Price spike, Agile hits its 100p cap (the December “dunkelflaute”)
Wed 11 Dec · Thu 12 Dec · Fri 13 Dec
Research notes
Figures are for London unless they say otherwise.
What happened
- The most expensive days of the quarter. Thu 12 Dec: London hit the 100p cap at 16:00 and averaged 49.7p across the whole day, more than double the month's 20.7p average.
- Wed 11 Dec: London max 89.9p, average 39.1p, and the cap was already reached in South Western England. Fri 13 Dec: max 67.7p, average 31.5p.
Likely causes
- Wind fell to almost nothing for three days. Drax Electric Insights: around 12 Dec wind dropped "to 6% of total supply" and gas power stations ramped up to their highest output ever recorded, supplying more than 73% of Britain's electricity "and sending power prices soaring". Source: Drax Electric Insights Q4 2024. (confirmed by source)
- NESO data backs both numbers. Wind averaged 3.4GW, 2.1GW and 3.1GW on the three days (5% of supply on the 12th). Gas peaked at 27.9GW at 08:00 on 12 Dec, the highest half-hour of the quarter, and reached 72.8% of total supply (73.5% if imports and storage are left out) at about 06:30 to 07:00. Source: NESO historic generation mix. (confirmed by source)
- Bloomberg, 10 Dec: a "dearth of windy days" pushed the UK day-ahead price to £175.05/MWh for delivery on Wed 11 Dec (Epex Spot), the highest since Jan 2023, with contracts in Italy, Switzerland and the Netherlands also at their highest since at least Jan 2023. Source: Bloomberg, 10 Dec. (confirmed by source, from the headline and search summary; article paywalled). Thursday's auction must have cleared higher still given Agile's figures, but I found no published number for it. (inference)
- Fortune, 12 Dec: at 14:00 that Thursday the UK was getting 5.9% of its electricity from wind against an annual average of 31.8%. Source: Fortune, 12 Dec. (confirmed by source)
- Imports could not fill the gap because the neighbours were short too. Drax: on the 12th "imports from abroad fell by half relative to the surrounding days". Germany's day-ahead price passed €900/MWh for 17:00 to 18:00 on 12 Dec, its highest in about 18 years. Sources: Drax Electric Insights Q4 2024, Bundesnetzagentur, Fortune. (confirmed by source)
- High midwinter demand on working days. NESO total supply reached 45.4GW at 17:00 on 11 Dec, the highest of any event day this quarter (the November spell peaked near 40.8GW). Source: NESO historic generation mix. Figure (confirmed by source); its role in the price (inference).
- Biomass and run-of-river hydro raised output by 40% and 60% on 12 Dec compared with the weekends either side, which shows how hard everything dispatchable was being pulled on. Source: Drax Electric Insights Q4 2024. (confirmed by source)
- The Elexon Market Index Price peaked at £309/MWh on the 11th and £370/MWh on the 12th, both in the 16:00 to 17:00 hour, and averaged £197/MWh across the 12th. Source: Elexon market index, 12 Dec. (confirmed by source)
Sources conflict
- Drax says NESO issued a capacity market notice on 12 Dec. Elexon's system warnings feed shows none between 10 and 14 Dec, and New Civil Engineer counted the 8 Jan 2025 notice as the winter's third (the others being 14 Oct and 3 Dec). Treat "a capacity market notice was issued on 12 Dec" as unverified and probably wrong. Elexon feed, 10 to 14 Dec, New Civil Engineer, 9 Jan 2025
- Drax describes "a long cold snap" that winter, while the Met Office says December 2024 was the UK's fifth warmest December on record. Carbon Brief: Met Office review of 2024. I found no temperature source for 11 to 13 Dec specifically, so do not call these days cold without checking.
Wider context that week
- Norway: the same lull sent southern Norway's price to its highest since 2009 on Thu 12 Dec. Energy minister Terje Aasland called it "an absolutely shit situation", and both governing parties talked of scrapping the Denmark interconnector, with the junior partner wanting to renegotiate the links to the UK and Germany. Brussels Signal, Watt-Logic
- Fri 13 Dec: the government published its Clean Power 2030 Action Plan, in the same week gas set a record for GB generation. GOV.UK, Carbon Brief analysis
- Two days later wind set an all-time record (see next section).
Confidence
High for the cause (low wind across north-west Europe, record gas burn, scarce imports). Low for any specific GB day-ahead auction figure for 12 Dec, because none was found.
Gaps
No free source for the 12 Dec GB day-ahead auction result (N2EX or Epex). No Met Office account of the weather pattern or temperatures on these three days. No Octopus statement about Agile hitting the cap.