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Osmotic power, salinity gradient power or blue energy is the energy available from the difference in the salt concentration between seawater and river water. Two practical methods for this are reverse electrodialysis (RED) and pressure retarded osmosis (PRO). Both processes rely on osmosis with ion specific membranes. The key waste product is brackish water. This byproduct is the result of natural forces that are being harnessed: the flow of fresh water into seas that are made up of salt water. In 1954 Pattle suggested that there was an untapped source of power when a river mixes with the sea, in terms of the lost osmotic pressure, however it was not until the mid ‘70s where a practical method of exploiting it using selectively permeable membranes by Loeb was outlined. The method of generating power by pressure retarded osmosis was invented by Prof. Sidney Loeb in 1973 at the Ben-Gurion University of the Negev, Beersheba, Israel.〔^ Israel Patent Application 42658 of July 3, 1973. (see also US patent 3,906,250, granted September 16, 1975. Method and apparatus for generating power utilizing pressure-retarded-osmosis.] Erroneously shows Israel priority as 1974 instead of 1973 (--US Patent 3906250 )〕 The idea came to Prof. Loeb, in part, as he observed the Jordan River flowing into the Dead Sea. He wanted to harvest the energy of mixing of the two aqueous solutions (the Jordan River being one and the Dead Sea being the other) that was going to waste in this natural mixing process.〔^ Weintraub, Bob. "Sidney Loeb," Bulletin of the Israel Chemical Society, Dec. 2001, issue 8, page 8-9. https://drive.google.com/file/d/1hpgY6dd0Qtb4M6xnNXhutP4pMxidq_jqG962VzWt_W7-hssGnSxSzjTY8RvW/edit 〕 In 1977 Prof. Loeb invented a method of producing power by a reverse electrodialysis heat engine.〔(United States Patent US4171409 )〕 The technologies have been confirmed in laboratory conditions. They are being developed into commercial use in the Netherlands (RED) and Norway (PRO). The cost of the membrane has been an obstacle. A new, lower cost membrane, based on an electrically modified polyethylene plastic, made it fit for potential commercial use.〔(History of osmotic power (PDF) at archive.org )〕 Other methods have been proposed and are currently under development. Among them, a method based on electric double-layer capacitor technology.〔D. Brogioli, ''(Extracting renewable energy from a salinity difference using a capacitor )'', Phys. Rev. Lett. 103 058501-1-4 (2009).〕 and a method based on vapor pressure difference.〔M. Olsson, G. L. Wick and J. D. Isaacs, ''(Salinity Gradient Power: utilizing vapour pressure differences )'', Science 206 452--454 (1979)〕 ==Basics of salinity gradient power== Salinity gradient power is a specific renewable energy alternative that creates renewable and sustainable power by using naturally occurring processes. This practice does not contaminate or release carbon dioxide (CO2) emissions (vapor pressure methods will release dissolved air containing CO2 at low pressures—these non-condensable gases can be re-dissolved of course, but with an energy penalty). Also as stated by Jones and Finley within their article “Recent Development in Salinity Gradient Power”, there is basically no fuel cost. Salinity gradient energy is based on using the resources of “osmotic pressure difference between fresh water and sea water.”〔(Jones, A.T., W. Finley. “Recent developments in salinity gradient power”. Oceans. 2003. 2284-2287.)〕 All energy that is proposed to use salinity gradient technology relies on the evaporation to separate water from salt. Osmotic pressure is the "chemical potential of concentrated and dilute solutions of salt".〔(Brauns, E. “Toward a worldwide sustainable and simultaneous large-scale production of renewable energy and potable water trough salinity gradient power by combining reversed electrodialysis and solar power?” Environmental Process and Technology. Jan 2007. 312-323.)〕 When looking at relations between high osmotic pressure and low, solutions with higher concentrations of salt have higher pressure. Differing salinity gradient power generations exist but one of the most commonly discussed is pressure-retarded osmosis (PRO). Within PRO seawater is pumped into a pressure chamber where the pressure is lower than the difference between fresh and salt water pressure. Fresh water moves in a semipermeable membrane and increases its volume in the chamber. As the pressure in the chamber is compensated a turbine spins to generate electricity. In Braun's article he states that this process is easy to understand in a more broken down manner. Two solutions, A being salt water and B being fresh water are separated by a membrane. He states "only water molecules can pass the semipermeable membrane. As a result of the osmotic pressure difference between both solutions, the water from solution B thus will diffuse through the membrane in order to dilute the solution".〔(Brauns, E. “Toward a worldwide sustainable and simultaneous large-scale production of renewable energy and potable water through salinity gradient power by combining reversed electrodialysis and solar power?.” ''Environmental Process and Technology''. Jan 2007. 312-323.)〕 The pressure drives the turbines and power the generator that produces the electrical energy. Osmosis might be used directly to "pump" fresh water out of The Netherlands into the sea. This is currently done using electric pumps. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Osmotic power」の詳細全文を読む スポンサード リンク
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