed tri-generation system is economically and environmentally viable under current conditions compared to an equivalent base case system.
2. The conditions and geographical locations in which the novel tri-generation system is economically and environmentally viable compared to an equivalent base case system.
3. The future feasibility of the novel tri-generation system with respect to projected changes in global energy resources, conversion techniques and cost.
Economic assessment
In this section, an economic assessment of the novel SOFC liquid desiccant tri-generation system operating within a UK economic climate is presented. The economic assessment compares the 1.5kWe and 2.0kWe capacity tri-generation systems to an equivalent base case system comprising grid electricity, natural gas fired boiler and electrically driven VCS over a 15 year time period. The economic evaluation metrics used are: net present cost (NPC), equivalent uniform annual cost (EUAC) and simple pay-back period (SPBP). The unit cost of electricity, unit cost of natural gas and the capital cost of the SOFC are varied, in a reasonable range, to carry out a sensitivity analysis of the NPC and SPBP. Using electrical unit cost data published by the International Energy Agency, the economic performance of the tri-generation system in the context of different countries is presented.
Next, section 1.2.1 describes the metrics used in the economic assessment.
Net present cost (NPC)
Net present value (NPV) is an economic tool used to equate the total cost of a project over a specified time period to the total cost today, taking in to account the time value of money. The present value (PV) of each annual cash flow is discounted back to its PV using a suitable interest or discount rate. The NPV is determined by summing the PV for each year, staring at year 0 i.e. the investment, to the final year (N). NPV is a good indicator of how much value an investment or project brings to an investor, and is widely used in economic engineering to assess feasibility. However, there are many kinds of systems or projects, such as the SOFC tri-generation system, where there are no sales or incomes. In this case it is common to use net present cost (NPC).
Equivalent uniform annual cost (EUAC)
The equivalent uniform annual cost (EUAC) is the annual cost of the project or system equivalent to the discounted total cost or NPC. EUAC is calculated by multiplying the NPC by the capital recovery factor (CRF).
Simple pay-back period (SPBP)
The simple pay-back period (SPBP) is used to determine the time required to recoup the funds expended in an investment, or to reach the break-even point. Generally, in engineering projects investors consider a SPBP of five years as acceptable. The SPBP does not account for the time value of money; however it is a useful tool for the quick assessment of whether a project or system is a viable option.
Economic assessment results
The following assumptions have been made for the economic assessment of the novel tri-generation and equivalent base case system.
▪ System lifetime (N): 15 years
▪ SOFC CHP system cost and installation: £20,950
▪ SDCS cost: £2700
▪ Potassium formate solution cost (20kg): £235
▪ SOFC stack replacement cost and system maintenance: £5000 every 5 years
▪ UK micro-CHP feed-in-tariff (FiT): 0.125 £.kWh-1
▪ Boiler and installation cost: £1300
▪ VCS capital cost: £500 per kW of cooling
▪ Annual VCS maintenance cost: 10% of VCS capital cost
▪ Annual gas check: £60
▪ Average natural gas unit cost: 0.0421 £.kWh-1
▪ Average electricity unit cost: 0.172 £.kWh-1
▪ Average yearly VCS COPel: 2 (Welch, 2008)
▪ Average heating system efficiency (boiler + distribution): 85.5%
▪ Annual cooling time required: 1200hr.yr-1
▪ Interest rate (ir): 7% (constant throughout assessment period)
▪ Inflation rate (if): 3% (constant throughout assessment period)
▪ Scrap value (SV): 10% of initial capital cost
In the UK, fuel cell CHP of 2.0kWe or less qualifies for the micro-generation FiT (DECC, 2014). Under this scheme, the UK government pays 0.125£.kWh-1 of electricity generated, regardless of whether it is consumed or exported. Where relevant, the economic assessments consider the FiT.
We compared NPC of the 1.5kWe and 2.0kWe tri-generation systems and equivalent base case systems over a 15 year period. The assessment considered the performance of the tri-generation system with and without FiT support. The initial NPC in year 0 is the system investment cost, which is much higher for the tri-generation system compared to the base case. The NPC of the systems increases over time due to the annual operating costs. The tri-generation system with FiT support displays only a marginal increase in the NPC over the 15 year period because the FiT almost pays for the annual operating cost of the system. For the tri-generation systems, an NPC spike is seen at year five and ten; this is due to stack replacement. The small dip in NPC at year 15 is due to the scrap value of the systems.
Without FiT support, the NPC of both the 1.5kWe and 2.0kWe tri-generation system are 26% and 10% higher than the equivalent base case system respectively. However, with FiT support there is a 31% and 90% reduction in the NPC of the 1.5kWe and 2.0kWe tri-generation system compared to the equivalent base case system respectively. When the FiT is considered the annual revenue means the tri-generation system has a favourable NPC compared to the base case in year 11.5 for the 1.5kWe tri-generation system and year 7 for the 2.0kWe tri-generation system. The NPC of the 1.5kWe tri-generation system is lower than the 2.0kWe tri-generation system when no FiT is considered, but higher when the FiT is considered. The higher NPC seen in the 2.0kWe tri-generation system without FiT is due to the higher fuel input requirement, and thus higher annual operating costs. However, when FiT is considered the 2.0kWe tri-generation system provides greater annual revenues and thus a lower NPC. Both with and without FiT support, the 2.0kWe tri-generation system has a lower SPBP compared to the 1.5kWe tri-generation system. Although the 2.0kWe tri-generation system suffers an electrical efficiency reduction and thus a greater fuel input, the higher electrical capacity means it is offsetting more grid derived electricity. Per kWh, grid derived electricity has a higher associated cost compared to natural gas, and thus the SPBP of the 2.0kWe tri-generation system is lower. Furthermore, the 2.0kWe tri-generation system has a greater cooling output, and thus the equivalent base case system requires more grid derived electricity for the VCS. In all cases the tri-generation system generates annual operating cost savings compared to the base case system. The high NPC and SPBP of the tri-generation system are therefore due to the capital cost of the SOFC.
The unit cost of electricity does not affect the NPC of the tri-generation system, only the base case system. As the unit cost of electricity increases from 0.05 to 0.6£.kWh-1 the NPC of the base case system increases, and thus the economic feasibility of the tri-generation system improves. At an electrical unit cost of 0.2458£.kWh-1 there is a NPC break-even point between the tri-generation and base case system. Above 0.2458£.kWh-1 the 1.5kWe tri-generation system has a better NPC and should be considered over the base case system. At an electrical unit cost of 0.2458£.kWh-1 the tri-generation system has a SPBP of 12 years. For the SPBP to fall below five years, an electrical unit cost of 0.55£.kWh-1 is required. In comparison, the 2.0kWe tri-generation system has a NPC break-even electrical unit cost of 0.1955£.kWh-1. Due to the continual rise in utility electricity prices, the break-even electrical unit costs which produce tri-generation system economic feasibility are realistic and not too far off current prices.
We compared the economic performance of the 1.5kWe tri-generation system and equivalent base case system with respect to the unit cost of natural gas. No FiT is considered. Natural gas unit cost affects both the tri-generation and base case systems NPC. As the unit cost of natural gas increases from 0.01 to 0.1£.kWh-1 the NPC of both the tri-generation and base case systems increase. The tri-generation system is more sensitive to changes in the unit cost of natural gas compared to the base case system due to a greater proportionate demand. For the 1.5kWe tri-generation system there is not a natural gas unit cost that makes the tri-generation system favourable i.e. a NPC break-even point. As the natural gas unit price is increased the reduction in NPC between the base case and tri-generation system increases, and as a result the SPBP increases. As the natural gas unit cost is increased from 0.01£.kWh-1 to 0.1£.kWh-1 the tri-generation system SPBP increases from 14 years to 51 years. The 2.0kWe tri-generation system does have a NPC break-even natural gas unit cost of 0.0233£.kWh-1. However this is very low and not realistic in the current economic climate where fossil fuels have such value.
We investigated NPC of a 1.5kWe and 2.0kWe equivalent base case system in a range of different counties with respect to electrical unit cost data published by the International Energy Agency. The NPC of the respective tri-generation systems (horizontal lines) are plotted to indicate which countries the novel system is currently economically viable in. Based on the current assumptions, the novel tri-generation system (1.5kWe and 2.0kWe) is only economically viable in Denmark where the unit cost of electricity is 0.262£.kWh-1. The largest different between the NPC of the tri-generation and base case system is in China, where the unit cost of electricity is as low as 0.0512£.kWh-1. Based purely on economic performance, the novel tri-generation system is more suited to European locations, where on average the unit cost of electricity is higher than Asia and the Americas. The 2.0kWe tri-generation system has a lower NPC break-even electrical unit cost. As a result, the 2.0kWe system is almost feasible in the current Australian economic climate.
We showed NPC of the 1.5kWe tri-generation system and equivalent base case system with respect to the SOFC capital cost. The capital cost of the tri-generation system, operating at a 1.5kWe capacity, needs to be £9715 or less for it to be economically viable compared to the base case system. At a 2.0kWe capacity the required SOFC capital cost is £16135. As the capital cost of the SOFC increases, the SPBP increases. At the 1.5kWe NPC break-even point of £9715 the SPBP is 12.8 years. Variation in the liquid desiccant system capital cost has a negligible impact on NPC and SPBP. Reducing the liquid desiccant system capital cost by 50% results in a 4.5% reduction in the SPBP. Reducing the SOFC capital cost by 50% results in a 32% reduction in the SPBP, demonstrating that tri-generation system economic viability presides with reducing the capital cost of the SOFC.
We showed the NPC for the 1.5kWe tri-generation and equivalent base case system with respect to SOFC capital cost and unit cost of electricity respectively. Up to an electricity unit cost of 0.11£.kWh-1, the base case system is always better than the tri-generation system. However at the electrical unit cost reference value of 0.172£.kWh-1, the 1.5kWe tri-generation system is competitive when the SOFC capital cost is less than £9500. At the intersection point, the tri-generation system is economically favourable if the SOFC capital cost is less than £4750 with an electrical unit cost of greater than 0.14£.kWh-1 (i.e. UK, Australia).
Economic assessment conclusions
Within a UK economic climate it has been demonstrated that the NPC of the novel tri-generation system is only favourable when FiT is considered, in which case the 2.0kWe output is best. The tri-generation system has a lower annual operating cost than the base case; however, NPC and SPBP analysis demonstrates that the novel system is currently uneconomical. This is primarily due to the SOFC capital cost and the requirement of stack replacement, not the liquid desiccant unit capital cost. In the current UK economic climate the SOFC capital cost needs to be less than £9000 for the tri-generation system to be competitive. PEMFC technology has demonstrated considerable price reduction over the last six years. The 1kWe Panasonic unit had a unit cost of £27,300 in 2009, but as of 2015 it is being supplied to energy companies for £3600. CFCL forecast that they can supply the BlueGEN unit for £5200 once in mass production. Currently, the much lower PEMFC unit costs are due to the technology being around five years ahead of SOFC. Many commercial developers believe the future of cheaper fuel cell technology lies with SOFC systems as they do not need to use expensive platinum catalysts like PEMFC. Based on the example of PEMFC cost reductions, significant SOFC cost reductions can be anticipated. The SOFC cost target figures presented in this chapter are therefore sensible and could be realistically achieved in the next five to ten years, making the tri-generation system economically viable in almost all cases.
Currently, the tri-generation system becomes competitive, and even demonstrates good profitability, compared to the base case system when government incubator support, such as the FiT is considered. With continued instability in governmental support for low carbon sustainable energy, the novel tri-generation system needs to become economically viable in its own right for it to be considered a viable alternative to conventional energy supply. Furthermore, a 2.0kWe base load capacity is large, and effective electrical utilisation may be problematic, particularly in a domestic building context. With the possibility of future withdrawal of government support for fuel cell CHP, maximising in-house electrical consumption will be essential to maintain economic viability. A lower electrical capacity fuel cell would therefore be required. The Japanese domestic market, which is estimated to be ten years ahead of the European market, is now focussing domestic fuel cell CHP development at capacities of 750We, a possible insight into the future of where European domestic fuel cell development needs to go.
