Final Report Summary - SFERA-II (Solar Facilities for the European Research Area-Second Phase)
Executive Summary:
CSP Research Infrastructures in Europe have served through the last 30 years as research tools in order to demonstrate the concept feasibility by exploring different pathways on how to produce high temperature heat, electricity, and more recently, solar fuels using concentrating solar radiation.
These developments were performed rather independently in research centres in Spain (in Spanish-German cooperation), France, Italy Israel, Switzerland and Germany. In October 2004 five major research labs (CIEMAT from Spain, CNRS from France, DLR from Germany and ETH and PSI from Switzerland have formed the Alliance of Laboratories for Research and Technology on Solar Concentrating Systems (“SolLab“; www.sollab.eu) to overcome this fragmented status. Later on, further steps have been taken to enhance integration, like the first SFERA project (2009), the ESFRI’s EU-SOLARIS infrastructure (2010) or the EERA Joint Program on CSP (2011).
Nowadays, the key point is to cooperate with the industry in order to reach the technology objectives listed above and gain a significant market share. Europe is leading the way, so far, but other countries are launching their own CSP promotion programs, like USA, India or China, and this advantage can be maintained only through an effort in innovation and for that ‘Research Infrastructures’ have a crucial role to play.
The program developed within the proposed joint research activities in SFERA-II has increased the basic scientific knowledge and available techniques for improved performance of concentrating solar systems. Calibration facilities and agreed procedures to calibrate sensors which are used for thermal performance testing and for measuring the solar resource have been stablished. A joint calibration facility for field pyrheliometer and pyranometer was erected at CIEMAT-PSA. In addition, double-modulation pyrometry has been implemented and tested at PSI’s 1 and 50 kW solar simulators and at a small vertical solar furnace at PROMES. New experimental techniques to enhance the services offered within partners’ research infrastructures in order to improve this material knowledge hence the component lifetime and performance have been also developed. Harmonization of the testing procedures applied in research infrastructures for characterization of solar concentrators has been attained and a new test bench has been implemented at CIEMAT-PSA for collectors’ inter-connections. Finally, an easy-to consult standalone database containing properties and applications of: molten nitrates, phase change materials (PCM), chemical storage systems and solids as sensible heat storage materials, has been prepared.
SFERA-II partners have disseminated such results widely in the scientific community and industry through the networking activities proposed. The direct contacts of experienced scientists with newcomers and interested students have also been guaranteed primarily through the transnational access programme. This will strengthen and improve the network of partner institutions, which will become established as the core of research in this field, leading to a structured long-term influence in this fast-growing area of renewable energy science and technology. It can be now publicised by the numbers of infrastructure users involved, and the scientific papers and new projects generated.
Project Context and Objectives:
Context
To achieve a secure and sustainable energy supply, and in view of growing climate change concerns, the EU has taken on the role of Kyoto protocol promoter and set out ambitious goals to achieve a large share of renewable energy in the European market.
The challenging European policy goals for non-nuclear energy are for the renewable energy contribution to triple up to 20% of primary energy by 2020.
Solar Energy, as the primary source of renewable energy, will contribute a major part of this share, and its conversion by concentrating technologies for concentrating solar power (CSP) and heat generation has long been proven cost-effective for a wide range of applications. Several CSP projects have recently been put into operation. Some 2.400 MW are under construction and several GW are in advanced stages of planning, particularly in Spain, but also in other Southern European countries, like France, Greece and Portugal.
Based on the experience gathered in current SFERA-I ‘Integrating Initiative’, a process was established to harmonize and improve the basic services of the research facilities. The specific focus was related to the development of common performance testing guidelines, the evaluation of improvements to reach ultra-high flux distributions and to allow accelerated aging testing and, finally, the establishment of guidelines to set up new test facilities for thermal energy storage materials and systems.
Through co-ordinated integration of their complementary strengths, efforts and resources, progress will be made in SFERA-II, more effective by:
• Increasing the scientific and technological knowledge base in the field of concentrating solar systems in both depth and breadth.
• Providing and improving the research tools best-suited for the scientific and technologic community in this field.
• Strengthening the European industry through stimulating technology transfer by fostering the use of World-class R&D facilities.
• Increasing general awareness and especially of the scientific community in the possible applications of concentrated solar energy, including creation of new synergies with other scientific disciplines (e.g. materials treatment).
The commercial success of renewable energy technologies and in particular in CSP technologies in recent years have led to the situation that facilities are used more intensively by industrial users who typically want to qualify their prototypes for a further scale-up step or a direct commercialisation. Therefore, in the scope of the SFERA-II project, the proposed joint research activities are more focused to provide a better service to industrial users.
Objectives
In view of this challenge for research, development and application of concentrating solar systems involving a growing number of European industries and utilities in global business opportunities, the purpose of this project is to integrate, coordinate and further focus scientific collaboration among the leading European research institutions in solar concentrating systems that are the partners of this project and offer European research and industry access to the best-qualified research and test infrastructures.
One goal of these efforts is to create a unified virtual European Laboratory for Concentrating Solar Systems, easily accessible to interested researchers, both from the academia and from the industry, and thus serving as the structural nucleus for growing demand in this field in the developing European research area.
Such a European Solar Lab would also contribute to a sustainable, secure European energy supply and to a firm basis for global competitiveness of European technology suppliers in this field, with strong prospects of growing worldwide markets in the coming decades.
Another goal is to enhance cooperation with CSP industry, looking for new innovative products and processes to reach the market, thus increasing competitiveness of European CSP industry and of CSP technologies in front of the fossil and other renewable ones in the energy market.
Some activities proposed in that way are:
• Organization of specific training courses for industrial technicians and researchers.
• Fostering the use of the facilities offered by industrial researchers.
• Creating a specific joint working group to identify and develop products and processes suitable for commercial exploitation.
The proposed networking activities will help to promote and to accelerate innovation in CSP, through the creation of a common knowledge base and cooperation culture among the researchers of this project. Another target is also to guarantee a broad information exchange with the scientific and industrial communities, as a sound base for further commercial deployment but also the development of different technological aspects in the joint research activities.
Innovation actions aim at developing the conditions to set a world-class eco-system that may speed up the process from knowledge (generated by activities at the Research Infrastructures) to new products, processes and services. Also with the strong accent put on external communication (conferences, training courses, summer schools, etc..) the networking activities aim at targeting new users potentially interested in the ‘access’ activities, as it already happened in SFERA-I.
The transnational access will play a key role in serving to increase technical collaboration and possible new synergies with new user groups from neighbouring or new fields, a model that has been realized with success during earlier access programs at CIEMAT-PSA and PROMES, for instance.
Increased participation of industrial users will be promoted, addressing this community through the associations like ESTELA, PROTERMOSOLAR, etc.
Joint research that is addressed in SFERA-II project aims to improve the quality and service of the existing infrastructure and to extend their services taking benefit from the specific competences and experiences of the individual labs and jointly achieve a common level of high scientific quality and service through this synergistic approach. One essential subject for the industrial clients is related to the calibration of sensors. Research centres and industry need joint calibration facilities and agreed procedures to calibrate sensors which are used for thermal performance testing and for measuring the solar resource. Development and standardization of calibration facilities is focused in SFERA-II.
A second subject addressed concerns the development of pyrometric temperature measurement methods suitable for use on surfaces exposed to concentrated radiation as prevail in high-concentration solar facilities (e.g. solar towers or solar furnaces) and arc lamp-based solar simulators.
A third subject to be focused on is the determination of physical properties of CSP materials under concentrated solar irradiation to extend the capabilities in the existing CSP research infrastructure that allows for a better evaluation of the material behaviour, such as high temperature steels or SiC ceramics.
Since the characterization of solar concentrators for CSP plants is a growing demand activity in several facilities within the SFERA consortium, another objective of this project is to define common protocols to be applied at the participating research infrastructures for characterization of solar concentrators, as well as the design and implementation of a test bench for collectors interconnections (ball joints, flexible hoses and hybrid interconnections).
Additionally, the design and implementation of a suitable test bench for collectors’ interconnections will improve the testing capacities available within the European research infrastructure because industrial external users (manufacturers, engineering companies and plant owners) are demanding such a facility, which did not exist before SFERA-II project.
Finally, for the evaluation of experiments most users require detailed thermophysical properties of heat transfer fluids and heat storage materials (HTF/HSM). Only for a very few (like water-steam) reliable information is easily available, for many others the properties are either very specific or changing with time. An important service of the research facilities is to provide precise data of for these materials which is another objective to be tackled by the joint research activities planned in SFERA-II project.
Project Results:
Figures and table attached in a pdf document.
