Negative prices
Research notes
Figures are for London unless they say otherwise.
What happened
London down to −3.1p at 11:30 and below zero for 4.5 hours from 11:00. All regions negative, lowest −3.8p in Northern Scotland. Daily average 13.2p.
Likely causes
- Solar-led on a low-demand Saturday. Solar peaked at about 10.3GW around midday, and total transmission-connected supply bottomed at 16.6GW at 15:00. (confirmed by source: grid data) PV_Live 31 May · Elexon FUELHH 31 May 2025
- Wind was moderate rather than strong (averaging 6.4GW, rising to 9.5GW late evening), so the timing of the negative spell, late morning to mid-afternoon, points to sun plus weekend demand. (inference from grid data)
- May 2025 was a record month for solar (2.5TWh, 11.6% of UK electricity) and the UK's second-sunniest May. (confirmed by source) Carbon Brief, 4 Jun 2025
Wider context that week
- Last day of the sunniest UK spring on record (653 hours, beating 2020). Carbon Brief, 4 Jun 2025
- Same price cap and Argus context as the 24 to 25 May section. London's May average of 16.2p was the lowest month of this period.
Confidence
Medium. Grid data supports the explanation; no report found for this date.
Gaps
No news or NESO item found for 31 May specifically.