Wind power can't meet UK demand

BARRY Lees (Debate, 17 January) quotes Leuchars mean annual wind speeds for two months in summer and winter over the 58 years 1949-2007 to show the flatness of the wind speed graph. This is irrelevant to the way in which wind power is actually used.

UK public electricity demand is continuous but varies in power level throughout each day in well-established seasonal patterns but with contingency events. In order to maintain system frequency at the required mean level of 50 Hertz, demand must be met second by second via responsive generation.

This is throttle controlled either manually or automatically under National Grid supervision of thermal and hydro turbines.

Wind turbines respond only to wind speed, which varies in patterns unrelated to electricity demand. Such turbines are, therefore, connected to the grid and allowed to run freely outwith national control.

They are categorised as "embedded generation" along with process-dependent steam turbines in large industrial undertakings, such as oil refineries or chemical works, because they can't follow the second-by-second rate of demand either of the transmission grid or the distribution networks.

The output of wind turbines and other non-responsive types of renewable energy is regarded by National Grid as uncontrolled "negative demand" of which the total national demand is net. As long as it forms only a small percentage of total demand the risk to stability of the grid is low.

However, government aspirations to increase wind power to meet a major percentage of demand are (apparently unwittingly) endangering the future stability of the whole UK electricity system.

Dr Alan Shaw, Norwich