PROMOTION OF INNOVATION IN CSP BASED ON SFERA-I ACTIVITIES
Increasing the potential of innovation of SFERA by addressing the innovation opportunities created by the project activities and by reinforcing links with companies that drive innovation, was faced through the whole project. The key tasks proposed were based on developing the conditions to set a world-class eco-system that may speed up the process from knowledge (generated by the research activities of the solar concentrating research infrastructures) to new products, processes and services.
It is important to highlight that the partnership with industry has been reinforced along the project thanks to a strong collaboration established with ESTELA (European Solar Thermal Electricity Association) which is the main industrial association in CSP and the organization of four training for industry courses, bringing research and innovation together.
Initially and by the hand of a subcontractor, all the access users have been contacted to explore with them the possibilities and opportunities for exploiting their experimental work carried out within the framework of SFERA-II transnational access activity. For these purposes, a questionnaire was drafted by the external consultant to gather all important information related to the exploitation of the access results. A follow-up will be done one year after the end of the project to see what will be the impacts of R&D activities carried out within the transnational access activities, not only on the scientific community but on the industrial/commercial side.
As identified in the results of the questionnaire, most of the access projects have a really low TRL, starting even sometime at TRL 1. In addition, the replies to the questionnaire have helped to formulate interesting conclusions on the actions to be implemented to boost the exploitation of these access projects (figure 1).
The list of potential innovations extracted from the JRA has already been mapped in deliverable 3.5. Further to that, a focus has been done on WP11 which showed the most promising activities for a further commercialization.
EXCHANGE OF BEST PRACTICES FOR HARMONIZATION OF APPROACHES
For a better harmonization of the CSP activities within Europe and a better understanding of what is at stake at each other partners’ laboratory, it is crucial to emphasize the exchange of best practices. This has been implemented along SFERA-II project in two ways:
• Inter-comparison campaign of flux measurement instruments at CNRS and PSI. Best practices on practical and technical aspects of the instruments have been shared in order to standardize the use of these instruments among the partners. A particular attention was turned to solar flux measurement at the focus of concentrating systems because it is a key data for the evaluation of system efficiency (receivers, reactors, output of secondary concentrators...). It remains of interest to hold a flux inter-comparison by using solar simulators in order to check the spectrum sensibility of the flux sensors: if significant calibration differences are observed as expected between solar and electrical light, a more careful monitoring of the atmospheric conditions will be required when using flux sensors in order to have a good enough evaluation of the real time spectrum.The follow-up of these activities will be carried out outside of SFERA-II project, after the end of the project, since all of this is of strong interest for the industry, there is the need to go further in the harmonization of these practises.
• Exchange of personnel between SFERA-II partners in order to share know-how, participate in common R&D activities and to promote common technical and management methods. Nine mobilities have been taken place between 2016 and 2017. Specifically, four mobilities occurred during the inter-comparison campaign (CNRS to CIEMAT-PSA and DLR; DLR to CNRS) and five more were related to other JRAs: CIEMAT-PSA to DLR for the application of advanced analytical techniques for the characterization of solar reflector samples subjected to different corrosive environments; CIEMAT-PSA to CNRS for an exchange on Direct Steam Generation with line-focus solar collectors. All results can be found in the deliverable 5.4. These mobilities were a success in terms of transfer of knowledge and harmonization of procedures and led to several joint publications between the different research centres.
DEVELOPMENT OF JOINT CALIBRATION PROCEDURES AND FACILITIES FOR SENSORS
Standardized Calibration facility for thermal irradiance sensors
Within WP11 in JRA, a calibration test stand for pyrheliometers and pyranometers was implemented at the CIEMAT-PSA METAS facility in 2014 (figure 2). The resulting facility enables CIEMAT-PSA staff and guest researchers to calibrate various thermal irradiance sensors at the same time even beyond the project duration. Two PMO absolute cavity pyrheliometers (PMO6 0106 Ciemat and PMO6-cc 0807 DLR) for the DNI and one Kipp&Zonen CMP22 pyranometer (SN 110288) for the DHI are used as reference sensors.
The calibration test uses a solar heliostat from CIEMAT-PSA as tracker for the pyrheliometers mounted on a metal plate. The DNI reference absolute cavity radiometers (ACR) are placed inside a weather-proof cabinet. During measurement, two windows are opened which allow an irradiation of the reference sensors. Pyranometers are calibrated using a sensor table next to the reference pyranometer on top of the METAS BSRN platform. All sky images are taken and the aerosol optical depth and the sunshape are measured during the calibration. The all sky images are used to filter out inadequate data points that are affected by clouds.
In total four calibration campaigns (2014, 2015, 2016, and 2017) were jointly carried out by CIEMAT-PSA and DLR personnel, with extra support from CNRS at CIEMAT-PSA in 2016. Results are public via deliverables D11.2 and D11.3. Deliverable D11.2 consists of a report describing mainly the implementation of the joint calibration facility at CIEMAT-PSA METAS test site. D11.3 contains the results of all calibrations and investigations carried out during the calibration campaigns.
Standardization of RSI (Rotating Shadow-band Irradiometer) calibration
SFERA-II scientists from DLR and experts from the US and Germany discussed the possibility of improving RSI correction functions for systematic errors in a more physical and less empirical way. CIEMAT-PSA and DLR performed a round robin test by calibrating a single RSI according to different methods at the Plataforma Solar the Almeria (PSA) and at an additional CIEMAT test site facility in Madrid.
In consideration of a DNI value around 1000W/m², the observed rmsd values correspond to a relative rmsd between 1 to 3%. The results were presented in report D11.4.
Calibration facility for heat transfer fluid mass flow sensors and thermal capacity
This task was initiated with a comprehensive uncertainty analysis, calculating the combined uncertainty of the heat capacity measurement bypass including a sub-device measurand resolved uncertainty weighting. This measure identified individual influences (sensitivities) in the heat capacity measurement of all single measurands and recognized effects on the measurement, such as heat losses for instance.
Finally, a detailed understanding of all uncertainty components and their combination, which is indispensable for any high precision measurement using heat transfer fluids, was attained. The overall combined measurement uncertainty of the cp-measurement was proved to be smaller than 1.0 % at mean operation temperatures between 25 and 60°C. More details can be found in the deliverable D11.6 “Report on measurement uncertainty”.
In addition, and due to the lack of methods to calibrate built-in flow meters under its working conditions without removing them from a parabolic trough HTF loop, the bypass to measure the heat capacity was upgraded with a reference Coriolis sensor. An adequate mass flow sensor was selected to be operated at temperatures up to 350°C and under typical test loop mass flow conditions of about 5 kg/s (Deliverable D11.7). The calibration facility for heat transfer fluid mass flow sensors and thermal capacity was used for various measurement campaigns at the parabolic trough rotating platform KONTAS (DLR/CIEMAT) at CIEMAT-PSA (see figure 3).
As being modular, the bypass can be mounted to any other installation in order to characterize the specific heat capacity or recalibrate installed mass flow sensors of the installation. Further details can be found in deliverable D11.8 “Report on Calibration of First Testing Facility Using the Calibration Bypass”.
PYROMETRIC TEMPERATURE MEASUREMENT METHODS FOR HIGH-CONCENTRATION SOLAR FACILITIES AND SOLAR SIMULATORS
Develop “Double Modulation” pyrometry for use in arc lamp based solar simulators
Main achievements have been published in a research article titled “Double modulation pyrometry: A radiometric method to measure surface temperatures of directly irradiated samples” in Review of Scientific Instruments. It documents the custom design and implementation of the flux modulator, a key component of the method that utilizes the symmetry of the imaging furnace. It presents the methodology and experimental setup for a two-step calibration procedure required prior to any measurements and discusses a systematic error that may affect accuracy. The calibration procedure results in the estimation of 5 calibration coefficients. An error analysis focusing on how uncertainty in any of the calibration coefficients affects the accuracy of the measurement (see figure 4) is also discussed. It demonstrates that the method performs well under harsh conditions with a typical error of 20 K when measuring on a highly reflective and thus difficult to measure thin strip of Platinum.
The method was also implemented at PSI’s 50 kW high-flux solar simulator and used to measure the temperature of different ceramic foams such as SiSiC, ZrO2, and Al2O3 used as functional materials in CSP applications.
Two experimental campaigns in CNRS-PROMES (France) were successfully carried out. A very good agreement has been observed between three instruments: PSI’s double modulation prototype pyrometer, a double modulation pyrometer prototype by CNRS and CNRS’s reference solar blind pyrometer, proving the potential of the double modulation pyrometric method in suitable conditions for the wide range of tested materials.
In addition, the methodology for the in-situ reflectance measurement was developed and its application to dynamically correct the sample’s emissivity was demonstrated.
