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Thread: Osmotic Power - New form of renewable energy which exploits the salinity gradient between fresh river water and salt sea water.

  1. #1 Osmotic Power - New form of renewable energy which exploits the salinity gradient between fresh river water and salt sea water. 
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    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.
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  3. #2  
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    Quote Originally Posted by Adriano View Post
    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.
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    There is something wrong with this. A 1MW output from 1 m/sec flow of fresh water implies 1kg/sec yields 1kW, enough to power an electric kettle. That is extremely implausible. Can you check the units?


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    Consider that the osmotic power plant will be located at the point where the river flows into the sea. The amount of flow is therefore at these levels. I believe this video will be very helpful (youtube.com/watch?v=Oc5bXa5PcWo).
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  5. #4  
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    Quote Originally Posted by Adriano View Post
    Consider that the osmotic power plant will be located at the point where the river flows into the sea. The amount of flow is therefore at these levels. I believe this video will be very helpful (youtube.com/watch?v=Oc5bXa5PcWo).
    No problem with believing in volumes of flow measured in m3/sec. The point is that I have trouble believing a flow as little as 1kg/sec has enough potential energy stored via osmotic pressure to power a 1kW kettle. It implies 1g of water has 1Joule of energy stored in this way. I feel sure the units are wrong by several orders of magnitude.

    P.S. I make a point of not watching videos about science: there is so much shit on youtube and even regular TV. I couldnot access the original reference you provided, as it seems to be subscription only. Is there any other written reference you can provide, or can you perhaps check the units by reading the article?
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    The amount of energy is around 2.88 MJ per 1 m3 of fresh water when it is mixed with a large amount of salt water. I agree with your perspective about youtube-science but this particular video was from the pilot plant in Norway (title in youtube: Statkraft - Osmotic Power Plant - Free energy - How it works).

    Here are some free pdf links:
    gwri-ic.technion.ac.il/pdf/IDS/384.pdf ,
    sheliaksystem.com/Osmotic_Power_Domain/Waterpower_XVI_-_Power_production_based_on_osmotic_pressure_tcm9-5100.pdf ,
    aqwatec.mines.edu/publications/CathPub/10_Power_generation_with_PRO.pdf .
    Last edited by Adriano; September 13th, 2014 at 03:54 PM.
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  7. #6  
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    Quote Originally Posted by Adriano View Post
    The amount of energy is around 2.88 MJ per 1 m3 of fresh water when it is mixed with a large amount of salt water. I agree with your perspective about youtube-science but this particular video was from the pilot plant in Norway (title in youtube: Statkraft - Osmotic Power Plant - Free energy - How it works).

    Here are some free pdf links:
    gwri-ic.technion.ac.il/pdf/IDS/384.pdf ,
    sheliaksystem.com/Osmotic_Power_Domain/Waterpower_XVI_-_Power_production_based_on_osmotic_pressure_tcm9-5100.pdf ,
    aqwatec.mines.edu/publications/CathPub/10_Power_generation_with_PRO.pdf .
    Thank you very much. I've read the first article, thought about it some more, and have to withdraw my objections.

    Since 1 calorie is 4.18J, the release of an energy density of 1J/gm would only warm the water by 0.25C deg. On further reflection this seems quite plausible. (I suppose I could track down some enthalpies of solution to corroborate the numbers, but I don't quite have the enthusiasm at present.) What an interesting idea.

    I suppose the practical problem is how to channel a significant proportion of river flow through such a system.
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    The biggest concern is the lack of suitable membranes for this process. To increase the flow of fresh water through the membrane and therefore the power density, the membranes must combine great water permeability, low salt permeability and high salt diffusion rate. Currently, membranes are far from the goal of 5 W/m2.

    The amount of energy that can be extracted as work is calculated in this pdf: http://www.see.ed.ac.uk/~shs/Desalin...%20Osmosis.pdf
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