Osmotic Power

Osmotic power, also called salinity gradient power or blue energy, is energy extracted from the difference in salt concentration between seawater and river water where they meet, most often using pressure-retarded osmosis or reverse electrodialysis across a semipermeable membrane. Norwegian utility Statkraft opened the first prototype osmotic power plant on the Oslo fjord on November 24, 2009, generating an initial 4 kilowatts against a stated goal of scaling to 25 megawatts by 2015; Statkraft discontinued the pilot in January 2014 after concluding that then-available membrane technology could not reach an economically viable output from ordinary river-to-sea salinity gradients. Development has continued elsewhere: Danish company SaltPower is building a commercial plant using the steeper salinity gradients available in high-salinity brines from geothermal and desalination sources rather than river water, and laboratory researchers have reported boron nitride nanotube membranes theoretically capable of roughly 4 kilowatts per square meter, still an experimental result rather than a deployed technology.