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Reinventing the wheel

Energy - A mill renovation in Welwyn Garden City, UK, may give a new lease of life to an old technology - the water wheel. Adrian Greeman reports.

A visit to the UK Department of Industry's Clear Skies alternative energy website will find no mention of the water wheel among the technologies eligible for 'green friendly' grant support. The environmental credentials of this once universal clean technology simply do not make it.

'In general, ' says Dr Gerald M³ller, a civil engineering researcher at Southampton University, 'small scale hydropower is virtually written off in Europe by most governments and support agencies. Sites suitable for the smaller turbines are almost all used up, it is assumed, because of early industrial development.' Potential turbine sites may be hard to find, but there are still thousands of places where water wheels could be fitted, says M³ller, usually where the Industrial Revolution first located them in its mills and streamside factories. But although wheels can use the much lower water heads at these sites, they are deemed inefficient as electricity generators, offering little more than 75% energy conversion. It is not cost effective, says the government.

M³ller disagrees: 'The later designs evolved in Victorian times are comparable with modern turbines.' Research leads him to believe wheels could be up to 10% more efficient than they are now.

Turbines are up to 94% efficient, he says, 'but by the time you allow for in- and out-flow losses they are about the same as wheels at 86-87%.' Turbines also damage fish stock, he says. Bigger fish are simply cut to pieces and smaller ones suffer damage to their air-filled swim bladders because of low pressure in the blade chamber. Water wheels simply drop the water to a new level.

M³ller hopes to prove his point with a working wheel currently being installed at an old mill just outside Welwyn Garden City in Hertfordshire, UK, built in 1863 on a site first used in the 1700s.

The picturesque, three storey, Grade Two listed grain mill is being renovated by local travel company Rambler Holidays for a new headquarters office.

It so happens that Rambler Holidays has its own 'green' ethos, being a semi-charitable company organising natural walking holidays and closely tied to bodies like the Ramblers' Association. And it so happens too that one of its voluntary directors is a civil engineer at consultant Atkins, Robert Fisher.

This combination made the company keen to explore the ecological possibilities of the mill, which originally had an internally mounted water wheel. This had been removed in an earlier prizewinning conversion to workshop space in the 1980s, but the wheel enclosure was still present.

First thoughts were to put in a turbine, but this proved too expensive - probably at least $180,000, says M³ller. And it would not have provided the interesting visible showpiece for the mill interior, which the company wanted. Fisher says that they hoped to make a point with the installation and perhaps even use it for occasional educational visits.

An article on mill restoration in Devon put them on to specialist company Hydrogeneration, and to M³ller, who has been researching the topic. He in turn located Hydrowatt, a German company which has installed a number of wheels in southern Germany in the last decade.

The result, via a visit to Germany in March this year, was a decision to go ahead with a 'breast-shot' wheel installation (see box). The company has just been on site fitting the wheel.

Like most modern wheels it has a steel frame. M³ller explains that older completely wooden wheels were not durable and needed replacing every 8-10 years. They also distorted, affecting performance. 'As soon as wrought iron became available in the 1820s it was adopted, although wooden paddles are still used.' The wheel, modelled on a late nineteenth century design, sits in a specially shaped trough which traps most of the water within the curved blades. Forming this trough required some civils work because the 1980s renovation had altered the height of the wheel enclosure and a smaller diameter wheel than was originally fitted is now in place.

'That has made it a little more costly, ' says Rambler director Tony Lock. 'The payback will be less than we thought.' Provision of two large glass inset panels - to allow visitors to watch the wheel - has not helped contain costs, although the company has been lucky in actually exporting the electricity.

A substation sits just 100m away which means connection is short and inexpensive.

The expense is increased perhaps by the sheer complication in the UK of obtaining approvals for every aspect of a wheel from environmental regulator the Environment Agency, power agencies, planning authorities and heritage bodies. It is also complex to sell the power to the variety of privatised generating bodies that now exist. European and US regulations are much simpler, says Fisher.

Even so, the 15kW output will be sold to the grid rather than being used directly because otherwise the night-time output would be wasted, Fisher explains.

But despite having to buy a normal office supply, the surplus should still pay off the wheel cost - perhaps some $126,000 - over the next 20 years.

It would break even more quickly if installation economy had been the first principle and the wheel housing the right shape, M³ller points out.

He also thinks wheels could be more efficient: he is researching how the wheel and blade geometry can be re-designed, and he thinks 78% efficiency for the breast-shot wheel can be improved to as much as 87% or 88%.

'These are small enhancements, ' he hastens to add. 'We are not re-inventing the wheel.'

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