In a recent published letter I challenged the statement By Jeff Rice that wind power can easily provide 20% of UK electricity before its variability becomes an issue. He has asked me to explain.
Wind speeds can vary widely and change rapidly. As a result electricity generation by the turbines will at times fall far short of their maximum generating capacity in a way that poses problems for managers of the grid, who must keep conventional power stations on standby. There is however a practical limit to the extent to which this can be done.
The figure of 20% bandied about by the wind turbine industry represents the percentage of the total installed generating capacity that might be taken up by taken up by turbines. Because of wind unreliability turbines in the UK will on average produce about 28% of the output that would be obtained if they worked at full blast all the time. Hence the output of the turbines over a year is equivalent to 6% ( 28% of 20% ) of the maximum output available from the total installed capacity working full out. However, as the electricity consumed over time is about 2/3 of this maximum output, the turbines would yield about 9% of the electricity used.
In his acclaimed paper that has been awarded the Telford Gold Medal by The Institution of Civil Engineering Hugh Sharman, the principal of an international energy consultancy and broking company, argues that the UK will find it impractical to install much over 10 GW of wind generating capacity without major new storage schemes or inter-connections. This 10GW is equivalent to about 13% of our total installed generating capacity, not 20%. Application of the 28% factor leads to the conclusion that the wind turbines would contribute about 6% of the electricity used.
Mr Rice might have heard that Denmark produces a substantial proportion of energy from wind power. But the circumstances are exceptional; it exports a lot of electricity to countries with much larger power systems. Two of these countries have a large component of hydropower, which is flexible enough to balance fluctuations in wind power.
Roy Faust, High Wray Close, Sheffield S11
25 April 2008
|Wind Watch relies entirely
on User Funding