Technology, Green Energy - Making waves the Wave energy

The prospects for wave power have risen and fallen, appropriately enough, for years. But now the technology finally seems to be making headway. Not only is the world's first commercial wave farm due to be switched on and connected to the electricity grid in Portugal this summer—but an even newer type of wave-power generator could drastically reduce the cost of extracting energy from the sea. As you may be aware of that Wave power refers to the energy of ocean surface waves. Though often co-mingled, wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents.

Wave power first attracted interest in the 1970s, when Stephen Salter of the University of Edinburgh devised a device that converted the motion of waves into electricity. The potential is vast: a report published earlier this year by the Carbon Trust, an organisation set up by the British government to help meet its targets for reducing greenhouse-gas emissions, concluded that 20% of Britain's electricity could be provided by wave and tidal power. This is four times more than previous estimates, and means that marine energy alone could enable Britain to reach its emissions-reduction targets. In America, meanwhile, the Department of Energy's National Renewable Energy Laboratory has estimated that the use of wave power on the east coast could provide 10-25 times more electricity than the total wind potential of the Great Plains.

Given this potential, why is it that so far, not a single commercial wave-power generator is in operation? “The biggest problem with wave-power generators is that they are relatively expensive. Most produce electricity at a cost of between 18-36 cents per kilowatt hour (kWh), whereas electricity produced from natural gas costs around 8 cents/kWh. One reason for the expense of wave power is the need to make the equipment impervious to storm damage and corrosion. Of the countless wave-power concepts invented over the years, most have been heavily over-engineered to reduce the chances of breakdown at sea. This reduces their efficiency, increasing the cost per kWh and preventing wave power from making progress.

But now things seem to be changing. Near Póvoa de Varzim, off the northern coast of Portugal, three 150-metre-long articulated snake-like pontoons, called Pelamis Wave Energy Converters, are in the final stages of being hooked up to the country's national grid, says Andrew Scott of Ocean Power Delivery, the firm behind them. Each one has three power-converter modules distributed along its length, which transform the flexing motion at the snake's joints into electricity as the snakes are buffeted by the waves. The three snakes are the first stage of a planned 24-megawatt wave-power farm, which will be capable of providing 15,000 households with power. The Pelamis's design avoids the trade-off between resilience and efficiency by switching to a higher-efficiency mode in calm seas.

But the new device, called the Snapper, increases efficiency still further. Electrical generators tend to work most efficiently when a small force is applied at high speed—which is just the opposite of what wave power provides says the inventor of Snapper. This invention works much like a typical linear generator, in which a magnet is moved up and down inside coils of wire, inducing electrical currents in the process. But there is a crucial difference: alongside the coils are a second set of magnets of alternating polarity. These prevent the central magnet from moving up and down smoothly. Instead, magnetic forces repeatedly halt its motion, so that it moves up and down in a jerky fashion. The resulting series of short, rapid movements is more suitable for generating electricity than a slow, smooth movement. Early tests suggest that it could be as much as ten times more efficient than existing wave generators. Having spent years floundering in the water, could wave power finally be ready to make a splash?. Only time will tell.