From David Ridpath
Julie Rehmeyer’s article gave an interesting account of the emerging technology and economics of desalination by reverse osmosis (1 July, p 30). I was particularly intrigued by the suggestion that wind power be used to power the plants.
However, it seems to me that she missed a trick here. The implication of her article was that conventional wind turbines would provide electrical power to drive the desalination plants via the electricity grid. Surely the neater solution would be to house the desalination tubes in the towers of offshore windmills.
They would neatly fit in vertical arrays around the inside of the tower. Pumps at the top of the tower could be directly driven, mechanically, from the windmill shaft. The “fresh” water could then be pumped ashore, again using mechanical wind power. Electrical losses in the generator, transmission cables and pumps would be avoided, and, surely, laying and maintaining pipes must be cheaper and easier than cables.
Wind generation of electricity is often criticised because the product cannot be stored, and so spare capacity elsewhere is needed to cover for windless times. This criticism disappears if the product is fresh water, which is routinely stored in reservoirs.
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Intuitively, it seems to me that the relatively high torque and low speed of wind generator sails would be ideal to drive suitably designed high-pressure desalination pumps directly.
Lydbrook, Gloucestershire, UK
