April 18, 2012--Rivers flowing into the sea offer vast potential as electricity source (Science Daily)

A new genre of electric power-generating stations could supply electricity for more than a half billion people by tapping just one-tenth of the global potential of a little-known energy source that exists where rivers flow into the ocean, a new analysis has concluded. A report on the process -- which requires no fuel, is sustainable and releases no carbon dioxide (the main greenhouse gas) -- appears in ACS' journal Environmental Science & Technology. Menachem Elimelech and Ngai Yin Yip explain that the little-known process, called pressure-retarded osmosis (PRO), exploits the so-called salinity gradient -- or difference in saltiness -- between freshwater and seawater. In PRO, freshwater flows naturally by osmosis through a special membrane to dilute seawater on the other side. The pressure from the flow spins a turbine generator and produces electricity. The world's first PRO prototype power plant was inaugurated in Norway in 2009. With PRO appearing to have great potential, the scientists set out to make better calculations on how much it actually could contribute to future energy needs unde