Negative prices (summer bank holiday)
Research notes
Figures are for London unless they say otherwise.
What happened. London down to −1.6p at 13:30, below zero for 3 hours from 12:30, but the day still averaged 20.4p with a 42.8p evening peak.
Likely causes
- Bank holiday in England, Wales and Northern Ireland, so weekday demand was missing. Catalyst's next report refers to "the bank holiday weekend" (confirmed by source) Catalyst 1 Sep
- Decent wind and sun together: wind averaged 7.8 GW, solar peaked at 10.2 GW, and nuclear was back up to 4.9 GW. At 13:30 gas plant was down to 1.2 GW (confirmed by data) Elexon FUELHH 31 Aug, PV_Live 31 Aug
- The high average despite negative hours is the gas price: NBP was 162p on Fri 28 Aug and jumped to about 174p on Tue 1 Sep after Norwegian maintenance at Kollsnes stepped up over the weekend (confirmed by source, same Catalyst report).
Wider context that week. Ofgem had announced the Oct cap on 26 Aug. On 30 Aug US forces struck Revolutionary Guard launchers on Larak Island and Iran hit bases in Jordan; a tanker hit mines on 31 Aug; the US launched wider strikes on 1 Sep Wikipedia: September 2026 US strikes on Iran. Note that Catalyst says Heysham 1 reactor 1 "went offline 31 August for 17 days" while its 17 Aug report said the same unit came off on 17 Aug for 15 days; I could not resolve that.
Confidence. Medium to high. Bank holiday plus data is a solid explanation; nothing published discusses the day's power prices.
Gaps. No source on 31 Aug demand or prices specifically.