Where fresh water meets saltwater there is a potential to harvest energy. Stanford University researchers have developed a device that can use this use the mixing of the two water types and pull out more energy that they put in. A container holds fresh water, with positive and negative electrodes at either end, is charged and then submerged in saltwater. The device allows the two waters to mix. Since saltwater contains more ions of sodium and chlorine, the electrical potential between the electrodes increases.
Researcher Yi Cui elaborates, "The voltage really depends on the concentration of the sodium and chlorine ions you have. If you charge at low voltage in freshwater, then discharge at high voltage in sea water, that means you gain energy. You get more energy than you put in."
His idea is to place these devices when rivers, or other fresh water supplies, meet saltwater bodies, like the ocean. He claims that is every river mouth, estuaries, were tapped, 13% of the worlds electricity need would be met. (2 terawatts)
The battery could be 85% efficient, says Cui. To achieve this rating, the positive electrode is made of nanorods of manganese dioxide. This allows more surface area for the sodium ions to interact, move in and out, and speed up the process. This is not the first time electricity has been produces from the mix of saltwater and fresh water. However, this time both sodium and chlorine ions are used to generate power.
The next step for the team is to try this process with sewage water.
For the record, funding for Yi Cui's project has come from The King Abdullah University of Science and Technology (KAUST) and the U.S. Department of Energy.
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