History of wave energy generators
Wave energy generators have been in development since the 1970s when design engineer Stephen Salter created Salter’s Duck (a wave power converter), so called because the device resembled a duck as is nodded up and down as the waves passed underneath it.
But the move from design stage to commercial implementation for wave power technology has been hampered by the high capital cost of wave power devices.
How the Waveswing works
It is well known that the energy absorbed by a wave power system is proportional to the ‘swept volume’ of the device. In other words, the more water that is affected the greater the energy absorbed. Most wave power systems have been designed to rest on the ocean surface and capture their ‘swept volume’ through ‘bobbing’ or ‘nodding’ motions in relation to the ocean waves – but these interactions between the device and the ocean surface are limited because waves come in all shapes and sizes.
The Waveswing™ however operates in a completely different way – it is a compressible sub-sea device which expands and contracts in response to the changes in pressures exerted by a passing wave. Therefore the motion (and hence swept volume) is not limited to wave height, but is related to the change in relative pressure. In this way, the Waveswing can achieve motions considerably in excess of wave height – thus achieving a true 'point absorber' effect.
In terms of bandwidth, the resonance of the Waveswing is dependant on an active mechanical spring rather than a passive hydrodynamic spring as is the case with a simple floating buoy. Furthermore, the correct spring constant is independent of draft – again a step forward from a floating buoy.
Applying new technology
AWS Ocean Energy, a UK company based in Alness, Scotland, is now developing a 250kW demonstrator unit which will be tested at the European Marine Energy Centre (EMEC). This unit will have a diameter of 8m metres and will be moored in 50m of water via a tension leg. The crown of the floater will be submerged 9m below low-tide. The interior of the device is at low pressure with the hydrostatic forces being balanced by a combination of high-pressure gas springs and active hydraulics. Power generation is via hydraulically driven induction generators.
The Waveswing design means it can absorb twice the power in a typical year compared to a simple heaving buoy and use a third of the materials making the device considerably more cost effective.
Furthermore, as a sub-sea device, damage from storm conditions is reduced and maintenance procedures can be conducted even when conditions above the surface are more treacherous. The only option of floating devices is to return them to port for maintenance as they require very specific conditions for access that rarely occur in UK waters.
Investment and construction
The company has backing from Shell Technology Ventures and institutional investors, plus a £2.1m grant from the Scottish Government which will assist with the construction of the demonstrator unit. Further technology developments are planned for the future, and the company sees the EMEC trial as a vital step in the evolution of the Waveswing into a truly commercial wave power system.
Institution Fellow John Parkin is the one of the company’s Principal Engineers. He believes the technology has huge potential for the UK renewable energy sector.
"Our challenge at AWS Ocean Energy is to harness the abundant resource and make wave energy a sustainable and economic reality. It’s an exciting time to be working in the clean-tech sector and with a company that is one of the leaders in its field. Delivery of the Waveswing demonstration project along with pioneering other transformative technologies will be a major step forward for AWS Ocean Energy and for the sector in general."