Like other small scale tri-generation systems presented in the literature, the economic performance of the SOFC liquid desiccant tri-generation system is most sensitive to the unit cost of natural gas. The tri-generation system is economically superior, compared to the base case system, when the unit cost of electricity is greater than 0.24£.kWh-1 and as a result Denmark is currently the only country investigated where the tri-generation is economically viable. However, with the extraction of easily accessible fossil fuels diminishing, the unit cost of electricity in many countries is set to continue to rise, thus strengthening the economic case of the tri-generation system.
Conclusions
This chapter has provided an economic and environmental assessment of the novel tri-generation system operating in a UK economic and energy system context. The assessment has used the BlueGEN SOFC tri-generation system performance data presented in section 7.2. The tri-generation system has been compared to a base case system comprised of grid electricity, natural gas fired boiler and electrically driven VCS. Sensitivity analysis has been used to assess the performance of the tri-generation system across a range of operating scenarios.
The economic assessment has demonstrated that the novel tri-generation system is viable only in certain cases. The tri-generation system has a lower annual operating cost than the base case, however, the high capital cost of the SOFC and requirement of stack replacement means that the tri-generation system NPC is only favourable when FiT is considered. However, with anticipated SOFC capital cost reductions the economic performance is predicted to improve. The current tri-generation system does not have a SPBP of less than five years, and is thus not immediately attractive to investors. Furthermore, with the possibility of future withdrawal of government support, a move mirroring the Japanese market towards smaller electrical capacity domestic fuel cells may be required to achieve/maintain economic viability. The economic performance of the tri-generation system is sensitive to natural gas and electrical unit cost. The future economic feasibility of the system will therefore be dependent upon future energy prices, which can be highly volatile. Currently, the tri-generation system is only economically viable in Denmark due its high unit cost of electricity.
The environmental assessment has demonstrated that the novel tri-generation system is viable across a large range of operational values. Within a UK energy system context, annual CO2 emission reductions of up to 51% compared to the equivalent base case system have been demonstrated. The environmental performance of the tri-generation system is more sensitive to changes in the natural gas emission factor than the base case system. The CO2 emissions of the tri-generation system are insensitive with respect to electricity emission factor. However, electricity emission factor does affect the relative performance of the tri-generation system with respect to the equivalent base case system. The tri-generation system is environmental superior when the electricity emission factor is greater than 0.23kgCO2.kWh-1. As a result, the tri-generation system is not currently viable in France and Norway. Australia and China demonstrate the greatest environmental benefit from adopting the novel tri-generation system. With a transition to hydrogen-fed fuel cells, the novel tri-generation system will be highly competitive in almost all scenarios.
This chapter has provided a detailed economic and environmental assessment of the novel tri-generation system. The following general conclusions, with respect to the chapter aims set out in section 1.1 are as follows:
(4) The system is currently only economically viable with government support. SOFC capital cost and stack replacement are the largest inhibitors to economic viability. Environmental performance is closely linked to electrical emission factor, and thus performance is heavily country dependent.
(5) The countries, in which the system is environmentally viable, are in general the counties in which the system is not economically feasible. This is primarily due to the play off between cheap electrical generation from fossil fuels and more expensive cleaner electrical generation from renewables or nuclear.
(6) The economic and environmental feasibility of the novel tri-generation system will improve with predicted SOFC capital cost reductions and the transition to clean hydrogen production.
Although the SDCS has been developed with the aim of integration alongside a SOFC into a complete tri-generation system, the SDCS shows significant potential for integration with other CHP prime mover technologies such as ICE or SE. Due to the lower capital cost of ICE and SE technology (roughly ten times that of SOFC) and cheaper maintenance/part replacements, the economic performance of an ICE/SE based liquid desiccant tri-generation system can be expected to be much better than the current SOFC based system. However, the environmental performance of the SOFC based system will remain favourable compared to alternative options due to high electrical conversion efficiency and the provision for zero carbon energy conversion with the transition to a pure hydrogen fuel feed.
This chapter has demonstrated that the novel tri-generation system is, in certain cases, economically and environmentally viable.
The project aims to develop a low temperature solid oxide fuel cell (LT-SOFC) tri-generation system for low carbon buildings.
The LT_SOFC will waste up to a half of the primary energy supplied as heat, and so by exploiting the waste heat for domestic heating and cooling (tri-generation) will improve the performance of the fuel cell in comparison to conventional SOFCs and increase its commercial value. The project integrates a LT-SOFC with a fibre membrane liquid desiccant dehumidification and cooling system to enable the system to produce electricity, heat and cooling.
The consortium has made significant advances in materials technology that will contribute to improved SOFC performance and other conversion technologies such as solar photovoltaics. Power density of almost 800mW/cm2 at 550C and improved performance over conventional FCs at 550C.
The LT-SOFC cell and stack design as well as of the entire generator system for a low cost application has been optimised.
Design of a complete SOFC power system capable of meeting the varying power demands of a low carbon building over a comfortable life space has been achieved.
A 2-cell 6cm x 6cm planar-type SOFC produced around 12W at 530C and in the best case we produced over 2.0 OCV and generated nearly 20W.
Good repeatable single cell performance was achieved at 1.1OCV and 9W at 540C.
Work was carried out investigating thin membrane stacks (~0.5mm thickness) and results showed output of over 2.0 OCV and 18W.
100W stack has been developed with 15 6cm x 6cm membranes in a stack, producing 100W and 12.0OCV at 550C.
Improvement of materials and design for membrane desiccant technology:
The consortium has developed two types of membrane desiccant systems; a combined desiccant and cooling system and a separate desiccant and cooling system. It was found that the combined system was more difficult to optimise as the three parts could not be operated independently, and the complexity of the arrangement caused some leakage to both the supply air stream and to the surroundings of the unit.
Integration of LT-SOFC and desiccant components into an application under challenging constraints including system efficiency, lifetime and cost targets to meet market requirement;
The consortium has successfully proved the concept of a SOFC tri-generation system using a conventional (micro-tubular) SOFC. Delays in development of the LT-SOFC stack meant that the consortium could not deliver a 1-1.5kWe LT-SOFC within the project timeline.
System testing both in the lab and in field-trials under real-life context to improve the whole-system design and the understanding of degradation mechanisms of LT-SOFC stacks.
The consortium has demonstrated performance in the lab and in field trials under real-life context.
An environmental assessment has shown that the LT-SOFC tri-generation system is environmentally advantageous in terms of reducing carbon emissions based on a range of environments. In a UK energy system context the tri-generation system generates up
to 51% annual CO2 emission reductions compared to the base case. The system was only environmentally unsuitable in France and Norway, which contained substantial nuclear and renewable energy supplies.
An economic assessment concluded that at current costs, only a small number of countries would benefit from the installation of a LT-SOFC system. However, component parts, such as LT-SOFC single component technology, membrane separation and open cycle cooling, balance of plant, control and monitoring systems could all be marketed independently of the overall system.
Project Context and Objectives:
Summary description of project context and objectives
Due to the increasing concern over the provision of future energy and global warming, there is a significant interest in the development of alternative clean energy sources and efficient power generators. According to the World Business Council for Sustainable Development, buildings consume 40% of the world’s primary energy using for cooling, heat and power, and most of it is from electricity generated at centralised power stations, where at present up to 70% of available energy is lost. The overall system efficiency is low leading to high waste of energy resources resulting in considerable CO2 emissions and unnecessarily high running costs. Reducing the energy consumption of buildings can make a substantial contribution towards attaining the European Union’s 20/20/20 targets and at least 80% reduction in its carbon dioxide emissions in 2050. But this will only be achieved by moving from conventional centralised power generation systems to onsite highly-efficient clean micro-generation technology.
One of the more promising possibilities for this future energy generation is the solid oxide fuel cell (SOFC), which uses the hydrogen from the gas stream to generate electricity through chemical reactions in the anodes, and the only by-product is water vapour and a modest amount of carbon dioxide. This is more efficient than simply combusting the fuel. The technical assessment demonstrated that if the CHP (combined heat and power) technology is used with SOFC, the total system efficiency can be as high as 90%. CFCL (Ceramic Fuel Cell Ltd, Australia) reported that the SOFC residential market is 17,000 kW per year, thus a big market potential. Even a moderate size city such as Stockholm has a plan to construct green residences incorporating 6000 units (5 kW) fuel cell CHP units.
Unfortunately, although the technical assessment for the SOFC micro-generation system shows a promising future for high energy efficiency with a potential big market, the durability and lifetime of the SOFC system has yet to be solved. These problems arise from fuels, such as natural gas (methane), the widely available fuel in residential buildings, also containing sulfur. Sulfur poisoning and carbon deposition from methane are two major issues inhibiting application of conventional SOFCs with Ni-YSZ (yttrium stabilized zirconia) as anodes. High operating temperature is a further considerable challenge. To achieve a better performance, the conventional SOFCs using YSZ are usually operated around 1000 ºC, but this can only be achieved at technical complexity and consequently cost that inhibits commercialization. A breakthrough on low temperature SOFC (LT-SOFC) materials has been made by the applicant in KTH, based on ceria-carbonate two- or multi-phase nanocomposite, showing an excellent tolerance to the sulphur poisoning and carbon deposition, reaching a high power density of 1.2 W/cm2 at temperature as low as 500 °C. Furthermore, the invented materials have provided feasibility for manufacturing LT-SOFC stacks below 400 €/kWe, compared to more than 1000 €/kWe of the conventional SOFC stacks. Some of these exciting research achievements were recently highlighted by Materials Views and Nature Nanotechnology.
Desiccant system, in the context of HVAC (Heating, Ventilation, and Air Conditioning) applications of indoor environmental comfort, are used primarily where simultaneous maintenance of temperature and humidity control is an important benefit to the user. This technology is often used in tri-generation, also called CCHP (combined cooling, heat and power), where the desiccant system is driven by the heat by-product. If the waste heat from SOFCs is used to drive the desiccant unit, then a tri-generation system will result, supplying not only the power and heat as the conventional CHP technology to the buildings, but also cooling and humidity controlling. According to the extensive work carried out by applicant in NOTT, this desiccant unit could increase the total system efficiency by 13-16%. So, the overall aim of this project is to develop a low-cost durable LT-SOFC tri-generation prototype, based on the breakthroughs in LT-SOFC and the desiccant technologies already made by applicants involved in this project. The proposed system could be used for residential and commercial buildings (e.g. school buildings/offices), providing cooling, heat and power for the living space. It will be tested under real-life context using a unique zero-carbon modular home as part of the Creative Energy Homes at the University of Nottingham. The environmental sustainability of the prototype will be assessed by means of Life Cycle Assessments studies, and the result obtained will be disseminated to industry and research as proof-of-concept of fuel cell systems for stationary applications for sustainable low carbon buildings.
Despite SOFC technology lagging PEMFC and MCFC by a number of years it presents a significant opportunity for many applications, including buildings, due to its fuel flexibility. More stimulus is needed to advance SOFC technology, particularly in Europe, and a low carbon building application will provide this. TriSOFC aims to define, develop and deliver LT-SOFC tri-generation technology in low carbon buildings for early market application. The project will be carried out as an integration of material, nanotechnology, device fabrications and stack, unit constructions to system integrations, field-trials and public demonstration joining closely to the marketing explorations.
