Nine hours of negative prices
Research notes
Figures are for London unless they say otherwise.
What happened
London fell to −8.5p at 12:30 and was below zero for 9 hours straight from 07:00. Average 4.5p, maximum only 18.8p at 20:00. Lowest anywhere −9.5p in Northern Scotland.
Likely causes
- Wind and sun on a Saturday. "Day-ahead baseload settled at just £19.40/MWh on Friday and day-ahead peak turned negative as a weekend of strong solar and wind pushed midday system prices below zero." (confirmed by source) Prestige, 15 Jun 2026
- The GB day-ahead daily average on 13 Jun was €27.42/MWh, "its lowest price since April 12". (confirmed by source) AleaSoft, 15 Jun 2026
- Bloomberg ran "UK Power Prices Turn Negative as Renewables Set to Flood Grid" on Fri 12 Jun. A rewrite of it says wind was expected at 20 to 24 GW, over three-quarters of demand, with clear sunny conditions over England and Wales. A search snippet attributed to the same story gives "below zero for nine hours, falling as low as minus £25 per megawatt-hour, according to Epex Spot data", which matches the nine hours in the Agile data. (headline confirmed; the details are second-hand and not read at source) Bloomberg, 12 Jun 2026, Techgolly rewrite
- An installer's blog written that day describes "a bright, breezy June Saturday" and quotes the same Agile figures as the site's data (−9.5p at 12:30 and 23.2p at 20:00 in Northern Scotland), crediting Energy Stats UK. (confirmed by source; a useful cross-check on the data rather than on the cause) AMP Renewables, 13 Jun 2026
Wider context that week
- Markets sold off on Fri 12 Jun after Washington signalled no further escalation against Iran and President Trump suggested a deal could be signed that weekend. Brent fell to eight-week lows (about $87/bbl) and the Strait of Hormuz was reported reopening on Mon 15 Jun. Prestige, 12 Jun, Prestige, 15 Jun
- Octopus dates the initial US-Iran peace agreement (a memorandum of understanding) to 18 Jun. Octopus Energy blog
- Nuclear: six reactors wholly or partly offline, including both Sizewell B units and unplanned outages at Heysham and Hartlepool. Prestige, 12 Jun 2026
- EU gas storage was 43.1% on 9 Jun, the lowest for the date since 2022. Prestige, 12 Jun 2026
Confidence
High. Three independent sources agree on wind plus sun plus weekend, and one matches the nine-hour duration.
Gaps
- The broker's own report of Fri 12 Jun said "Wind is forecast to drop sharply over the weekend", which sits oddly with its Monday report of "a weekend of strong solar and wind". Saturday was probably the windy day and Sunday the drop, but no source says so.
- No NESO figures for the day. "An Atlantic storm system" appears in one search snippet, but no named storm affected the UK in June.