How does Osmotic Power work? © Getty Images

How does Osmotic Power work?

Osmotic power, or salinity gradient power, uses the natural process of osmosis to generate electricity.

Asked by: Anonymous


Osmosis is a common biological process where water moves from a dilute to a concentrated solution, across a semi-permeable membrane, to balance the concentrations. This increases the pressure on one side of the membrane. Using this pressure to generate power was proposed in the 1970s, but a better membrane was needed to make it cost effective.

In 2009, the Norwegian company Statkraft opened the first prototype osmotic power plant near Oslo. The prototype membrane is 2000m2, with an efficiency of 1-2W/m2, enough power per square metre to boil a kettle. As the system relies on one side of the membrane being saltier than the other, osmotic power plants have to be built where freshwater meets seawater. They’re able to continually generate electricity regardless of weather conditions, and no pollutants are produced, making them reliable sources of green electricity. The full-scale Statkraft plant was intended to be ready by 2015 and to generate 5W/m2. A plant the size of a football pitch (with a 5 million m2 membrane) would power 30,000 households. Osmotic power is thought to have a global potential of up to 1700 TeraWatt hours.


Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.