System operator predicts de-rated capacity margin of 10.3 per cent

National Grid has raised its forecast for the capacity margin over the coming winter due to an increase in the amount of gas and biomass generation which is expected to be available.  

The system operator has predicted a de-rated capacity margin of 10.3 per cent – or 6.2GW – in its winter outlook for 2017/18 – up from a preliminary estimate of 6.2 to 8.2 per cent. The loss of load expectation is just 0.01 hours per years.

In a first for the annual report, the capacity margin has been calculated on the basis of underlying demand rather than transmission demand to reflect an increase in the amount of distributed generation on the system.

The change means distributed generation is treated as generation rather than as a reduction in demand. When calculated using the old method the de-rated capacity margin is 11.5 per cent, marking a substantial increase over the 6.6 per cent margin forecast in last year’s winter outlook.

National Grid expects 66.1GW of de-rated capacity to be available over the coming winter, having previously predicted a maximum of 64.9GW.

“In the preliminary view base case, a coal plant and a combined cycle gas turbine (CCGT) were assumed to remain operational without [capacity market] contracts,” the report states.

“These generators have now been joined by capacity from one CCGT and two biomass conversion plants plus additional capacity from an existing CCGT already considered in the base case.”

Based on market modelling, a further 2.4GW of net imports are expected to be available via interconnectors, made up of 2.1GW of imports from Continental Europe and 0.3GW of imports from Ireland.

The forecast for average cold spell peak underlying demand remains unchanged at 62.3GW. The figure includes a 900MW requirement for contingency reserve to cover the largest potential load loss.

“The forecast surplus margin for this winter is 10.3 per cent,” said National Grid director of UK system operator Phil Sheppard. “This is the additional power we expect to have available over and above what is needed to manage anticipated electricity demand.

“The margin has increased from last year which is encouraging as we enter the first main delivery year of the capacity market.

“We expect there to be sufficient gas supplies this winter and expect them to be met from a wide range of supply sources.”