What is Blue Energy Anyway? Two Takes on Osmotic Power

fjord in norway photo

photo: mozzercork via flickr

Here's one more way to harness the power of water to create energy: It's been dubbed Blue Energy by Ode Magazine in a recent article and involves harnessing the energy released from the process of osmosis. All you need for an osmotic power system is a supply of salt water, a supply of fresh water and an alternating series of ion-exchange membranes. How hard can it be, right? Lets take a look:

pressure retarded osmosis systems image
Reverse Electrodialysis
The first method described, being worked on by Redstack (a company affiliated with the Dutch organization Wetsus) is known as reverse electrodialysis.
As Ode describes it, "In a RED system, saltwater and fresh water are brought together through an alternating series of ion-exchange membranes, which harvest the energy released as the fresh water is drawn towards to saltwater."

How much energy can be produced this way? Right now, the trial system produces enough power to run a vacuum cleaner. Not much, but it's a start.

Pressure Retarded Osmosis
Another method is being worked on by Norway's Statkraft and uses Pressure Retarded Osmosis. The difference from the RED process is that in a PRO system is that the latter uses "the hydrostatic pressure created when fresh water passes through the membrane to the salt water side. The pressure spins a turbine, which is plugged into a generator to produce electricity."

Statkraft's PRO project isn't that much farther along than the Redstack project, the prototype facility has a capacity of 2-4 kW at the moment.

How Much Power Could This Produce?
So, the payoff: How much potential power is there in osmotic power? According to Statkraft, provided that the process can be refined to make it cost-effective—right now they're producing power at about 3 watts per square meter of membrane, with 5 watts per square meter seen as the break-even point—blue energy could produce 25 terrawatts hours of power, equivalent to 20% of Norway's power production.

Assuming that profitability on osmotic power systems can be reached, which isn't a certainty on any large scale, one main advantage of the technology with Ode touts is that a blue energy plant could be built wherever saltwater and fresh water meet, "from the fjords of Norway to Asia's estuaries."

Too bad Asia's estuaries may be devastated by climate change-induced sea level rise before a bevy of osmotic power plants could be built...

More: Ode Magazine
second image: Statkraft
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