Negative prices
Sun 22 Jun · Mon 23 Jun
Research notes
Figures are for London unless they say otherwise.
What happened
- Sun 22 Jun: London min -4.9p at 14:00, avg 9.6p, max 28.8p. Below zero for 7.5h in one spell from 07:30. Lowest anywhere -5.9p (Northern Scotland). The deepest negative price in the summer's list.
- Mon 23 Jun: London min -4.2p at 13:00, avg 6.6p, max 25.6p. Below zero for 4.5h, with a spell from 03:30 in the small hours as well as around midday.
Likely causes
- Wind jumped as the first June heatwave broke. Transmission wind averaged 10.7GW on 22 Jun (peak 13.9GW) and 12.6GW on 23 Jun (peak 15.1GW, the second windiest day of the summer), after only 2.5GW on Thu 19 Jun during the heat. (confirmed by source) Elexon FUELHH 19 to 23 Jun
- The Met Office had forecast exactly that change: "Temperatures will ease from the west on Sunday as fresher air arrives from the Atlantic", with "westerly mobility" bringing cloud and rain into the following week. The previous day, Sat 21 Jun, had been the hottest of the year so far at 33.2°C. (confirmed by source) Met Office, 19 Jun 2025, ITV News on the 21 Jun record
- 22 Jun was a Sunday. Gas output averaged 3.0GW, the second lowest of the summer, and net interconnector flow was close to zero over the day with exports up to 2.2GW. (confirmed by source) Elexon FUELHH 22 Jun
- On 23 Jun at 03:30 to 04:00, when the overnight negative spell began, wind was 13.4 to 13.6GW and Britain was exporting 4.7 to 5.3GW. At 13:00 wind was 12.0GW, solar peaked at about 10.1GW at 13:30, and gas was down to 2.0GW. (confirmed by source) Elexon FUELHH 23 Jun, PV_Live 23 Jun
- NESO: market "predominantly long" on 22 Jun and "mostly long" on 23 Jun, with thermal constraints across England, Scotland and Wales. Balancing cost £13.44m and £18.07m. (confirmed by source) NESO daily balancing costs, Jun 2025
- So: strong Atlantic wind arriving on a Sunday in midsummer, with solar on top, then even more wind on the Monday including overnight when demand is lowest. (inference)
Wider context that week
- This happened while gas prices were at their highest for months. The US struck three Iranian nuclear sites on 22 Jun (Wikipedia summary). Dutch TTF gas had reached €41.9/MWh on 19 Jun, "the highest since early April", on fears for LNG shipping through the Strait of Hormuz. On 24 Jun, after the Israel and Iran ceasefire was announced, TTF opened about 10% down at €36.4. Anadolu Agency, 24 Jun 2025, Argus, 24 Jun 2025
- That is a useful point for a post: expensive gas raises Agile's evening peaks, but it makes no difference in the hours when wind and solar are setting the price. The evening maximums on these two days (28.8p and 25.6p) were ordinary. (inference)
- England had its warmest June on record and the UK its second warmest. Met Office June 2025 stats
Confidence
High that the cause was the windy breakdown of the heatwave over a weekend. The forecast, the generation data and NESO's commentary all agree. No article ties the GB price to it directly.
Gaps
- No GB-specific news story on negative prices for 22 or 23 Jun 2025 (a Mining.com.au headline about a UK heatwave turning prices negative came up in searches but I could not confirm its date, so it is not used).
- I could not find a day-ahead auction figure in £/MWh for these days from Epex or N2EX.