Active temperature regulation in solar furnaces
IR camera prototype at CIEMAT-PSA solar furnace has been employed. In the worst conditions (a surface reflectance of 0.60 and the highest concentration), the camera with the band-pass filter centred at 3320 nm measures surface temperatures with a relative error, due to the solar distortion, of less than 5 % above a surface temperature of 750 K. In experiments where it is used a quartz window, this combination of filter and camera allows to measure through the quartz window. The experimental comparison showed that at 3320 nm the camera is as solar blind as the IMPAC pyrometer at 1400 nm.
In the same conditions, if the filter centred at 4720 nm is selected in the filter wheel of the camera, it is possible to measure with a relative error of less than 5 % above a surface temperature of 450 K. If a quartz window is used in a test, this filter allows the camera to measure the surface temperature of the window to control its safety levels. The experimental comparison showed that working at 4720 nm the camera is even better than the IMPAC pyrometer.
To simulate test experiments, a temperature dynamical model of a rectangular metal tube was developed. One side of the tube is exposed to the concentrated solar power, and a fluid (water) circulated inside the tube to remove heat and to “protect” the exposed side of the tube. It is known from previous works that the heliostats do not produce the same flux on the furnace focus, and the responses times of the heliostats are not equal. But to capture the main dynamics one can assume that all heliostats are equal, they produce the same “mean” flux and move between the ON and OFF positions with the same speed.
The objective is to use a control algorithm that must select the number of heliostats (to schedule heliostats) to deliver a given power level such that a small temperature tracking error is obtained. But by selecting heliostats it implies that the applied power do not change continuously as with a “normal shutter” but is quantized. This fact may induce small oscillations in the controlled temperature. In order to obtain a finer power adjustment, a possible solution is to explore and combine the differences between fluxes produces by the real heliostats. But this line of research was not explored within SFERA-II project.
DETERMINATION OF PHYSICAL PROPERTIES OF CSP MATERIALS UNDER CONCENTRATED SOLAR IRRADIATION
Determination of thermo-mechanical properties under concentrated solar radiation
New instruments and methods for in-situ thermo-mechanical investigation using solar acoustic methods have been implemented within WP13. A novel device upgraded for strain measurement by photomechanical method has been designed: it would allow a better evaluation of the materials damages (figure 5). Experimental tests and their comparison with the proposed thermo-mechanical behaviour have been published in deliverable 13.2.
Determination of thermo-optical properties: spectral directional emissivity measurements at high temperature
A new spectroradiometer at CNRS-PROMES has been employed for investigation on improving the capacity for spectral directional emissivity measurements depending on the sample temperature. Main results achieved are summarized here:
• The noise level of the two sensors (spectrophotometer and spectroradiometer) and their data path during the acquisition has been characterised which led to limiting the usable wavelengths depending on the temperature of the sample. This means the usable signal-noise ratio has been investigated notably to cope for lower photons (actual signal) at low temperatures.
• New mechanical supports for the spectroradiometer and the old radiometer have been installed on the experimental MEDIASE carriage in order to have high quality accurate reproducible aiming direction on the solar heated samples.
• The software developed has been pursued, both on the backend (algorithms) but mostly on the frontend (user interface). The LabVIEW-based software now allows easier report quality outputs of the processed data, such as: angular polar plots, spectral plots, temperature dependence plots, bandwidth plots...
The work about spectral directional measurement of the emissivity is reported in Deliverable 13.4 about the assessment of this upgrade and in Deliverable 13.3 which focuses on the comparison between CNRS and CIEMAT methods of hemispherical measurement of emissivity for selected bands for selected tests materials.
Determination of key properties in the case of porous materials in CSP applications
A solar test bench was developed by CNRS in order to characterize the solar-to-thermal efficiency of reticulate porous ceramics made of SiC with open pores: improvements with current state-of-the-art were made by the use of a homogenizer, ensuring quasi-1D incident solar flux irradiation. This solar setup has also been used to age samples used to optimize the techniques to evaluate their surface characteristics (figure 6).
A numerical and experimental analysis of porous materials transfer properties has been performed by ETHZ with the test case of the solar-driven thermochemical reduction of ceria as part of a H2O/CO2-splitting redox cycle. A transient heat and mass transfer model has been developed to simulate reticulated porous ceramic (RPC) foam-type structures, made of ceria, exposed to concentrated solar radiation. The RPC features dual-scale porosity in the mm-range and lm-range within its struts for enhanced transport. The numerical model solves the volume-averaged conservation equations for the porous fluid and solid domains using the effective transport properties for conductive, convective and radiative heat transfer. These in turn are determined by direct pore-level simulations and Monte-Carlo ray tracing on the exact 3D digital geometry of the RPC obtained from tomography scans. Experimental validation has been accomplished in terms of temporal temperature and oxygen concentration measurements for RPC samples directly irradiated in a high-flux solar simulator with a peak flux of 1200 suns and heated to up to 1940 K. Effective volumetric absorption of solar radiation was obtained for moderate optically thick structures, leading to a more uniform temperature distribution and a higher specific oxygen yield. The effect of changing structural parameters such as mean pore diameter and porosity has been investigated. This work was reported in the deliverables 13.5 and 13.7.
CHARACTERIZATION OF SOLAR CONCENTRATORS AND INTERCONNECTING ELEMENTS
Two main achievements attained throughout SFERA-II project are:
• Definition of common protocols to be applied at the participating research infrastructures for characterization of solar concentrators.
• Design and implementation of a test facility for collectors’ inter-connections (ball joints, flexible hoses and hybrid interconnections).
Development of new test protocols
The following protocols have been developed in WP14 during the project:
• Protocol for characterization of the geometry of complete concentrators using photogrammetry or deflectometry (Deliverable 14.4).
• Protocol for evaluating optical quality, thermal losses and incident angle modifier of parabolic trough collectors (Deliverable 14.6).
• Protocol for optical and geometrical evaluation of heliostats (Deliverable 14.7).
These protocols are now available for R&D centres and related industries. In particular, the protocol D14.6 has been already used in 2016 for the new international standard IEC-62862-3-2 “General requirements and test methods for parabolic-trough collectors”, thus contributing to the harmonization of test protocols implemented at R&D centres devoted to concentrating solar thermal technologies. The outstanding experience gained by CIEMAT-PSA and DLR during more than 20 years with the testing and evaluation of solar concentrators has been melted in the new protocols developed.
In addition, CIEMAT-PSA and DLR have performed round robin tests and inter-comparisons of their test procedures to check the reliability and accuracy of several test methods, which is something essential to find the best test protocols by identifying the advantages and disadvantages of different options.
Parallel to the elaboration process of D14.7 and discussions inside the SFERA project consortium, different versions have been internationally discussed by a group of R&D and industry experts as members of the IEA Technology Collaboration Programme SolarPACES Task III during the task meetings of the SolarPACES conferences. These comments are greatly acknowledged and have increased the quality of this protocol considerably.
New testing facility for collectors’ interconnections
A new testing facility has been designed and implemented at CIEMAT-PSA to evaluate, under real working conditions (hot oil), the performance, reliability and durability of ball joints, flexible hoses and hybrid interconnections used to connect the receiver tubes of line-focus collectors. This facility, the so-called REPA facility (figure 7), is the only facility of this type currently available in a European public R&D centre. Several companies operating commercial solar thermal power plants have shown their willingness to get access to this facility for accelerating ageing and testing of the inter-connection elements they are using in their plants, because there is no other similar facility available in Europe.
In addition, a system for outdoor evaluation of the mechanical torsion in parabolic trough collectors has been also developed. Since the structural stiffness is very important in parabolic trough collectors due to its impact on the overall performance of the collector, the availability of a device to measure the torsion of the supporting structure under real working conditions is very useful for the industry and plant owners.
CHARACTERIZATION OF HEAT TRANSFER FLUIDS AND HEAT STORAGE MATERIALS
Guidelines and procedures for standardized testing protocols
An agreement, among the partners involved in WP15 (ENEA, CEA, CIEMAT, UTV) has been attained upon standardized analytical tools to investigate HTF and HSM against their thermos-physical and compatibility properties. The results have been reported in Deliverable 15.1. In this context, it was also developed a general ranked state of the art review about the most important thermal fluids and materials, as described in Deliverable 15.5.
The obtained outcome show the necessity to continue the collaboration between the European companies working in this field, in order to establish common procedures and to validate them by comparing experimental results.
Improvement of performances for laboratory test equipment
Thermophysical Property Laboratory of the University of Rome “Tor Vergata” (TPL-UTV) has an expertise in building probes for thermal conductivity tests in the temperature range between -20°C and 100°C.
The need to measure thermal conductivity at high temperature requires a quite different procedure for probe construction. In particular, the working temperature ranges for molten nitrates can be between 100°C and 600°C. At this aim, a new thermal conductivity probe for high temperature (till to 600 °C) was designed, built, and tested.
