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The diagram shows how electricity is produced by a system called Ocean Thermal Energy Conversion, or OTEC.
Overall, the system uses warm seawater from the surface of the ocean and cold seawater from deep in the ocean to make electricity. It also produces drinking water and waste salt water.
First, warm seawater at the surface of the ocean, which is about 29°C, goes into an evacuated evaporation chamber. In this chamber, the warm seawater is changed into water vapour by solar energy, and the salt is left behind. Then, the water vapour without salt goes up and turns a turbine, and this creates electricity.
After that, the water vapour goes down to a condensing chamber. At the same time, cold seawater, which is about 5°C, is pumped from 1,000 metres below the surface. The cold water cools the water vapour in the condensing chamber, so it becomes pure water, which people can drink. Finally, the waste salt water from the system goes back into the ocean.