First commercial

In an average day, tropical oceans absorb about 278 petawatt-hours of solar energy. Harvesting just 1/4000th of that energy would supply the entire world's daily electricity – and ocean thermal energy conversion provides a possible method.

Harvesting energy from the temperature differential between the warm surface and the cold deep ocean is certainly not a new idea – indeed, it was first trialed 142 years ago in 1881, and a 22-kilowatt OTEC plant was built in Cuba in 1930.

The basic idea is this: you go to an area with a consistently large temperature differential – somewhere in the tropics, reasonably close to land, where you can tap a cool 4 °C (39 °F) at a depth around 800 m (2,625 ft) and grab warm water at over 25 °C (77 °F) from the surface, all through the year.

You then set up a floating barge, moored to the sea floor and equipped with a closed loop power system, using a refrigerant-style liquid like ammonia with a boiling point in between those two temperatures. The warm surface water boils this liquid, which expands as a gas and drives a turbine to generate electricity, then you cool and condense the liquid using cold water brought up from the deep ocean through an insulated pipe, and cycle it through again.

Such a system generates electricity reliably, 24/7, at a constant rate suitable for baseload usage. It can be ramped up and down within seconds to account for demand peaks and troughs. And if deployed en masse via thousands and thousands of floating OTEC barges, it could potentially do something to limit the rise of sea surface temperatures, which have been spiking wildly in 2023.