§ Mr. Altonasked the Secretary of State for Energy in the latest full year for which figures are available, what was the total over-capacity of power stations connected to the national grid including the insurance margin, as a percentage of (a) maximum peak demand and (b) average demand.
§ Mr. Norman LamontThe maximum peak demand on the CEGB system during the 1978–79 winter occurred on 19 December 1978 and was 44.1 GW. The declared net capability of all CEGB power stations in England and Wales in December 1978 was 55.8 GW: this represented a plant margin of 26.5 per cent. to cover plant breakdown, non-availability and all other operating contingencies. At the time of peak demand a total of 44.3 GW of plant (including 0.6 GW of outside sources) was delivering electricity to the grid; plant available for service at that time totalled 46.1 GW.
In calculating the size of margin required, the CEGB plan with respect to 329W expected maximum system demand. The demand for electricity varies widely from hour to hour so that a figure for average demand is of little value. However, the maximum demand on an average weekday last winter was 42.5 GW.