Testing a typical low melting ternary molten salt (18% in mass of NaNO3, 52% KNO3, and 30% LiNO3) at 120°C and 150°C there was a good agreement with similar data extrapolated for the standard solar salt (60% NaNO3, 40% KNO3), even if there is a big difference in chemical composition of the two mixtures, and even if the solar salt is solid at these temperatures. At 200°C a meaningful difference is found between the thermal conductivity of the two salts, likely due to the start of free convection. This phenomenon highly reduces the usability of the probe at high temperatures, given the low viscosities of the molten salt at these temperatures.
In order to overcome this problem it is necessary to extrapolate data from lower temperatures, taking into account that the extrapolation can lead to higher uncertainties (that can be statistically evaluated), or, alternative, to add to the molten salts a small quantity (lower than 2% in mass) of a substance which could deeply increase their viscosity. Results are summarized in Deliverable 15.2.
ENEA developed a system to investigate the chemical stability of thermal fluids, in particular molten salts (figure 8).
This set-up allows to work under a controlled gas atmosphere, to homogenise the reaction temperature and to check the gas evolution and composition over the degradation time. Furthermore, the molten salt can be periodically sampled and analysed. It has been demonstrated to be a valuable tool for following in real time the change in composition of thermal fluids, and can and will be employed to determine the chemical stability of HTF and HSM for research or industrial purposes. Results are reported in Deliverable 15.3.
In addition, DLR developed an in situ electrochemical method to detect and analyse impurities in molten salts (Deliverable 15.4 figure 9).
Development of an electronic database for materials and components features concerning CSP
The collected information was inserted in a searchable standalone database.
There is definitely a great interest, both from public research institutions and industries about an accurate and precise characterization of materials for heat transport or storage. Besides the thermos-physical properties, a main issue is an exact determination of their upper temperature limits, along with their compatibility with CSP structural materials at several temperatures. In this respect, the results obtained in WP15 and reported in public domain deliverables can certainly be of great utility, and can be looked up in the prepared database. Moreover, there are some aspects that need to be improved:
• Corrosion tests concerning molten salts, especially between 400 and 500°C.
• Methods to properly measure the thermal conductivity at high temperatures.
• The establishment of definitive common criteria and methodologies to determine the chemical stability of HTF and HSM.
• In general, a better accuracy and precision for thermochemical properties.
• Validation and completion of multicomponent phase diagram, including the development of predictive simulation models.
A complete state of the art review about the most interesting HTF and HSM has been carried out. Table 1 summarizes the HTF and/or HSM taken into account and the related deliverables from WP15. Where possible, the literature data were experimentally completed and validated and applications were reported.
Potential Impact:
Figures and table attached in a pdf document.
Development of SFERA-II project has involved three principal activities: Networking, Trans-national Access and Joint Research Activities. Each one has shown a potential impact according to the final results achieved.
Networking activities has involved not only the organization of international conferences on CSP technology which addressed a global audience; but also training courses for industries and summer/winter schools’ attaining the creation of a common training framework, providing regularized, unified training of young researchers in the capabilities and operation of concentrating solar facilities.
Joint Research Activities have achieved a common level of high scientific quality and service through a synergistic approach. During the consecution of SFERA-II project it has been generated an up-to-now no existing European identity for Research on Concentrating Solar Technologies. Scientific and technological excellence have been strengthened due to an envisaged harmonization and the most effective use of large-scale infrastructures, as well as the establishment of virtual working groups and an extended dissemination strategy. It must be highlighted the main activities carried out through the different research WP such as the development of new calibration facilities for sensors (pyrheliometers, pyranometers, RSI, etc.), advances in pyrometric temperature measurement methods for high concentration solar facilities and solar simulators, design and development of new testing protocols for characterization of solar concentrators and interconnecting elements and heat transfer fluids, as well as new testing facilities in general. Those activities have been tackled thanks to a complete integration between SFERA-II partners and interested industry showing a significant upgrade, improvement and impact on the European Research Area on CSP.
It is also important to stress that the protocols and new test facilities developed along SFERA-II project will be very useful not only to R&D centres, but also to plant operators and manufacturers, thus contributing to the harmonization of the concentrating solar thermal sector and to the acceleration of its developing curve.
Finally, the achievement of Transnational Access activities within the frame of SFERA-II project has unified all European large scale infrastructures and makes them available to European and international Researchers and companies (figure 10). This ‘open-door’ policy has shown to revert on the benefit of the own research groups and facilities themselves, as usually the visiting scientists provide new ideas for solar research and new technical possibilities and advances to the well-established operating procedures. They normally come from non-solar scientific communities, then stimulating the way of thinking of the facilities’ researchers, helping them to identify new possible applications for the solar energy. Access activity have forced facilities’ researchers to keep the facilities up and running, optimizing the operating and maintenance procedures and, last but not least, enriching culturally as European citizens by sharing our working days with people from 25 countries worldwide.
DISSEMINATION AND PUBLICITY
The main objective has been putting strong emphasis on external communication towards the general public, dissemination of the main results, publicity regarding the whole project and outreaches the user community. In addition, a strong advertisement of the transnational access campaigns within SFERA-II project has been carried out.
The main foregrounds are summarized as follows:
• A general informative brochure has been designed and printed and a final one containing the most successful transnational access stories within SFERA-II (attached to the final report).
• SFERA-II main S&T results as well as transnational access publicity has been done also through several booths included in the exhibition program of four SolarPACES conferences (figure 11) and two CSP Today Conferences along the whole project duration. Active participation as exhibitor to other conferences such as ICRI (promoted by the European Commission) was also carried out. In addition, research works included in the proceedings of such international conferences were included in the USB key with the logo of SFERA-II and distributed to the booth visitors.
• Two publications were included in specialist magazines on renewable energies with special sections on CSP topic. It was largely distributed during the EUSEW event of the European Commission in order to attain a more general public rather than only CSP specialists.
• SFERA-II project is strongly present in social and professional networks. In particular a SFERA-II group has been created in LinkedIn, in which articles related to the project are openly published to inform on the project activities: https://www.linkedin.com/grp/home?gid=8313632&sort=POPULAR&trkInfo=clickedVertical%3Agroup%2CclickedEntityId%3A8313632%2Cidx%3A1-1-1%2CtarId%3A1441206052589%2Ctas%3Asfera+II&trk=tyah
At the moment, there are 283 members on the group. It is expected to grow up to 300 by mid-2018.
• Finally, a dynamic contact database has been generated with more than 800 contacts receiving news related to SFERA-II project activities. Currently, the database is available on the online platform http://insightly.com/ and with a direct link for the partners of the project who have a password to access it: https://8o3e1vsq.insight.ly/contacts
EDUCATIONAL OUTREACH ACTIVITIES: ORGANIZATION OF TRAINING COURSES AND SCHOOLS
Four one-week training courses for researchers, engineers and technicians from industry have been designed within the framework of SFERA-II. Each course was prepared and conducted by one beneficiary. The overall course manager (DLR) was responsible for the coordination, announcement and selection process. The courses were designed for a maximum of 15 participants to guarantee the active participation in practical exercises, lively discussions and close proximity of engineers from industry and lecturers during and after the course. The course managers with the assistance of ESTELA decided to open the course not only to European companies because the new CSP markets are also placed outside Europe, e.g. in the MENA region or India. The topics of the four courses have been selected jointly between the task partners and ESTELA with the aim to provide newest research tendencies to industries in order to support the right technical decisions in the industry. Table 2 shows an overview of the four training courses.
In addition, four doctorial colloquiums have been implemented along SFERA-II project, attaining higher attendance compared to SFERA-I project. An average of 40 PhD students coming from different partners was reached each year, gathering all together for increasing collaboration and knowledge of what is going on at the other partners’ institution. Other four SFERA-II public schools (summer/winter schools) have been also organized on topics that are really mainstream at the moment in the CSP community. The attendance was also quite high with the same average of participants (and a few of them from the industry sector) in each edition, than in the doctoral colloquiums. These schools have become a good way to inform about SFERA-II project and get the experts of the project into disseminating their knowledge to the scientific community and industry which always creates strong interests.
Topics of each summer/winter school celebrated within SFERA-II have been the following: Solar receiver and reactors, Thermal storage, Heat Transfer Fluids & Innovative R+D Subjects and Modelling and Validation.
EXPLOITATION OF RESULTS
Main R&T results obtained within the tasks in Joint Research Activities developed along SFERA-II project have been mainly exploited by scientific (peer reviewed) publications, the elaboration of flyers containing the main results obtained throughout the project and patents.
More details can be extracted from tables A1 and A2 and Section B (all tables attached below).
