OCGT reliance emerges as UK electricity system feels the strain

The UK is becoming increasingly reliant on flexible but expensive open-cycle gas turbine (OCGT) power plants to avert insufficient electricity supply margins when its power system comes under duress, latest generation data show.

Transmission system operator (TSO) National Grid issued its first system warning of the winter on Saturday 11 February. At its peak on the day, OCGT power plant was generating at 711MW – more than twice the previous high recorded this winter, and the highest level of OCGT generation since at least the start of 2011.

The figure underlines the increasing importance of flexible OCGT plant to the UK’s electricity supply going forwards, when an increased penetration of intermittent renewable generation will need to be backed up by more dispatchable capacity.

Saturday’s system warning was issued after “a chunk of generation” was unexpectedly lost from the system, according to a TSO spokesman, which coincided with a gradual loss of wind power generation.

The warning read: “There is a risk of widespread serious disturbance to the whole or part of the transmission system,” citing “significant generation shortfalls” as the reason.

The spokesman was unable to confirm which plants had gone offline, but generation data show power production from combined-cycle gas turbines (CCGTs) fell by 550MW at 10:00 hours London time, 30 minutes before the initial system warning was posted.

Prior to the warning being posted, output from dispatchable pumped storage generation and OCGTs had been turned up to meet soaring demand amid freezing temperatures, while the 1.0GW BritNed interconnector switched from exporting to importing power.

The loss of the CCGT output coincided with a further spike in pumped storage production, the ramping-up of BritNed to import at full 1.0GW capacity, and output from OCGTs peaking at 711MW.

Trend

A trend has emerged in recent months among the UK’s Big Six energy suppliers for converting gas-fired plant to operate more flexibly, so taking advantage of higher rates on the Peakload profile and the balancing market.

Saturday’s cash-out high – the amount paid by National Grid to buy power to balance the system – peaked at £246 (€293)/MWh. By comparison, peak cash-out levels throughout January averaged £95/MWh.

The Weekend Baseload contract had expired on Friday 10 February at £52.50/MWh.

Last month utility SSE said it would remove 1.45GW of gas-fired capacity from the grid in March until an unknown date in 2013 to increase its flexibility, while both E.ON and Centrica have converted gas-fired plants to more flexible models (see EDEM 31 January 2012).

During the previous week, the UK system was relatively stretched on 6-7 February, resulting in a £9.75/MWh cumulative gain on Day-ahead Baseload. On this occasion the cash-out price peaked at £122/MWh.

This was enough to trigger two major spikes on pumped storage generation, while the BritNed cable switched to import power, but virtually no OCGT generation was called upon, indicating that higher price signals – as seen on Saturday – are required to incentives gas-burn through OCGTs.

Last year, SSE published a wide ranging study looking at means of encouraging investment in the UK power generation sector.

“Potential shortfalls in terms of capacity will occur at peak times, caused by sudden or unexpected changes in wind velocity,” it said, citing the government’s electricity market reform consultation.

It then added: “If this were the problem, the solution would be flexible ‘peaking plant’, for example, OCGT.” JS