World’s first salt power plant opens tomorrow

by thomas on November 23, 2009 (Feature image by Statkraft)

Osmotic power membranes coiled up inside pressure vessels

Starting tomorrow, the world’s first power plant generating power from salt water will be opened at Tofte in Norway.

Back in May, I did a little roundup of various ways to get power from water. One of the more experimental technologies I mentioned was salt power – or osmotic power, which is the more precise (and slightly more complicated sounding) name for it.

Europe’s largest renewable energy company, Statkraft, has now developed this technology far enough to open their first prototype power plant, with their sights set on building a commercially viable plant within a few year’s time (Statkraft’s press release).

How osmotic power/salt power works

I simplified things in the first paragraph to avoid scaring readers away. There’s a bit more to it than just salt water. Not much, though – the principle isn’t very complicated:

  1. Water is pumped into a container, salty ocean water on one side and fresh water on the other side of a membrane.
  2. The natural process osmosis pulls the freshwater through the membrane. Since the membrane only allows water to flow in this one direction, pressure builds on the salt water side.
  3. The built-up pressure is used to power a turbine, thereby generating power.

This kind of power plant could be built anywhere fresh water flows into salt water, typically where a river flows into an ocean. Statkraft has calculated that the worldwide potential of osmotic power is somewhere between 1600 and 1700 TWh, roughly equivalent to 50 percent of the EU’s total production. Not too shabby.

What are the advantages of osmotic power?

So, you might ask, why bother developing this technology? Why develop an entirely new technology, instead of improving existing renewable technologies like, say solar power? Here are the reasons I can think of off the top of my head:

  • No huge installations needed
    Osmotic power plants can be built in the basements of existing buildings.
  • Virtually no unwanted side effects
    The power generation basically piggybacks on a natural process (ie. the mixing of fresh water and salt water) that would’ve occurred anyway. No birds or fish being killed by turbine blades, no huge dams flooding valleys and so on.
  • Continuous power generation
    This is a big one. One of the more difficult aspects of moving to renewable energy is the intermittency of the power generation many of them provide. Solar power needs the sun to shine and wind power needs the wind to blow. Osmotic power just needs the river to not dry out.
  • More choice
    No single technology will be a good fit for every situation and context. Solar power is good for deserts, wind power is good for windy areas (well, duh) and osmotic power is good for coastal areas with rivers running into the ocean. The greater the number of options available, the better.

I tried to come up with some disadvantages to osmotic powers, but couldn’t really think of any. Can you think of any? Or are there advantages I’ve missed? Set me straight in the comments :-)

{8 comments... read them below or add one }

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{ 8 comments… read them below or add one }

thomas July 13, 2013 at 23:54

@Cassandra: Thank you for commenting. As I understand it, very little wiping out is needed to build one of these power plants, and virtually none of it would be underwater.

The whole plant would be built on land. This is both easier and cheaper than building underwater, and it’s easier to do so without harming the local ecosystems. The only intrusion into the marine environment would be that freshwater is pumped out of the river before it meets the ocean water, ocean water would be pumped out of the ocean and the resulting mix of fresh and salty water would be discharged somewhere suitable – presumably where it wouldn’t upset the existing salt levels in the water too much.

The whole need to locate these power plants somewhere where fresh water meets ocean water is based only on practicalities and energy efficiency. In theory, osmotic power plants could be located far inland, but then the energy cost of pumping the ocean water and the “exhaust water” over large distances would reduce the energy and cost efficiency of the whole concept.

Cassandra July 13, 2013 at 18:41

The downside of this is that the meeting of salt and fresh water is the area of the most abundant natural life on this planet. So many life cycles of so many species depend on the area where salt and fresh water intermingle.

I’m not saying that it wouldn’t work or that there aren’t areas where it would be appropriate, but the statement that no fish are killed is clearly false—if you wipe out an entire zone of fish because you’re wrecked where they breed, I think it would count as killing them.

thomas November 30, 2011 at 18:07

@NamU: Heh ;-) One might think so, but luckily, no. No fresh water is actually spent during this process. The salt power plant pretty much just piggybacks on somewhere fresh water is flowing into salty water anyway. For example where a river runs into the ocean. The fresh water is then diverted into the power plant, salty ocean water is pumped from the ocean and they’re both combined through the osmotic process described above. The resulting product is water that has a salt level somewhere between the salty ocean water and the fresh water – and power, of course ;-) This somewhere-in-between water is then pumped back into either the river or the ocean, depending on which is closer.

NamU November 29, 2011 at 23:52

Wouldn’t there be a depletion of the fresh water resource? Just wondering, but the overall plan sounds cool. Need to stop burning up fossil fuels.

thomas November 30, 2009 at 17:00

@Bjørn Olsson: Thanks for commenting. At the moment, the profitability is certainly low at the plant Statkraft has opened. Then again, that particular plant isn’t intended as a commercially viable plant – it’s a prototype for further research.

As noted in my reply to kk above, the current main obstacle is membrane efficiency. Their best current membrane has an efficiency of 2-3 watts per square meter. They have to get that number up to 5 for the concept to be viable. They also have to improve the transfer of pressure to the turbine.

Only the future will tell if they’ll accomplish this, of course, but they seem reasonably optimistic about it. They have 2015 as the target year for a full scale commercial plant – and given the size, resources and experience of Statkraft, I trust them to not fling out overly optimistic promises.

But, as you write, who knows? :-)

Bjørn Olsson November 30, 2009 at 16:45

You missed one disadvantage: lousy profitability. Very small chanse that it ever gets profitable. But who knows?

thomas November 24, 2009 at 13:12

@kk: The technology is built modularly to scale well, so the minimum water flow required isn’t too bad. Once they build a full scale commercial plant, they’ll need one cubic meter of fresh water per second to generate 1 MW. This should make osmosis power plants feasible for even moderately sized rivers, although I suppose larger scale installations will be more cost effective, as is so often the case.

At the moment, improving the membrane efficiency is the stumbling block. The membranes Statkraft is running their protoype on generates less than 1 watt per square meter (keep in mind that the membranes are rolled up inside pressure vessels (see picture above), so this isn’t as space wasting as it sounds). They’ll switch to membranes with an efficiency of 2-3 watts per square meter after running the prototype for a while, with the future goal of getting to a 5 watts efficiency.

kk November 24, 2009 at 11:52

Osmotic power looks a very attractive renewable energy source. One disadvantage I could think of is the potential required. What flow of fresh water is needed to produce, let’s say, 1 kW of electricity?

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