ELECTRIC BLUE: New projects aim to generate energy by harnessing the salinity-balancing effects where freshwater rivers flow into salty seas.
Image: © NASA/ROBERT SIMMON
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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.
Wetsus, with the collaboration of a spin-off company called Redstack, is pursuing a version of salt power dubbed "blue energy". A pilot-scale installation that is about two times the size of a big American refrigerator is up and running in Harlingen, by the Wadden Sea, says Gert Jan Euverink, Wetsus's deputy scientific director. The technology relies on reverse electrodialysis, wherein a series of fresh and saltwater streams are diverted via underground pipes to opposite sides of two kinds of membranes. These let sodium or chlorine ions—the constituent elements of salt—dissolved in the water to pass into separated freshwater streams. This builds an electrical potential across the membranes, like a battery, and this charge reacts with iron to form an electric current. Joost Veerman, a researcher at Wetsus, says the company aims to get five watts per square meter of membrane, the same result as Statkraft's process.
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10 Comments
Add CommentI love the idea, but for one concern.
Reply | Report Abuse | Link to thisThese areas where rivers meet the sea are some of the most sensitive areas, ecologically speaking. I'm not much of an environmentalist and I don't usually find myself on the side of the nay sayers when it comes to building things, but this case sounds particularly full of potential to disrupt the way these natural systems works.
You'd pretty much have to do this "in situ" for the volume of water to be enough for full scale use. You can't pump the sea water or the fresh water all that far or you'll loose the energy gain. You also can't do it by just adding salt to regular water in less sensitive locations because you end up creating a lot of salt water which you then have to either desalinate or change the ratio of fresh to salt water in the area.
If you do this work at the place where these rivers meet the ocean, you have to take water out of the river upstream, let it flow through to where your plant is -- presumably at the coast itself, and let it run through your plant then back out into the ocean. Doing that will change the location where the mixing happens. Do that at a large enough scale, and maybe you risk changing the entire local ecosystem.
Can the same principles be applied to other kinds of reactions? Maybe some where the outcome product is beneficial in some other ways?
AJP's got some good points, although the ideas seem attractive under the surface ;-)
Reply | Report Abuse | Link to thisWhat I'd like to see is a use of these principles in conjunction with desalination. If research resources are to be devoted this process, then it shouldn't be too hard to direct them to a combined operation at this early stage.
5 watts per square meter?!? Sheesh. Even the most horribly inefficient solar cells can get 10 times that much.
Reply | Report Abuse | Link to thisfrgough - yes its low at 5 watts/sq. m, but these membranes are usually cylindrical, so their footprint for a given area is much smaller.
Reply | Report Abuse | Link to thisRegardless, 10 times the power is useless if it isn't consistent. As the article noted, this tech has the benefit of easily meeting baseload demnads. Plus, infrastructure costs may be low compared to making and installing solar cells (not to mention the land requirements).
The importance is on the fact that humanity needs more and more energy. So go ahead!
Reply | Report Abuse | Link to thisThe importance is on the fact that humanity needs more and more energy. So go ahead!
Reply | Report Abuse | Link to this"Statkraft estimates salt power's worldwide electricity-generating potential at up to 1,700 terawatt-hours, or about 10 percent of global demand."
Reply | Report Abuse | Link to thisYet again editors that should know better are confusing the public, already confused about the difference between power and energy. The phrasing should be:
"Statkraft estimates salt power's worldwide electricity-generating potential at up to 1,700 terawatt-hours per year, or about 10 percent of global demand."
Or, just use average power:
"Statkraft estimates salt power's worldwide electricity-generating potential at up to 200 gigawatts, or about 10 percent of global demand."
http://en.wikipedia.org/wiki/Watt#Confusion_of_watts_and_watt-hours
In reply to commenters who pooh-pooh all difficult innovations as pie-in-the-sky: this is Scientific American, not Popular Mechanics, yet even most Popular Mechanics readers enjoy far-out technologies. Thanks SciAm for reporting broadly on this research, but maybe take a hint from the nay-sayers and avoid publishing too much wishful prophecy, even if you do balance it with concerns.
It's gonna take all these imperfect methods combined to replace our dismal array of fossil fuels. The answer is not "this thing or that thing now makes all our power instead of the old way", it's "what do we have here, some geothermal, sure we can use that, solar over there, aquatic turbulence here, windy over there, micro-hydro up the mountain, we can use it all."
Reply | Report Abuse | Link to thisEventually, all those small percentages add up to a big number, and before you know, we have many companies, in many sub-industries, with specialists, engineers, designers, equipment mfg, distribution, maintenance... innovation, competition... sound familiar? Look at all these new things for people to do, instead of just sell saudi gas on the corner for minimum wage.
Hey Adam, cool article. I wrote about this for Science Illustrated during my internship at popsci two summers ago. Unfortunately, it doesn't seem like much (or any) progress has been made in the subsequent year and a half. But I like the basic salt-power idea, so I'm keeping my eyes open for new developments.
Reply | Report Abuse | Link to thisI will follow closely the development. The whole science is known, there is no special pressure or higher temperatur involved. The whole apparatus can be made from simple plastic tubing and valves.No corrosion, wich means long trouble free life. I would talk with people that use reverse osmosis about their experience with
Reply | Report Abuse | Link to thisthe maintenance problems. Good luck. Dr.Kamlander@aon.at