Zero and negative prices
Thu 7 Aug · Fri 8 Aug · Sat 9 Aug
Research notes
Figures are for London unless they say otherwise.
What happened
- Thu 7 Aug: touched exactly 0.0p at 14:30 but did not go below. Avg 12.1p, max 30.4p.
- Fri 8 Aug: London min -0.5p at 13:30, below zero for 1.5h from 13:00. Avg 13.7p, max 30.7p.
- Sat 9 Aug: London min -1.0p at 12:30, below zero for 3h (longest spell 2h from 12:00). Avg 10.5p, max 28.7p.
- All 14 regions at or below zero on each day. Wed 6 Aug is not in the list.
Likely causes
- The windy spell after Floris carried on. In its 4 Aug forecast the Met Office warned of "a further period of unseasonable wet and windy weather" on Thursday in the north-west, with "gusts over 50mph... possible for a time", and changeable weather in the north into the weekend with drier conditions in the south. (confirmed by source) Met Office, 4 Aug 2025
- Wind averaged 10.1GW on 7 Aug, 8.0GW on 8 Aug and 8.6GW on 9 Aug, all well above the 6.0GW summer average. (confirmed by source) Elexon FUELHH 7 to 9 Aug
- Solar was strong on the Friday and Saturday, peaking at about 11.4GW and 11.8GW at 13:30, which matches the negative prices falling around midday. Thursday was duller (about 7.8GW), which fits it only reaching zero. (confirmed by source for the figures, inference for the reading) PV_Live 7 to 9 Aug
- Sat 9 Aug had the lowest transmission demand of the entire summer: INDO fell to 13.3GW at 14:30 to 15:00. Weekend demand, mild weather and a lot of embedded solar all push that number down. (confirmed by source) INDO 9 Aug
- NESO: market "predominantly long until 15:30" on 7 Aug and "long during the daytime" on 9 Aug, when it again needed trades for downward regulation. Constraints were "predominantly in Scotland/Northern England" on 9 Aug. Balancing costs £17.38m, £19.46m and £17.97m. (confirmed by source) NESO daily balancing costs, Aug 2025
- So these three days look like the tail of the Floris weather pattern: above-average wind, joined by strong sun on the Friday and Saturday and very low Saturday demand. (inference)
Wider context that week
- The weather then flipped. Heatwave conditions were met in parts of central and eastern England from 11 to 15 Aug, wind dropped to 2.5 to 4GW, and gas output hit its summer high of 12.3GW on 13 Aug. Bloomberg ran "UK Heat Wave Cuts Wind Output, Exposing Power Supply Gaps" on 13 Aug (headline only, paywalled). Met Office August 2025 stats, Bloomberg, 13 Aug 2025, Elexon FUELHH 13 Aug
- Gas was cheap and calm: Montel gives an average NBP price of £27.26/MWh for Q3, down 3% on the year. Markets were watching the Trump and Putin meeting in Alaska on 15 Aug. Montel Q3 2025 summary, Fortune, 15 Aug 2025
- Nuclear output was down to about 3.0GW by 8 Aug. Elexon FUELHH 8 Aug
Confidence
Medium to high. The Met Office forecast and the data line up, and the blog linked in the Floris section independently names 8 and 9 Aug as surplus days, but there is no mainstream report on GB prices for these dates.
Gaps
- No news coverage of GB negative prices on 7, 8 or 9 Aug 2025.
- No Met Office article found that reports (rather than forecasts) the wind on 7 Aug.