Researchers reconsider osmotic power prospects

Researchers at Griffith University in Queensland, Australia claim to have demonstrated sound prospects for harnessing the energy created in salinity gradients - where, for example, freshwater meets the sea. Earlier studies failed to provide convincing indications that the vast theoretical potential of this renewable source of power could realise an economical return.

Researchers, Fernanda Helfer and professor Charles Lemckert from Griffith's School of Engineering reviewed findings from other previous studies into the potential of salinity gradient energy, which is released when waters with different salinities mix. Their paper: The Power of Salinity Gradients: An Australian Example, focused on the potential in - Pressure Retarded Osmosis (PRO) - where a turbine taps the osmotic pressure from a salinity gradient to generate power.

Progress with PRO has been by uneconomic rate of energy generation but Helfer and Lemckert have claimed that rising energy prices and growing concern over climate change have improved the prospects for PRO and salinity gradient energy.

The researchers said Australia was particularly suited to osmotic power production with "various sources of saline solutions that could be used as draw solutions for PRO plants."

The sources included salt lakes, brine from desalination plants and saline groundwater. They said the siting of the continent's largest cities on the coast and close to river mouths create ideal conditions for osmotic power plants.

The study revives the suggestion of the use of brine rejected during desalination, as a source of osmotic energy. "Even taking into account the current inefficiencies of PRO, and based on the power generated under laboratory conditions and published by other institutions, a mixture of seawater and brine could generate power in a PRO plant adjacent to a desalination plant," said Helfer.

"This power would be used in the desalination process while the PRO plant, in turn, would use the reject brine as the draw solution and seawater as the feed solution," Heifer added.

Helfer and Lemckert acknowledged that that significant technical and economic improvements were required to ensure the commercial viability and credibility of PRO membrane technology.

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