By a different approach based on battery design which use nanomaterials there is a way of economically harvest the energy.
The scientist from Stanford University developed a new device which uses two electrodes that attract the positive sodium ions and also the negative chlorine ions. Once electrodes are immersed in the saltwater, they draw ions from the water and their movement creates an electrical current. The electrodes are recharged by replacing the fresh water and applying a relatively low-voltage electrical current. This low electrical current draws back the ions to the electrodes. After the freshwater is drained, the electrodes are ready to attract more ions from the saltwater next.
“It is the opposite process of water desalination, where you put in energy and try to generate freshwater and more concentrated saltwater,” says Yi Cui, an engineering and materials science professor at Stanford University and the study’s lead author. “Here you start with freshwater and concentrated saltwater, and then you generate energy.”
The research team converted to electricity with a yield of 74 percent of the potential energy that exists between saltwater and freshwater, with over 100 cycles no decline in performance. By placing the electrodes closer together, the author says, that could allow the battery to achieve an efficiency of 85 percent.
After a team’s estimation and using this technology in a power plant near a river delta where freshwater meets the sea, the drawing of 50 cubic meters of river water per second, could produce up to 100 megawatts of power. If all of the freshwater from all of the world’s coastal rivers were harnessed, his salinity-gradient process could generate 2 terawatts, or approximately 13 percent of the energy currently used around the world.
This utopian idea to use in such a wide scale would seriously disturb sensitive aquatic environments. “I think you would only be able to utilize a very small fraction of this or it would be an ecological disaster,” says Menachem Elimelech, director of the Environmental Engineering Program at Yale University. He says it would be necessary to treat the water before, to remove living organisms and suspended material. This processing would require energy, will add costs, and itself seriously will disturb the ecosystem if done on a large scale.