Negative prices
Research notes
Figures are for London unless they say otherwise.
What happened
- London min -1.1p at 14:30, avg 9.1p, max 31.9p at 18:30. Below zero for 2h (longest spell 1.5h from 14:00). All 14 regions at or below zero.
Likely causes
- A Saturday with wind averaging 11.5GW (fifth windiest day of the summer, peak 13.0GW) and solar peaking at about 11.7GW at 13:30. Both were high at the same time in the early afternoon. (confirmed by source) Elexon FUELHH 28 Jun, PV_Live 28 Jun
- Britain was a net exporter over the day (average 1.6GW of exports, up to 4.1GW). Transmission demand fell to 15.7GW at 14:00 to 14:30. (confirmed by source) Elexon FUELHH 28 Jun, INDO 28 Jun
- NESO: the market was "long for most of the day" apart from the very early morning and 17:30 to 20:00. Constraints were being managed in southern England as well as Scotland and northern England. Balancing cost £18.78m. (confirmed by source) NESO daily balancing costs, Jun 2025
- Wind plus strong solar on a weekend afternoon. (inference)
Wider context that week
- The second June heatwave was building. Two days later, Mon 30 Jun, the UK reached 33°C and NESO recorded "a high volume of trades... to help meet demand and reserve requirements during a period where the system was very constrained". That leads into the 1 Jul spike below. ITV News, 30 Jun 2025, NESO daily balancing costs, Jun 2025
- Gas had fallen back after the 24 Jun ceasefire (see the previous section).
Confidence
Medium to high. The data is clear; no news report or Met Office article specific to the day was found.
Gaps
- No Met Office article found describing the wind on 28 Jun itself.
- No press coverage of GB prices that day.