/ 4 December 2009

Power of osmosis to deliver eco-friendly energy

The world’s first test plant to harness osmotic power, a new emission- free source of energy, opened on November 24 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 sea water.

Statkraft, the Norwegian energy firm behind the test plant, says osmotic power could produce up to 1 700 terawatt hours worldwide — the equivalent of half of the energy generated in the European Union (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. 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.”

Statkraft says osmotic power would be well suited to generate electricity for large cities.

‘Many [cities] 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, says 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 25MW — enough to supply 30 000 households,” he says.

But Skedsmo sounds a note of caution: ‘The infrastructure built can have an impact on the biodiversity of the area … so it’s important to choose the right location.”

The new technology is based on the principle of osmosis. At the test facility fresh water and salt water are guided into separate chambers, divided by an artificial membrane.

When the fresh and sea water meet on either side of the membrane, the fresh water is drawn towards the sea water. The flow puts pressure on the sea water side and that pressure can be used to drive a turbine, producing electricity.

Statkraft has invested 100-million kroner (about R130-million) in the project since 1997, in addition to the 50-million kroner 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.

The challenges are many. First is the price. As with many renewables, and because 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 and €100 a MWh. But electricity prices in Norway are hovering between €30 and €40 a MWh.

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. Statkraft isn’t 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, but 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 at osmotic power as a possible way to provide enough water for long-term manned space missions. —