For further information, please visit SFERA-II website: https://sfera2.sollab.eu/
List of Websites:
https://sfera2.sollab.eu/
CSP Research Infrastructures in Europe have served through the last 30 years as research tools in order to demonstrate the concept feasibility by exploring different pathways on how to produce high temperature heat, electricity, and more recently, solar fuels using concentrating solar radiation.
These developments were performed rather independently in research centres in Spain (in Spanish-German cooperation), France, Italy Israel, Switzerland and Germany. In October 2004 five major research labs (CIEMAT from Spain, CNRS from France, DLR from Germany and ETH and PSI from Switzerland have formed the Alliance of Laboratories for Research and Technology on Solar Concentrating Systems (“SolLab“; www.sollab.eu) to overcome this fragmented status. Later on, further steps have been taken to enhance integration, like the first SFERA project (2009), the ESFRI’s EU-SOLARIS infrastructure (2010) or the EERA Joint Program on CSP (2011).
Nowadays, the key point is to cooperate with the industry in order to reach the technology objectives listed above and gain a significant market share. Europe is leading the way, so far, but other countries are launching their own CSP promotion programs, like USA, India or China, and this advantage can be maintained only through an effort in innovation and for that ‘Research Infrastructures’ have a crucial role to play.
The program developed within the proposed joint research activities in SFERA-II has increased the basic scientific knowledge and available techniques for improved performance of concentrating solar systems. Calibration facilities and agreed procedures to calibrate sensors which are used for thermal performance testing and for measuring the solar resource have been stablished. A joint calibration facility for field pyrheliometer and pyranometer was erected at CIEMAT-PSA. In addition, double-modulation pyrometry has been implemented and tested at PSI’s 1 and 50 kW solar simulators and at a small vertical solar furnace at PROMES. New experimental techniques to enhance the services offered within partners’ research infrastructures in order to improve this material knowledge hence the component lifetime and performance have been also developed. Harmonization of the testing procedures applied in research infrastructures for characterization of solar concentrators has been attained and a new test bench has been implemented at CIEMAT-PSA for collectors’ inter-connections. Finally, an easy-to consult standalone database containing properties and applications of: molten nitrates, phase change materials (PCM), chemical storage systems and solids as sensible heat storage materials, has been prepared.
SFERA-II partners have disseminated such results widely in the scientific community and industry through the networking activities proposed. The direct contacts of experienced scientists with newcomers and interested students have also been guaranteed primarily through the transnational access programme. This will strengthen and improve the network of partner institutions, which will become established as the core of research in this field, leading to a structured long-term influence in this fast-growing area of renewable energy science and technology. It can be now publicised by the numbers of infrastructure users involved, and the scientific papers and new projects generated.
Project Context and Objectives:
Context
To achieve a secure and sustainable energy supply, and in view of growing climate change concerns, the EU has taken on the role of Kyoto protocol promoter and set out ambitious goals to achieve a large share of renewable energy in the European market.
The challenging European policy goals for non-nuclear energy are for the renewable energy contribution to triple up to 20% of primary energy by 2020.
Solar Energy, as the primary source of renewable energy, will contribute a major part of this share, and its conversion by concentrating technologies for concentrating solar power (CSP) and heat generation has long been proven cost-effective for a wide range of applications. Several CSP projects have recently been put into operation. Some 2.400 MW are under construction and several GW are in advanced stages of planning, particularly in Spain, but also in other Southern European countries, like France, Greece and Portugal.
Based on the experience gathered in current SFERA-I ‘Integrating Initiative’, a process was established to harmonize and improve the basic services of the research facilities. The specific focus was related to the development of common performance testing guidelines, the evaluation of improvements to reach ultra-high flux distributions and to allow accelerated aging testing and, finally, the establishment of guidelines to set up new test facilities for thermal energy storage materials and systems.
Through co-ordinated integration of their complementary strengths, efforts and resources, progress will be made in SFERA-II, more effective by:
• Increasing the scientific and technological knowledge base in the field of concentrating solar systems in both depth and breadth.
• Providing and improving the research tools best-suited for the scientific and technologic community in this field.
• Strengthening the European industry through stimulating technology transfer by fostering the use of World-class R&D facilities.
• Increasing general awareness and especially of the scientific community in the possible applications of concentrated solar energy, including creation of new synergies with other scientific disciplines (e.g. materials treatment).
The commercial success of renewable energy technologies and in particular in CSP technologies in recent years have led to the situation that facilities are used more intensively by industrial users who typically want to qualify their prototypes for a further scale-up step or a direct commercialisation. Therefore, in the scope of the SFERA-II project, the proposed joint research activities are more focused to provide a better service to industrial users.
Objectives
In view of this challenge for research, development and application of concentrating solar systems involving a growing number of European industries and utilities in global business opportunities, the purpose of this project is to integrate, coordinate and further focus scientific collaboration among the leading European research institutions in solar concentrating systems that are the partners of this project and offer European research and industry access to the best-qualified research and test infrastructures.
One goal of these efforts is to create a unified virtual European Laboratory for Concentrating Solar Systems, easily accessible to interested researchers, both from the academia and from the industry, and thus serving as the structural nucleus for growing demand in this field in the developing European research area.
Such a European Solar Lab would also contribute to a sustainable, secure European energy supply and to a firm basis for global competitiveness of European technology suppliers in this field, with strong prospects of growing worldwide markets in the coming decades.
Another goal is to enhance cooperation with CSP industry, looking for new innovative products and processes to reach the market, thus increasing competitiveness of European CSP industry and of CSP technologies in front of the fossil and other renewable ones in the energy market.
Some activities proposed in that way are:
• Organization of specific training courses for industrial technicians and researchers.
• Fostering the use of the facilities offered by industrial researchers.
• Creating a specific joint working group to identify and develop products and processes suitable for commercial exploitation.
The proposed networking activities will help to promote and to accelerate innovation in CSP, through the creation of a common knowledge base and cooperation culture among the researchers of this project. Another target is also to guarantee a broad information exchange with the scientific and industrial communities, as a sound base for further commercial deployment but also the development of different technological aspects in the joint research activities.
Innovation actions aim at developing the conditions to set a world-class eco-system that may speed up the process from knowledge (generated by activities at the Research Infrastructures) to new products, processes and services. Also with the strong accent put on external communication (conferences, training courses, summer schools, etc..) the networking activities aim at targeting new users potentially interested in the ‘access’ activities, as it already happened in SFERA-I.
The transnational access will play a key role in serving to increase technical collaboration and possible new synergies with new user groups from neighbouring or new fields, a model that has been realized with success during earlier access programs at CIEMAT-PSA and PROMES, for instance.
Increased participation of industrial users will be promoted, addressing this community through the associations like ESTELA, PROTERMOSOLAR, etc.
Joint research that is addressed in SFERA-II project aims to improve the quality and service of the existing infrastructure and to extend their services taking benefit from the specific competences and experiences of the individual labs and jointly achieve a common level of high scientific quality and service through this synergistic approach. One essential subject for the industrial clients is related to the calibration of sensors. Research centres and industry need joint calibration facilities and agreed procedures to calibrate sensors which are used for thermal performance testing and for measuring the solar resource. Development and standardization of calibration facilities is focused in SFERA-II.
A second subject addressed concerns the development of pyrometric temperature measurement methods suitable for use on surfaces exposed to concentrated radiation as prevail in high-concentration solar facilities (e.g. solar towers or solar furnaces) and arc lamp-based solar simulators.
A third subject to be focused on is the determination of physical properties of CSP materials under concentrated solar irradiation to extend the capabilities in the existing CSP research infrastructure that allows for a better evaluation of the material behaviour, such as high temperature steels or SiC ceramics.
Since the characterization of solar concentrators for CSP plants is a growing demand activity in several facilities within the SFERA consortium, another objective of this project is to define common protocols to be applied at the participating research infrastructures for characterization of solar concentrators, as well as the design and implementation of a test bench for collectors interconnections (ball joints, flexible hoses and hybrid interconnections).
Additionally, the design and implementation of a suitable test bench for collectors’ interconnections will improve the testing capacities available within the European research infrastructure because industrial external users (manufacturers, engineering companies and plant owners) are demanding such a facility, which did not exist before SFERA-II project.
Finally, for the evaluation of experiments most users require detailed thermophysical properties of heat transfer fluids and heat storage materials (HTF/HSM). Only for a very few (like water-steam) reliable information is easily available, for many others the properties are either very specific or changing with time. An important service of the research facilities is to provide precise data of for these materials which is another objective to be tackled by the joint research activities planned in SFERA-II project.
Project Results:
Figures and table attached in a pdf document.
