Energy: Pearl of power

Aquamarine’s Oyster marine-energy converter is positioned near shore, making it cheaper to install than other devices

winner/oyster/aquamarine power/queen’s university
belfast/university of edinburgh

Marine-energy generation is at an interesting stage of development. The UK and Ireland, with the mighty Atlantic on one side and the enormous tidal pool of the North Sea on the other, are among the world’s best-placed nations to extract energy from waves and tides but, as yet, there is no dominant technology. A bewildering array of devices that bob, rock and sway as waves pass over them, or spin in the tidal race, are under development, awaiting their places at sea trials.

Among these is the Oyster from Aquamarine Power, one of a cluster of marine-power technology firms based in Edinburgh. Beginning sea trials at the European Marine Energy Centre’s wave-power test site off the Orkney Islands, Oyster takes a subtly different tack from other wave-energy converters that is said to make it easier and cheaper to install and maintain than its competitors.

Most wave-energy converters are designed to sit in reasonably deep water, at or near the surface, and extract energy from the up-and-down motion of the sea as waves pass. Their electricity-generating equipment is integral to their construction and they send their power ashore via underwater cables. Oyster, however, is a near-shore device, sitting some 500m off the coast in about 13m of water and, rather than being integral, its generating turbines are a separate construction, sited on shore.

‘The fundamental thing about our device is that it’s very simple; much simpler than other wave devices on the market,’ said Ronan Doherty, chief technology officer of Aquamarine Power.

The Oyster is a large, buoyant flap made from steel and hinged at its bottom edge, which sits on the sea bed. As waves roll over the device, the flap oscillates up and down, pumping two water pistons attached to each side. These pressurise water and shoot it down a pipe towards the shore, where it enters what Doherty describes as ‘virtually a catalogue-style hydroelectric plant’. The water jet spins a Pelton-wheel turbine – with spoon-shaped buckets around the edge to harness the energy of the pressurised water – and a squirrel-cage induction generator. ‘We have all these more sensitive and complicated components onshore where we can get to them 24/7 and all we have offshore are these simpler, easy-to-maintain structures in shallow water,’ he said.

Unlike other wave-energy converters, Oyster doesn’t use the vertical component of wave motion; instead, it uses the horizontal thrust of the wave as it comes ashore, the same energy that pushes a surfer forwards. ‘That actually makes power extraction very easy,’ said Doherty.

‘Most other wave converters need active control to tune their devices from wave cycle to wave cycle so that they move by the correct amount – so they have oil hydraulics on board that give them that fine degree of active control. They also use oil-hydraulic generators to make electricity. The Oyster is just an oscillating flap, so it doesn’t need any active control at all. That means we can use the simpler water hydraulics.’

Oyster was originally developed at Queen’s University of Belfast by Prof Trevor Whittaker, a veteran developer of wave-power converters that work by the oscillating-water-column principle, harnessing the power of waves crashing onshore to turn a generator. ‘Trevor’s experience with these devices led him to believe that some of the capital costs and some of the problems of using that kind of technology were insurmountable,’ Doherty said. ‘So he started searching for a cleverer, lower-cost way to extract the energy. He started by researching flaps hinged at the top and that evolved to bottom-hinged flaps on devices sitting on the sea bed. Oyster’s development started there.’

That was around 2001. Four years later, Aquamarine was started up as a vehicle to commercialise the technology. Doherty explained that there is a huge, unexploited resource on Atlantic coasts, which the company is aiming to target in the next few years.

‘It’s a function of the sea itself, the amount of energy in the waves and the shape of the seabed,’ he said. ‘Scotland in particular, the west coast of Ireland and Portugal all have these sorts of waves. If you wind the clock forward a few years, we’d be looking at a very large deployment – 100MW-plus installations up and down the coastline. That would be 100-150 devices and we reckon to get 20-25MW per kilometre of coastline – that’s a very efficient deployment density for wave-energy devices.’

In all, Doherty said, the UK and Ireland have around 5GW of exploitable commercial wave power that would be accessible by Oyster installations, with a capacity factor – the amount of time that the devices produce useful energy – of around 40 per cent. Each hydroelectric station can service 10-15 offshore devices.


With this sort of visible, relatively large onshore installation, Doherty admits Oyster might face planning problems. ‘There’s an awful lot of coastline that’s underexploited,’ he said. ‘Some beaches and headlands are likely to be good surfing spots and of course the coast is a leisure amenity and some areas are regions of natural beauty, but there are hundreds and hundreds of miles of coastline and a lot of it isn’t an amenity area. I don’t think wave power and tourism are likely to clash straight on, but proper strategic planning of the coastline – how the natural resources are going to be managed – is very important. It’s analogous to what the wind industry has been going through onshore. The planners are going to have to strike a delicate balance.’

Oyster development is continuing apace. While the sea-trial version starts producing results off Orkney, Prof Whittaker and his team are beginning scale-model tank trials of the next version, Oyster 2. ‘Oyster 1 is a full-scale proof of concept model, but Oyster 2 is likely to be our first commercial offering,’ Doherty said. ‘It’s a little larger than Oyster 1 and should produce a higher energy yield. Oyster 2 should be in the water by 2011 and we’re hoping it’ll cross the commercial hurdle in 2013 or 2014.’

The technology has already attracted commercial interest, with Airtricity – the renewable-energy-development arm of Scottish and Southern Energy – forming a joint venture with Aquamarine Power to develop 1GW worth of commercial sites for Oyster devices off the UK and Ireland by 2020.

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