Green power from the sea using hydraulic technology

A huge new machine called Oyster - designed to harness the power of ocean waves and turn it into green electricity - has been installed on the seabed off the Atlantic shores of the Orkney Isles north of Scotland.

The machine is undergoing demonstration trials to prove whether its innovative technology could lead to a commercial source of renewable energy for use in seashores around the world.

In contrast to many other wave power devices, Oyster uses hydraulic technology to transfer wave power to shore, where it is converted into electricity.

"A key design feature is an 18-metre-wide oscillator based on fundamental research at Queen's University Belfast led by Professor Trevor Whittaker using their wave tanks," said Dr Ronan Doherty, Chief Technical Officer of Aquamarine Power, the Edinburgh-based company that developed Oyster. The design won the company the Innovator Award at this year's British Renewable Energy Awards.

The oscillator is fitted with pistons and, when activated by wave action, pumps high-pressure water through a subsea pipeline to the shore. Onshore, conventional hydroelectric generators convert this high-pressure water into electrical energy.

"The whole field of generating electricity from wave power is groundbreaking," added Dr Doherty. "But Oyster's technology is highly innovative because it relies on simplicity. Its offshore component - a highly reliable flap with minimal submerged moving parts - is the key to its success when operating in seas vulnerable to bad weather where maintenance can be very difficult.

"There is no underwater generator, power electronics or gearbox underwater to go wrong. All the complex power generation equipment remains easily accessible onshore."

The machine is designed to be deployed at near-shore water depths of 12 to 16 m, benefiting from the more consistent seas and narrower directional spread of the waves in this location.

The reduced wave height and load enhance survivability and allow a high percentage of annual average power and consistent power delivery. Any excess energy is spilled over the top of the flap, its rotational capacity allowing it to dip under the waves.

The environmental risks associated with the device are minimised by using only water as its hydraulic fluid, rather than oil, and there are no toxic substances involved. It is also silent in operation.

Based on figures from the Carbon Trust, each Oyster's annual carbon saving could be as much as 500 tonnes. Although at an early stage of development, the concept could have significant potential for use in many places across the world.
Dr Doherty added: "Our computer modelling of coastlines suitable for this technology shows that Spain, Portugal, Ireland and the UK are ideal candidates in Europe. But globally there is huge scope in areas like the north-west coast of the USA and coastlines off South Africa, Australia and Chile. We estimate that the potential size of the market could be in excess of 50 billion pounds."

The marine renewable research capacity at the Environmental Engineering Research Centre, Queen's University Belfast, is said to be among the best in the world and, in collaboration with Aquamarine, Oyster will be the centre's sixth wave-power sea trial. Research at Queen's, which contributed to the Oyster technology, was supported by the Engineering & Physical Sciences Research Council.