High temperature electrolysis(HTC) is a technology to producing hydrogen from water. High temperature electrolysis is more efficient than traditional room-temperature electrolysis. At 100 degree Celsius, 350 megajoules of thermal energy are required(41% efficient) and at 850 degree Celsius, 225 megajoules are required(64% efficient).
Possible supplies of cheap high temperature heat for HTE are all nonchemical, including high temperature nuclear reactors, concentrating solar thermal reactors, and geothermal sources.