TriSOFC aims to design, optimise and build a 1.5 kW low-cost durable LT-SOFC tri-generation prototype, based on the integration of a novel LT-SOFC stack and a desiccant unit. Additional components of the system are a fuel processor to generate reformate gas when natural gas utilized as fuel and other equipment for the electrical, mechanical and control balance of plant (BoP). All these components will be constituents of an entire fuel cell tri-generation prototype system to supply cooling, heat and power, which will first be tested in the lab and, after further optimisation and miniaturisation, under real-life context in the Creative Energy Homes platform built at the University of Nottingham. TriSOFC is primarily aiming at the low carbon building platform using natural gas but will also integrate with other available resources (e.g. alcohol, propane, renewable biomass liquid fuel and biodiesel) with simple modifications. Natural gas was chosen as the fuel due to its widely availability in current residential and commercial buildings compared to hydrogen and other fuel resources. Other renewable fuels will also widely suitable for North European regions, e.g. fuels made from biomass resources. The design of the tri-generation system will be primarily driven by the high efficiency, low-cost and long–term duration. It will open opportunities for exploitation in other sustainable low carbon applications.
Project objectives of the period
The main technical objectives of the period are listed below:
• Improvement of materials for LT-SOFC technology with respect to power density and minimising degradation of cell performance;
• Optimisation of LT-SOFC cell and stack design as well as of the entire generator system for a low cost application; Design of a complete SOFC power system (i.e. including balance of plant and control system) capable of meeting the varying power demands of a low carbon building over a comfortable life space;
• Improvement of materials and design for membrane desiccant technology;
• Integration of LT-SOFC and desiccant components into an application under challenging constraints including system efficiency, lifetime and cost targets to meet market requirement;
• System testing both in the lab and in field-trials under real-life context to improve the whole-system design and the understanding of degradation mechanisms of LT-SOFC stacks.
• Environmental sustainability assessment by Life Cycle Assessments studies carried out according to the International Life Cycle Data System (ILCD) handbook requirements;
• Evaluate the prototype system to international standards and finish the risk assessment, defining the requirements in the applications in sustainable buildings and developing recommended practice for the tri-generation concept.
• Economic assessment and investigation of spin-off opportunities into other market sectors, especially residential building applications;
• Dissemination of information to industry and research via a regularly updated website as well as publications and presentations at relevant conferences;
• Development of exploitation routes for bringing the new technology to market;
• Strengthening of the European position in this technological field.
Achievements of the period
• Improvement of materials for LT-SOFC technology with respect to power density and minimising degradation of cell performance;
The consortium has made significant advances in materials technology that will contribute to improved SOFC performance and other conversion technologies such as solar photovoltaics. Power density of almost 800mW/cm2 at 550C and improved performance over conventional FCs at 550C.
• Optimisation of LT-SOFC cell and stack design as well as of the entire generator system for a low cost application; Design of a complete SOFC power system (i.e. including balance of plant and control system) capable of meeting the varying power demands of a low carbon building over a comfortable life space;
A 2-cell 6cm x 6cm planar-type SOFC produced around 12W at 530C and in the best case we produced over 2.0 OCV and generated nearly 20W.
Good repeatable single cell performance was achieved at 1.1OCV and 9W at 540C.
Work was carried out investigating thin membrane stacks (~0.5mm thickness) and results showed output of over 2.0 OCV and 18W.
100W stack has been developed with 15 6cm x 6cm membranes in a stack, producing 100W and 12.0OCV at 550C.
• Improvement of materials and design for membrane desiccant technology;
The consortium has developed two types of membrane desiccant systems; a combined desiccant and cooling system and a separate desiccant and cooling system. It was found that the combined system was more difficult to optimise as the three parts could not be operated independently, and the complexity of the arrangement caused some leakage to both the supply air stream and to the surroundings of the unit.
• Integration of LT-SOFC and desiccant components into an application under challenging constraints including system efficiency, lifetime and cost targets to meet market requirement;
The consortium has successfully proved the concept of a SOFC tri-generation system using a conventional SOFC. Delays in development of the LT-SOFC stack meant that the consortium could not deliver a 1-1.5kWe LT-SOFC within the project timeline.
• System testing both in the lab and in field-trials under real-life context to improve the whole-system design and the understanding of degradation mechanisms of LT-SOFC stacks.
The consortium has demonstrated performance in the lab and in field trials under real-life context.
• Environmental sustainability assessment by Life Cycle Assessments studies carried out according to the International Life Cycle Data System (ILCD) handbook requirements;
The consortium has shown that the LT-SOFC tri-generation system is environmentally advantageous in terms of reducing carbon emissions based on a range of environments from UK, Portuguese and Hong Kong climates.
• Evaluate the prototype system to international standards and finish the risk assessment, defining the requirements in the applications in sustainable buildings and developing recommended practice for the tri-generation concept.
The risk assessment and international standards evaluations have shown that the market for the LT-SOFC tri-generation system is wide and highlighted factors that needed to be considered in order to commercialise the system, which include reductions in first cost, major improvements in reliability and durability as well as evaluating incentives (feed-in tariffs, subsidies, etc) for the take-up of renewable and low carbon technologies.
• Economic assessment and investigation of spin-off opportunities into other market sectors, especially residential building applications;
The economic assessment concluded that at current costs, only a small number of countries would benefit from the installation of a LT-SOFC system. However, component parts, such as LT-SOFC single component technology, membrane separation and open cycle cooling, balance of plant, control and monitoring systems could all be marketed independently of the overall system.
• Dissemination of information to industry and research via a regularly updated website as well as publications and presentations at relevant conferences;
A website has been set up since the beginning of the project and is regularly updated with information and news. The consortium is engaged in many scientific, engineering, business and industrial activities and has published over 100 journal and conference papers.
• Development of exploitation routes for bringing the new technology to market;
The consortium has engaged with the fuel cell and hydrogen community to understand better the current market and future trends. Ibrahim Pamuk of Vestel Industries is leading efforts to engage with businesses in the power generation and domestic/commercial building industries
• Strengthening of the European position in this technological field.
The major breakthroughs in nano-scale composite materials development will put the European Union at the forefront of technological development, not only in terms of SOFC technology but other conversion technologies.
Description of S & T results/foregrounds
Work packages and tasks of the period
WP1 Project management and co-ordination
WP2 Desiccant unit development
WT2.1 Heat and mass transfer
WT2.2 Working fluid and membrane evaluation
WT2.3 Heating/cooling unit design and test
WT2.4 Heat storage investigation
WP3 LT-SOFC component and single cell fabrication
WT3.1 Material engineering and production
WT3.2 Cell component/MEA development
WT3.3 MEA and single cell fabrication
Task 3.4: Scale up
Task 3.5: Testing and evaluation
Task 3.6: Development of carbonate free nanocomposite cell:
WP4 LT SOFC stack development
WT4.1 Stack construction and development
Task 4.2: Flat-tubular/group type stack
Task 4.3: Planar type stack
Task 4.4: Micro-tubular type stack:
WT4.5 Modelling
Task 4.6: Testing and evaluation
WP5 Tri-generation system integration
WT5.1 Reformer development for natural gas and bio-fuel
WT5.2 Thermal management system
WT5.3 Power management system
WT5.4 Electronic control system
WT5.5 Tri-generation system design
WP6 Prototype system testing
WT6.1 Laboratory test of the components
WT6.2 Assemble of the prototype
WT6.3 Testing and modification of the prototype
WT6.4 Analysis of the testing results
WP7 Field trials of the prototype system
WT7.1 Prototype system installation and commission
WT7.2 Prototype system testing under real-life context
WT7.3 Thermal management analysis
WP8 Economic and environmental assessments
WT8.1 International standard evaluation
WT8.2 Economic evaluation
WT8.3 Environmental sustainability assessment
WT8.4 Risk assessment
WP9 Dissemination activities
WT9.1 project website
WT9.2 Dissemination activities
The deliverables for the period
D2.1 Working fluid and membrane evaluation
D2.2 Desiccant cooling/heating unit
D2.3 Desiccant heat storage unit
D3.1 LT-SOFC material and production report
D3.2 Component, MEA and single cell fabrication
D3.3 Progress report of on carbonate free nanocomposite fuel cell testing
D3.4 Report on performance and durability of carbonate free fuel cell
D4.1 Device construction report
D4.2 Report planar stack
D4.3 Report on micro-tubular type stack
D4.4 Carbonate free Device/stack modelling and performance testing results
D5.1 Reformer development report
D5.2 Thermal management system
D5.3 Power management system
D5.4 Electronic control system
D5.5 Tri-generation system design report
D6.1 Main component pro-testing results
D6.2 Prototype detail construction data
D6.3 Prototype testing and evaluation report
D7.1 Prototype installation and commission report
D7.2 Prototype testing and analysis results
D7.3 Prototype demonstration
D8.1 International standard evaluation report
D8.2 Economic assessment results
D8.3 Environmental assessment results
D8.4 Risk assessment report
D9.1 Project website
D9.2 Dissemination activity reports
Project Results:
Modifications to the original DoW were requested to take account of one partner withdrawing from the project due to bankruptcy and technical challenges in developing single component materials and stacks within the framework of the project. A summary of the amendments requested and granted is provided below:
Modification 1: The consortium proposes that some funds are transferred from KTH budget to UBHAM budget to enable them to carry out tri-generation systems integration (WP5) and prototype systems testing (WP6). The plan is to buy a SOFC suitable for tri-generation integration and testing with the funds and enable the UBHAM partners to contribute to its development. In the original DoW, UBHAM played a minor role in WP5, but with the abandoning of plans to develop microtubular stacks, the personnel will contribute more time and resources in these work packages. We propose that 8,550Euro is transferred from KTH to UBHAM direct costs budget to enable them to fund the acquisition of an off the shelf fuel cell and ancillary equipment required to set up the system, as suggested in the mid-term review report.
Modification 2: The original DoW allocated 17 person months to prototype systems testing, but the consortium does not intend to request an extension to the project and so we request that some of the person months are re-allocated to WP3 and WP4, so that UBHAM can continue to investigate the application of carbonate free nanocomposite materials in microtubular fuel cells. If we can show a breakthrough in materials development and processing in this particular application then the consortium will have achieved a significant outcome and the application of the single component system will have much wider potential. We request that the personnel allocation of 17 months in WP6 should be reduced to 11PMs, with the remainder increasing allocation to 12PMs in WP3 and 12PMs in WP4. An additional work task has been added to the DoW, WT3.6 to enable us to develop the single later nanocomposite materials and membranes, and two further deliverables are proposed, D3.3 “Progress report of on carbonate free nanocomposite fuel cell testing” and D3.4 “Report on performance and durability of carbonate free single cell”. D3.3 will become a stop/go point in the project and if no progress is made then the project officer will be able to terminate the contract.
Modification 3: KTH do not have the capability to mass produce materials and manufacture large scale planar-type membranes, so we propose that some of the person months allocated to KTH should be reallocated to UBHAM, to enable them to carry out more work that was set out in the original DoW. In the first amendment, the personnel allocation for KTH was increased from 40PMs to 69.5PMs when all tasks were reallocated from GETT to KTH. As KTH are unable to carry out some of these tasks, we propose that KTH personnel allocation is reduced from 69.5PMs to 63.5PMs. In parallel, UBHAM personnel allocation will be increased from 42PMs to 48PMs.
Modification 4: The original target for the development of a 1-layer LT-SOFC was for 1-1.5kWe but delays in the work plan have meant that this outcome is unlikely to be successfully realised. The consortium is proposing that to meet realistic objectives within the timeline, we ‘prove the concept’ by building a small planar LT-SOFC fuel cell stack. An additional deliverable D4.4 “Carbonate free Device/stack modelling and performance testing results” has been added to the DoW.
Modification 5: The development of a LT-SOFC tri-generation system requires the development of a LT-SOFC stack, but the stack will require a great deal of research and development to reach the point of integration with other systems. Therefore, we propose to obtain a conventional SOFC that is capable of tri-generation capability. The mid-term review report recommended that the consortium purchase an off-the-shelf SOFC to enable us to carry out prototype development, integration and field trials. One unit has been identified as a 200We/1kWh SOFC manufactured by Adelan Ltd, UK. We propose that some of the resources re-allocated to UBHAM and resources available to NOTT will be used to purchase the unit, as recommended in the mid-term review report. The plan is for the unit to be installed and set up in UBHAM laboratories and its performance monitored for up to 100hours. NOTT and UBHAM will collaborate to develop the CHP/tri-generation system. On completion of fuel cell performance testing, the system will be transported to NOTT to be integrated in the tri-generation system. The system will then be monitored over a range of operating conditions at NOTT. The total cost of the unit is estimated to be around 13K Euro, and the costs will be split approximately 60:40 between NOTT and UBHAM.
