Pressure Retarded Osmosis

One method to utilize salinity gradient energy is called pressure-retarded osmosis. In this method, seawater is pumped into a pressure chamber that is at a pressure lower than the difference between the pressures of saline water and fresh water. Freshwater is also pumped into the pressure chamber through a membrane, which increase both the volume and pressure of the chamber. As the pressure differences are compensated, a turbine is spun, providing kinetic energy. This method is being specifically studied by the Norwegian utility Statkraft, which has calculated that up to 2.85 GW would be available from this process in Norway. Statkraft has built the world's first prototype PRO power plant on the Oslo fjord which was opened by Princess Mette-Marit of Norway on November 24, 2009. It aimed to produce enough electricity to light and heat a small town within five years by osmosis. At first, it did produce a minuscule 4 kilowatts – enough to heat a large electric kettle, but by 2015 the target was 25 megawatts – the same as a small wind farm. In January 2014 however Statkraft announced not to continue this pilot.