Focus Corner

Sustainable electricity from the salt of the earth

March 18th, 2009 by   (View Author Profile)
How osmotic power works

How osmotic power works

Imagine a new power plant at the mouth of the Shannon, generating clean electricity . . . not from the waves or the tides, nor from the flow of water, but driven by the salt in the surrounding sea. And as a bonus, the system doesn’t disturb the estuary’s environment or get in the way of shipping traffic.

How might this be done? By osmosis!

A pilot power plant will be opened shortly near Oslo, and the electricity will be generated by harnessing the osmotic difference between fresh and salty water.

According to a recent survey of this innovative technology in New Scientist this ‘blue power’ could generate 7% of the world’s electricity needs, making it a serious player in the growing green power market.

Now, I don’t know about you, but instinctively I feel there must be more we can do to harness the tremendous energy of the oceans, yet I’d no idea we’d be able to do this by exploiting the difference between fresh water and the sea.

The idea, it seems, has its roots in the process used to desalinate water: there, electricity is used to derive clean water from salty water by pressing it through a semi-permeable membrane. (If this rings bells, it may be because you remember that old osmosis experiment from school science)

To generate sustainable electricity, you just put the process into reverse: provide sufficient fresh and salty water, as at an estuary, and exploit the difference in osmotic potential to generate power.  Read an explanation here.

Except, of course, nothing is that simple (there are major technological issues around the membrane design, for instance), which is why this isn’t yet widely used.

But is a few months, a Scandinavian power company, Statkraft, will switch on a pilot plant at a paper mill near Oslo, producing a nett 3kW of power, enough initially to power just one 3-bar electric fire.  So, it’s a small start, but the firm believes it can scale up the technology to produce 10% of Norway’s electricity needs.

Meanwhile, a Dutch team is researching an alternative approach at Wetsus, centre of excellence for sustainable water technology.

If osmotic power takes off, it could turn the world’s estuaries into great power generating batteries. And the Shannon could be harnessed not just at Ardnacrusha, but again at Limerick where it meets the sea.

A thought to leave you with on this St Patrick’s Day, some 80 years after the Ardnacrusha power plant was switched on to provide electricity for Ireland’s modern nation-building project.

(c) Mary Mulvihill 2009

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