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One has gone green

They will keep the Queen's two iPods charged, make sure the Duke of Edinburgh's Roberts radios keep going over breakfast and ensure that the corgis are warm at night.

In the next few weeks, two huge Archimedes screws placed in the River Thames a few hundred yards from Windsor castle will be switched on to provide a steady stream of green electricity for the royal household.

Spinning gracefully at 22 revolutions a minute, the 1.7m turbines will generate 300 kilowatts — enough power for 400 homes, or half a royal palace.

The royal project is the largest of its kind in southern England and was supposed to serve as a flagship for Britain's hydropower industry.

Yet this week, the company behind the Queen's turbines has suspended all new hydropower projects, claiming it can "no longer trust" the government to continue backing renewable energy.

David Dechambeau, managing director of Southeast Power Engineering, said the unexpected slashing of subsidies for solar panels and the long-delayed review of renewable power grants is threatening the hydropower industry. He isn't alone in his concerns.

Industry chiefs say that dozens of other schemes worth a total 100m have been put on ice while the coalition decides what to do with the feed-in tariff scheme.

It's a damning indictment of a government that less than two years ago pledged to be "the greenest ever".

Hydroelectric turbines have been generating electricity in Britain for more than a century, and today have capacity to generate 1.7GW — or 2% of the country's capacity.

Yet the industry believes there is plenty more scope for water power and that it could generate another 12GW.

Some of that will come from conventional hydropower schemes relying on dams or waterfalls, but the kind of Archimedes screws installed at Romney Weir at Windsor could also play a key role.

Based on a 2,000-year-old design from the Greek mathematician and engineer Archimedes, they are designed to generate power from a small drop, or "head", of water of one or two metres, and could turn Britain's rivers into a valuable source of green power.

Each of the Windsor steel screws is 12 metres long and weighs 40 tonnes. They sit in a steel trough shaped like a half moon and work at full capacity for 95% of the time. Only in the worst of a summer drought will the water level of the Thames fall enough to stop them spinning.

The screws are invisible above the weir, but can be seen from below. The engineers have lined the blades with rubber to reduce damage to fish, and have installed a fish run to allow migratory trout, eels and salmon to move up and down stream.

Archimedes screws have been used on the Continent for more than 40 years. Although a handful of smaller projects have popped up around Britain in recent years, this is the largest to date.

The Windsor turbines — which were installed despite the scepticism of the Duke of Edinburgh — will be turned on in the next couple of months and should cut the royal family's carbon emissions by 790 tonnes a year.

During the day the generators will supply the castle, but at night, when demand falls from the royal household and its 500 staff, excess electricity will be sold to the national grid.

Southeast Power Engineering has two other projects on the Thames, at Marlow and Bell Weir near Staines. However, after the government's recent u-turn on feed-in tariffs, the company said no more schemes are in the pipeline.

Feed-in tariffs were introduced in 2010 to give investors a secure return for installing small-scale renewable electricity generators.

In opposition, the Conservatives and Liberal Democrats backed the scheme. In the first year of the tariffs, however, solar panels proved far more popular, and cheaper, than expected. In 12 months, 28,000 schemes were installed.

Last spring, the coalition announced that large-scale photovoltaic projects would be axed, and in October, it slashed the rate for smaller schemes from 43.3p per kilowatt hour to 21p. The move was declared unlawful and is now subject to an appeal.

The Department of Energy and Climate Change also announced a review into the rates for all other types of renewable energy. The review was due last July, was put back to December and is now expected at the end of this month. The u-turns and delays have left investors frustrated.

Dechambeau said: "We have suspended all further developments because we don't trust this government to stand behind renewable energy. Sometimes I wish we were in the business of drilling for oil because the government doesn't seem to have a problem with that."

Across the rest of the industry there are similar concerns.

The British Hydropower Association estimates there are more than 100m of approved hydro schemes on hold, pending the tariff review.

"That represents nearly 50 schemes, each with a capacity of between 100kW and 3,500kW and it does not include a substantial number of micro hydro schemes of 100kW or less," said David Williams, chief executive of the association. "The delay has created much uncertainty. We are talking about hundreds of jobs in jeopardy."

The department was unable to confirm when the consultation into tariffs would be published.

"We understand the need for certainty and aim to provide greater clarity as soon as possible," it said.

At Romney Weir on the Thames, the final cables are being connected to Windsor castle. Electricity should start flowing by March — when the Queen takes up official fulltime residence for the month. By then, energy developers should have a clearer idea of whether a technology devised 2,000 years ago is the future of green power or the relic of a bygone era.

Copyright David Derbyshire 2012