Modification 6: It will not be possible within the timeframe of the project to carry out field trials with either the LT-SOFC stack or the integrated SOFC highlighted in Amendment 6, so we propose to install the tri-generation system in one of the creative energy houses at NOTT. Field trials will be carried out over about 6 months and should be concluded by month 36 of the project.
Modification 7: Following the recommendations of the mid-term review we have amended the DoW part B to include an exploitation plan and engagement strategy with the European and World-wide fuel cell and hydrogen community. Please refer to the document for further details.
Modification 8: IDMEC ceased to exist after 31st December 2015 and it was merged (personnel, equipment, installations) with the existing INEGI. From this date on, all rights and obligations of IDMEC in this project will be transferred to INEGI. The amendment requests that IDMEC is terminated from the consortium and that INEGI is added to the consortium as a beneficiary.
Work Package 2: Desiccant unit development
D2.1. Working fluid and membrane evaluation
Introduction
Up to a half of all energy consumption and up to a third of carbon dioxide emissions in the developed world are from buildings and almost a half of this is due to heating in winter in cold climates and cooling in summer in hot and humid climates. A combination of energy efficiency measures within buildings and efficient building services systems could dramatically reduce energy consumption and carbon dioxide emissions in the building sector. Combined heat and power (CHP) and combined cooling, heating and power (CCHP), also known as Trigeneration, could reduce carbon dioxide emissions in domestic and non-domestic buildings by exploiting waste heat for heating in winter and cooling in summer, improving the overall efficiency of the power generation system, replacing conventional heating and cooling plant and more fully utilising the waste heat.
The low temperature solid oxide fuel cell being developed through this project, wastes up to a half of the primary energy supplied as heat, and so the exploitation of this heat will improve the performance of the fuel cell in comparison to conventional solid oxide fuel cells.
Waste heat can be stored sensibly in conventional tanks as hot water, stored as latent heat using ice or other phase change materials (PCMs), or chemically, as binary systems that absorb or desorb the heat of absorption/desorption. Partner 4 is carrying out analysis of the options for storing the waste heat from the fuel cell.
Modelling work is an essential task for the design, building, testing and optimisation of the liquid desiccant air conditioning unit for the TriSOFC system. Modelling work has been used to identify the important operating parameters of the desiccant unit, to facilitate optimisation, to predict the performance of the unit under variable conditions and to assist in sizing of a unit suitable for the application. Two stages of modelling work have been conducted for the desiccant unit. A preliminary 1-D model was used to obtain initial estimates and to select a suitable working fluid, then a more comprehensive 2-D model was developed for specific unit sizing and fabrication.
One-dimensional modelling
Preliminary modelling work has been carried out for the desiccant dehumidification system. The performance of a desiccant air conditioning system is strongly related to the quantity of water condensed from the humid air to the desiccant solution in the dehumidifier. In the literature there are numerous validated models predicting this quantity, however it should be stated that the majority of these correlations are only valid to the specific desiccant unit and solutions for which the correlations were obtained. Therefore, a simplified model to estimate the preliminary performance of the novel cellulose fibre packed bed system based on fundamental equations would be valuable at this stage of modelling work.
The preliminary modelling task has called upon the work of (Gandhidasan 2004; Gandhidasan 2005). Gandhidasan describes a relatively simple model for the preliminary design of a liquid desiccant air conditioning system, using dimensionless vapour pressure and temperature difference ratios. These ratios are used to derive an expression to determine the mass of water vapour condensed from the air to the solution in the liquid desiccant dehumidifier shown and for the mass of water vaporised from the desiccant solution to the scavenging air stream in the regenerator, both in terms of known operating parameters. The model has been validated by well-regarded experimental data presented in the literature provided by Fumo and Goswami (2002) with very good agreement.
Basic working principle
In the dehumidifier mass transfer (dehumidification) occurs due to differences in vapour pressures. The cool concentrated desiccant solution exhibits a vapour pressure which is lower than that of the water vapour present in the humid air, therefore the moisture moves from the air to the solution. In addition to this in summer it is expected that the temperature of the humid air that enters the desiccant dehumidifier is higher than the desiccant solution temperature, therefore sensible heat transfer will also occur. The greater the cooling of the desiccant solution prior to entering the dehumidifier, the greater the heat and mass transfer, and thus the greater cooling output. Following dehumidification, the weak desiccant solutions needs to be regenerated i.e. re-concentrated. This takes place in the regenerator. Prior to entering the regenerator the desiccant is heated first in the desiccant to desiccant heat exchanger (also used to pre-cool the desiccant flowing to the dehumidifier), then using an external source e.g. the fuel cell. In the regenerator, the heated weak desiccant solution will have a vapour pressure higher than that of the scavenging air stream, thus the water vapour present in the solution will transfer to this air stream, thus re-concentrating the desiccant solution ready for dehumidification in the dehumidifier.
The modelling work was carried out using Engineering Equation Solver (EES), a general equation solving program that can numerically solve thousands of coupled non-linear algebraic and differential equations. Air and water property routines are inbuilt functions in EES, making calculations involving psychrometric functions much easier. Once the model had been developed, and adjusted such that the output results were in good agreement with the experimental and theoretical results presented by Gandhidasan (2004) and Fumo, parametric analyses were carried out. Parametric analysis for the dehumidifier and regenerator has looked at the variation of mass condensed/evaporated in the dehumidifier/regenerator respectively with:
• Cooling water temperature
• Regeneration temperature
• Fluid flow rates (air and desiccant)
• Fluid flow rate ratios
• Heat exchanger effectiveness
• Different desiccant solutions – LiCl, CaCl2 and CHKO2
Furthermore a parametric analysis of the inlet operating conditions of the desiccant unit was investigated; this was to see the effect environmental conditions had on performance. In this analysis, the following were assessed in terms of cooling output:
• Air inlet temperature
• Air inlet relative humidity
The parametric analysis has been used to identify the parameters that have the greatest influence on performance. It has also shown the optimum environmental conditions for which the system should be operated in. The initial stage of preliminary modelling results is split into two sections: dehumidifier and regenerator.
Summary of initial modelling results
The moisture removal rate of the process supply air is strongly controlled - assuming constant mass flow rate, by desiccant temperature and cooling water temperature. The air inlet conditions have a large influence on performance in terms of cooling output. The unit will generally perform better in a hot and more humid climate such as southern China, or the Middle East as opposed to drier cooler climates such as the UK. The Potassium Formate desiccant solutions shows the highest cooling performance for the given conditions, and with its lower environmental impact compared to LiCl and CaCl2, is a suitable solution for the desiccant unit in the TriSOFC system.
As the regeneration heat source temperature increases, the mass of water vapour vaporised from the weak desiccant solution increases. Although too high a desiccant concentration is not always required, a higher regeneration temperature could mean a lower desiccant and air flow rates are required (beneficial to COP) in order to yield a similar outlet concentration and for the mass balance between dehumidifier and regenerator to be satisfied.
Although basic, this modelling has helped understand the fundamentals of the liquid desiccant system, namely the interactions observed in the parametric analysis. The current model does however have its limitations and is not particularly robust; for example it does not include the heat and mass exchanger effectiveness of the cellulose fibre membrane, geometry of the contactor or desiccant carry-over. Furthermore, there have been some issues encountered with the described model such as assessing the variation of desiccant concentration and mass flux condensed/vaporised. However the above model has provided a valuable quick evaluation tool for operational performance of liquid desiccant dehumidification systems.
This initial modelling work will be essential for the development of a more comprehensive 2D component based model and future intended experimental work.
The next stage of modelling will aim to develop a model in order to obtain more accurate, specific results for the novel cellulose fibre based liquid desiccant air condition unit, operating with a potassium formate solution. Following the development of the more comprehensive desiccant contactor model, the aim will be to develop a system model, linking the dehumidifier and regenerator models together, including a desiccant to desiccant heat exchanger. This work will enable parametric analyses to be carried out to determine the optimum operating strategies for improved system COP, as this will be crucial to the fuel cell tri-generation systems overall performance.
Summary of the recommendations from previous reviews
The mid-term review highlighted severe delays in the project and acknowledged the difficulties arising from the novel character of the materials and recipes used in developing the LT-SOFC fuel cell, the withdrawal of GETT Fuel Cells from the project due to bankruptcy and inadequate coordination and co-operation between partners. The consortium has agreed to submit an amendment to the DoW that would address some of the delays and enable the project to reach a successful conclusion.
Work progress and achievements during the period
WP2: 1-D and 2-D modelling of the desiccant dehumidification and cooling system. Analysis of individual components and the whole system have been developed and tested against published data. Computer simulations developed for the modelling were modified to analyse the geometry of the individual heat/mass exchangers and to evaluate and compare different working fluids. It was concluded that Potassium Formate offered the best combination of thermophysical properties, dehumidification and regeneration performance and health and safety considerations.
A desiccant dehumidifier and cooler has been designed, commissioned and built. It will combine a regenerator, a dehumidifier and cooler and an intercooler in one unit. The unit has been tested in laboratory conditions at the University of Nottingham and has demonstrated cooling output of 1.8kWh for a heat input of around 1.5kWh giving an average COP of 1.2.
Investigation of phase change materials (PCMs) for storing heat from the SOFC and was found that for a fuel cell operating 21 hours per day, the PCMs could store enough energy to maintain indoor temperatures at approximately 20ºC for winter heating conditions in Porto. However, for the situation on Nottingham, the PCMs could only store enough energy to maintain indoor temperatures at 16ºC, and so back-up heating would be required. It was concluded that desiccant storage offered a better solution to storage and thermal management.
A SOFC with a heat output of 1.5kW would be suitable for use directly in a dwelling in winter. Therefore, there would be no need for winter storage. However, the heat demand from a desiccant cooler in would be higher than its maximum output, so storage of heat or the storage of coolth is required. A thermal storage system has been designed to store desiccant solution suitable for the heat output of the fuel cell and the cooling requirements of a dwelling in Nottingham.
WP3: This work package focuses on the optimising the functional nanocomposite materials, ceria-based two or multi-phase materials, to fabricate LT-SOFC components and MEAs. Fabrication protocols with different MEA structures will be considered during developing the program. Various methods will be combined for fabricating single cell. Three types of single cells will be fabricated: the conventional planar type cell, the flat-tubular with completed single cell technology developed by GETT/KTH and the micro-tubular type cell developed by IVF. This amendment proposes that the consortium concentrates on the planar and micro-tubular fuel cells. GETT were tasked with developing and scaling up the stack, but their expertise in flat tubular stacks has been lost to the consortium as well as causing delays in cell development. In the remainder of the project, it is proposed that KTH/VSS develop the planar single cells and UBHAM/IVF develop the micro-tubular single cells. The testing will be performed to components and single cells to evaluate the different process condition and modify the fabrication procedure. Based on the optimization process, the fabrication sizes will be scaled-up to meet applications of LT-SOFC stacks in the tri-generation system.
Materials
The research activities on single-layer fuel cells (SLFCs) or “Three in One” fuel cell have opened new doors for keeping ahead with two major areas of focus: improvement of SLFC performances by contributing new materials, and scientific understanding of the SLFC nature and science as well as technological developments. The successful developments of design and synthesized new materials composed of the ionic ceria based materials and the semiconductors, e.g. mixed transition metal oxides, LiNiCu based-oxide etc., perovskite oxides as well as layered structured metal oxides, combining ionic and semiconducting properties for SLFCs as given below:
■ Ion conducting materials:
Doped and co-doped ceria, e.g. SDC (Sm3+ doped CeO2), ceria-composites, with or without carbonates were prepared.
