RETIRED after 40 years in the electricity supply industry, I am saddened to read that ScottishPower's Whitelee 322-megawatt project will provide enough "green energy" to power 200,000 homes. This misleading half-truth is unworthy of a reputable electric power utility whose core staff are chartered engineers with a professional commitment to objective truth.

The electricity generated by the project will, because of its entirely wind-based origin, be instantaneously unpredictable and intermittent. It can only provide the MWh amount of electricity implied above on a cumulative annual basis. Also, it will only operate at its full 322MW power rate for little more than 10per cent of the total 8760 hours in any year.

For the remainder of that time its output will range from just below full load to zero. Indeed, there will be periods of many days, particularly during still, cold, anticyclonic weather, when it will be at a complete standstill. If the claimed 200,000 homes were not permanently connected to the national grid there would be no day-to-day security of supply at all.

Yet elsewhere, among our uncomprehending senior politicians, there are those suggesting that the national grid is out of date and redundant, replaceable by forms of microgeneration which neither they nor anyone else can even specify. Does the governmental left hand know what the right hand is doing?

Furthermore, National Grid plc, in its capacity as GB system operator, will be saddled with the complex and costly task of finding at any time throughout the year fully controllable generating plant with response times rapid enough to meet every variation in wind strength.

The total conventional plant committable at any time would have to be prepared to match the 322MW full load capacity of these wind turbines and involve our limited reserves of pumped storage as well as natural-flow hydro and gas turbines which alone are f lexible enough to balance many of the vagaries of wind.

Alan Shaw, 25 Sears Close, Aylsham, Norwich.

AS A retired marine (steam) engineer (quarter Scottish), I enjoyed Robert Durward's letter (April 28). He made a good engineering case for abandoning this helter-skelter race to destroy our countryside, but he overlooked what I believe could be another serious objection to windmills.

I wonder if anybody has carried out a lifetime CO 2/carbon audit. How much carbon is emitted during the manufacture and installation of a windmill, including the massive concrete foundation and by all the machinery to transport, erect and construct the road needed to its location? And it must not be forgotten it will all happen again at the end of the windmill's life (or will it? ). All this for an inefficient machine that requires another source of power standing by for when the wind is blowing a gale or not at all, whose carbon emissions (unless nuclear) must be included in the audit.

When so-called independent commentators announce how many homes this windmill is capable of supplying they should add "when the wind is blowing at the right strength".

Keith Denison, Laga Bay, Ardnamurchan.