Salt batteries could power coastal cities?

New Scientist: "...[R]ather than constructing a huge barrage or dotting the river bed with turbines, Veerman and his colleagues at Wetsus, the Dutch Centre for Sustainable Water Technology in Leeuwarden, believe they can tap energy locked up in the North Sea's saltwater by channelling it, along with fresh water from the Rhine, into a novel kind of battery.

"With a large enough array of these batteries, he says, the estuary could easily provide over a gigawatt of electricity by a process they've called Blue Energy - enough to supply about 650,000 homes.

"'Salinity power' exploits the chemical differences between salt and fresh water, and this project only hints at the technology's potential: from the mouth of the Ganges to the Mississippi delta, almost every large estuary could produce a constant flow of green electricity, day and night, rain or shine, without damaging sensitive ecosystems or threatening fisheries.

"One estimate has it that salinity power could eventually become a serious power player, supplying as much as 7 per cent of today's global energy needs...."