Professional Engineering

In his letter (July) Dr Jones gives a correct definition of efficiency of wind turbines, but ignores the context in which the comment was made, which was in relation to the overall average system efficiency of wind turbine driven generators. Actually, the situation is much more serious than the quoted figure of 25% implies.

A recent report by Stuart Young Consulting, supported by the conservation charity the John Muir Trust, makes clear that quoting even average output gives a highly misleading impression of wind turbine generation utility. The study covered the period from November 2008 to December 2010 (the last date for which figures are available). The principal findings were that wind generation was: below 20% capacity for half the time, below 10% capacity for a third of the time, below 2.5% capacity for the equivalent of one day in 12 and below 1.25% capacity for just under one day per month. On 124 days the output fell to 20MW or below, which in relation to the installed capacity was effectively zero. Furthermore, changes in output in excess of 100MW over a five minute period were not uncommon, which could cause control difficulties.

Proponents often argue that hydro generated power will fill the gaps. But our entire pumped storage hydro capacity can provide up to 2.8 GW for only 5 hours, it then drops to 1.1GW, and finally runs out of water after 22 hours. By way of contrast, Britain’s wind turbines currently have an installed capacity of 4.7 GW onshore and 1.6 GW offshore. The report concludes “It is clear from this analysis that wind cannot be relied upon to provide any significant level of generation at any defined time in the future. There is an urgent need to re-evaluate the implications of reliance on wind for any significant proportion of our energy requirement.”

In 2010, some 2.6% of our electricity was produced by roughly 3000 wind turbines. Slightly more came from hydro generation, but on present plans any significant future increase over the next 8 years can only be met by wind generation. This implies that to meet our EU target of 20% from renewables would require something like 32000 wind turbine generators. One could argue over the numbers, so I will leave the reader to calculate approximately how many would need to be installed every day over the next 8 years to meet this target and decide whether or not this is practicable, not least for those to be installed offshore, but it can hardly be less than 10 per day. Additionally, one must seriously question the justification for an investment of the size required even to attempt to achieve this, with its concomitant massive visual impact on our countryside, the decimation of our bird population and the visual and navigational impact at sea. Domestic consumers and industry will also have to find the massive subsidies that will be paid to the generators and landlords once these turbines are installed. Nor should the cost of the massive back-up capacity nor the cost and complexity of the extensive power network required be overlooked. Many will argue this immense total will be worth paying to avoid catastrophic climate change, even if it does impoverish the UK economy.

But it has to be recognised that there has been no significant increase in annual global temperature for the past 14 years in spite of the concentration of CO₂ in the atmosphere continuing to rise unabated. Of this, the UK contributes less than 5%, of which less than 3% is due to human activity. Is the devastation of our countryside and inshore waters, at great cost and with all that that entails for global competitiveness, worth the considerable sacrifice entailed when the result would, at best, be a very small saving in the CO₂ entering the atmosphere? Is it time for a rethink on our renewables policy? Would it not be better to concentrate our money and efforts on alternative solutions, such as tidal and nuclear powered generation, even at the cost of missing the EU target, and exploit our considerable reserves of shale gas to provide a breathing space whilst these more practical and reliable sources of electrical power are developed and introduced? After all, with the present state of the Euro, how many of our partners in Europe are going to even attempt to meet the target set? And if the UK does, what material good will it do us?

Geoffrey Glover, Ferndown, Dorset

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