Scaling them up could power the planet (Image: Sunset/Rex Features)

A fleet of sailing ships could harvest energy from the wind blowing over the vast tracts of ocean too far from the shore for wind turbines, a scheme unveiled last month claims.

The ships would turn wind power into hydrogen, which would be stored on board, to be unloaded later and used to generate electricity.

The idea comes from Max Platzer and Nesrin Sarigul-Klijn at the University of California, Davis. “Our proposal makes ocean wind energy available for exploitation – a huge energy reservoir because the oceans cover 70 per cent of the globe,” Platzer says. It “offers the opportunity to make a decisive contribution to the solution of the energy and climate crisis”.


Generators in tow

The ships would tow hydropower generators consisting of two wing-like underwater blades that would be made to oscillate by the force of the water as they plough through it. This motion would turn a crankshaft connected to a generator. The electricity this produces could then be used to split seawater into hydrogen and oxygen.

Sailing ships can reach speeds of up to 25 knots (46 kilometres per hour). A ship with 400 square metres of sail, operating in a strong, force 7 wind of 15 metres per second, could generate up to 100 kilowatts of electrical power, Platzer and Sarigul-Klijn calculate. They also say it should be possible to build larger ships capable of generating up to 1 megawatt. With enough ships, the energy needs for the entire planet could be met this way, Platzer says.

“Obviously, this is a roundabout way of generating electricity instead of converting wind or water flow energy directly into electricity using stationary windmills or hydroturbines,” Platzer says. This will clearly lead to some losses, but he calculates that the electricity can be converted into hydrogen and back again with about 30 per cent efficiency.

Concentrated energy

Extracting energy from flow of water rather than directly from air has advantages, as the power density is much higher. Platzer says the water flow through the underwater generator has a power density of 36 kilowatts per square metre – far more than the 1.2 kilowatts per square metre typical of air blowing through a rotating wind turbine. The more concentrated energy means that the equipment needed to harvest it can be smaller.

Stephen Salter, an engineer at the University of Edinburgh, UK, who in the 1970s invented the “nodding duck” wave power device, says the idea looks sound.

Platzer and Sarigul-Klijn presented their paper at an American Society of Mechanical Engineers energy sustainability conference in Phoenix, Arizona, on 19 May.