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Power Science

Harvesting Power When Freshwater Meets Salty 151

Posted by samzenpus
from the power-up dept.
ckwu writes "As a way to generate renewable electricity, researchers have designed methods that harvest the energy released when fresh and saline water mix, such as when a river meets the sea. One such method is called pressure-retarded osmosis, where two streams of water, one saline and one fresh, meet in a cell divided by a semipermeable membrane. Osmosis drives the freshwater across the membrane to the saltier side, increasing the pressure in the saline solution. The system keeps this salty water pressurized and then releases the pressure to spin a turbine to generate electricity. Now a team at Yale University has created a prototype device that increases the power output of pressure-retarded osmosis by an order of magnitude. At a full-scale facility, the estimated cost of the electricity generated by such a system could be 20 to 30 cents per kWh, approaching the cost of other conventional renewable energy technologies."
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Harvesting Power When Freshwater Meets Salty

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  • Big problem here... (Score:5, Informative)

    by Andy Dodd (701) <atd7@@@cornell...edu> on Monday December 02, 2013 @06:44PM (#45579031) Homepage

    It requires saline that is MUCH more concentrated than seawater... So you need to somehow concentrate the saltwater before using it.

    Although this might allow for some rather unconventional solar power projects - feeding brine from salt concentration ponds might be workable here.

  • by cirby (2599) on Monday December 02, 2013 @07:04PM (#45579227)

    You should note that, despite what many believe, we don't really "subsidize" fossil fuels to any major degree. The majority of the "subsidies" people whine about are just plain old tax deductions - the same ones that other businesses get. The oil companies didn't even get those deductions for a long time, and people complained when they finally got to deduct for exploration and drilling expenses in the same way normal businesses deduct for operations.

    There are a few real deductions they get, though - alternative energy research, for example. And, technically, the Strategic Petroleum Reserve counts (although that's just the government buying and storing oil in case of an emergency - and counts for about 2/3 of all actual subsidies). Compared to the size of the industry, it's tiny. Overall, the "subsidies" fossil fuels get don't affect the end-user price much - maybe a half-cent per kilowatt-hour in some markets.

    Compare to the various alternative energy sources, which get massive subsidies - and are still three to five times as expensive.

  • by crioca (1394491) on Monday December 02, 2013 @07:24PM (#45579445)

    You should note that, despite what many believe, we don't really "subsidize" fossil fuels to any major degree. The majority of the "subsidies" people whine about are just plain old tax deductions - the same ones that other businesses get. The oil companies didn't even get those deductions for a long time, and people complained when they finally got to deduct for exploration and drilling expenses in the same way normal businesses deduct for operations.

    Bullshit:

    http://www.nei.org/corporatesite/media/filefolder/60_Years_of_Energy_Incentives_-_Analysis_of_Federal_Expenditures_for_Energy_Development_-_1950-2010.pdf [nei.org]

    http://www.elistore.org/Data/products/d19_07.pdf [elistore.org]

  • by ShanghaiBill (739463) on Monday December 02, 2013 @08:41PM (#45580007)

    If it's concentrated enough, why can't you use sea water as "fresh", since it is powered by the difference in salinity, not the absolute value.

    Research has been done [rsc.org] on this, and I believe that a pilot plant may be built in the UAE or Oman in the next few years. It will use brine, concentrated in solar ponds, as the source of NaCl, and plain seawater as the sink.

  • by AcidPenguin9873 (911493) on Monday December 02, 2013 @11:54PM (#45580927)

    Yes, desalination obviously requires more energy than you get out of this method. But the point of the desalination is not energy production, it's freshwater production. You get freshwater out of your desalination plant. That requires using some amount of energy X. Instead of dumping the waste product of the desalination plant (highly-concentrated brine) somewhere, you use it with one of these devices to produce some amount of energy Y where Y is less than X.

    The net result is that you end up with freshwater, and instead of spending X energy to get it, you had to spend only (X - Y) energy.

  • by ISayWeOnlyToBePolite (721679) on Tuesday December 03, 2013 @03:48AM (#45581707)
    So how do they arrive at the 20-30 cents/kWh? Infinite durability? This has been tried in Norway http://en.wikipedia.org/wiki/Statkraft_osmotic_power_prototype_in_Hurum [wikipedia.org] with rather underwelming results, outputting 4kW (not a typo) under ideal conditions. Granted this new plant is rated as 60 times more efficient it seems like a long way from a sound investment as the upfront cost is just to high.

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