■ Semiconducting materials:
1) Various transition element oxides, Ni, Cu, Co, Fe, Mn etc;
2) Perovskite oxides, BaSrCoFe, LaSrCo, LaSrCoFe, LaSrMn, LaSrMnFe, LSCT, SmSrCo, SrFeMo, BaSrFeMo etc (novel perovskite cathode material) and BaCaCoFe composite cathode were synthesized.
3) Layered structured materials: LiMOx (M=Ni, Cu, Co, Fe, Mn, Mo), thousands designs and recipes were tested with extensive efforts.
D3.1: The main objective of the TriSOFC project is to develop a low temperature (500-600C) solid oxide fuel cell suitable for use in domestic dwellings. The ambitious target of producing a low cost (<400euro/kWe), durable (>40,000 hours) system is being delivered by teams across the European Union with expertise in fuel cells and trigeneration systems. The first year of the project has been targeted at the basic science of developing the novel single component nano-composite material, fabricating and testing single fuel cell elements, developing scale-up methods and investigating novel working fluids, membranes and storage methods for the trigeneration system. Single component materials have been developed by KTH (LiNiCuZn) and tests on pellets have shown improved performance compared to two and three component systems. The maximum performance achieved in this period was
OCV = 0.95 V, I = 1016 mA/cm2 at 230 mV @ 550ºC
Compared to a three component pellet with performance of
OCV= 0.95 V, I = 875 mA/cm2 at 180 mV @ 550ºC
D3.2: Nano-composite materials have been developed by KTH with single component characteristics. Tests have been carried out and good results have been obtained. At an operational temperature of 500-550C the OCV achieved was 0.95V and the current density was 1016 mA/cm2 at 230 mV. A 6cm x 6cm x 1mm thickness fuel cell has been developed with a maximum power output of 16W.
Micro-tubular cells have been fabricated by UBHAM by extrusion. Test results show performance comparable with KTH (OCV = 0.9V I = 0.8A P = 0.22W. Durability is poor (150-200 min). Micro-tubes thin walled and off-centered. An Investigation into the extrusion of thicker walls to improve performance and durability is to be carried out. New extrusion dies and barrels have been commissioned. Iso-static pressing was to be investigated but the equipment has not been delivered, and so the work has been delayed.
D3.3: KTH is continuing its efforts for electrolyte free fuel cell recipes which are internationally recognized by fuel cell experts which are success of this project. An article has been accepted for publication in Journal of Power Sources as given below. FP7 TriSOFC project contribution has been acknowledged in this work. Another paper was submitted in 5th World Hydrogen Technologies Convention (WHTC 2013)-Shanghai Conference. Our research work was selected for oral presentation in the conference where we have successfully presented the work for advanced fuel cell technology. The work has been published in the International Journal of Hydrogen Energy. The abstract of this work is given below. KTH has got an achievement making joint efforts with its strategic partners and an electrolyte with high conductivity for fuel cell application is generated recently as explained below. By preparing the composite electrodes a very high device performance is achieved. ‘‘Scaled up low-temperature SOFCs with MgZnSDC composite electrolytes for applications’’, in this study, a new type of the Mg0.4Zn0.6O/Ce0.8Sm0.2O2-δ (MZSDC) composite electrolyte was synthesized using one step co-precipitation method. Recently world record results have been achieved in the experiments with OCV = 1.19 V for EFFC with repeated results by KTH.
At UBHAM, all as-prepared micro-tubular LT-SOFC single cells are tested in the UBHAM lab. Besides of the tubes itself, the influences of temperature, flow rate, cell sealing conditions are also investigated. The durability of some selected tubes was also checked for up to 100 hours operation at 550C. Due to the poor durability of the tubes with current Nanocomposite materials, all testing are still conducted with H2.The experimental results demonstrated the power performance is highly sensitive to the tube structure, although the testing conditions do have some influence. The power performance of tubular LT-SOFCs can be potentially improved by the optimal structure, but the durability is still a big challenge at the moment and this can hopefully be addressed by the new generation of Nanocomposite material which was recently confirmed by KTH.
D3.4: The research and development activities have been done on our recent research breakthrough based on the single-layer fuel cells (SLFCs) or “Three in One” fuel cells from new functional semiconductor-ionic materials, technologies for device and stack demonstrations. We have succeeded in the targets according to the project deliverables as below:
1. New materials have been scaled up for production at kgs level thus guaranteed extensive uses for the project (WP3)
2. Scaling up of 6x6 cm2 cells fabricated and about 2000 of 6x6 cm2 engineering fuel cells with new materials and new invention of the single layer fuel cell (SLFC) devices instead of the conventional anode/electrolyte/cathode structure. (WP3)
3. Each 6x6 cm2 SLFC reached at 8-10W (Targeted at min 5W) below 550C. (WP3)
Scaling up production of the core material and single cells have been performed; Nanocomposite single component materials have been developed by KTH. A variety of single cells have been fabricated with different combinations of semiconductors and ionic conductors. Tests have been carried out and good results have been obtained by KTH. Carbonate-free new single component materials with better performances have been successfully developed and subjected for scaling up productions in kgs. The single-component nanocomposite free electrolyte-free fuel cells (EFFCs) have been scaled up for engineering large size 6x6 cm2 fabrications by investment for purchasing combined with the hot-pressing machine.
At an operational temperature of 500-550C the OCV achieved was 0.95V and the current density was 1016 mA/cm2 at 230 mV. A 6cm x 6cm x 1mm thickness fuel cell has been developed with a maximum power output of 16W.
Micro-tubular cells have been fabricated by UBHAM by extrusion. Structure analysis demonstrated the networking distribution of the semiconductor phases and ionic conductive phases in pellets; Single-component micro-tubular SOFCs, with ID 1.5-1.6 mm and OD 2.3-3.2 mm, were extruded and tested. The OCV reached 1.0 V. The maximum power density obtained was 260 mW cm-2 at 550C. The durability tests of 15 hours was performed and the current dropped from 0.52 A to 0.22 A at 0.5 V;
WP4: A planer-type stack is to be developed by KTH/IVF/GETT. The withdrawal of GETT from the project due to financial difficulties and problems with producing stable and durable materials has delayed this work task. 6cm x 6cm membranes have been tested in a two cell stack. Output of 12W at 550C has been demonstrated. KTH reported durability of over 100hours.
VSS/GETT has carried out mathematical modelling of a SOFC planar stack. A three component (anode/cathode/electrolyte) was analysed and its results compared to work carried out on a fuel cell obtained by VSS.
Dr. Zhu from KTH established a joint lab with a strategic partner matching local finance to develop cells and stack. It involves metal bipolar plate, soft mica sealing materials and single layer engineering and big amount of numbers for large size cells fabrications. The single cell tests have achieved great successes with one cell delivering 10W (6x6 cm2) in average at 500-600C; based on the single cell measurements, we started construction of two and five cells short stacks. We have achieved the two cell stack OCVs at 2.2 V (reached perfect expected value) and the power outputs between 3-4 watts at temperature 380-500C. Though we have not enabled to measure our stack at desired temperature 550-600C as designed power outputs at 20W, these results are the first world record on such extremely low temperature SOFC stack data. It proved our single-component electrolyte free fuel cell (EFFC) has taken away the electrolyte bottleneck with great low temperature breakthroughs. In the latter development, improved the two cell stack power outputs at 12W at around 500C using the bipolar plates with improved gas distribution channels and sealing-free stack design.
Due to integration of new resources for both invested machine/facilities and team/manpower takes time, our stack developments have just started. Initial results are promising but not reached the expected power outputs. To overcome the current technical problems, our new solutions with new efforts will be soon restarted. For a time being we will overcome the current technical challenges and present more successful results in next term period.
D4.4: By modelling, according to former planar type stack design studies and experiences two type of stack were designed, verified by performing flow simulations and manufactured. Planar type LT-SOFC stacks fabricated from 6x6 cm2 cells were tested based on 2-5 cells installation, and the optimal stack with 4 cells has been operated in accumulating for 100 hours, subjecting 10 thermal cycling from operational temperature shut-down to room temperature. A 100W stack was successfully demonstrated using 15 pieces of 6x6 cm2 SLFC cells. In parallel, we also co-developed 1000W conventional SOFC stack using NiO-YSZ anode supported thin film YSZ incorporated by GDC buffer layer and LSCF cathode, we reached at 1020W at 700C. The conventional 250We micro-tubular SOFC stack was also tested with industrial propane for ca. 130 hours, including 19 thermal cycles
from room temperature to operating temperature (ca. 700C), 1 forced stop and 1 severe sulfur poisoning. These joint efforts from Partner 2, 3 and 6 also effectively supported new material stack developments.
WP5: Results of this work showed that bi-metallic Ru-Ni containing ceria-alumina supported catalysts were more stable than mono-metallic catalysts containing only Ni or Ru, in the reforming reaction of kerosene. A reforming catalyst was developed and produced based on 500-600C range. And using numerical studies reforming reactor design was done based on 500-600C range and 100W output power with assumed fuel utilization.
In our studies direct decomposition, steam reforming and autothermal reforming of methane, used to obtain hydrogen rich gas mixture were examined. In this conversion process the catalysts containing “Ni”, “Fe” and “Ru” metals were prepared by using commercial alumina as carrier. Methane conversion was examined by experiments and the gas mixture which came into effect as experimental result was analysed by the help of Agilent branded gas chromatography device and the volumetric percentages of hydrogen which went out were compared. In the conversion experiments of methane with steam reforming and autothermal reforming the effect of parameters such as temperature, gas feeding velocity and the amount of steam to “H2 “ quantity was examined. The coking period was associated with the decrease of hydrogen quantity in the gas mixture going out during direct decomposition, steam reforming and autothermal reforming of methane experiments. It was observed that the coking periods differed according to conversion methods and depending on the experimental conditions in three methods investigated.
WP6:
Because of delays in developing a planar type LT SOFC stack for integration with the tri-generation system, the consortium applied for an amendment to the description of work. This entailed developing the LT SOFC membranes and stack in parallel with proving the concept of a tri-generation SOFC. In order to prove the concept, the consortium obtained a commercially available SOFC based on micro-tubular membrane technology developed by Adelan Ltd (UK). The SOFC had a performance of 250W electrical output and approximately 1000W waste heat output. This was assessed as appropriate for domestic scale applications where low power constant output electricity was required and where a large quantity of heat could provide heating and cooling to the building.
The micro-SOFC units was totally tested at UBHAM for approximately 130 hours, including 19 thermal cycles from room temperature to operating temperature (@ 700C), with one forced stop and one severe event of sulphur poisoning at around 80 hours. High purity propane gas (99.5%) was used for approximately 66 hours for the first 8 cycles, and then BBQ propane gas was used from the 9th thermal cycle until the end. Results showed stable voltage output of 12.3-12.4V and a maximum power output of 250We. Sulphur poisoning at 80 hours caused a rapid fall-off in output, but power output recovered to 140W after about , but demonstrated recovery of over half of the original performance after about 90 hours.
Following fuel cell performance tests at UBHAM, the unit was transported to NOTT for integration with the desiccant unit. A second desiccant dehumidification and cooling unit was designed, constructed and tested following the identification of problems with the original design and comments from the mid-term reviewers that work should be done to reduce the size of the unit. The first version combined the regenerator, dehumidifier and intercooler into one unit. The second version separated the three processes so that they could be operated independently.
Results show increased dehumidifier performance with increasing inlet air temperature, relative humidity, air volumetric flow and desiccant solution volumetric flow. A maximum moisture removal rate and cooling output achieved were 0.3203 g/s and 954 W respectively. Over the testing conditions presented, the latent (dehumidifier) effectiveness was in the range of 30 – 40%. Unlike the IDCS, the SDCS dehumidifier component tests have been conducted within the environmental chamber. As a result, the water and desiccant fluids were at ambient temperature, this had an impact on the moisture absorption capacity of the desiccant solution and the cooling output.
