If's a clean energy promoter's dream. Imagine an open landscape rolling for 40 miles. Then imagine 200 wind turbines twirling along the route like giant white daffodils. They will supply the energy needs of half a million homes and contribute around 6 per cent of the UK's renewable energy targets. Wouldn't you be proud to live nearby? Wouldn't you be overjoyed to know that a forest of turbines, each one the size of a jumbo jet, is helping to deliver a green'n'- clean, low-carbon future?

Lewis Wind Power wants to build Britain's biggest wind farm on the north moors of Lewis, the largest island in the Outer Hebrides and one of the windiest places in Britain. It will produce 702mW of electricity for 25 years. The proposal is supported by Highlands and Islands Enterprise and the Stornoway Trust. Two smaller wind farms are also in the planning stages. All together they will produce the energy equivalent of two nuclear power stations.

Bill McAllister, head of Highland Renewable Energy Group (Hireg), claims 200 turbines in Lewis could do the job of 700 in the south. And he decries those "who prefer empty glens to development for the future". "We're the good guys," he says.

Western Isles Council recently voted by 19 to eight to support the application. Calum Iain MacIver, head of economic development, points out that traditional industry on Lewis "is slowly contracting around us". The population is falling and incomes are lower than the UK average. "We've got to persuade our young people to stay." Clean energy offers Lewis a star position as "the energy capital of Europe".

Some are less enthusiastic. Fin-lay McLeod, a crofter who lives near a planned cluster of turbines, claims "There has been little attempt to sell the idea to local people." Many crofters, he says, would support community based wind farms, and several are established. But a huge commercial development in which they receive no benefit is a different matter. "If we are saving the planet, why are we talking about destroying such a precious part of it?" asks McLeod. "It's madness." Western Isles Council denies that the islanders were not fully consulted.

Some 6,130 objections were received by the Scottish Executive, two-thirds from the Western Isles. There were only 22 messages of support. Together with objections made to another planned win farm at Eisge on the island south-easter side, there have been nearly 10,000 objections, from an electoral roll for the whole of the Western Isles of 21,694 (out of a population of 26,370). Objectors have formed a pressure group, Moorland without Turbines, to fight the development.

On Lewis, clean energy will come at an environmental price. It will need about 160km of new road capable of supporting low-loaders carrying heavy machinery. Each road will have to be 30m wide. Five substantial quarries will be needed to provide the 4 million tonnes of rock for new roads and hardstandings. And almost the entire development is to be sited on wet peat, notorious for its tendency to collapse or to set off slides of mud into the water supply. Pessimists predict the project will result in a huge sodden mess. And then there are the birds.

Much of the North Lewis Moors is protected under European law as an SAC (Special Area for Conservation). It is home to about 3,400 pairs of dunlin and 1,800 pairs of golden plover, making it the most important nesting ground for these birds not only in Britain but in the EU. The area is also used by divers, corncrakes, merlins, golden eagles, whooper swans and barnacle geese.

The remoter parts of North Lewis contain some of Britain's most extensive and intact examples of blanket bog, an intricate and wildly beautiful landscape of pools, hummocks of moss and drifts of white, fluffy-headed cotton-grass.

The role of Don Quixote, tilting at the gigantic windmills (140m high, with a diameter of 100m), has fallen to the Royal Society for the Protection of Birds. Like all green pressure groups, the RSPB supports the Government's targets on renewable energy. "We objected to only 10 per cent of wind farm developments in the UK," says the RSPB's head of planning and development, Anne McCall.

However the organisation is adamantly opposed to this one. Even the developer's environment statement admits that many eagles and other birds will meet an untimely end by colliding with the turbines. Hundreds of eagles have been killed by turbines at Altamont in California, while a colony of sea eagles was quickly wiped out by a new and relatively small wind farm at Smola on the Norwegian coast. And as birds which tend to fly in straight lines on regular flight-paths, Lewis's "nationally important" numbers of red and black-throated divers are particularly vulnerable.

Moreover, says the RSPB, this wind farm is not as clean as it looks. It disputes the developers' "worst-case scenario" that 1,900 hectares of peatland will be disturbed. A survey commissioned by RSPB claims it will take years for the carbon "saved" by the wind farm to be offset against the millions of tonnes released when the peat is disturbed. The developers deny this, claiming that the farm will "break even" in carbon after about nine months.

Plans will soon be submitted to the Scottish Executive for a wind farm that is approved in principle. In a nod to the opposition, Lewis Wind Power will scale down its plan for 234 turbines to around 190 - though it will still be Britain's biggest wind farm. The executive will then need to decide whether "imperative reasons of public interest" override concerns such as wildlife protection and crofters' rights.

Will Lewis become a shiny offshore battery to power mainland Britain? Or will Don Quixote see off the windmills and save the dunlin - an outcome which one local councillor described as a potential "body blow to the island". There is no meeting of minds here. Like the swirling 100m turbine blades, this conflict is set to run and run.

Winds of change: how the turbines could affect Lewis

Species Dunlin

Numbers 3,400 pairs

Predicted effect Loss of 314 pairs through habitat destruction and disturbance (developer's statement). RSPB says 640 pairs could die

Species Golden plover

Numbers 1,800 pairs

Predicted effect Loss of 350 pairs (1 per cent of British and Irish population) through habitat loss and disturbance. RSPB claims up to 700 pairs could be lost.

Species Red-throated diver

Numbers 80 pairs

Predicted effect 100 to 250 birds killed by collision during lifetime of wind farm.

Species Merlin

Numbers 20 pairs

Predicted effect 50 individuals killed by collision during lifetime of wind farm

Species Golden eagle

Numbers five pairs

Predicted effect 50 individuals killed by collision during lifetime of wind farm

Peatland habitat The "worst-case scenario" is 1,905 hectares lost. However a study commissioned by peat expert Richard Lindsay predicts impacts up to 30 times greater.

Figures from Lewis Wind Power's environment statement and RSPB briefing statement

'If we are saving the planet, why are we talking about destroying such a precious part of it?'