PROMOTION OF INNOVATION IN CSP BASED ON SFERA-I ACTIVITIES
Increasing the potential of innovation of SFERA by addressing the innovation opportunities created by the project activities and by reinforcing links with companies that drive innovation, was faced through the whole project. The key tasks proposed were based on developing the conditions to set a world-class eco-system that may speed up the process from knowledge (generated by the research activities of the solar concentrating research infrastructures) to new products, processes and services.
It is important to highlight that the partnership with industry has been reinforced along the project thanks to a strong collaboration established with ESTELA (European Solar Thermal Electricity Association) which is the main industrial association in CSP and the organization of four training for industry courses, bringing research and innovation together.
Initially and by the hand of a subcontractor, all the access users have been contacted to explore with them the possibilities and opportunities for exploiting their experimental work carried out within the framework of SFERA-II transnational access activity. For these purposes, a questionnaire was drafted by the external consultant to gather all important information related to the exploitation of the access results. A follow-up will be done one year after the end of the project to see what will be the impacts of R&D activities carried out within the transnational access activities, not only on the scientific community but on the industrial/commercial side.
As identified in the results of the questionnaire, most of the access projects have a really low TRL, starting even sometime at TRL 1. In addition, the replies to the questionnaire have helped to formulate interesting conclusions on the actions to be implemented to boost the exploitation of these access projects (figure 1).
The list of potential innovations extracted from the JRA has already been mapped in deliverable 3.5. Further to that, a focus has been done on WP11 which showed the most promising activities for a further commercialization.
EXCHANGE OF BEST PRACTICES FOR HARMONIZATION OF APPROACHES
For a better harmonization of the CSP activities within Europe and a better understanding of what is at stake at each other partners’ laboratory, it is crucial to emphasize the exchange of best practices. This has been implemented along SFERA-II project in two ways:
• Inter-comparison campaign of flux measurement instruments at CNRS and PSI. Best practices on practical and technical aspects of the instruments have been shared in order to standardize the use of these instruments among the partners. A particular attention was turned to solar flux measurement at the focus of concentrating systems because it is a key data for the evaluation of system efficiency (receivers, reactors, output of secondary concentrators...). It remains of interest to hold a flux inter-comparison by using solar simulators in order to check the spectrum sensibility of the flux sensors: if significant calibration differences are observed as expected between solar and electrical light, a more careful monitoring of the atmospheric conditions will be required when using flux sensors in order to have a good enough evaluation of the real time spectrum.The follow-up of these activities will be carried out outside of SFERA-II project, after the end of the project, since all of this is of strong interest for the industry, there is the need to go further in the harmonization of these practises.
• Exchange of personnel between SFERA-II partners in order to share know-how, participate in common R&D activities and to promote common technical and management methods. Nine mobilities have been taken place between 2016 and 2017. Specifically, four mobilities occurred during the inter-comparison campaign (CNRS to CIEMAT-PSA and DLR; DLR to CNRS) and five more were related to other JRAs: CIEMAT-PSA to DLR for the application of advanced analytical techniques for the characterization of solar reflector samples subjected to different corrosive environments; CIEMAT-PSA to CNRS for an exchange on Direct Steam Generation with line-focus solar collectors. All results can be found in the deliverable 5.4. These mobilities were a success in terms of transfer of knowledge and harmonization of procedures and led to several joint publications between the different research centres.
DEVELOPMENT OF JOINT CALIBRATION PROCEDURES AND FACILITIES FOR SENSORS
Standardized Calibration facility for thermal irradiance sensors
Within WP11 in JRA, a calibration test stand for pyrheliometers and pyranometers was implemented at the CIEMAT-PSA METAS facility in 2014 (figure 2). The resulting facility enables CIEMAT-PSA staff and guest researchers to calibrate various thermal irradiance sensors at the same time even beyond the project duration. Two PMO absolute cavity pyrheliometers (PMO6 0106 Ciemat and PMO6-cc 0807 DLR) for the DNI and one Kipp&Zonen CMP22 pyranometer (SN 110288) for the DHI are used as reference sensors.
The calibration test uses a solar heliostat from CIEMAT-PSA as tracker for the pyrheliometers mounted on a metal plate. The DNI reference absolute cavity radiometers (ACR) are placed inside a weather-proof cabinet. During measurement, two windows are opened which allow an irradiation of the reference sensors. Pyranometers are calibrated using a sensor table next to the reference pyranometer on top of the METAS BSRN platform. All sky images are taken and the aerosol optical depth and the sunshape are measured during the calibration. The all sky images are used to filter out inadequate data points that are affected by clouds.
In total four calibration campaigns (2014, 2015, 2016, and 2017) were jointly carried out by CIEMAT-PSA and DLR personnel, with extra support from CNRS at CIEMAT-PSA in 2016. Results are public via deliverables D11.2 and D11.3. Deliverable D11.2 consists of a report describing mainly the implementation of the joint calibration facility at CIEMAT-PSA METAS test site. D11.3 contains the results of all calibrations and investigations carried out during the calibration campaigns.
Standardization of RSI (Rotating Shadow-band Irradiometer) calibration
SFERA-II scientists from DLR and experts from the US and Germany discussed the possibility of improving RSI correction functions for systematic errors in a more physical and less empirical way. CIEMAT-PSA and DLR performed a round robin test by calibrating a single RSI according to different methods at the Plataforma Solar the Almeria (PSA) and at an additional CIEMAT test site facility in Madrid.
In consideration of a DNI value around 1000W/m², the observed rmsd values correspond to a relative rmsd between 1 to 3%. The results were presented in report D11.4.
Calibration facility for heat transfer fluid mass flow sensors and thermal capacity
This task was initiated with a comprehensive uncertainty analysis, calculating the combined uncertainty of the heat capacity measurement bypass including a sub-device measurand resolved uncertainty weighting. This measure identified individual influences (sensitivities) in the heat capacity measurement of all single measurands and recognized effects on the measurement, such as heat losses for instance.
Finally, a detailed understanding of all uncertainty components and their combination, which is indispensable for any high precision measurement using heat transfer fluids, was attained. The overall combined measurement uncertainty of the cp-measurement was proved to be smaller than 1.0 % at mean operation temperatures between 25 and 60°C. More details can be found in the deliverable D11.6 “Report on measurement uncertainty”.
In addition, and due to the lack of methods to calibrate built-in flow meters under its working conditions without removing them from a parabolic trough HTF loop, the bypass to measure the heat capacity was upgraded with a reference Coriolis sensor. An adequate mass flow sensor was selected to be operated at temperatures up to 350°C and under typical test loop mass flow conditions of about 5 kg/s (Deliverable D11.7). The calibration facility for heat transfer fluid mass flow sensors and thermal capacity was used for various measurement campaigns at the parabolic trough rotating platform KONTAS (DLR/CIEMAT) at CIEMAT-PSA (see figure 3).
As being modular, the bypass can be mounted to any other installation in order to characterize the specific heat capacity or recalibrate installed mass flow sensors of the installation. Further details can be found in deliverable D11.8 “Report on Calibration of First Testing Facility Using the Calibration Bypass”.
PYROMETRIC TEMPERATURE MEASUREMENT METHODS FOR HIGH-CONCENTRATION SOLAR FACILITIES AND SOLAR SIMULATORS
Develop “Double Modulation” pyrometry for use in arc lamp based solar simulators
Main achievements have been published in a research article titled “Double modulation pyrometry: A radiometric method to measure surface temperatures of directly irradiated samples” in Review of Scientific Instruments. It documents the custom design and implementation of the flux modulator, a key component of the method that utilizes the symmetry of the imaging furnace. It presents the methodology and experimental setup for a two-step calibration procedure required prior to any measurements and discusses a systematic error that may affect accuracy. The calibration procedure results in the estimation of 5 calibration coefficients. An error analysis focusing on how uncertainty in any of the calibration coefficients affects the accuracy of the measurement (see figure 4) is also discussed. It demonstrates that the method performs well under harsh conditions with a typical error of 20 K when measuring on a highly reflective and thus difficult to measure thin strip of Platinum.
The method was also implemented at PSI’s 50 kW high-flux solar simulator and used to measure the temperature of different ceramic foams such as SiSiC, ZrO2, and Al2O3 used as functional materials in CSP applications.
Two experimental campaigns in CNRS-PROMES (France) were successfully carried out. A very good agreement has been observed between three instruments: PSI’s double modulation prototype pyrometer, a double modulation pyrometer prototype by CNRS and CNRS’s reference solar blind pyrometer, proving the potential of the double modulation pyrometric method in suitable conditions for the wide range of tested materials.
In addition, the methodology for the in-situ reflectance measurement was developed and its application to dynamically correct the sample’s emissivity was demonstrated.
