See gallery: “The next wave of energy from the sea“
An explosion of designs for harvesting wave energy could make the process competitive at last – and they’re heading out to the ocean for testing
WRINGING electricity from the sea is no small task. But as firms start to test their wave-energy harvesters in the open ocean that could be about to change.
Heaving water holds 40 times more energy than air moving at the same speed, and sea states change more slowly than breezes, making it easier for utilities to predict the availability of energy. Yet the tools needed to make use of the sea’s energy are gargantuan.
Pelamis Wave Power’s wave energy device, P2, is a case in point. Currently stored at the Leith Docks in Edinburgh, UK, it uses spools of steel cable several times human height, and floats that are as big as a car. But this is just window dressing for the machine itself: a red rig that looks like a 180-metre-long subway train.
Pelamis and Aquamarine Power, also based in Edinburgh, are the big players in what remains a small industry of generating energy from waves. Each is now fielding full-scale prototypes that could make wave energy competitive in terms of cost with other renewable energy sources, such as offshore wind.
Alongside them are dozens of smaller competitors, building a menagerie of strange devices that they hope will leapfrog ahead of existing machines in the race to provide inexpensive power from the sea. “Wave energy has been talked about for hundreds of years,” says Neil Kermode, managing director of the European Union-funded European Marine Energy Centre (EMEC). “Now it’s actually starting to happen.”
In the UK, the waters around the Orkney Islands off northern Scotland, home to some of the world’s cruellest weather, are used as EMEC’s proving grounds, as they offer a stiff test for wave-energy devices. As Kermode puts it: “This is the playground for the big boys.”
For all its impressive size, on the inside the P2 looks more like a data centre than a ship’s hull. Duplicate server racks, fibre-optic communication systems and emergency power supplies allow programmers to upload software on the fly without interrupting power production.
The P2 generates energy when its large floating tubes, connected by hinged joints, bob in the waves, moving hydraulic rams that pump high-pressure fluid to drive turbine. And while the hardware has been upgraded from previous prototypes, it is the algorithm controlling them that makes the difference. By decreasing resistance in the rams when waves are small and increasing it when they are larger, the algorithm maximises energy production in any sea state. As a result, the P2 produces 750 kilowatts of electricity – twice as much as prior prototypes.
“It’s the active control of these algorithms that allows us to tune the machine to be in resonance regardless of wave conditions,” says Pelamis engineer Ross Henderson.
Active control of the algorithms means the device can be tuned to any wave conditions
Last month, Aquamarine Power finished the construction of its second full-scale wave power device, the Oyster 800. This consists of a hinged flap that sticks out of the water and is pushed shut with each passing wave. When the flap moves, it drives hydraulic pistons that deliver high-pressure water via a pipeline to an onshore turbine. With an output of 800 kilowatts, the device is built to be 2.5 times as powerful as its predecessor (see “The ocean is your oyster”).
“If you can get that sort of level of performance improvement then the economics suddenly start to look a lot more favourable,” says Stephen Wyatt, head of technology acceleration at The Carbon Trust, a UK-government-funded organisation charged with catalysing a low-carbon economy.
A study published by The Carbon Trust in July estimated the cost of energy harvested from waves at 43 pence per kilowatt-hour, or almost three times the cost of offshore wind. To become cost competitive with other sources of renewable energy, companies will have to find ways to squeeze more power out of their devices, says Wyatt.
Meanwhile, a host of start-up companies are heading for EMEC’s “nursery” – a test facility built in sheltered waters for designs that are not yet ready for the open ocean – each hoping their device will be the next game changer.
One of the most promising, according to a three-year study by The Carbon Trust, is Anaconda by Checkmate Seaenergy, based in Sheerness, UK. This is a snake-like rubber tube filled with water that floats just below the surface. As waves hit the front of the device they squeeze the tube, creating a bulge of water that travels along it. When the bulge reaches the end, the pressurised water drives a turbine.
An 8-metre long prototype has been tested, but the firm says it will be several years before its full-scale 1-megawatt device, which would be 150 metres long, is ready.
An equally unusual machine, the 1600-tonne Penguin, will soon begin testing at EMEC. Built by Finnish company Wello, the 500-kilowatt rig has an asymmetrically shaped hull that causes it to roll, heave and pitch – much like the stilted stride of a penguin – with each passing wave. The movement spins a flywheel inside the hull, driving a generator.
With such devices arriving with increasing frequency, it’s too early to tell which technology will win out in the end. “That is part of the excitement,” Kermode says. “It may be something completely new or variations on something we have already seen.”
See gallery: “The next wave of energy from the sea“
The ocean is your oyster
The Oyster 800, the newest wave energy device developed by UK-based Aquamarine Power, produces 250 per cent more energy than its predecessor. Most of the improvement came from making the hinged flap that harnesses wave energy wider – it is now 26 metres wide and 12 metres high.
Gains also came from subtle changes in the device’s design, such as wider edges on the flap’s sides to reduce water turbulence. Conversely, tapering Oyster’s width along the top of its flap allows it to cut through the water more efficiently, boosting energy output by 3 per cent.
“I’m confident that there is still more power to get out,” says Matthias Haag of Aquamarine Power.
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