A UK engineer has invented a device that harnesses wave power to pump sea water uphill, from where it can flow downhill to create hydroelectricity, raising hopes of a cheap, abundant source of renewable energy.

In trials, the device, called the Searaser, has pumped water more than 160ft above sea level, using little more than the natural motion of the waves. There are now plans for a much larger version, capable of pumping to a height of more than 650ft.

Inventor Alvin Smith reckons that each full-size device would be able to pump enough water to supply electricity to 470 homes. He also calculates that a fleet of 43,000 could generate enough power for a staggering 20 million households.

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