Osmotic power plants utilise the osmotic pressure difference between seawater and freshwater to drive a turbine, which in turn generates electricity.

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, we feed freshwater and seawater into separate chambers, separated by an artificial membrane. The salt molecules in the seawater then draw the freshwater through the membrane, causing the pressure on the seawater side to increase. This pressure corresponds to a water column of 120 metres, or a large waterfall, and can be utilised in a turbine which generates electricity.

An idea dating from the 1970s
The idea to generate power through osmosis originates from the 1970s. At the time, however, the membranes were not very effective and power prices were too low to enable anyone to profitably invest in such a project. Many years later, research scientists at SINTEF brought the idea to Statkraft's innovation environment. The collaboration was initiated in 1997, and the climate for energy projects was by then very different.
In recent years, the osmotic power concept has been tested in small-scale test facilities, including a laboratory at SINTEF in Trondheim and on the shore at Sunndalsøra. In 2008, Statkraft will construct the world's first prototype osmotic power plant at Tofte, southwest of Oslo. In total, Statkraft has invested over NOK 100 million in the development of osmotic power, and there is more to come.

Enormous potential
Osmotic power plants can be constructed anywhere were freshwater flows out into the sea, provided that the salt concentration is sufficiently high. Unlike hydropower and wind power, osmotic power plants are not affected by fluctuations in the weather. The global potential is estimated to be an impressive 1600-1700 TWh – equivalent to China’s electricity consumption in 2002. In Norway alone, we will be able to generate 12 TWh per year – equivalent to 10% of our total power consumption. If osmotic power becomes a reality, it will give a considerable contribution to the generation of renewable energy.

Can be built out of sight
Around the world, rivers flow out into the sea in urban and industrial areas where it will be possible to construct osmotic power plants. A power plant the size of a football stadium could supply around 10,000 households with electricity. These power plants can be built underground, e.g. in the basement of an industrial building or under a park, minimising their visual impact. Osmotic power plants give off no polluting discharges to the atmosphere or water, and do not affect the fauna or flora of rivers or the seafloor. Osmotic power can become our most environment-friendly energy source, in every sense.