Neptune to trial DECM

Trials are set to begin on an electromagnetic marine energy device that uses only one moving part to convert wave movement into electricity.

UK renewable energy specialist Trident Energy claims that a number of the devices in a 1km² array could produce as much as 100MW.

The technology uses a linear generator powered by the motion of floats in the sea. The generator comprises a tubular translator contains permanent magnets, and an armature containing coils.

The device begins to work as the translator bobs up and down with the motion of the waves through the armature. As its magnets move back and forth past the armature's coils, electricity is generated. These two parts do not make contact and the energy conversion is entirely electromagnetic.

Unlike other marine renewable power devices, Trident's direct energy conversion method (DECM) does not use hydraulics or air compression. The result, claims the developer, is a reduction in the cost of construction, installation and maintenance.

Hugh-Peter Kelly, Trident's founder and the architect of its marine energy technology, said the idea came to him following his invention of the tubular linear motor.

This is an electric motor used worldwide in the automation industry, and Kelly said it occurred to him that the device had real potential to generate marine energy.

'Any electric motor of this type can work backwards as a linear generator, and I thought I could perhaps use a linear generator to capture wave power and use it as a source of renewable energy,' he said.

Kelly conducted an initial experiment in 1999 off the north coast of Devon with a scaled-down prototype. While it was a small-scale test, it did prove Kelly's principle that such a device could be used to generate electricity from the sea. With this success, the Department of Trade and Industry commissioned Durham University to lead a study into the effectiveness of using linear generators as an alternative to hydraulics for wave energy capture.

Kelly founded Trident in 2003 and assembled a team of engineers and scientists to help him further research and develop his device.

The team confirmed the commercial viability of the system in 2005 after a series of successful wave tank tests at Northumberland's New and Renewable Energy Centre.

With additional private equity and a research and development grant from the East of England Development Authority in 2007, Trident began assembling its first big offshore test project. further trials of a prototype rig are planned in the North Sea off the Suffolk coast early next year.

With good sea conditions, the test rig is predicted to generate about 20kW from eight full-scale linear generators. The company hopes that with a successful three-month offshore trial period it will be able to increase the rig size and number of generators installed, thereby delivering multi-megawatt generation.

Kelly is optimistic about the North Sea trial, although conditions may prove difficult. 'We don't have any concerns about the technology itself, but we need the rig to survive in storm conditions,' he said.

He said his team has spent a significant amount of time researching and designing 'tension mooring lines' to anchor the rig to the seabed and help it survive treacherous weather. It has also been built with its own self-protection mechanism to help keep it safe during storms.

When onboard detectors sense weather conditions such as high winds, the linear generator switches into reverse motor mode and retracts the floats from the sea, storing them in protective chambers above the water line.

'The system is still under development and it is something that will be made more sophisticated as we progress further on down the line,' said Kelly.

If the North Sea trial goes according to plan, Trident's next step will be to seek government funding through the Marine Renewables Deployment Fund to support the pre-commercial phase.

Kelly is confident that, with careful planning, his device will reach full commercialisation.

'The whole business of taking something like this forward is a careful mixture of getting the technology right; acquiring all the permissions, which are expensive; the funding; the eventual capital cost; ease of connection to the National Grid; ease of deployment and the commercialisation of the entire thing,' he said.

'You can't ever say sea-based devices are technology driven — all those other factors must also be taken into account.'

Other marine energy developers know this too well. Around the world there are about 80 wave or tidal energy devices in various stages of development, and the majority of this work is taking place in the UK.

The Pelamis Wave Energy Converter, for example, developed by Scottish company Pelamis Wave Power, was installed off the coast of Portugal this September.

And the installation of the world's first commercial tidal generator also began this year off the coast of Strangford Lough, Northern Ireland.

The UK is well placed to exploit marine energy. Kelly knows Trident faces a lot of competition that is vying to tap into this reserve, and his company is conducting studies that will show where its technology can best compete with others.

'It just happens the UK is the favourite European country as far as wave energy is concerned,' he said. 'We will conduct studies of the Atlantic waves, North Sea waves and waves around the top of Scotland in an attempt to work out the best areas to produce the most energy at the cheapest cost.'

Siobhan Wagner