Dehumidifier performance will need to be balanced by the available regeneration capacity obtainable from the SOFC CHP system during tri-generation system integration. Next, the regenerator component analysis is presented.
Results show increased regenerator performance with lower inlet air temperature and relative humidity, increased air volumetric flow and desiccant solution volumetric flow. Regenerator performance is also improved with increasing hot water volumetric flow in the heating circuit and hot water flow temperature. A maximum moisture addition rate of 0.4331g/s was achieved, with a regenerator thermal input of 1588 W. During tri-generation system integration, the performance of the regenerator will be largely dictated by the available thermal energy from the SOFC CHP system. To ensure balanced SDCS operation, this will inform the permissible moisture removal rate that the dehumidifier should be operated at.
WP7:
Technical and commercial issues have meant the 1.5kWe building installed (BlueGEN) SOFC CHP system was not available for tri-generation system integration. However, using collected empirical SOFC and SDCS data, a theoretical tri-generation system integration analysis has been completed. The tri-generation system performance has been evaluated at a 1.5kWe and 2.0kWe capacity. The two cases generate a cooling output of 332W and 649W respectively. The highest tri-generation efficiency of 71.1% is achieved at a 2.0kWe capacity; however the electrical efficiency is lower than the 1.5kWe case. As a result, the 1.5kWe case produces the greatest cost and emission savings of 61% and 69% respectively. The inclusion of liquid desiccant air conditioning technology provides an efficiency increase of up to 28% compared to SOFC electrical operation only. The performance of the novel tri-generation system is competitive with other systems of this capacity reported in the literature. The results demonstrate effective pairing of SOFC and liquid desiccant air conditioning technology in a tri-generation system application. The theoretical tri-generation system integration analysis has achieved the thesis technical objective of a 1.5kWe system operating at an electrical efficiency of 45% or more. The encouraging performance is primarily due to the high electrical efficiency of the SOFC and the reasonable thermal COP of the liquid desiccant system. Technical and commercial issues with the SOFC highlight the real challenge of fuel cell deployment in the built environment.
Following the failure of the 1.5kWe SOFC, a 250We micro-tubular SOFC had to be acquired. The novel tri-generation system concept has been proven experimentally using the micro-tubular SOFC. The experimental results demonstrate regeneration of the potassium formate solution using the thermal output from the SOFC in the first of its kind tri-generation system. Optimisation has shown that a 2.2L.min-1 regenerator desiccant volumetric flow facilitates best performance. The novel system can generate 150.4W of electrical power, 442.6W of heat output and 278.6W of cooling. Due to its low temperature regeneration requirement, potassium formate at a 0.65–0.7 mass concentration is an appropriate desiccant solution for a SOFC tri-generation system. When integrated with the micro-tubular SOFC, the SDCS demonstrates a COPth of 0.62 an encouraging value for a waste heat driven cooling system of this capacity. Instantaneous tri-generation system efficiency is low at approximately 25%. This is primarily due to the low capacity and poor performance of the micro-tubular SOFC. Sulphur poisoning has caused a 40% reduction in micro-tubular SOFC electrical output to 150W. Insufficient WHR means only 450W of thermal energy is available for regeneration purposes, and thus the cooling output is low. However, it has been suggested that if these issues are addressed, the novel system can provide higher overall efficiency. A daily tri-generation performance analysis is presented which serves to demonstrate the novel system operating in a building application. In such a scenario, 527W of cooling is produced and a daily tri-generation efficiency of 37.91% is presented. This is an encouraging value for a tri-generation system of this capacity. Compared to a base case scenario, the novel tri-generation system generates a cost and emission reduction of 56% and 42% respectively, demonstrating the potential of the novel tri-generation system in applications that require simultaneous, electrical power, heating and dehumidification/cooling.
The difference in performance seen between the two tri-generation systems presented demonstrates the significance of (a) the performance of the SOFC component and (b) the requirement of optimal pairing of components, in the development of an efficient and effective tri-generation system. The micro-tubular SOFC was acquired at short notice to replace the 1.5kWe BlueGEN SOFC. As seen in the low thermal output, it is not the ideal match for the developed SDCS. However, the novel tri-generation concept has been successfully demonstrated. Both tri-generation system analyses presented have considered balanced liquid desiccant system operation. This is a stipulation other tri-generation systems employing liquid desiccant technology reported in the literature have not reported and demonstrates the strength and rigour of the work presented.
The aim of the prototype development is to design, develop and test an efficient and effective tri-generation system based on SOFC and liquid desiccant air conditioning technology. This chapter has demonstrated a clear contribution to new knowledge with the development and evaluation of two SOFC liquid desiccant tri-generation systems and as a result it is proposed that the thesis aim has been completed.
Based upon the experimental work, three general conclusions are provided with respect to the design, development and testing of an efficient and effective tri-generation system based on SOFC and liquid desiccant air conditioning technology for building applications.
• SOFC and liquid desiccant is an effective technological pairing. The inclusion of liquid desiccant can bring significant improvement to system performance, particularly in applications requiring simultaneous electrical power, heating and dehumidification / cooling.
• Overall tri-generation system performance is more influenced by the SOFC component than the liquid desiccant. Appropriate matching of component capacity is necessary.
• The novel tri-generation system concept has been demonstrated experimentally. Future work needs to focus on improving the current unreliability and sensitivity of fuel cell technology.
WP8: In our economic assessment (WT8.2) we demonstrated that the novel tri-generation system was viable only in certain cases. The tri-generation system has a lower annual operating cost than the base case, however, the high capital cost of the SOFC and requirement of stack replacement means that the tri-generation system NPC is only favourable when FiT is considered. However, with anticipated SOFC capital cost reductions the economic performance is predicted to improve. The current tri-generation system does not have a SPBP of less than five years, and is thus not immediately attractive to investors. Furthermore, with the possibility of future withdrawal of government support, a move mirroring the Japanese market towards smaller electrical capacity domestic fuel cells may be required to achieve/maintain economic viability. The economic performance of the tri-generation system is sensitive to natural gas and electrical unit cost. The future economic feasibility of the system will therefore be dependent upon future energy prices, which can be highly volatile. Currently, the tri-generation system is only economically viable in Denmark due its high unit cost of electricity.
The environmental assessment (WP8.3) has demonstrated that the novel tri-generation system is viable across a large range of operational values. Within a UK energy system context, annual CO2 emission reductions of up to 51% compared to the equivalent base case system have been demonstrated. The environmental performance of the tri-generation system is more sensitive to changes in the natural gas emission factor than the base case system. The CO2 emissions of the tri-generation system are insensitive with respect to electricity emission factor. However, electricity emission factor does affect the relative performance of the tri-generation system with respect to the equivalent base case system. The tri-generation system is environmental superior when the electricity emission factor is greater than 0.23kgCO2.kWh-1. As a result, the tri-generation system is not currently viable in France and Norway. Australia and China demonstrate the greatest environmental benefit from adopting the novel tri-generation system. With a transition to hydrogen-fed fuel cells, the novel tri-generation system will be highly competitive in almost all scenarios.
This chapter has provided a detailed economic and environmental assessment of the novel tri-generation system. The following general conclusions, with respect to the chapter aims set out in section 1.1 are as follows:
(1) The system is currently only economically viable with government support. SOFC capital cost and stack replacement are the largest inhibitors to economic viability. Environmental performance is closely linked to electrical emission factor, and thus performance is heavily country dependent.
(2) The countries, in which the system is environmentally viable, are in general the counties in which the system is not economically feasible. This is primarily due to the play off between cheap electrical generation from fossil fuels and more expensive cleaner electrical generation from renewables or nuclear.
(3) The economic feasibility of the novel tri-generation system will improve with predicted SOFC capital cost reductions and the transition to clean hydrogen production.
Although the SDCS has been developed with the aim of integration alongside a SOFC into a complete tri-generation system, the SDCS shows significant potential for integration with other CHP prime mover technologies such as ICE or SE. Due to the lower capital cost of ICE and SE technology (roughly ten times that of SOFC) and cheaper maintenance/part replacements, the economic performance of an ICE/SE based liquid desiccant tri-generation system can be expected to be much better than the current SOFC based system. However, the environmental performance of the SOFC based system will remain favourable compared to alternative options due to high electrical conversion efficiency and the provision for zero carbon energy conversion with the transition to a pure hydrogen fuel feed.
This chapter has demonstrated that the novel tri-generation system is, in certain cases, economically viable.
From the risk register it was observed that the most serious risks were that of first cost and unreliability. A second order risk that could affect commercialisation is changes to incentives for adopting low carbon technologies. Many countries and regions have adopted policies that provide financial incentives to promote renewable and low carbon technologies, but others do not have incentives or do not have consistent long term policies, and so at current cost projections, the most likely places to take up the TriSOFC system are those offering incentives.
Many countries around the world operate feed-in-tariffs, including most members of the European Union, China, Malaysia, Japan, Brazil and Argentina and a small number of countries in Africa (mainly solar and hydro related), whilst some states or regions within countries operate a feed-in-tariff regime, including the USA and Australia. It can be observed that many countries and regions in the world would be suitable for installation of the TriSOFC system, including southern European Countries such as Greece, Turkey, Portugal and Spain, as well as tropical countries such as Malaysia, Southern China and Japan.
Reductions in first cost is a major priority and the consortium is well placed to scale-up manufacture, adopt mass production methods and reduce the cost of membranes, stacks and BoP. Reliability and durability are major concerns of potential customers, not only with respect to the TriSOFC prototype, but most SOFCs. Further work will focus on producing repeatable, reliable and durable fuel cells.
Other factors come into play when comparing existing and competitive systems, such as space taken up by plant and machinery, which could otherwise be used for occupants. In domestic dwellings, anything larger than a washing machine or fridge would reduce space available for other appliances and reduce useable space. In commercial buildings, this would mean less room for lettable space and may require investment in strengthening building structures to take the extra weight. Most of the other risks identified are easily mitigated at the design stage and so should not present risks either technically, economically or environmentally.
The case will be made that the overall system has advantages over existing and competitive technologies over and above issues about space.
WP9:
Website:
A website has been created and is used to disseminate information to the general public and others outside the consortium and EU commission. www.trisofcv.com In addition, we have set up a drop-box system where we can share confidential information between partners, such as minutes of meetings, presentations and progress reports. www.dropbox.com.
Dissemination:
The consortium has been very active in promoting and disseminating results from the research and development emerging from the project. Many significant results and discoveries have been unearthed as a result of the project and this report highlights these achievements. We have also taken on board comments by the mid-term reviewers, who recommended that we should engage more with the international fuel cell and hydrogen community, therefore we highlight these activities as well as reports on publications and conference participation. The following section lists the activities undertaken by each consortium member, but many of the activities were either engaged in jointly with other members, or materials and content were shared between members.
We report over 25 journal papers, over 30 conferences and over 20 Fuel cell and hydrogen community related activities.
Potential Impact:
Environmental Impact
In this section, an environmental assessment of the novel tri-generation system operating within a UK energy system context is presented. The environmental assessment compares the 1.5kWe and 2.0kWe tri-generation system with an equivalent base case system comprising grid electricity, natural gas fired boiler and electrically driven VCS. The evaluation metric used in the environmental assessment is the annual CO2 emission. This is determined through the multiplication of the annual natural gas and electrical demand by their respective emission factors and summing the result. The emission factors of natural gas and electricity are varied, in a reasonable range, to carry out a sensitivity analysis of the environmental performance. The assumptions used in the environmental assessment are the same as those presented in the economic assessment in section 1.2.2. The emission factors used are based on a UK energy system context, and are as follows:
▪ Average natural gas emission factor: 0.184 kg CO2.kWh-1 (EST, 2014)
▪ Average electricity emission factor: 0.555 kg CO2.kWh-1 (AMEE, 2014)
We compared CO2 annual emissions for the cases of a SOFC with 1.5kWe and 2.0kWe output, and found that tri-generation systems produce a respective 51.3% and 50.2% reduction in annual CO2 emissions compared to the equivalent base case system.
