Ocean thermal energy conversion can produce electricity by using temperature difference between warm tropical water and cold deep ocean water to run heat engine and to produce useful work.  OTEC can generate minimum amount of electricity. It has potential to contribute continuously renewable energy resources. OTEC supplies large quantities of cold water and distil fresh water as by-products. When it runs with a large temperature difference it gives greater efficiency. Open-cycle makes electricity directly from warm surface water. Closed-cycle systems use fluid with a low boiling point. It has the potential to produce electrical power based on Land-based, Shelf-based and floating. OTEC has good impact of environment OTEC plants use very large flows of both warm surface and cold deep seawater to generate constant renewable power.