Osmotic power is based on the natural phenomenon of osmosis, defined as the transport of water through a semi-permeable membrane. This is how plants can absorb moisture through their leaves – and retain it.

In an osmotic power plant, freshwater and salt water are channelled into separate chambers, separated by an artificial membrane. The salt molecules in the seawater draw the freshwater through the membrane, causing the pressure on the seawater side to increase. This pressure is equivalent to a water column of 120 metres or, in other words, quite a significant waterfall. This pressure can be used in a turbine to make electricity.

Idea from the 70s

The idea of generating power through osmosis popped up in the 1970s. Back then, however, the membranes were so poor and power prices so low that no one found it profitable to invest in such a project. Many years later, SINTEF researchers brought the idea to Statkraft's innovation staff. A collaboration effort was started in 1997 under a very different climate for alternative energy projects.

In recent years, the osmotic power concept has been tested in small pilot facilities, including in a laboratory at SINTEF in Trondheim and at Sunndalsøra. On 24 November 2009, Statkraft  opened the world's first prototype osmotic power plant at Tofte, southwest of Oslo. Statkraft has invested more than NOK 100 million towards development of osmotic power, with more to come.

Testing the technology

The prototype at Tofte will be used to test the technology. The main challenge is to develop a membrane which draws through enough water to create an effective pressure to run the turbine. When the membrane is good enough, osmotic power can become a competitive source of renewable energy.
 
Statkraft is working together with research and industrial groups in Norway, Germany and the Netherlands to improve the membrane technology. Membrane performance has improved dramatically since Statkraft became involved in developing osmotic power in 1997.