Ocean Thermal Energy Conversion (OTEC) utilizes the temperature difference between warm surface seawater and cold deep seawater to produce electricity via a Rankine cycle. It can also desalinate water and support mariculture. OTEC uses the sun's heating of the ocean's top layers and input of cold water from polar regions to create a heat source and sink. While offering clean energy, OTEC is limited to tropical ocean sites and has high capital costs, with no systems yet demonstrated at full scale long-term.