Scandinavians mix sea and river water to generate electricity
mongabay.com
December 19, 2005
SUMMARY: Two Scandinavian groups have invented devices that generate electricity by mixing sea and river water. The technologies work based on the difference in salt concentration between ocean water and freshwater.
“It’s basically harvesting the energy that comes free from a natural process,” says Johannes Boonstra, managing director of Dutch Centre for Sustainable Water Technology (Wetsus).
Norwegians, Dutch Mix Sea and River To Make Power
By Anna Mudeva, Reuters
December 19, 2005
LEEUWARDEN, Netherlands — “Water will be the coal of the future,” French science-fiction writer Jules Verne predicted in 1874.
More than a century later in a world seeking clean alternatives to fossil fuels, Dutch and Norwegian scientists believe they can help turn Verne’s dream into reality.
The Dutch Centre for Sustainable Water Technology or Wetsus, and Norway’s independent research organization SINTEF, working with power company Statkraft, have invented devices that generate electricity by mixing sea and river water.
It might seem like an exercise in scientific theory destined only for high-tech laboratories, but the process’ creators and the European Union, which funds the Norwegian research, believe the idea’s time might have come.
“There is huge potential in Europe to use this new way of producing electricity,” Philippe Schild, scientific officer at the European Commission’s energy directorate, told Reuters.
“It’s a renewable source which does not cause any environmental damage and we think it can play a big role in helping meet our target to increase renewable energy,” he said.
Global warming and high oil prices have renewed interest in sustainable energy, with solar, wind, biomass, hydrogen fuel cells, tidal and wave power getting most attention.
But researchers in Norway and the Netherlands, known for their water technology know-how, say there is room for other alternatives given the world’s ever-growing appetite for energy.
WATER BATTERY AND HOTDOGS
The new devices are based on a natural process — when a river runs into the ocean, a huge amount of energy is unleashed because of the difference in salt concentration.
“It’s basically harvesting the energy that comes free from a natural process,” Wetsus managing director Johannes Boonstra said in his agency’s laboratory in the Dutch town of Leeuwarden.
“You have the fuel for free and it’s very sustainable — no greenhouse gas emissions.”
The two projects use different methods to harness the electricity — the Dutch apply something called reverse electrodialysis while the Norwegians use a kind of osmosis.
Both methods rely on membranes or thin films made of special material used for chemical separation. In the Dutch project, separation is done by membranes using an electrical current.
“It works like a water battery,” Wetsus project manager Sybrand Metz said.
The Norwegian device applies pressure to force the water through membranes. Its inventors liken the process to putting a hot dog in hot water. The skin of the hotdog acts as a membrane, allowing more water in than the amount of salty water it lets out. This increases the pressure inside and the hotdog bursts.
The principle behind the Norwegian device is that fresh water and salt water are channeled into a membrane module. The fresh water is transported through the membranes and over into the pressurized sea water. The pressurized mixture of sea water and fresh water flows out of the module and into a hydropower turbine that generates electricity.
The two inventions, however, have still a long way to go before they can be applied commercially.
The Wetsus project, supported by a consortium of Dutch companies, has yet to be tested in a pilot plant. The Norwegian project is more advanced. It started in the 1990s and its creators have already installed two small-scale plants, but have yet to build a bigger demonstration plant to boost production.
TOO EXPENSIVE
Like other alternative energy technologies, cost is the biggest hurdle. Power produced by mixing sea with river water is several times more expensive than wind or solar energy.
The idea of producing electricity from salt and fresh water was first explored during the energy crisis of the 1970s, but membrane technology was not sufficiently advanced and scientists dismissed the process as hopelessly expensive.
The membrane industry has matured since then and is now widely used in water and pollution treatment, power generation, production of medical, biotech and electronics devices.
The main challenge is finding membranes that are efficient and robust enough to boost production, but also cheap.
“We have to be competitive with electricity from coal or gas,” Boonstra said. The scientists believe it will take at least 5 years to develop cheaper membranes, test them and be able to put the project on the market.
Norwegian project manager Rolf Jarle Aaberg believes power-from-water will be ready to seriously challenge other renewable energy technologies between 2010 and 2015.
The new power plants can be built wherever fresh water meets salt water, such as the outlets from existing hydroelectric power stations, and could even be placed underground.
Statkraft and the European Commission put the production potential in Europe at 200 terawatt hours a year, or nearly twice the electricity consumption of a country like Norway.
The potential in Norway alone is estimated at 10 percent of its annual power needs. The river Rhine, for instance, could deliver 3,000 megawatts of power where it flows into the sea in the Netherlands — the equivalent of five big coal-fired plants.
The new technique has attracted some skepticism, the scientists say, but they find comfort in history.
“When the first wind energy turbine was installed in Germany in 1985, the whole industry laughed,” said Frank Neumann of the International Energy Agency’s ocean energy programme.
“It was a big failure then and millions were lost. But look at it now and how fast wind energy is expanding.”
