The main thing the report by the Renewable Energy Foundation proves is that statistics can be spun to support your case (16 December 2006, p 7).

Let us not forget the REF is a pressure group opposing onshore wind farms.
The UK government's target for average productivity for wind is 30 per cent of theoretical maximum.

"Average" means that some turbines will be below 30 per cent capacity and some above.
The year chosen by the REF gives an average capacity factor of 28.4 per cent - or to put it another way: "Wind turbines hit government targets by 95 per cent in 2005!"

Martin Ashby London, UK

Comment - by J R Etherington

This letter highlights the danger of simply decrying wind turbines because they have a low load factor (between 25% and 30% onshore average).

As long ago as 2003, Lord Sainsbury, for the DTI, told the House of  Lords that wind turbines achieve "a load factor of 30 per cent onshore and 35 per cent offshore."

So Mr Ashby is quite right - in the year which REF analysed they produced c. 95% of predicted yield.

Not bad.

What Mr Ashby fails to say and what makes all the difference, is that the capital cost of wind power, per unit of installed capacity, is a bit more than the per unit capital needed for fossil fuelled plant. Run as baseload the fossil plant will yield a load factor of 90% (or better) but wind achieves only 30% load factor at best.

Thus the capital cost per achieved megawatt hour of windpower is more than three times that of conventional generation!

This fact makes wind uneconomic and no one would build windfarms unless an unprecedentedly large subsidy were available as the CEO of E.ON UK has pointed out. The subsidy is provided by the Renewables Obligation, its market increment and the exemption of renewables from the Climate Change Levy tax.

As a result we are paying a fortune for a very small saving of CO2-emission which is why the  House of Commons Public Accounts Committee has said that  "The Renewables Obligation is currently at least four times more expensive than the other means of reducing carbon dioxide currently used in the United Kingdom......" (2005 report on Department of Trade and Industry: Renewable energy).

There is a further crucial problem. Windpower generation is not an 'all or nothing' 30% but varies continuously and unpredictably. Our German cousins, with a far greater windpower percentage than the UK have already warned of the grid control problems this will cause.