The ups and downs of water power
Tidal turbines have to be massive to take on their environment but its links to the mainland that are making life difficult
The wave and tidal resources are huge round the UK, and although it’s not how seafarers usually see it, the places around the north of Scotland are especially blessed.
Although the Gulf Stream has some input, this is also partly because of the shape of the seabed: for example around Orkney and off Anglesea the seabed profile actually accelerates the water flow, it picks up speed as it passes through the constrained channels. The Pentland Firth especially has a lot of deep water, funnelled between the islands. “The morphology of the bottom makes a great deal of difference, not just for tide but for wave power too,” explains Mr Krohn.
However, although the current provides a powerful force to be harnessed, at present there is no sense in going bigger than 1.2MW. Mr Krohn explains that while you have 7MW wind turbines in development, these have to pick up ‘peaks’ in the wind. However, he adds that the tidal turbines have “a greater capacity factor” as basically, the tidal turbine is working for a larger percentage of the time.
The Meygen project in Skegness could see some large tidal arrays. This project is interesting because it is going to be using different types of tidal turbines. David Krohn points out that some shapes or designs are good for turbulent or multidirectional flows, while some would be best in the ocean away from turbulence so specific devices for different places seems a good idea.
The first 20MW installed will be supplied by both ARC and Tidal Generation Limited on a fifty-fifty basis.
Many projects are now just really beginning to come to fruition, with a number in the initial stage of deployment. For example the Tidal Generation-Rolls Royce project is looking at its first array being installed this summer, and Vattenfall have plans to purchase the first of ten Pelamis sea snake devices later this year. These will form the 10MW Aegir wave power project off the Shetland Islands.
In addition to Aquamarine Power’s Oyster 800 and 801 project at EMEC, the company has secured a 200MW seabed lease off the west coast of the Orkney Mainland from seabed owner the Crown Estate, plus a 40MW site off the west coast of Lewis.
In order to commence development at the Lewis site – which is scheduled to begin in 2014, the company will have to overcome challenges which are, as Neil Davidson says, “financial as much as technical.”
Securing grid connections has been the most challenging part. “If we are to capitalise fully on the wind and wave resource of the Western Isles, the renewables industry will need a 450V HVDC subsea high voltage interconnector to the islands, where a large part of the renewable energy resource is located.”
This would allow wind and wave developers to get onto the UK national grid. Ofgem is currently proposing very high transmission charges, at a level so high as to make it unfeasible – the proposed figure is £7.7m per annum for a 100mW farm, compared to the mainland or the Isle of Skye, which is around £1m per annum for the same capacity.
“It’s very frustrating, it goes completely contrary to government policy which acknowledges the need for renewable energy in the mix,” says Mr Davidson. He goes on to explain that if the cost were to be spread it would mean 2p per household per annum across the UK. But Ofgem’s view that the cost should be borne by early stage developers on the Western Isles. “It is like saying we need to build a new motorway, but the people at the end of the road should pay for it,” he adds.
One of the other ironies it that this policy stands so much in opposition to that in the South of England, which currently pays people to create energy. “Yes” he says, “this has stopped people – there’s a number of developers who wanted to go ahead with wind power from the Western Isles, but they were previously unable to underwrite the cost of the interconnector because of the transmission charges.”
Remote places like the Western Isles, Orkney and Shetland are crying for this industry but they are being stymied by Ofgem’s attitude, says Mr Davidson.
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