Anywhere fresh water enters the sea, such as river mouths or estuaries, could be potential sites for a power plant using such batteries, Yi Cui, Stanford University associate professor of materials science and engineering, said.
Cui's team says if all the world's rivers were put to use, their batteries could supply about 2 terawatts of electricity annually, about 13 percent of the world's current energy consumption, a Stanford release said Tuesday.
The battery consists of two electrodes, one positive and one negative – immersed in water containing electrically charged ions of sodium and chlorine, the components of ordinary table salt.
The battery is filled with fresh water and a small electric current is applied to charge it. The fresh water is then drained and replaced with seawater, which because it is salty contains 60 to 100 times more ions than fresh water.
This increases the electrical potential, or voltage, between the two electrodes, giving back far more electricity than the amount used to charge the battery.
"If you charge at low voltage in fresh water, then discharge at high voltage in sea water, that means you gain energy," Cui said. "You get more energy than you put in."
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