# Salinity gradient

Energy released where fresh river water mixes with salty seawater ('blue energy').

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

Natural sources · Solar-derived flows · No. 7

- Natural sources
- Origin: Indirect solar
- Renewable: Yes
 Natural sources · Solar-derived flows · Foundation · Energy

Every river mouth hides a waterfall: fresh water meeting the sea pushes like a column of water 270 metres tall.

Chart: Illustration: Salinity gradient

##### Where it comes from

Chart: Map of where it comes from

When fresh and salt water mix, the osmotic pull is about 26 bar, the pressure at the foot of a 270 m water column, and membranes can harvest it.

##### Three things to know

1. Asia holds about 208 GW of technical potential and South America about 199 GW.
2. Saturated brine can raise the energy to about 15 MJ per cubic metre, against 1.4 MJ in an ordinary estuary.
3. Japan's Fukuoka plant uses concentrated seawater from a desalination works and should give about 0.88 GWh a year.

##### The journey

1. 1 **River water**Fresh water flows towards the coast
2. 2 **Seawater**Salty water waiting at the estuary
3. 3 **Membrane**Osmosis or ion flow across a barrier
4. 4 **Pressure or current**About 26 bar of osmotic push
5. 5 **Electricity**Only pilot plants so far, like Fukuoka

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## Other sections

- [Overview](https://www.materialinsights.org/energy/e_salinity/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_salinity/correlation/index.md)
- [How energy resides](https://www.materialinsights.org/energy/e_salinity/resides/index.md)
- [Abundance](https://www.materialinsights.org/energy/e_salinity/abundance/index.md)
- [Fluctuation in time](https://www.materialinsights.org/energy/e_salinity/time/index.md)
- [Across the Earth](https://www.materialinsights.org/energy/e_salinity/geography/index.md)
- [Impact on nature](https://www.materialinsights.org/energy/e_salinity/nature/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_salinity/links/index.md)