What renewable-energy technology generates electricity from the temperature difference between warm surface seawater and cold deep seawater?

Ocean thermal energy conversion generates electricity from the temperature difference between warm surface seawater and cold deep seawater.

The technology, commonly abbreviated OTEC, uses the ocean's natural thermal gradient. In a closed-cycle system, warm seawater vaporizes a working fluid with a low boiling point, such as ammonia. The vapor drives a turbine, while cold deep seawater condenses it back into liquid.

Open-cycle systems vaporize seawater itself under low pressure, producing steam that can drive a turbine and leave fresh water as a by-product. Hybrid systems combine features of both approaches.

OTEC works best in tropical oceans, where surface water is warm and deep water remains cold. Its challenges include expensive deep-water pipes, corrosion, marine-environment impacts, and the small temperature difference available compared with conventional heat engines.