Japan has opened its first osmotic power plant

Summary

Japan has opened its first osmotic power plant, in the south-western city of Fukuoka.Only the second power plant of its type in the world, it is expected to generate about 880,000 kilowatt hours of electricity each year – enough to help power a desalination plant that supplies fresh water to the city and neighbouring areas.That’s the equivalent of powering about 220 Japanese households, according to Dr Ali Altaee from the University of Technology Sydney (UTS), who specialises in the development of alternative water sources.While it is still an emerging technology being used only on a modest scale as yet, it does have an advantage over some other renewable energies in that it is available around the clock, regardless of the wind or weather or other conditions.It relies simply on the mixing of fresh and salt water, so the energy flow can continue day and night, providing a steady source of electricity.So what is osmotic power and could it be used elsewhere?What is osmotic power? Osmosis is the natural process where water moves across a semipermeable membrane from a less concentrated solution to a more concentrated one, in an attempt to balance the concentration on both sides.Picture a cup divided vertically by a thin, semi-permeable layer – if one side holds salty water and the other side pure freshwater, the water will flow towards the salty side to dilute it, because the salt itself cannot pass through the membrane.Osmotic power plants use this same principle, by placing freshwater and seawater on either side of a special membrane, with the seawater slightly pressurised.As water flows across to the saltier side, it increases the volume of pressurised solution, which can then be harnessed to produce energy.In the Fukuoka facility, fresh water – or treated wastewater – and seawater are placed on either side of a membrane. As the side with seawater increases in pressure and decreases in salinity, some of the water is channelled through a turbine that is connected to a ...