Bringing sustainable hydrogen power towards commercialisation
Hydrogen is a promising clean energy source which could revolutionise our energy systems. Combining hydrogen and oxygen in a fuel cell can produce electricity, with water and heat as the only by-products. Yet many methods for producing hydrogen (for example from methane) are not emission-free, and risk exacerbating existing problems relating to climate change. Hydrogen created free from these harmful emissions is known as ‘green hydrogen’. In the EU-funded HYDROSOL-beyond project, researchers worked to culminate a series of past projects to bring sustainable green hydrogen to commercialisation. The team has been improving the technology they started on 20 years ago: an innovative hydrogen production plant able to create green hydrogen through solar energy. “The technology utilises concentrated solar energy targeted on a reactor, to achieve the high temperatures required for solar thermochemical redox reactions – to split water and produce solar hydrogen,” explains Souzana Lorentzou, a chemical engineer at the Centre for Research & Technology Hellas (CERTH) in Greece. This effectively stores solar energy in an energy carrier that can be used whenever and wherever it is required, avoiding the temporal and local limitations of solar energy, says Lorentzou.
Identifying challenges and testing new solutions
The technology is applied at a solar facility that consists of a heliostat field, and a solar tower similar to the concentrated solar plants used to generate electricity from the sun. The solar reactor is located on the solar tower, and the heliostat field directs and focuses the sun's rays on the aperture of the reactor. Further concentration of the solar radiation is achieved with the use of a secondary concentrator at the aperture of the reactor, which reduces spillage at the entrance of the reactor. In the HYDROSOL-beyond project, the team were working to identify and tackle some of the challenges of the system, including inert gas minimisation, waste heat recovery and hydrogen production with an efficiency above 5 % in field tests. Activities focused on developing new concepts for integration into the existing solar platform and conducting solar experiments at the Plataforma Solar de Almería in Spain.
Enhancing the abilities of the green hydrogen production plant
The team created and tested, at lab scale, novel lattice structures of redox metal oxides used to split water and trap oxygen. “These structures showed long-term durability, maintaining hydrogen yield after over 1 100 cycles,” says Lorentzou. An innovative oxygen trapping concept also successfully reduced inert gas consumption successfully, also at lab scale. In the final project phase, key achievements included upscaling a novel hybrid ceramic-metallic heat exchanger and integrating it into the platform for heat recovery. Repairs and improvements were made to reactors and optics to ensure safe and efficient operation.
Enhancing solar energy utilisation
The project deepened the team’s understanding of operational aspects within a solar tower facility, identifying strengths and weaknesses. However, solar hydrogen production results from different reactor concepts tested in real environments were discouraging in terms of techno-economic viability. “While solar thermochemical processes theoretically hold promise, significant technical and economic challenges must be overcome before large-scale deployment,” notes Lorentzou. Nevertheless, the achievements of HYDROSOL-beyond underscore the promise of solar thermochemical technologies, opening new avenues for European leadership in high-temperature solar technologies, she adds.
Keywords
HYDROSOL-beyond, solar, energy, green hydrogen, reactions, thermochemical
