The great potential utility of fuel cells as dispersed power sources has made them the subject of a widespread and intensive development effort. Mitsubishi Electric is engaged in developing both of the two main types, phosphoric-acid fuel cells, and the molten-carbonate fuel cells that promise even higher efficiencies. The basic technology has been established for phosphoric-acid fuel cells. These fuel cells are expected to satisfy the stringent requirements of environmental protection and to provide excellent response to load changes and highly efficient power generation. Practical development of a power-generating system that will exploit their many advantages as dispersed power sources is now proceeding rapidly.