We assessed annual CO2 emissions of the 1.5kWe and 2.0kWe tri-generation systems and equivalent base case systems with respect to natural gas emission factor. Over the investigated natural gas emission factor range of 0.05 to 0.3kgCO2.kWh-1 the tri-generation system always has a lower annual CO2 emission. Both the tri-generation and base case system have a natural gas requirement. However, the greater proportionate natural gas demand in the tri-generation system means its annual CO2 emission reductions are more sensitive to changes in the natural gas emission factor. Consequently, as the natural gas emission factor is increased, the relative reduction in annual CO2 emissions compared to the equivalent base case system is diminished. The 2.0kWe tri-generation system is more sensitive to changes in the natural gas emission factor than the 1.5kWe tri-generation system due to a lower electrical efficiency.
We showed that annual CO2 emissions of the 1.5kWe and 2.0kWe tri-generation systems and equivalent base case systems with respect to electrical emission factor. The tri-generation system has no electrical demand, and thus only the base case system is affected by the electrical emission factor. The tri-generation system has a lower annual CO2 emission compared to the equivalent base case system when the electrical emission factor is greater than 0.2363kgCO2.kWh-1 for the 1.5kWe case and 0.2305kgCO2.kWh-1 for the 2.0kWe case.
We showed that annual CO2 emissions of the 1.5kWe and 2.0kWe equivalent case system in a range of different counties using published electrical emission factor data. The annual CO2 emissions of the respective tri-generation systems (horizontal lines) were plotted to indicate the countries in which the novel system is currently environmentally viable. The 1.5kWe and 2.0kWe tri-generation system is feasible in all the countries investigated except France and Norway as these countries have an average electrical emission factor of less than 0.1kgCO2.kWh-1. France and Norway have an energy system that is largely characterised by the use of nuclear and renewables. As a result, the average electrical emission factor is low. We showed that the 1.5kWe and 2.0kWe tri-generation system is most environmentally viable in Australia and China. Australia and China generate a large proportion of their electricity from coal, which has a high emission factor per kWh of electricity generated, and thus strengthens the environmental benefit of adopting the novel tri-generation system. Based on the data presented, Denmark is currently the only country investigated where the novel tri-generation system is both economically and environmentally viable. Interestingly, the countries where the tri-generation system is not economically feasible due to a low electrical unit cost are in general the countries in which the system is most environmentally feasible i.e. Australia and China. This is primarily due to cheap electrical generation from easily accessible, more polluting fossil fuels such as low grade coal.
Environmental assessment conclusions
The environmental assessment is based on annual CO2 emissions of the novel tri-generation system compared to an equivalent base case system. Sensitivity analysis has been used to assess the impact natural gas emission factor, electricity emission factor and country of operation has on environmental performance.
The environmental assessment has demonstrated that the tri-generation system is environmentally viable in almost all scenarios. In a UK energy system context the tri-generation system generates up to 51% annual CO2 emission reductions compared to the base case. Over the investigated natural gas emission factor range, the tri-generation system is always superior. The tri-generation system’s environmental performance is not directly influenced by changes in the electrical emission factor, however the base case is. As a result, changes in the electrical emission factor have a marked impact on the relative performance of the tri-generation system with respect to the base case system. The tri-generation system is environmentally viable when the electricity emission factor is greater than 0.23kg CO2.kWh-1. France and Norway have a large nuclear and renewable (hydro-electric) energy capacity. As a result, their electricity emission factor is low, and thus the tri-generation system does not provide an environmental benefit in such a setting. Countries such as Australia and China demonstrate the greatest environmental benefit from adopting the novel tri-generation system. However, the move to a hydrogen economy and with it the transition from the use of hydrocarbon to pure hydrogen-fed fuel cells in the next 30 years provides the potential for highly efficient, zero carbon energy conversion. With such a transition the novel tri-generation system would be highly competitive in almost all scenarios. This is discussed further in section 9.4.
This section has provided an economic and environmental assessment of the novel tri-generation system operating in a UK economic and energy system context. The assessment has used the BlueGEN SOFC tri-generation system performance data. The tri-generation system has been compared to a base case system comprised of grid electricity, natural gas fired boiler and electrically driven VCS. Sensitivity analysis has been used to assess the performance of the tri-generation system across a range of operating scenarios.
The economic assessment has demonstrated that the novel tri-generation system is viable only in certain cases. The tri-generation system has a lower annual operating cost than the base case, however, the high capital cost of the SOFC and requirement of stack replacement means that the tri-generation system NPC is only favourable when FiT is considered. However, with anticipated SOFC capital cost reductions the economic performance is predicted to improve. The current tri-generation system does not have a SPBP of less than five years, and is thus not immediately attractive to investors. Furthermore, with the possibility of future withdrawal of government support, a move mirroring the Japanese market towards smaller electrical capacity domestic fuel cells may be required to achieve/maintain economic viability. The economic performance of the tri-generation system is sensitive to natural gas and electrical unit cost. The future economic feasibility of the system will therefore be dependent upon future energy prices, which can be highly volatile. Currently, the tri-generation system is only economically viable in Denmark due its high unit cost of electricity.
The environmental assessment has demonstrated that the novel tri-generation system is viable across a large range of operational values. Within a UK energy system context, annual CO2 emission reductions of up to 51% compared to the equivalent base case system have been demonstrated. The environmental performance of the tri-generation system is more sensitive to changes in the natural gas emission factor than the base case system. The CO2 emissions of the tri-generation system are insensitive with respect to electricity emission factor. However, electricity emission factor does affect the relative performance of the tri-generation system with respect to the equivalent base case system. The tri-generation system is environmental superior when the electricity emission factor is greater than 0.23kgCO2.kWh-1. As a result, the tri-generation system is not currently viable in France and Norway. Australia and China demonstrate the greatest environmental benefit from adopting the novel tri-generation system. With a transition to hydrogen-fed fuel cells, the novel tri-generation system will be highly competitive in almost all scenarios.
This section has provided a detailed economic and environmental assessment of the novel tri-generation system. The following general conclusions, with respect to the chapter aims set out in section 1.1 are as follows:
(1) The system is currently only economically viable with government support. SOFC capital cost and stack replacement are the largest inhibitors to economic viability. Environmental performance is closely linked to electrical emission factor, and thus performance is heavily country dependent.
(2) The countries, in which the system is environmentally viable, are in general the counties in which the system is not economically feasible. This is primarily due to the play off between cheap electrical generation from fossil fuels and more expensive cleaner electrical generation from renewables or nuclear.
(3) The economic and environmental feasibility of the novel tri-generation system will improve with predicted SOFC capital cost reductions and the transition to clean hydrogen production.
Although the SDCS has been developed with the aim of integration alongside a SOFC into a complete tri-generation system, the SDCS shows significant potential for integration with other CHP prime mover technologies such as ICE or SE. Due to the lower capital cost of ICE and SE technology (roughly ten times that of SOFC) and cheaper maintenance/part replacements, the economic performance of an ICE/SE based liquid desiccant tri-generation system can be expected to be much better than the current SOFC based system. However, the environmental performance of the SOFC based system will remain favourable compared to alternative options due to high electrical conversion efficiency and the provision for zero carbon energy conversion with the transition to a pure hydrogen fuel feed.
Economic Impact
Introduction
The economic and environmental assessments uses the BlueGEN SOFC tri-generation system performance data presented in section WP07 reports operating at a 1.5kWe and 2.0kWe capacity. These data, as opposed to the simulation data and laboratory testing data, are used because the system demonstrates good performance and is based upon commercially available components which have long-term stable performance, accurate costing figures and qualify for government support.
The aim of the economic and environmental assessment is to establish:
1. Whether the proposed tri-generation system is economically and environmentally viable under current conditions compared to an equivalent base case system.
2. The conditions and geographical locations in which the novel tri-generation system is economically and environmentally viable compared to an equivalent base case system.
3. The future feasibility of the novel tri-generation system with respect to projected changes in global energy resources, conversion techniques and cost.
Economic assessment
In this section, an economic assessment of the novel SOFC liquid desiccant tri-generation system operating within a UK economic climate is presented. The economic assessment compares the 1.5kWe and 2.0kWe capacity tri-generation systems to an equivalent base case system comprising grid electricity, natural gas fired boiler and electrically driven VCS over a 15 year time period. The economic evaluation metrics used are: net present cost (NPC), equivalent uniform annual cost (EUAC) and simple pay-back period (SPBP). The unit cost of electricity, unit cost of natural gas and the capital cost of the SOFC are varied, in a reasonable range, to carry out a sensitivity analysis of the NPC and SPBP. Using electrical unit cost data published by the International Energy Agency, the economic performance of the tri-generation system in the context of different countries is presented.
Next, section 1.2.1 describes the metrics used in the economic assessment.
Net present cost (NPC)
Net present value (NPV) is an economic tool used to equate the total cost of a project over a specified time period to the total cost today, taking in to account the time value of money. The present value (PV) of each annual cash flow is discounted back to its PV using a suitable interest or discount rate. The NPV is determined by summing the PV for each year, staring at year 0 i.e. the investment, to the final year (N). NPV is a good indicator of how much value an investment or project brings to an investor, and is widely used in economic engineering to assess feasibility. However, there are many kinds of systems or projects, such as the SOFC tri-generation system, where there are no sales or incomes. In this case it is common to use net present cost (NPC).
Equivalent uniform annual cost (EUAC)
The equivalent uniform annual cost (EUAC) is the annual cost of the project or system equivalent to the discounted total cost or NPC. EUAC is calculated by multiplying the NPC by the capital recovery factor (CRF).
Simple pay-back period (SPBP)
The simple pay-back period (SPBP) is used to determine the time required to recoup the funds expended in an investment, or to reach the break-even point. Generally, in engineering projects investors consider a SPBP of five years as acceptable. The SPBP does not account for the time value of money; however it is a useful tool for the quick assessment of whether a project or system is a viable option.
Economic assessment results
The following assumptions have been made for the economic assessment of the novel tri-generation and equivalent base case system.
▪ System lifetime (N): 15 years
▪ SOFC CHP system cost and installation: £20,950
▪ SDCS cost: £2700
▪ Potassium formate solution cost (20kg): £235
▪ SOFC stack replacement cost and system maintenance: £5000 every 5 years
▪ UK micro-CHP feed-in-tariff (FiT): 0.125 £.kWh-1
▪ Boiler and installation cost: £1300
▪ VCS capital cost: £500 per kW of cooling
▪ Annual VCS maintenance cost: 10% of VCS capital cost
▪ Annual gas check: £60
▪ Average natural gas unit cost: 0.0421 £.kWh-1
▪ Average electricity unit cost: 0.172 £.kWh-1
▪ Average yearly VCS COPel: 2 (Welch, 2008)
▪ Average heating system efficiency (boiler + distribution): 85.5%
▪ Annual cooling time required: 1200hr.yr-1
▪ Interest rate (ir): 7% (constant throughout assessment period)
▪ Inflation rate (if): 3% (constant throughout assessment period)
▪ Scrap value (SV): 10% of initial capital cost
In the UK, fuel cell CHP of 2.0kWe or less qualifies for the micro-generation FiT (DECC, 2014). Under this scheme, the UK government pays 0.125£.kWh-1 of electricity generated, regardless of whether it is consumed or exported. Where relevant, the economic assessments consider the FiT.
We compared NPC of the 1.5kWe and 2.0kWe tri-generation systems and equivalent base case systems over a 15 year period. The assessment considered the performance of the tri-generation system with and without FiT support. The initial NPC in year 0 is the system investment cost, which is much higher for the tri-generation system compared to the base case. The NPC of the systems increases over time due to the annual operating costs. The tri-generation system with FiT support displays only a marginal increase in the NPC over the 15 year period because the FiT almost pays for the annual operating cost of the system. For the tri-generation systems, an NPC spike is seen at year five and ten; this is due to stack replacement. The small dip in NPC at year 15 is due to the scrap value of the systems.
