# OTEC and salinity power

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

Source page: https://www.materialinsights.org/energy/e_otec/

Capture · Water and ocean · No. 33

- Capture
- Output: Electricity, fresh water
 Capture · Water and ocean · Foundation · Energy

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 surface**Tropical sea water near 25 °C
2. 2 **Cold depths**Pumped up from 800-1,000 m
3. 3 **Heat engine**Ammonia vapour or steam drives a turbine
4. 4 **Or membranes**Fresh meets salt water, making pressure or voltage
5. 5 **Outputs**Electricity, plus fresh water for islands

##### Go deeper pick a tab to open it in full

## Other sections

- [Overview](https://www.materialinsights.org/energy/e_otec/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_otec/correlation/index.md)
- [Efficiency](https://www.materialinsights.org/energy/e_otec/efficiency/index.md)
- [Techniques](https://www.materialinsights.org/energy/e_otec/techniques/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_otec/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_otec/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_otec/links/index.md)