Abstract
One of the renewable energies is salinity gradient power which converts salinity gradient energy existing between salt water such as sea water and fresh water such as river water into electricity. Mixing 1 m3 of seawater with 1 m3 of fresh water theoretically generates 1.7 MJ of energy, which is equivalent to about 500 Wh. Salinity gradient power is expected as a base load power source derived from renewable energy with low environmental impact, high equipment utilization rate, and small footprint. There are two types of salinity gradient power using separation membranes: Pressure Retarded Osmosis （PRO） using semipermeable membranes, turbine and generators, and Reverse ElectroDialysis （RED） using ion exchange membranes. There were reports that in the case of using seawater, RED will be superior to PRO, and in the case of high concentration salt solution such as concentrated sea water etc. PRO will be better than RED. World's first RED power generation pilot plant was installed in Afsluitdiik, Netherlands. Recently, SWRO-PRO hybrid plant was built in Busan, Korea. In the future, the improvement in the performance of the forward osmosis membrane and ion exchange membrane will give practical applications of the two technologies.
