Power of osmosis used to deliver eco-friendly energy

A Norwegian firm is testing a renewable and emission-free source of energy that harnesses the power of water through osmosis
Gwladys Fouché
guardian.co.uk, Wednesday 25 November 2009 17.45 GMT
The world's first test plant to harness osmotic power, a new emission-free source of energy, opened on Tuesday, in Norway. Nestled amid pine-covered hills on the banks of the Oslo fjord, 60km south of the Norwegian capital, the facility will exploit the energy produced when fresh water meets seawater.
Statkraft, the Norwegian energy firm behind the test plant, says osmotic power could produce up to 1,600–1,700 terawatt hours worldwide – the equivalent of half of the energy generated in the EU today.
"Osmotic power has great potential," says Arild Skedsmo, head of climate and energy at WWF Norway. "In theory the power is available and it's an emission-free way of producing energy."
He adds: "This is an immature technology. But like all renewables, we need a whole range of technologies to be available. Osmotic power can definitely be part of the solution."
The right site
Statkraft says osmotic power would be especially suited for generating electricity for large cities. "Many are situated at the point where large rivers flow into the sea," says Sverre Gotaas, senior vice-president for innovation and growth at Statkraft. "So you would not need to transport the electricity over long distances."
Another advantage, argues Gotaas, is that a commercial plant would be modest in size, but still produce a significant amount of energy. "A facility the size of a football field could generate 25 megawatts – enough to supply 30,000 households," he says.
However, Skedsmo at WWF Norway sounds a note of caution, explaining that an osmotic plant could have the same environmental impact as a hydropower facility. "The infrastructure built can have an impact on the biodiversity of the area … so it's important to choose the right location," he says. "It should not be built in unspoilt river deltas or protected areas."
Could osmotic power plants appear in the UK? "Certainly," says Gotaas. "Any area where river flows into the ocean could be suitable … Another important aspect is that the rivers can't be too polluted. If it's muddy, we would have to clean the water [before using it]. But you have clean rivers in the UK."
The new technology is based on the principle of osmosis, the diffusion of water through a semi-permeable membrane, which is how plants draw water from the soil.
At the test facility, fresh water and salt water is guided into separate chambers, divided by an artificial membrane. When the fresh and seawater meet on either side of the membrane, the fresh water is drawn towards the seawater. The flow puts pressure on the seawater side, and that pressure can be used to drive a turbine, producing electricity.
The two-storey, tennis-court-size plant, situated next to a pulp mill, will generate little power. "It will produce two to four kilowatts. You might be able to run a coffee machine on it, if you are lucky," says Gotaas.
There is no river at the site, situated outside the village of Tofte, so Statkraft will use the water from a nearby lake piped by the pulp mill.
Statkraft has invested 100m crowns (£10.7m) in the project since 1997, in addition to 50m crowns it received from Norwegian and EU funds. The company hopes to launch the first commercial plant between 2015 and 2020 – if everything goes to plan.
Cost of change
The challenges are many. First is the price. As with many renewables, and since it is a new technology, osmotic power is expensive to run. Statkraft says the company can break even if the electricity price reaches between €70 (£63) and €100 a megawatt hour. But current electricity prices in Norway are lower, hovering between €30 and €40 a megawatt hour.
Another challenge is technical. The key to the technology is the membrane, but Statkraft says it needs to be made five times more efficient than it is today. Yet another issue is developing the business, with Statkraft looking to find business partners, such as membrane manufacturers and utility companies.
Statkraft is not the only company trying to harness osmotic power: the Dutch firm Redstack is commercialising a similar technology and is planning to develop a pilot plant in the north of the Netherlands. However, the plan appears to have run into problems. Dutch utility firm Eneco, which had previously said it would help finance the plant, pulled out of the project in October. "We could not agree with the other partners," says Cor de Ruijter, a press officer at Eneco. Executives at Redstack were unavailable for comment.
Nasa is also looking into osmotic power. Researchers at the US space agency are looking to the technology as a possible way to provide enough water for long-term manned missions to the moon or Mars. The idea is a system using osmotic power could separate salt and water from wastewater and purifies human liquid wastes, such as urine and non-potable water, into water that is safe to drink.