Solar Thermochemical Water Splitting
Hydrogen is one of the promising options of increasing the overall share of renewables in the traffic and heat sector, because it is a fully storable fuel. It can be either used directly and preferably in high efficiency fuel cells with special tanks or it can be used as the basic product for the generation of hydrocarbons such as methane, methanol or synthetic DIESEL and later use in conventional combustion engines or gas turbines. Used as a fuel it can compensate for the strongly fluctuating offer of renewable electricity or heat especially in the middle European countries. The thermochemical water splitting process operated in HYDROSOL-PLANT uses high-temperature heat (800°C–1400°C) to drive a series of chemical reactions that produce hydrogen. The metal-oxides used in the process are reused within each cycle, creating a closed loop that consumes only water and produces hydrogen and oxygen according to the scheme in the figure.
In HYDROSOL-PLANT, three reactors have been designed and built up with a thermal capacity of 250 KW each. As metal oxides Nickel-Ferrite and Ceroxide are used. Whereas in the first three HYDROSOL projects mainly metal-oxide coated porous ceramics (honeycombs) have been used, which have been taken over from conventional applications the current project additionally uses full metal-oxide porous ceramic foams. From this approach, longer lifetimes and less degradation are expected. A further innovation of HYDROSOL-PLANT in relation to the prior projects is the improved heat recovery. This is necessary to further approach the theoretical efficiency potential of the process. Finally, the objective of the project is the up-scaling to “plant dimensions” of about 750kW. The heat is generated with a large field of moveable mirrors (heliostats), which concentrate the radiation onto the top of a tower, where the reactors are placed. Since most of the solar power is used for the REDOX-phase of the cycle, the cycles in the three reactors are operated with some time shift to each other. This enables a homogeneous workload of the field.
Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT, Spain)
Hellenic Petroleum (HELPE, Greece)
Aerosol and Particle Technology Laboratory (APTL, Greece)
Co-funded by the European Commission, Horizon 2020, Fuel Cell and Hydrogen Joint Undertaking