River + Ocean = Electricity
Tapping the power potential of the difference in salinity between fresh water and salt water could supply electricity for 520 million people, according to research funded by the Environment and Water Industrial Development Council of Singapore. Pressure-retarded osmosis (PRO) is an alluring process because it is available anywhere fresh water and salt water meet: Less-concentrated fresh water naturally wants to mingle with more-concentrated salty water. When the fresh water is run through a semi-permeable membrane, pressure from the flow can be tapped to drive a turbine that generates electricity—with no carbon dioxide emissions.
The Norwegian renewable-power company Statkraft has operated a prototype PRO facility near Oslo (at left) since 2009. By 2015 the facility is expected to produce 25 megawatts, the equivalent of a small wind farm.
Researchers Menachem Elimelech and Ngai Yin Yip calculate that the target of a half-billion customers could be reached by relying on one-tenth of the world’s river water flow. They note that the same amount of electricity produced by a coal-fired power plant would release over one billion metric tons of greenhouse gases annually.
Photo by Statkraft.
Reed McManus is a senior editor at Sierra. He has worked at the magazine since Ronald Reagan’s second term. For inspiration, he turns to cartoonist R. Crumb’s Mr. Natural, who famously noted: “Twas Ever Thus.”