AMERICAN researchers have developed a battery that takes advantage of the difference in salinity between freshwater and seawater to produce electricity.
Anywhere freshwater enters the sea, such as river mouths or estuaries, could be a site for a power plant using such a battery, according to Yi Cui of Stanford University.
The theoretical limiting factor, he says, is the amount of freshwater available, though there is an infinite amount of seawater.
As an indicator of the battery’s potential for producing power, Cui’s team calculated that if all the world’s rivers were put to use, their batteries could satisfy roughly 13% of the world’s current energy consumption. The battery itself is simple and consists of two electrodes – one positive, one negative – immersed in a liquid containing electrically charged particles or ions. In water, the ions are sodium and chlorine, the components of ordinary table salt.
Initially, the battery is filled with freshwater and a small electric current is applied to charge it. The freshwater is then drained and replaced with seawater. Because seawater is salty, containing 60 to 100 times more ions than freshwater, it increases the voltage, between the two electrodes. That makes it possible to reap far more electricity than the amount used to charge the battery.