What is osmotic power?

Osmotic power is the energy derived from the difference in salinity between seawater and fresh water, which is harnessed to generate electricity.

When fresh water is separated from seawater by a semipermeable membrane, the fresh water moves by osmosis through the membrane into the seawater. The resulting osmotic pressure, combined with the permeation flow rate, turns a hydraulic turbine, producing electricity.

To learn more about osmotic power, see the data sheet [PDF 1.2 Mb]

Statkraft’s prototype osmotic power plant in Norway. © Statkraft

Current state of knowledge

Osmotic power is in the prototype and demonstration stage. Statkraft, the world leader in the field, tested a prototype osmotic power plant in Norway’s Oslo Fjord from 2009 to 2013.

From February 2012 to December 2013, Statkraft and Hydro-Québec joined forces in an osmotic power R&D project. Their primary goal was to develop techniques for pretreating water, assess the impact of water quality on membrane performance, and evaluate the process’s repercussions for sustainable development.

Osmotic potential

In Canada, the mouths of large rivers hold considerable long-term potential for osmotic development.

In Québec, studies by Hydro-Québec's research institute (2011) estimated the exploitable osmotic potential for the 30 large rivers emptying into salt water to be 1,860 MW. Fourteen of them (1,060 MW) empty into the Golfe du Saint-Laurent (Gulf of St. Lawrence) and its estuary. The challenge today is to generate osmotic power at a competitive cost by 2020.

Output and costs

Statkraft projects that once the technology has reached maturity, gross generating costs will be between 7¢ and 14¢/kWh. Net costs should be based on generating station efficiency estimates of 60% to 75%.

Advantages and disadvantages

  • Steady, predictable output
  • Adaptable for small or large generating stations
  • Scalable or modular design (membrane modules added as required), making it possible to increase installed capacity
  • Generating sites near load centers, limiting power transmission needs
  • Good potential for power plant sites
  • Technology similar and complementary to that of hydroelectric power, with osmotic power plants able to be built on already-harnessed rivers
  • High risk of clogging and gradual degradation of semipermeable membranes, necessitating pressure-filtering pretreatment of fresh water and periodic membrane replacement (every 5 to 7 years)

Sustainable development

At this time, little is known about the social and environmental impact of osmotic generating station operations and maintenance. To a certain degree, they are similar to those of water purification plants that use membrane filtration, which are however very well documented:

  • Modification of habitat and vegetation, with potential repercussions on aquatic fauna. Among other things, the changes in salinity and regular large-volume discharges of brackish water may affect the natural mix of river water and seawater.
  • Potential effects of the use of cleaning products
  • Production of wet waste (sludge and used membranes)
  • Impact on the host environment to be expected if a dike or basin has to be built to optimize a site’s potential
  • Possible conflicts with shipping, fishing, etc.
  • Zero greenhouse gas and atmospheric contaminant emissions during operation

See also

To learn more about osmotic power, see the data sheet.

  • How an osmotic power plant works
  • Canada’s osmotic potential
  • The Statkraft prototype
  • Research around the world
  • Climate change and air quality
  • Life cycle assessment
  • Ecosystems and biodiversity
  • Health and quality of life
  • Land use, regional economy and social acceptability