2014 Volume 83 Issue 2 Pages 103-107
The highly insolated “sun-belt” or “solar-belt” regions of the world include the South-western United States, southern Europe (the Mediterranean coast), most of Australia, and broad regions of the developing world. The direct normal irradiation (DNI) exceeds 1800 kWh/m2/year in these regions. Some modern solar-concentrating systems, such as central towers, parabolic dishes and advanced reflective tower (beam-down) systems, have maximum concentration factors in the 1000-5000 range and can provide high-temperature solar thermal heat at 800-1500°C at the solar receiver or reactor. The concentrated solar high-temperature heat has the potential to produce hydrogen via solar thermochemical processes such as solar multi-step water splitting cycles, the solar reforming of natural gas and the solar gasification of coal. The paper reviews recent R&D activities for solar thermochemical water splitting cycles, especially, two-step metal oxide cycles. The two-step thermochemical cycles require solar heat above 1400°C. Therefore, there have been challenges to develop novel solar reactor concepts resulting in several types of “windowed” solar reactors. Some of the solar reactors have been demonstrated as solar energy systems in Europe, the USA, and Japan.
