Negative prices
Fri 4 Jul · Sat 5 Jul
Research notes
Figures are for London unless they say otherwise.
What happened
- Fri 4 Jul: a single half-hour at -0.5p at 15:00. Avg 13.5p, max 29.6p.
- Sat 5 Jul: London min -1.1p at 13:30, avg 7.7p, max 28.6p. Below zero for 2h (longest spell 1h from 15:00). All 14 regions at or below zero on both days.
Likely causes
- The heat broke and the wind arrived. The Met Office weekend forecast published on 3 Jul said high pressure was retreating, with low pressure moving in from the north-west; for Saturday, "Strong winds will accompany the rain, making for blustery conditions", worst in western Scotland and south-west England. (confirmed by source) Met Office weekend weather, 3 Jul 2025
- Wind averaged 8.8GW on 4 Jul (peak 13.3GW) and 11.4GW on 5 Jul (peak 13.3GW, seventh windiest day of the summer). Three days earlier it had been 3.8GW. (confirmed by source) Elexon FUELHH 4 to 5 Jul
- The two days differ. Fri 4 Jul was sunny (solar peaked at about 11.8GW at 13:30), so the brief dip below zero at 15:00 was wind plus solar on a weekday. Sat 5 Jul was cloudy and wet (solar peaked at only about 5.6GW), so that day's negative prices were almost entirely wind on low Saturday demand, with net exports reaching 5.7GW. (confirmed by source for the figures, inference for the reading) PV_Live 4 to 5 Jul, Elexon FUELHH 4 to 5 Jul
- NESO: on 5 Jul the market was "mostly long during the daytime". 4 Jul was the most expensive balancing day of all the event days at £22.97m, with constraints managed in Scotland and England throughout; 5 Jul cost £14.50m. (confirmed by source) NESO daily balancing costs, Jul 2025
Wider context that week
- This was the same week as the 1 Jul spike. London's daily average went from 22.8p on Tue 1 Jul to 7.7p on Sat 5 Jul, which shows how quickly Agile follows the weather.
- Three days later, at 12:30 on Tue 8 Jul, Britain set a solar record of just over 14GW. Drax gives it as the first time above 14GW; Solar Energy UK and NESO put it at 14,023MW. July went on to be the record month for solar share at 14.4% of generation. Drax Electric Insights Q3 2025, Solar Energy UK, NESO on solar
- 8 Jul itself did not go to zero on Agile (it is not in the data file), and wind that day was only 6.1GW on average. That supports the point that record sun alone did not push prices negative in summer 2025; it took wind. (inference) Elexon FUELHH 8 Jul
Confidence
High that the return of windy Atlantic weather caused it (forecast and data agree). No press coverage specific to GB prices on these dates.
Gaps
- No news article on negative GB prices for 4 or 5 Jul 2025.
- No day-ahead £/MWh figures found.