Energy Out of the Blue: Generating Electric Power from the Clash of River and Sea Water

Two pilot projects are testing the potential of “salt power,” a renewable energy that relies on the differing salinities at river mouths to make watts

In the hunt for alternatives to polluting and climate-warming fossil fuels, attention has turned to where rivers meet the sea. Here, freshwater and saltwater naturally settle their salinity difference, a phenomenon that two pioneering projects in Europe will try to harness to generate clean energy.

This concept of “salt power”—also known as osmotic, or salinity-gradient, power—has been kicked around for decades, and now, proponents hope, technology has advanced enough to make it economically competitive.

On November 24, the world’s first large-scale prototype facility for developing a form of salt power called pressure-retarded osmosis is expected to begin fully operating in Norway. “The big reason to build this thing is to answer important questions [about osmotic power], and while we’ve done a lot of theoretical studies, we need live experience,” says Stein Erik Skilhagen, vice president of osmotic power at Statkraft, Norway’s state-owned power utility that built the plant. The prototype will have no customers, although the very small amount of electricity it generates will technically be directed into the power grid.

Statkraft’s approximately $5-million prototype plant is a converted paper mill in the seaside village of Tofte, about 60 kilometers south of Oslo. The plant’s pressure-retarded osmosis setup will place freshwater and brine on either side of a semipermeable membrane that prevents the passage of salt particles but allows water through. Water from the fresh side naturally flows into the salty side, generating pressure equivalent to a column of water 120 meters high. This pressurized water can be used to turn a turbine to make electricity. Statkraft’s goal is to yield five watts per square meter of membrane, although current capacity is about three watts. If successful, the utility hopes to build a commercial salt power plant for paying customers around 2015 with a targeted cost ranging from seven to 14 cents per kilowatt-hour (pdf) (at current euro–dollar conversion rates), which at the low end would be competitive with coal and natural gas prices.

To the south in the Netherlands, a Dutch research firm called Wetsus has fired up its own salt power experiment to evaluate what is essentially a saltwater–freshwater battery.

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Tags: brine, clean energy, fossil fuels, osmosis, pilot projects, pioneering projects, power grid, proponents, prototype facility, renewable energy, river mouths, scale prototype, semipermeable membrane

This entry was posted on Wednesday, October 21st, 2009 at 7:06 pm and is filed under Cutting-edge Research, Innovation, Innovation Needed, Project Energy, Scientific American, environment. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.