Osmotic power is a form of renewable energy under development which exploits the salinity gradient between fresh river water and salt sea water. The phenomenon is based in osmosis principle and called Pressure Retarded Osmosis (PRO). The two fluids are separated by a semi-permeable membrane which allows only water molecules, in the ideal situation, to pass through the membrane, causing osmotic flow capable to rotate a turbine producing electricity. In a plant using PRO, power production can occur with continuous inflow of fresh water and sea water and continuous discharge of the brackish effluent that resulted from the mixing of the two solutions. The amount of energy produced depends on the availability of fresh water and the salinity of sea water. As a rule of thumb, the continuous flow of 1 m3/s of fresh water when mixed with sea water of salinity 3,5% NaCl yield about 1 MW. This promising form of energy has not yet exploited on a commercial scale, but after several decades of research on laboratory and the first pilot plant of 4kW launched in 2009 was the reason to investigate the ability of PRO to be regarded as reliable and competitive form of energy compared with other renewable energy. Link: researchgate.net/publication/263039298_Power_production_by_PRO_-_Feasibility_study_of_an_osmotic_power_plant_1_MW
The osmotic power production capacity from some major rivers across the world has been stated here: researchgate.net/publication/259515041_Osmotic_power_with_Pressure_Retarded_Osmosis_Theory_performance_and_trends__A_review Statkraft, the company which have costructed the first pilot plant, estimates the cost to be 0.12€/kWh.
Statkraft halts osmotic power investments December 2013 Statkraft Shelves Osmotic Power Project March 2014 Both have basically the same statement from Starkraft: "Our main challenge has been to make the technology efficient enough to achieve energy production costs on par with competing technologies. With the current market conditions, we see that we cannot achieve this in the foreseeable future. There are other technologies which have developed enormously in recent years. These are more competitive and relevant investments for us in the future." They are not building anymore plants, nor considering anymore plants, until the cost comes down.
Statkraft halt their investment after 15 years of development because of the high membrane cost. But companies like IDE stated "“Although Statkraft does not believe PRO is competitive in the European market, IDE remains very interested in the technology and in our ability to serve the market. Following Statkraft’s decision, we are now considering how to move forward.” (desalination.com/wdr/50/4/membranes-not-pro%E2%80%99s-stairway-heaven). In addition, GS Engineering&Construction in Korea is building at the moment the next osmotic pilot plant: energyrecovery.com/osmotic-power-play-energy-recovery-teams-gs-engineering-construction-corp-develop-highly-available And do not forget the effort of universities around the world for new types of membranes.
