OTEC and salinity power

Plants that use the ocean's temperature or salt differences; some OTEC plants also make fresh water.

Capture · Water and ocean · No. 33

• Capture
• Output: Electricity, fresh water

OTEC plants run on a gap of only about 20 °C between warm surface water and cold water a kilometre down.

Chart: Illustration: OTEC and salinity power

Where it comes from

Chart: Map of where it comes from

Tropical seas keep warm water on top of cold water about 1 km down. OTEC runs an engine across that gap; salinity plants tap the energy released where rivers meet the sea.

Three things to know

1. Pumping vast volumes of seawater eats 20-30% of an OTEC plant's gross output; one early 120 kW pilot used about 90%.
2. A 100 MW OTEC plant would need a cold-water pipe about 10 m wide reaching 1,000 m down.
3. Mixing a cubic metre of river water with a cubic metre of seawater releases about 1.4 MJ, which salinity plants capture with membranes.

The journey

1. 1 Warm surfaceTropical sea water near 25 °C
2. 2 Cold depthsPumped up from 800-1,000 m
3. 3 Heat engineAmmonia vapour or steam drives a turbine
4. 4 Or membranesFresh meets salt water, making pressure or voltage
5. 5 OutputsElectricity, plus fresh water for islands

Go deeper pick a tab to open it in full