Research Solid energy conversions based on semiconductor devices can be utilized for various energy applications including those renewable energy resources even with low energy density. The solution to the high cost and low efficiency problems in the solid energy conversion will open a window for the future of renewable energy society. Our main research topics are the photoelectric conversion of solar energy and the thermoelectric conversion of excessive heat via solar cells and thermoelectric devices, respectively. In particular, the large-scale application of the solar cells could solve the depletion problem of fossil energy by using the inexhaustible solar energy. However, the reduction of the cost of solar cells, which plays a central role in the conversion of solar energy, is still considered an important issue. For this purpose, we are now developing a novel metallurgical direct reduction process, which is expected to overcome the disadvantages such as low yield in the conventional Siemens method and reduce the production cost.