Apart from solar photovoltaics and fuel cells, nearly all electricity generation depends on spinning a turbine, usually by creating a pressure differential by heating water to steam. In nature, by contrast, chemical gradients are ubiquitous in being used to do work. Now it seems that these approaches have converged with osmotic gradients being used as an alternative approach for generating electricity.
Osmosis is the phenomenon where, when separated by a semi-permeable membrane, water will flow from a low-concentration solution (e.g. freshwater) to a high-concentration solution (e.g. seawater). This increases the pressure in the high-concentration solution, which can be used to drive a turbine and generate power.
In principle, this technology can be applied wherever fresh and salt waters are in close proximity. In the Fukuoka plant, brine is provided by a desalination plant and using this waste stream to generate power has the added benefit of diluting the brine. The Fukuoka plant has a capacity of 110 kW and is expected to generate up to 888 MWh annually, equivalent to the energy needs of 220 Japanese homes.
The power plant does not produce carbon dioxide and can produce electricity consistently. However, there are significant energy losses incurred by friction as water flows across the face of the membrane and from the need to pump water, meaning there is significant room for improvement as the technology develops.
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