Active temperature regulation in solar furnaces
IR camera prototype at CIEMAT-PSA solar furnace has been employed. In the worst conditions (a surface reflectance of 0.60 and the highest concentration), the camera with the band-pass filter centred at 3320 nm measures surface temperatures with a relative error, due to the solar distortion, of less than 5 % above a surface temperature of 750 K. In experiments where it is used a quartz window, this combination of filter and camera allows to measure through the quartz window. The experimental comparison showed that at 3320 nm the camera is as solar blind as the IMPAC pyrometer at 1400 nm.
In the same conditions, if the filter centred at 4720 nm is selected in the filter wheel of the camera, it is possible to measure with a relative error of less than 5 % above a surface temperature of 450 K. If a quartz window is used in a test, this filter allows the camera to measure the surface temperature of the window to control its safety levels. The experimental comparison showed that working at 4720 nm the camera is even better than the IMPAC pyrometer.
To simulate test experiments, a temperature dynamical model of a rectangular metal tube was developed. One side of the tube is exposed to the concentrated solar power, and a fluid (water) circulated inside the tube to remove heat and to “protect” the exposed side of the tube. It is known from previous works that the heliostats do not produce the same flux on the furnace focus, and the responses times of the heliostats are not equal. But to capture the main dynamics one can assume that all heliostats are equal, they produce the same “mean” flux and move between the ON and OFF positions with the same speed.
The objective is to use a control algorithm that must select the number of heliostats (to schedule heliostats) to deliver a given power level such that a small temperature tracking error is obtained. But by selecting heliostats it implies that the applied power do not change continuously as with a “normal shutter” but is quantized. This fact may induce small oscillations in the controlled temperature. In order to obtain a finer power adjustment, a possible solution is to explore and combine the differences between fluxes produces by the real heliostats. But this line of research was not explored within SFERA-II project.
DETERMINATION OF PHYSICAL PROPERTIES OF CSP MATERIALS UNDER CONCENTRATED SOLAR IRRADIATION
Determination of thermo-mechanical properties under concentrated solar radiation
New instruments and methods for in-situ thermo-mechanical investigation using solar acoustic methods have been implemented within WP13. A novel device upgraded for strain measurement by photomechanical method has been designed: it would allow a better evaluation of the materials damages (figure 5). Experimental tests and their comparison with the proposed thermo-mechanical behaviour have been published in deliverable 13.2.
Determination of thermo-optical properties: spectral directional emissivity measurements at high temperature
A new spectroradiometer at CNRS-PROMES has been employed for investigation on improving the capacity for spectral directional emissivity measurements depending on the sample temperature. Main results achieved are summarized here:
• The noise level of the two sensors (spectrophotometer and spectroradiometer) and their data path during the acquisition has been characterised which led to limiting the usable wavelengths depending on the temperature of the sample. This means the usable signal-noise ratio has been investigated notably to cope for lower photons (actual signal) at low temperatures.
• New mechanical supports for the spectroradiometer and the old radiometer have been installed on the experimental MEDIASE carriage in order to have high quality accurate reproducible aiming direction on the solar heated samples.
• The software developed has been pursued, both on the backend (algorithms) but mostly on the frontend (user interface). The LabVIEW-based software now allows easier report quality outputs of the processed data, such as: angular polar plots, spectral plots, temperature dependence plots, bandwidth plots...
The work about spectral directional measurement of the emissivity is reported in Deliverable 13.4 about the assessment of this upgrade and in Deliverable 13.3 which focuses on the comparison between CNRS and CIEMAT methods of hemispherical measurement of emissivity for selected bands for selected tests materials.
Determination of key properties in the case of porous materials in CSP applications
A solar test bench was developed by CNRS in order to characterize the solar-to-thermal efficiency of reticulate porous ceramics made of SiC with open pores: improvements with current state-of-the-art were made by the use of a homogenizer, ensuring quasi-1D incident solar flux irradiation. This solar setup has also been used to age samples used to optimize the techniques to evaluate their surface characteristics (figure 6).
A numerical and experimental analysis of porous materials transfer properties has been performed by ETHZ with the test case of the solar-driven thermochemical reduction of ceria as part of a H2O/CO2-splitting redox cycle. A transient heat and mass transfer model has been developed to simulate reticulated porous ceramic (RPC) foam-type structures, made of ceria, exposed to concentrated solar radiation. The RPC features dual-scale porosity in the mm-range and lm-range within its struts for enhanced transport. The numerical model solves the volume-averaged conservation equations for the porous fluid and solid domains using the effective transport properties for conductive, convective and radiative heat transfer. These in turn are determined by direct pore-level simulations and Monte-Carlo ray tracing on the exact 3D digital geometry of the RPC obtained from tomography scans. Experimental validation has been accomplished in terms of temporal temperature and oxygen concentration measurements for RPC samples directly irradiated in a high-flux solar simulator with a peak flux of 1200 suns and heated to up to 1940 K. Effective volumetric absorption of solar radiation was obtained for moderate optically thick structures, leading to a more uniform temperature distribution and a higher specific oxygen yield. The effect of changing structural parameters such as mean pore diameter and porosity has been investigated. This work was reported in the deliverables 13.5 and 13.7.
CHARACTERIZATION OF SOLAR CONCENTRATORS AND INTERCONNECTING ELEMENTS
Two main achievements attained throughout SFERA-II project are:
• Definition of common protocols to be applied at the participating research infrastructures for characterization of solar concentrators.
• Design and implementation of a test facility for collectors’ inter-connections (ball joints, flexible hoses and hybrid interconnections).
Development of new test protocols
The following protocols have been developed in WP14 during the project:
• Protocol for characterization of the geometry of complete concentrators using photogrammetry or deflectometry (Deliverable 14.4).
• Protocol for evaluating optical quality, thermal losses and incident angle modifier of parabolic trough collectors (Deliverable 14.6).
• Protocol for optical and geometrical evaluation of heliostats (Deliverable 14.7).
These protocols are now available for R&D centres and related industries. In particular, the protocol D14.6 has been already used in 2016 for the new international standard IEC-62862-3-2 “General requirements and test methods for parabolic-trough collectors”, thus contributing to the harmonization of test protocols implemented at R&D centres devoted to concentrating solar thermal technologies. The outstanding experience gained by CIEMAT-PSA and DLR during more than 20 years with the testing and evaluation of solar concentrators has been melted in the new protocols developed.
In addition, CIEMAT-PSA and DLR have performed round robin tests and inter-comparisons of their test procedures to check the reliability and accuracy of several test methods, which is something essential to find the best test protocols by identifying the advantages and disadvantages of different options.
Parallel to the elaboration process of D14.7 and discussions inside the SFERA project consortium, different versions have been internationally discussed by a group of R&D and industry experts as members of the IEA Technology Collaboration Programme SolarPACES Task III during the task meetings of the SolarPACES conferences. These comments are greatly acknowledged and have increased the quality of this protocol considerably.
New testing facility for collectors’ interconnections
A new testing facility has been designed and implemented at CIEMAT-PSA to evaluate, under real working conditions (hot oil), the performance, reliability and durability of ball joints, flexible hoses and hybrid interconnections used to connect the receiver tubes of line-focus collectors. This facility, the so-called REPA facility (figure 7), is the only facility of this type currently available in a European public R&D centre. Several companies operating commercial solar thermal power plants have shown their willingness to get access to this facility for accelerating ageing and testing of the inter-connection elements they are using in their plants, because there is no other similar facility available in Europe.
In addition, a system for outdoor evaluation of the mechanical torsion in parabolic trough collectors has been also developed. Since the structural stiffness is very important in parabolic trough collectors due to its impact on the overall performance of the collector, the availability of a device to measure the torsion of the supporting structure under real working conditions is very useful for the industry and plant owners.
CHARACTERIZATION OF HEAT TRANSFER FLUIDS AND HEAT STORAGE MATERIALS
Guidelines and procedures for standardized testing protocols
An agreement, among the partners involved in WP15 (ENEA, CEA, CIEMAT, UTV) has been attained upon standardized analytical tools to investigate HTF and HSM against their thermos-physical and compatibility properties. The results have been reported in Deliverable 15.1. In this context, it was also developed a general ranked state of the art review about the most important thermal fluids and materials, as described in Deliverable 15.5.
The obtained outcome show the necessity to continue the collaboration between the European companies working in this field, in order to establish common procedures and to validate them by comparing experimental results.
Improvement of performances for laboratory test equipment
Thermophysical Property Laboratory of the University of Rome “Tor Vergata” (TPL-UTV) has an expertise in building probes for thermal conductivity tests in the temperature range between -20°C and 100°C.
The need to measure thermal conductivity at high temperature requires a quite different procedure for probe construction. In particular, the working temperature ranges for molten nitrates can be between 100°C and 600°C. At this aim, a new thermal conductivity probe for high temperature (till to 600 °C) was designed, built, and tested.
