Negative prices at midday as the heatwave ends
Sat 27 Jun · Sun 28 Jun
Research notes
Figures are for London unless they say otherwise.
What happened
- Sat 27 Jun: London dipped to −1.4p at 13:30, below zero for 3.5 hours from 11:00. Average 14.3p, evening peak 32.6p. Lowest regional price −1.4p in the East Midlands.
- Sun 28 Jun: London fell to −5.3p at 14:30, below zero for 6.5 hours from 09:30. Average 12.3p, evening peak 31.3p.
Likely causes
- Weekend demand and strong midsummer solar, with some wind returning. The broker on Fri 26 Jun said forecasts "pointed to cooler, windier conditions from the weekend", and described renewables as "doing the heavy lifting during daylight hours" while gas still supplied about 35% of output overall. (confirmed by source as a forecast; no outturn found) Prestige, 26 Jun 2026
- Weekend day-ahead baseload settled at £85.67/MWh, well below the £114 to £167 of the working week, "though that reflects weekend delivery rather than a directional shift". (confirmed by source) Prestige, 29 Jun 2026
- Both negative spells sit squarely in the solar hours and the evenings were still over 30p, so this was a solar surplus on otherwise expensive days, not an all-day glut like April's. Montel says Q2 had the highest solar output on record (8.0 TWh according to a reNEWS search snippet; the page itself returned 403) and that "record solar output" created "frequent low and negative wholesale pricing". (pattern is an inference; the quarterly record is confirmed by source) Montel Q2 2026
- Saturday's −1.4p floor, lowest in the East Midlands, suggests wholesale stopped at about zero that day (see 22 Apr and 4 Jun). Sunday's −5.3p, lowest in Northern Scotland, means wholesale was properly negative. (inference)
Wider context that week
- The heatwave was ending (it ran to 28 Jun), two days after England's new June record of 37.7°C on 26 Jun. Met Office recap, Wikipedia
- EDF halted further reactors on high river temperatures on 25 Jun. Prestige, 26 Jun 2026
- A US-Iran flare-up around the Strait of Hormuz inflated the risk premium during the week; both sides agreed over the weekend to halt hostilities and resume talks. Brent fell about 10% on the week to around $72/bbl. A second broker report mentions weekend missile exchanges and a cancelled negotiating round in Doha. Prestige, 29 Jun, Prestige, 30 Jun
- Monday 29 Jun was expensive again: day-ahead baseload £123.94/MWh on "a wind slump toward 4.3 GW", cooling demand and the reduced nuclear stack. Both Sizewell B units, much of Heysham and a Hartlepool unit were offline. Prestige, 30 Jun 2026
Confidence
Low to medium. The general picture (sun, weekend, some wind) is well supported, but nothing found describes either day's generation.
Gaps
- No solar or wind outturn for 27 or 28 Jun. No press coverage found.