Key Technology of Solar- Hydrogen Energy Systems

Hydrogen Energy Research Laboratories, Yokohama National University, Yokohama, Japan

Photosynthesis is the most fundamental activity for all the life on the earth. Its fundamental mechanism has a function that splits water by use of solar energy. The generated hydrogen combines with the carbon dioxide in the air and changes to biomass which is direct or indirect food for every living being. Solar hydrogen energy systems stress that the generated hydrogen should be utilised as clean and abundant energy carrier. Such hydrogen can also be raw chemical materials or clean agent for refining ones. The key technologies for such system are firstly an effective method of water decomposition using solar energy, next the transport and storage methods, and inova­tive utilisations. Thermodynamic fundamentals of water decomposition, direct thermal water decomposition, thermochemical cycle, and photoelectrochemical method are reviewed. Heat energy conversion and chemical heat pump by use of metal­metalhydride cycle are also briefly reviewed.