‘Salinity Power’ at Large Estuaries Could Provide a Constant Flow of Green Electricity

Monday, 02 March 2009 09:50

River estuaries, such at that of the Rhine where it flows into the North Sea, are a vast, yet untapped source of energy according to Dutch engineer Joost Veerman. Veerman and his colleagues at Wetsus, the Dutch Centre for Sustainable Water Technology in Leeuwarden, believe they can tap the energy locked up in the North Sea saltwater by channelling it along the fresh water from the Rhine into a new type of battery. With enough batteries they could produce energy to supply 650 000 homes using a process they’ve called Blue Energy. They would be producing over a gigawatt of electricity.

This process could produce a constant flow of green electricity, day and night, rain or shine without damaging sensitive ecosystems or disturbing fisheries.

“Salinity power” is based on the chemical differences between salt and fresh water.

In Norway engineers at the Norwegian power company Statkraft have been working on the PRO project which was developed from the early desalination plants.

In the late 1950s, Sidney Loeb and Srinivasa Sourirajan at the University of Los Angeles in California, came up with the idea of extracting drinking water from the sea using a synthetic membrane and high pressure pumps. This idea was developed into what is now used in desalination plants world wide.

Loeb, 15 years later, working at the Ben-Gurion University in Israel realised the design could be further developed to generate power. He named the process pressure retarded osmosis (PRO) and patented it in 1973. The key lay in developing a membrane that was permeable to water but not to salt and was durable but very thin. In 1986 he retired without realising his dream.

In 1997, with membrane technology greatly advanced and with the detailed calculations of Thor Thorsen and Torleif Holt who worked at the Norwegian research organization SINEF Statkraft was convinced that salinity power would pay off in Norway.

They used a design much like Loeb’s original but with Statfraft’s engineers improved membrane designs. The first membrane generated about 100 milliwatts per square metre with a later design generating 3 watts per square metre. Their target is 5 watts per square metre.

Stein Erik Skilhagen, manager of the PRO project at Statkraft considered the membranes to be efficient enough to be worth testing outside the lab. The world’s first prototype PRO plant will be at the Sodra Cell paper pulp factory in Tofte, 60 kilometers from Oslo

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