Most people are familiar with the potato battery or the lemon battery, two classic examples of the electrochemical cell. Similarly, there exists an electrical potential between salt water and fresh water, which can be exploited to harvest electrical energy. That is exactly what some enterprising researchers from Stanford have set out to do.
Stanford 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 potential sites for a power plant using such a battery, said Yi Cui, associate professor of materials science and engineering, who led the research team.
The battery itself is simple, consisting 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.
If you remember your electrochemistry lessons from high school, then you will know that the potential developed will be very small, less than 1 V, but the currents can be large depending on the size of electrodes used. To get higher voltages, the most common solution is to use boost converters. However, the electrodes tend to be costly (silver) or have negative environmental effects.
The researchers are very optimistic.
Cui’s team calculated that if all the world’s rivers were put to use, their batteries could supply about 2 terawatts of electricity annually – that’s roughly 13 percent of the world’s current energy consumption.
I hate to pour cold water on this idea but I have a few doubts. There are already a number of drawbacks as mentioned earlier (requires costly metals, power conditioning devices, environmental effects, not counting the costs of constructing structures in water, etc.). In addition, the method of charging the battery in freshwater and then discharging in salt water seems too cumbersome. I doubt that they will find much use for their research in the near future which is perhaps why the principals of this project had to ask for funds to the US government (Department of Energy) and the gullible Saudis (King Abdullah University of Science and Technology) who have lots of oil money on hand with no where to spend it.
Why did I report this news post? Well, who knows, someone, somewhere might find a new application for this concept and hit upon a way to profit from this idea. Such is the nature of science.