Tidal power starts to meet potential

Tidal stream technology is catching up with developments in wave power. The first commercial-scale unit – 1.2 megawatts in size – will be installed in Northern Ireland by the year’s end, while four other UK developers are planning 1MW units by 2009.

The world’s first commercial-scale tidal stream turbine will be installed off the coast of Northern Ireland by the end of the year. Marine Current Turbines will install the 1.2MW “Seagen” unit in Strangford Lough, a special conservation area south-east of Belfast. It will consist of two “flow rotors” 20 meters in diameter driving a generator and mounted either side of a steel monopile.

The company, which has received investment from EDF Energy, has consent from the Environment and Heritage Service (EHS) to operate for five years. But it must follow a strict programme of environmental monitoring to ensure the turbine does not impact on the marine bed or mammals.

The unit will generate electricity at a cost of around 18 pence per kilowatt hour, according to Martin Wright, the company’s managing director. But this will need to drop to 9p/kWh for the unit to be viable as an array. This drop should come with experience and improvements in the supply chain, he says.

The development suggests tidal stream technology is finally beginning to fulfil its potential. Last year, the Carbon Trust reported that the UK’s annual tidal stream resource was 18 terawatt hours – a seventh of UK electricity use – although only a fifth was suited to “near-term developments” being in waters 30-40 metres deep (ENDS Report 373, p 19 ).

Initial generating costs would also be 12-15p/kWh, it said. Seagen’s expected figures are higher than this, but they are still better than the Carbon Trust’s estimated generating costs for wave power of 22-25p/kWh.

Seagen comes some four years after MCT installed a 300kW pilot unit in the Bristol Channel (ENDS Report 332, pp 28-31 ). The main reason for the delay, according to Martin Wright is the time it has taken to complete an environmental impact assessment (EIA) and develop an environmental action plan. “More than a quarter” of the £10 million cost of the project has been spent on the EIA.

The regulator’s main concerns regarded the unit’s effect on marine mammals, especially seals and porpoises, he said. The company has undertaken a two-year visual survey of their populations combined with satellite tracking and thermal imaging to get baseline data. The surveys will continue for three years to assess the unit’s impact. The unit itself will also include a mechanism to shut down the turbine when mammals approach.

The EHS was also concerned about the anti-fouling coatings for the turbine. The company intended using a leach-proof copper-based coating, but this was rejected in spite of similar solutions being used to wash down slipways around Stanford Lough.

According to David Ainsworth, Seagen’s project manager, such high levels of scrutiny were unexpected. “Offshore wind is a relatively mature technology now and you’d have thought that would mitigate the monitoring we’d be required to do,” he said. The high level of monitoring should be a lesson to other firms about the hoops they will have to jump through to install units, he added.

At least four other developers intend to have units of 1MW or more operational by 2009, while Marine Current Turbines and Scotrenewables intend to have commercial arrays operational within five years (see table).

Major utilities are also becoming involved in the sector: Scottish Power is developing a 1MW unit with Norwegian firm Hammerfest Strøm, and Total and Eon have invested in Scotrenewables and Lunar Energy respectively.

“I think investors are starting to realise the advantages of tidal stream and that’s given us new momentum we didn’t have two years ago,” said James Ives, chief executive officer of OpenHydro, which has been trialling a 250kW unit at the European Marine Energy Centre in Orkney since last November.

“Being on the seabed’s a much easier place to operate than on the surface, and the predictability of tidal also makes it of tremendous interest to investors.”