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Osmotic power - a new form of renewable energy

  1. Sep 14, 2014 #1
    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. https://www.researchgate.net/publication/263039298_Power_production_by_PRO_-_Feasibility_study_of_an_osmotic_power_plant_1_MW
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  3. Sep 14, 2014 #2

    Doug Huffman

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    LOL How big was that membrane for the mass flux? But yes, the seawater/freshwater potential is about 250 meters water head.
  4. Sep 14, 2014 #3
    The membrane area is around 35,000.00 m2 when membrane power density is 3.0 W/m2. The membranes are stacked in modules in order to minimize the space. These modules have a high packing density, i.e. large membrane area in a small space.

    7-42090.jpg hqdefault.jpg
  5. Sep 15, 2014 #4


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    It sounds a good idea but would it not need good, clean sources of salt and fresh water, to prevent clogging of the membrane?
    How is the energy actually taken off and at what potential? I can find a lot about how 'good' the system is but nothing, so far, on nuts and bolts. I imagine it's full of Patents and commercial info.
  6. Sep 15, 2014 #5
    You are right, the sea water contains microorganisms (size of 0.01 - 10 μm), dissolved solids (size of <0.4 μm), solloidal particles (0.4 - 5 μm) and suspended solids (size of > 5 μm). Consider that an osmotic power plant is similar but the opposite of a desalination plant. The choice of pretreatment method for an osmotic PRO plant is more likely to be made by financial criteria to achieve low capital cost. Statkraft, the company which have costructed the first pilot plant, had used ultrafiltration for this purpose.

    This video is very helpful on how energy from an osmotic plant is produced: (title in youtube: Statkraft - Osmotic Power Plant - Free energy - How it works)

    The energy efficiency is around 40-45%.
    Last edited by a moderator: Sep 25, 2014
  7. Sep 15, 2014 #6


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    Damned barnacles could spoil your day!
  8. Sep 15, 2014 #7


    Staff: Mentor

    This idea sounds like a desalinization plant running in reverse. Instead of using electric power and reverse osmosis to separate salt from water, it produces power while letting the salt mix with fresh water.

    I have nothing to say about the viability of the idea, but I want to comment that the problems with structure, filtering and cleanliness should be about the same for desalinization as for osmotic power. There are many desalinization plants already engineered and built.
  9. Sep 15, 2014 #8


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    What's it called on the New York Stock Exchange?.....could be a good time to get in.
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