A self-contained regenerative power system includes a fuel cell operative to generate electric energy from hydrogen and oxygen, generating water as a byproduct, and an electrolyzer operative to generate hydrogen and oxygen from water by consumption of electric energy. A bi-directional DC-to-DC converter interfaces between the fuel cell and the electrolyzer on one side and the system to be powered on the other. A switch selectively connects either the fuel cell or the electrolyzer with the bi-directional DC-to-DC converter. The products of the fuel cell process can be supplied to the electrolyzer process, and vice versa. Alternately, the self-contained regenerative power system comprises a unitary fuel cell and electrolyzer.