Prompt power prices strengthened Monday morning on low nuclear power generation output, while rising wind generation capped further potential gains, market sources said.
On the OTC market, day-ahead baseload traded up 50 pence to GBP46.50/MWh following Friday's GBP1.40 gains, while peakload power was heard 70 pence higher at GBP52.25/MWh.
But on the N2EX exchange, the day-ahead power auction outturned at GBP57.51/MWh — just over 60 pence lower than Friday's auction for Monday power.
"Day-Ahead prices have strengthened to over GBP46/MWh on the back of lower nuclear power output of 6.7 GW forcing more costly gas burn to make up the shortfall," said a market source.
Nuclear generation levels began to wane at the end of last week following the shutdown of Oldbury's final 434 MW reactor earlier in the week and planned statutory maintenance at unit 2 of EDF Energy's 1,150 MW Heysham-1 nuclear plant in Lancashire which began Thursday.
In addition, EDF Energy confirmed Monday that units 1 and 2 of its 1,191 MW Sizewell B nuclear reactor had come offline on Friday evening for unplanned maintenance.
"The automatic shutdown of the reactor took place safely and post-trip procedures operated as expected," said a company spokesman. "The fault is on the conventional side of the plant and we are currently investigating the precise cause."
Total UK nuclear power generation fell to 6.7 GW Monday morning representing 14.7% of the energy mix, down from 8.6 GW at the same time last week, according to National Grid data.
But wind power output is forecast to double from 1.4 GW (or 3.2%) at midday Monday to 2.8 GW Tuesday evening, partially offsetting lower nuclear contributions.
Peak power demand Monday is expected to reach 51.25 GW, while Tuesday's peak demand is forecast to be marginally higher 51.4 GW.
Gas-fired power output at midday was 13 GW (or 28.7% of the energy mix) while coal remained the dominant fuel source at 21.5 GW (or 47.4%).
Baseload power for delivery this weekend was heard midday at GBP43.65/MWh, while the week 11 contract remained relatively unchanged at GBP44.75/MWh.
On the near curve power prices tracked losses on the UK's NBP market which fell Monday morning as mild weather allowed greater gas storage injection, with healthy LNG flows contributing to bearish fundamentals.
Gas for April delivery traded down 0.60 p/th to 57.45 p/th, while baseload power lost 50 pence to GBP44.20/MWh midday.