Without FiT support, the NPC of both the 1.5kWe and 2.0kWe tri-generation system are 26% and 10% higher than the equivalent base case system respectively. However, with FiT support there is a 31% and 90% reduction in the NPC of the 1.5kWe and 2.0kWe tri-generation system compared to the equivalent base case system respectively. When the FiT is considered the annual revenue means the tri-generation system has a favourable NPC compared to the base case in year 11.5 for the 1.5kWe tri-generation system and year 7 for the 2.0kWe tri-generation system. The NPC of the 1.5kWe tri-generation system is lower than the 2.0kWe tri-generation system when no FiT is considered, but higher when the FiT is considered. The higher NPC seen in the 2.0kWe tri-generation system without FiT is due to the higher fuel input requirement, and thus higher annual operating costs. However, when FiT is considered the 2.0kWe tri-generation system provides greater annual revenues and thus a lower NPC. Both with and without FiT support, the 2.0kWe tri-generation system has a lower SPBP compared to the 1.5kWe tri-generation system. Although the 2.0kWe tri-generation system suffers an electrical efficiency reduction and thus a greater fuel input, the higher electrical capacity means it is offsetting more grid derived electricity. Per kWh, grid derived electricity has a higher associated cost compared to natural gas, and thus the SPBP of the 2.0kWe tri-generation system is lower. Furthermore, the 2.0kWe tri-generation system has a greater cooling output, and thus the equivalent base case system requires more grid derived electricity for the VCS. In all cases the tri-generation system generates annual operating cost savings compared to the base case system. The high NPC and SPBP of the tri-generation system are therefore due to the capital cost of the SOFC.
The unit cost of electricity does not affect the NPC of the tri-generation system, only the base case system. As the unit cost of electricity increases from 0.05 to 0.6£.kWh-1 the NPC of the base case system increases, and thus the economic feasibility of the tri-generation system improves. At an electrical unit cost of 0.2458£.kWh-1 there is a NPC break-even point between the tri-generation and base case system. Above 0.2458£.kWh-1 the 1.5kWe tri-generation system has a better NPC and should be considered over the base case system. At an electrical unit cost of 0.2458£.kWh-1 the tri-generation system has a SPBP of 12 years. For the SPBP to fall below five years, an electrical unit cost of 0.55£.kWh-1 is required. In comparison, the 2.0kWe tri-generation system has a NPC break-even electrical unit cost of 0.1955£.kWh-1. Due to the continual rise in utility electricity prices, the break-even electrical unit costs which produce tri-generation system economic feasibility are realistic and not too far off current prices.
We compared the economic performance of the 1.5kWe tri-generation system and equivalent base case system with respect to the unit cost of natural gas. No FiT is considered. Natural gas unit cost affects both the tri-generation and base case systems NPC. As the unit cost of natural gas increases from 0.01 to 0.1£.kWh-1 the NPC of both the tri-generation and base case systems increase. The tri-generation system is more sensitive to changes in the unit cost of natural gas compared to the base case system due to a greater proportionate demand. For the 1.5kWe tri-generation system there is not a natural gas unit cost that makes the tri-generation system favourable i.e. a NPC break-even point. As the natural gas unit price is increased the reduction in NPC between the base case and tri-generation system increases, and as a result the SPBP increases. As the natural gas unit cost is increased from 0.01£.kWh-1 to 0.1£.kWh-1 the tri-generation system SPBP increases from 14 years to 51 years. The 2.0kWe tri-generation system does have a NPC break-even natural gas unit cost of 0.0233£.kWh-1. However this is very low and not realistic in the current economic climate where fossil fuels have such value.
We investigated NPC of a 1.5kWe and 2.0kWe equivalent base case system in a range of different counties with respect to electrical unit cost data published by the International Energy Agency. The NPC of the respective tri-generation systems (horizontal lines) are plotted to indicate which countries the novel system is currently economically viable in. Based on the current assumptions, the novel tri-generation system (1.5kWe and 2.0kWe) is only economically viable in Denmark where the unit cost of electricity is 0.262£.kWh-1. The largest different between the NPC of the tri-generation and base case system is in China, where the unit cost of electricity is as low as 0.0512£.kWh-1. Based purely on economic performance, the novel tri-generation system is more suited to European locations, where on average the unit cost of electricity is higher than Asia and the Americas. The 2.0kWe tri-generation system has a lower NPC break-even electrical unit cost. As a result, the 2.0kWe system is almost feasible in the current Australian economic climate.
We showed NPC of the 1.5kWe tri-generation system and equivalent base case system with respect to the SOFC capital cost. The capital cost of the tri-generation system, operating at a 1.5kWe capacity, needs to be £9715 or less for it to be economically viable compared to the base case system. At a 2.0kWe capacity the required SOFC capital cost is £16135. As the capital cost of the SOFC increases, the SPBP increases. At the 1.5kWe NPC break-even point of £9715 the SPBP is 12.8 years. Variation in the liquid desiccant system capital cost has a negligible impact on NPC and SPBP. Reducing the liquid desiccant system capital cost by 50% results in a 4.5% reduction in the SPBP. Reducing the SOFC capital cost by 50% results in a 32% reduction in the SPBP, demonstrating that tri-generation system economic viability presides with reducing the capital cost of the SOFC.
We showed the NPC for the 1.5kWe tri-generation and equivalent base case system with respect to SOFC capital cost and unit cost of electricity respectively. Up to an electricity unit cost of 0.11£.kWh-1, the base case system is always better than the tri-generation system. However at the electrical unit cost reference value of 0.172£.kWh-1, the 1.5kWe tri-generation system is competitive when the SOFC capital cost is less than £9500. At the intersection point, the tri-generation system is economically favourable if the SOFC capital cost is less than £4750 with an electrical unit cost of greater than 0.14£.kWh-1 (i.e. UK, Australia).
Economic assessment conclusions
Within a UK economic climate it has been demonstrated that the NPC of the novel tri-generation system is only favourable when FiT is considered, in which case the 2.0kWe output is best. The tri-generation system has a lower annual operating cost than the base case; however, NPC and SPBP analysis demonstrates that the novel system is currently uneconomical. This is primarily due to the SOFC capital cost and the requirement of stack replacement, not the liquid desiccant unit capital cost. In the current UK economic climate the SOFC capital cost needs to be less than £9000 for the tri-generation system to be competitive. PEMFC technology has demonstrated considerable price reduction over the last six years. The 1kWe Panasonic unit had a unit cost of £27,300 in 2009, but as of 2015 it is being supplied to energy companies for £3600. CFCL forecast that they can supply the BlueGEN unit for £5200 once in mass production. Currently, the much lower PEMFC unit costs are due to the technology being around five years ahead of SOFC. Many commercial developers believe the future of cheaper fuel cell technology lies with SOFC systems as they do not need to use expensive platinum catalysts like PEMFC. Based on the example of PEMFC cost reductions, significant SOFC cost reductions can be anticipated. The SOFC cost target figures presented in this chapter are therefore sensible and could be realistically achieved in the next five to ten years, making the tri-generation system economically viable in almost all cases.
Currently, the tri-generation system becomes competitive, and even demonstrates good profitability, compared to the base case system when government incubator support, such as the FiT is considered. With continued instability in governmental support for low carbon sustainable energy, the novel tri-generation system needs to become economically viable in its own right for it to be considered a viable alternative to conventional energy supply. Furthermore, a 2.0kWe base load capacity is large, and effective electrical utilisation may be problematic, particularly in a domestic building context. With the possibility of future withdrawal of government support for fuel cell CHP, maximising in-house electrical consumption will be essential to maintain economic viability. A lower electrical capacity fuel cell would therefore be required. The Japanese domestic market, which is estimated to be ten years ahead of the European market, is now focussing domestic fuel cell CHP development at capacities of 750We, a possible insight into the future of where European domestic fuel cell development needs to go.
Like other small scale tri-generation systems presented in the literature, the economic performance of the SOFC liquid desiccant tri-generation system is most sensitive to the unit cost of natural gas. The tri-generation system is economically superior, compared to the base case system, when the unit cost of electricity is greater than 0.24£.kWh-1 and as a result Denmark is currently the only country investigated where the tri-generation is economically viable. However, with the extraction of easily accessible fossil fuels diminishing, the unit cost of electricity in many countries is set to continue to rise, thus strengthening the economic case of the tri-generation system.
Conclusions
This chapter has provided an economic and environmental assessment of the novel tri-generation system operating in a UK economic and energy system context. The assessment has used the BlueGEN SOFC tri-generation system performance data presented in section 7.2. The tri-generation system has been compared to a base case system comprised of grid electricity, natural gas fired boiler and electrically driven VCS. Sensitivity analysis has been used to assess the performance of the tri-generation system across a range of operating scenarios.
The economic assessment has demonstrated that the novel tri-generation system is viable only in certain cases. The tri-generation system has a lower annual operating cost than the base case, however, the high capital cost of the SOFC and requirement of stack replacement means that the tri-generation system NPC is only favourable when FiT is considered. However, with anticipated SOFC capital cost reductions the economic performance is predicted to improve. The current tri-generation system does not have a SPBP of less than five years, and is thus not immediately attractive to investors. Furthermore, with the possibility of future withdrawal of government support, a move mirroring the Japanese market towards smaller electrical capacity domestic fuel cells may be required to achieve/maintain economic viability. The economic performance of the tri-generation system is sensitive to natural gas and electrical unit cost. The future economic feasibility of the system will therefore be dependent upon future energy prices, which can be highly volatile. Currently, the tri-generation system is only economically viable in Denmark due its high unit cost of electricity.
The environmental assessment has demonstrated that the novel tri-generation system is viable across a large range of operational values. Within a UK energy system context, annual CO2 emission reductions of up to 51% compared to the equivalent base case system have been demonstrated. The environmental performance of the tri-generation system is more sensitive to changes in the natural gas emission factor than the base case system. The CO2 emissions of the tri-generation system are insensitive with respect to electricity emission factor. However, electricity emission factor does affect the relative performance of the tri-generation system with respect to the equivalent base case system. The tri-generation system is environmental superior when the electricity emission factor is greater than 0.23kgCO2.kWh-1. As a result, the tri-generation system is not currently viable in France and Norway. Australia and China demonstrate the greatest environmental benefit from adopting the novel tri-generation system. With a transition to hydrogen-fed fuel cells, the novel tri-generation system will be highly competitive in almost all scenarios.
This chapter has provided a detailed economic and environmental assessment of the novel tri-generation system. The following general conclusions, with respect to the chapter aims set out in section 1.1 are as follows:
(4) The system is currently only economically viable with government support. SOFC capital cost and stack replacement are the largest inhibitors to economic viability. Environmental performance is closely linked to electrical emission factor, and thus performance is heavily country dependent.
(5) The countries, in which the system is environmentally viable, are in general the counties in which the system is not economically feasible. This is primarily due to the play off between cheap electrical generation from fossil fuels and more expensive cleaner electrical generation from renewables or nuclear.
(6) The economic and environmental feasibility of the novel tri-generation system will improve with predicted SOFC capital cost reductions and the transition to clean hydrogen production.
Although the SDCS has been developed with the aim of integration alongside a SOFC into a complete tri-generation system, the SDCS shows significant potential for integration with other CHP prime mover technologies such as ICE or SE. Due to the lower capital cost of ICE and SE technology (roughly ten times that of SOFC) and cheaper maintenance/part replacements, the economic performance of an ICE/SE based liquid desiccant tri-generation system can be expected to be much better than the current SOFC based system. However, the environmental performance of the SOFC based system will remain favourable compared to alternative options due to high electrical conversion efficiency and the provision for zero carbon energy conversion with the transition to a pure hydrogen fuel feed.
This chapter has demonstrated that the novel tri-generation system is, in certain cases, economically and environmentally viable.
