Could a taste for salt prove a significant source of renewable power?
Could the attraction of salt for freshwater molecules become a significant source of power? This is the question a forthcoming pilot plant for osmotic power – sometimes referred to as ‘blue energy’ – aims to answer.
Osmosis describes the movement of solvent molecules from water with a low salt content towards more saline climes, equalling out the salinity levels. But it’s not the tiny amounts of kinetic energy which are captured. Rather, it’s the difference in pressure created by this influx of molecules through a semi-permeable membrane which can be used to drive a turbine.
It’s a promising technology, but an expensive one at present. The new plant will act as a test bed for innovations to bring down the cost, as part of a three-year collaboration between Europe’s largest hydropower producer Statkraft and Canadian water utility Hydro-Québec. The 1-2MW plant will be an expansion of the world’s first prototype plant, built in 2009 at Tofte on the Oslofjord, Norway, which has a capacity of just 4kW. Construction will begin in 2013, and the plant should come on-stream by 2018.
One focus for the pilot project is how best to treat the freshwater, protecting the membranes from silt and natural organic matter. Membranes in an osmotic plant should last for seven to ten years, and it’s important to keep maintenance and repair costs to a minimum if this source of power is going to be cost-effective at scale. Statkraft is working with commercial partners in its search for solutions. One of these is Hydranautics, a subsidiary of the Japanese chemicals and plastics company Nitto Denko, which is looking to supply the osmotic power market in future.
For Statkraft, the achievement of a successful pilot plant is the first major milestone towards the commercialisation of osmotic power. The company has further ambitions to build a 25MW demonstration plant before 2030 – but this will only be possible if cost-effective technology and a suitable regulatory framework, with support mechanisms built in, come together.
Statkraft’s prototype facility enjoys easy access to sources of both seawater and freshwater – but osmotic power is not confined to coastal areas. In fact, it’s possible to run an osmotic power plant without any salt in the mix – as long as you have two different water types, one with a higher solute concentration than the other. And – unlike wind, which is an intermittent source of renewable energy – osmotic power generates a stable base load of electricity.
With as much coastline as a piece of string, it’s no great surprise that Japan is taking an interest. Its Osmotic Power Research Centre opened in 2010 at the Tokyo Institute of Technology. – Sara Ver Bruggen
Photo: Damian Heinisch / Statkraft