Testing a typical low melting ternary molten salt (18% in mass of NaNO3, 52% KNO3, and 30% LiNO3) at 120°C and 150°C there was a good agreement with similar data extrapolated for the standard solar salt (60% NaNO3, 40% KNO3), even if there is a big difference in chemical composition of the two mixtures, and even if the solar salt is solid at these temperatures. At 200°C a meaningful difference is found between the thermal conductivity of the two salts, likely due to the start of free convection. This phenomenon highly reduces the usability of the probe at high temperatures, given the low viscosities of the molten salt at these temperatures.
In order to overcome this problem it is necessary to extrapolate data from lower temperatures, taking into account that the extrapolation can lead to higher uncertainties (that can be statistically evaluated), or, alternative, to add to the molten salts a small quantity (lower than 2% in mass) of a substance which could deeply increase their viscosity. Results are summarized in Deliverable 15.2.
ENEA developed a system to investigate the chemical stability of thermal fluids, in particular molten salts (figure 8).
This set-up allows to work under a controlled gas atmosphere, to homogenise the reaction temperature and to check the gas evolution and composition over the degradation time. Furthermore, the molten salt can be periodically sampled and analysed. It has been demonstrated to be a valuable tool for following in real time the change in composition of thermal fluids, and can and will be employed to determine the chemical stability of HTF and HSM for research or industrial purposes. Results are reported in Deliverable 15.3.
In addition, DLR developed an in situ electrochemical method to detect and analyse impurities in molten salts (Deliverable 15.4 figure 9).
Development of an electronic database for materials and components features concerning CSP
The collected information was inserted in a searchable standalone database.
There is definitely a great interest, both from public research institutions and industries about an accurate and precise characterization of materials for heat transport or storage. Besides the thermos-physical properties, a main issue is an exact determination of their upper temperature limits, along with their compatibility with CSP structural materials at several temperatures. In this respect, the results obtained in WP15 and reported in public domain deliverables can certainly be of great utility, and can be looked up in the prepared database. Moreover, there are some aspects that need to be improved:
• Corrosion tests concerning molten salts, especially between 400 and 500°C.
• Methods to properly measure the thermal conductivity at high temperatures.
• The establishment of definitive common criteria and methodologies to determine the chemical stability of HTF and HSM.
• In general, a better accuracy and precision for thermochemical properties.
• Validation and completion of multicomponent phase diagram, including the development of predictive simulation models.
A complete state of the art review about the most interesting HTF and HSM has been carried out. Table 1 summarizes the HTF and/or HSM taken into account and the related deliverables from WP15. Where possible, the literature data were experimentally completed and validated and applications were reported.
Potential Impact:
Figures and table attached in a pdf document.
Development of SFERA-II project has involved three principal activities: Networking, Trans-national Access and Joint Research Activities. Each one has shown a potential impact according to the final results achieved.
Networking activities has involved not only the organization of international conferences on CSP technology which addressed a global audience; but also training courses for industries and summer/winter schools’ attaining the creation of a common training framework, providing regularized, unified training of young researchers in the capabilities and operation of concentrating solar facilities.
Joint Research Activities have achieved a common level of high scientific quality and service through a synergistic approach. During the consecution of SFERA-II project it has been generated an up-to-now no existing European identity for Research on Concentrating Solar Technologies. Scientific and technological excellence have been strengthened due to an envisaged harmonization and the most effective use of large-scale infrastructures, as well as the establishment of virtual working groups and an extended dissemination strategy. It must be highlighted the main activities carried out through the different research WP such as the development of new calibration facilities for sensors (pyrheliometers, pyranometers, RSI, etc.), advances in pyrometric temperature measurement methods for high concentration solar facilities and solar simulators, design and development of new testing protocols for characterization of solar concentrators and interconnecting elements and heat transfer fluids, as well as new testing facilities in general. Those activities have been tackled thanks to a complete integration between SFERA-II partners and interested industry showing a significant upgrade, improvement and impact on the European Research Area on CSP.
It is also important to stress that the protocols and new test facilities developed along SFERA-II project will be very useful not only to R&D centres, but also to plant operators and manufacturers, thus contributing to the harmonization of the concentrating solar thermal sector and to the acceleration of its developing curve.
Finally, the achievement of Transnational Access activities within the frame of SFERA-II project has unified all European large scale infrastructures and makes them available to European and international Researchers and companies (figure 10). This ‘open-door’ policy has shown to revert on the benefit of the own research groups and facilities themselves, as usually the visiting scientists provide new ideas for solar research and new technical possibilities and advances to the well-established operating procedures. They normally come from non-solar scientific communities, then stimulating the way of thinking of the facilities’ researchers, helping them to identify new possible applications for the solar energy. Access activity have forced facilities’ researchers to keep the facilities up and running, optimizing the operating and maintenance procedures and, last but not least, enriching culturally as European citizens by sharing our working days with people from 25 countries worldwide.
DISSEMINATION AND PUBLICITY
The main objective has been putting strong emphasis on external communication towards the general public, dissemination of the main results, publicity regarding the whole project and outreaches the user community. In addition, a strong advertisement of the transnational access campaigns within SFERA-II project has been carried out.
The main foregrounds are summarized as follows:
• A general informative brochure has been designed and printed and a final one containing the most successful transnational access stories within SFERA-II (attached to the final report).
• SFERA-II main S&T results as well as transnational access publicity has been done also through several booths included in the exhibition program of four SolarPACES conferences (figure 11) and two CSP Today Conferences along the whole project duration. Active participation as exhibitor to other conferences such as ICRI (promoted by the European Commission) was also carried out. In addition, research works included in the proceedings of such international conferences were included in the USB key with the logo of SFERA-II and distributed to the booth visitors.
• Two publications were included in specialist magazines on renewable energies with special sections on CSP topic. It was largely distributed during the EUSEW event of the European Commission in order to attain a more general public rather than only CSP specialists.
• SFERA-II project is strongly present in social and professional networks. In particular a SFERA-II group has been created in LinkedIn, in which articles related to the project are openly published to inform on the project activities: https://www.linkedin.com/grp/home?gid=8313632&sort=POPULAR&trkInfo=clickedVertical%3Agroup%2CclickedEntityId%3A8313632%2Cidx%3A1-1-1%2CtarId%3A1441206052589%2Ctas%3Asfera+II&trk=tyah
At the moment, there are 283 members on the group. It is expected to grow up to 300 by mid-2018.
• Finally, a dynamic contact database has been generated with more than 800 contacts receiving news related to SFERA-II project activities. Currently, the database is available on the online platform http://insightly.com/ and with a direct link for the partners of the project who have a password to access it: https://8o3e1vsq.insight.ly/contacts
EDUCATIONAL OUTREACH ACTIVITIES: ORGANIZATION OF TRAINING COURSES AND SCHOOLS
Four one-week training courses for researchers, engineers and technicians from industry have been designed within the framework of SFERA-II. Each course was prepared and conducted by one beneficiary. The overall course manager (DLR) was responsible for the coordination, announcement and selection process. The courses were designed for a maximum of 15 participants to guarantee the active participation in practical exercises, lively discussions and close proximity of engineers from industry and lecturers during and after the course. The course managers with the assistance of ESTELA decided to open the course not only to European companies because the new CSP markets are also placed outside Europe, e.g. in the MENA region or India. The topics of the four courses have been selected jointly between the task partners and ESTELA with the aim to provide newest research tendencies to industries in order to support the right technical decisions in the industry. Table 2 shows an overview of the four training courses.
In addition, four doctorial colloquiums have been implemented along SFERA-II project, attaining higher attendance compared to SFERA-I project. An average of 40 PhD students coming from different partners was reached each year, gathering all together for increasing collaboration and knowledge of what is going on at the other partners’ institution. Other four SFERA-II public schools (summer/winter schools) have been also organized on topics that are really mainstream at the moment in the CSP community. The attendance was also quite high with the same average of participants (and a few of them from the industry sector) in each edition, than in the doctoral colloquiums. These schools have become a good way to inform about SFERA-II project and get the experts of the project into disseminating their knowledge to the scientific community and industry which always creates strong interests.
Topics of each summer/winter school celebrated within SFERA-II have been the following: Solar receiver and reactors, Thermal storage, Heat Transfer Fluids & Innovative R+D Subjects and Modelling and Validation.
EXPLOITATION OF RESULTS
Main R&T results obtained within the tasks in Joint Research Activities developed along SFERA-II project have been mainly exploited by scientific (peer reviewed) publications, the elaboration of flyers containing the main results obtained throughout the project and patents.
More details can be extracted from tables A1 and A2 and Section B (all tables attached below).
For further information, please visit SFERA-II website: https://sfera2.sollab.eu/
List of Websites:
https://sfera2.sollab.eu/
