The System Operator (National Grid) ensures that there is sufficient reserve capacity ie flexible generating plant in responsive mode, on the system at any one time in order to manage the second by second balancing of generation and demand.
The reserve capacity that needs to be made available at any given time will vary dependent upon a number of factors, including the level of uncertainty of the demand forecast, the short term variability of wind output and the largest credible generation loss on the system. As the value of reserve required in the system varies half-hourly it is not possible to indicate with a single capacity figure the change in reserve requirements resulting from increased wind penetration compared with current levels.
A study by independent energy consultants SKM commissioned to support of the Renewable Energy Strategy Consultation available at
www.berr.gov.uk/files/file46772.pdf
determined that increasing the volume of wind generation to the higher levels indicated as necessary to meet the UK’s share of the EU 2020 target for renewable energy, does not lead to a requirement to increase the installed non-renewable capacity in order to ensure sufficient reserve is available to the operator, but that a greater proportion of that non-renewable capacity will be called upon more frequently than at present to manage variations in generation and demand.
The study indicated that the maximum half hourly generation output increase required to cope with demand variability is currently around 6,000 MW and that increasing wind generation does not modify this value (ie simultaneous large changes in demand and wind output are unlikely) but makes smaller changes more likely. The average half hourly increase in non-renewable generation output to cope with demand increases only is about 985 MW. This value increases to about 1,190 MW with wind generation based on around 35 per cent. of UK electricity demand being met from renewables.