Ocean thermal energy conversion systems (OTEC) is a fairly simple and theoretically well understood potential source of primary energy that utilizes the difference between ocean temperatures at the surface (it is therefore a form of derivative solar energy) and at depths of 1000+m. It requires a 20°C thermal differential, and because the temperature of the ocean is at a roughly constant 4°C at depth, this means that the surface temperature must exceed 25°C, which only occurs between 30° north and 30° south. While there are various basic designs (e.g. “closed cycle” systems using ammonia or another working fluid, “open cycle” systems directly using seawater, and hybrid systems) they all draw in cold water from the deep ocean using long pipe systems and utilize the temperature differential with surface water to run a heat engine and thereby generate electricity. OTEC faces several technical and potentially costly to fix challenges to widespread adoption. First and foremost is building and maintaining the piping system in deep water in the face of ocean energies and storm potential. Secondly, because ocean water must contact the heat exchangers at some point in either a closed or open system, microbial fouling has proven difficult to avoid without using chemicals that are toxic to marine life. While the potential primary energy from OTEC has been calculated using a global marine circulation model to be very large (~30 TW), translating to roughly 44,000 TWh per year, with a technical potential of 3.4-10 TW, the complexities and capital costs of operating in the ocean environment will likely limit its use to deep ocean islands that need locally sourced firm “round-the-clock” power and desalination services.