In the prototype, seawater and freshwater will be fed into the membrane rig. The pressure that will be utilised to generate electricity is then created in this rig.

Statkraft has hired premises from the Södra Cell Tofte paper pulp factory in the municipality of Hurum. In the old chlorine-bleaching plant down on the shore, Statkraft is building the world's first osmotic power prototype. The plant is situated in an established industrial area with plentiful supplies of both freshwater and saltwater, just 60km from Oslo.
This project is being financed by Statkraft with support from Enova and the Research Council of Norway. Construction of the prototype will start in 2008. If everything goes according to plan, the plant may begin generating electricity in early 2009. Statkraft, in collaboration with SINTEF, will be responsible for operating the plant.

Creates pressure
The most important components in the prototype are the membranes, the pressure exchanger and the turbine. In simple terms, seawater and freshwater are fed into separate pipes, via filters which remove humus and other particles which can block the membranes. The water is fed into the membrane system – the 'waterfall' in the power plant. The freshwater is drawn through the membrane across to the saltwater. The increase in volume creates a pressure which forces the water through the turbine, which in turn is connected to an electricity generator. The brackish water is then discharged into the sea.
While the prototype can only produce enough electricity to drive a hot-plate, a full-scale power plant will be able to supply enough electricity for almost 10,000 households. In order to achieve such an output, no less than five million square metres of membrane will be needed. The membranes will be mounted in compact spiral coils, which will be placed close to each other inside the power plant.

Performance improvements needed
The prototype will demonstrate that osmotic power actually works, and will be used to test the technology itself. The biggest challenge lies in developing a membrane which draws enough water through to create an effective pressure to drive the turbine. Only once membranes with a particular efficiency have been developed will osmotic power become a competitive source of renewable energy. Since Statkraft became involved in 1997, the performance of the membranes has been improved many times over. A commercial plant the size of a large football stadium could be ready as soon as 2015 if Statkraft succeeds with the project.