The world鈥檚 first prototype osmotic power station came on stream this week.
Sited on the banks of the Oslo fjord in southern Norway, it generates electricity using the natural process that keeps plants standing upright and the cells of our own bodies swollen, rigid and hydrated.
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Osmosis occurs wherever two solutions of different concentrations meet at a semipermeable membrane. The spontaneous passage of water from dilute to concentrated solutions through the membrane generates a pressure difference that can be harnessed to generate power.
鈥淭he potential is huge,鈥� said , the Norwegian minister for petroleum and energy, speaking at the new plant鈥檚 opening ceremony in Tofte, near Oslo, on Tuesday.
, the renewable-energy giant running the project, estimates the total global potential of osmotic power to be around 1700聽terawatt-hours per year 鈥� about 10聽per cent of the world鈥檚 current electricity consumption.
Fjord focus
In the prototype plant, the two solutions used are salt and fresh water, siphoned from near the point where they meet at the mouth of the fjord.
The two liquids are pumped to either side of a membrane, where osmosis creates a pressure equivalent to a column of water 120聽metres high. This is used to drive a turbine and generate electricity.
Many of the world鈥檚 major cities are on river estuaries that could be ideal for osmotic power generation. Unlike wind and solar power, it can provide a continuous source of energy, although seasonal river-level changes do cause some fluctuations.
Fancy a cuppa?
Discounting the power used to pump the water into the facility in the first place, the Tofte plant is currently producing just 4聽kilowatts 鈥� enough to continuously boil two or three kettles.
Scaling up the technology could prove difficult, critics say, because fundamental questions such as the effect of silt and river bacteria on the membranes鈥� performance over time have not been resolved.
Stein Erik Skilhagen, head of osmotic power at Statkraft, admits the uncertainties, but says it is important to have made a start. 鈥淭here are no doubt many challenges to come,鈥� he says. 鈥淚 can鈥檛 tell you what they will be.鈥�
