permaculture

["Lawrence F. London, Jr." <lfl@intrex.net>]

<http://news.yahoo.com/s/nm/energy_water_power_dc;_ylt=AgBcoO2I2UsxpKTNT5HFfZFhr7sF;_ylu=X3oDMTBiMW04NW9mBHNlYwMlJVRPUCUl>
Norwegians, Dutch mix sea and river to make power

By Anna Mudeva Fri Dec 16, 8:22 AM ET

LEEUWARDEN, Netherlands (Reuters) -
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The Dutch Center for Sustainable Water Technology or Wetsus, and Norway's independent research organization SINTEF, 
working with power company Statkraft, have invented devices that generate electricity by mixing sea and river water.
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The new devices are based on a natural process -- when a river runs into the ocean, a huge amount of energy is unleashed 
because of the difference in salt concentration.
"It's basically harvesting the energy that comes free from a natural process," Wetsus managing director Johannes 
Boonstra said in his agency's laboratory in the Dutch town of Leeuwarden.
"You have the fuel for free and it's very sustainable -- no greenhouse gas 
emissions."
The two projects use different methods to harness the electricity -- the Dutch apply something called reverse 
electrodialysis while the Norwegians use a kind of osmosis.
Both methods rely on membranes or thin films made of special material used for chemical separation. In the Dutch 
project, separation is done by membranes using an electrical current.
"It works like a water battery," Wetsus project manager Sybrand Metz said.
The Norwegian device applies pressure to force the water through membranes. Its inventors liken the process to putting a 
hot dog in hot water. The skin of the hotdog acts as a membrane, allowing more water in than the amount of salty water 
it lets out. This increases the pressure inside and the hotdog bursts.
The principle behind the Norwegian device is that fresh water and salt water are channeled into a membrane module. The 
fresh water is transported through the membranes and over into the pressurized sea water. The pressurized mixture of sea 
water and fresh water flows out of the module and into a hydropower turbine that generates electricity.
The two inventions, however, have still a long way to go before they can be 
applied commercially.
The Wetsus project, supported by a consortium of Dutch companies, has yet to be tested in a pilot plant. The Norwegian 
project is more advanced. It started in the 1990s and its creators have already installed two small-scale plants, but 
have yet to build a bigger demonstration plant to boost production.
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Like other alternative energy technologies, cost is the biggest hurdle. Power produced by mixing sea with river water is 
several times more expensive than wind or solar energy.
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