The present invention discloses a subsea power system for use in capturing "free" or "waste" energy (e.g., thermal, geothermal, pressurized subsurface gases or liquids, wind, wave, solar, or other free, waste, or low cost energy sources) to convert and/or store to power a subsea service or device during times when the free or waste energy supply is not as abundant, is not available, or demands require greater output than is provided at steady state. The subsea power system may include: (1) one or more energy-capturing devices--such as a turbine and/or thermoelectric generator--for harvesting free or waste energy, (2) a fuel cell, electrolyzer, and oxygen and hydrogen storage vessels for harvesting energy from the surrounding seawater, and (3) a power converter for receiving energy from the various sources and converting the energy into a useful form consumable by subsea devices.