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Optimism over the first turbine in Britain, and only the second in the
world, to generate electricity from offshore tidal currents, was tempered
last week by a report that sets out a long list of obstacles that could
rob the technique of a successful future.

Tidal flows off the coast of Britain carry immense energy. According
to the report, published last week by the government’s Energy Technology
Support Unit, underwater windmills – or tidemills – could supply Britain
with up to 58 terawatt-hours a year, or 19 per cent of the country’s demand
for electricity.

But the report emphasises the negative in its technical summary. ‘Machinery
would be subject to corrosion damage, encrustation by marine organisms and
fluctuating forces which could shorten project life,’ it says. ‘Movement
due to waves would present problems for transmitting energy to the shore.’

Many of the best sites for tidemills, such as the Channel Islands and
the Pentland Firth between Scotland and Orkney, are a long way from the
centres of energy demand, and transmission lines would have to cross ‘sensitive
landscapes’. According to the report, only machines at the best sites, and
capable of generating more than 100 kilowatts, could produce electricity
at prices below 10p per kilowatt-hour: still well above present competitive
prices.

The authors of the report include David Wardle of Engineering and Power
Development, a subsidiary of Balfour Beatty, and Peter Fraenkel of IT Power,
the company that initiated the tidemill project.

Wardle describes tidal current power as ‘a long-term possibility’. Fraenkel
is more upbeat. While admitting that it will be many years before tidemills
make a large contribution to Britain’s electricity grid, he argues that
on small islands such as Alderney in the Channel Islands, which is subject
to one of the strongest currents round Britain, the technique could be ‘immediately
cost effective’. Tidemills will succeed where wave energy has failed, he
said, ‘because it doesn’t need any new technology. We’re using wind power
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Fraenkel is working with Scottish Nuclear and NEL to build a 10 kilowatt,
two-blade turbine for Loch Linnhe. The turbine, which has blades 4 metres
across, will be suspended from a buoy and weighed down by two anchors. When
the tide and the current turns, the turbine will swing on its moorings through
180 degree.

Research, development and construction are expected to cost less than
£200 000, and Fraenkel says the mill will be working by July. The
report for ETSU calculated construction costs on the basis of tidemills
built on the sea flour. But Fraenkel says that suspending the turbine from
the surface has significantly lowered the cost.