Negative prices
Thu 2 Jul · Sat 4 Jul
Research notes
Figures are for London unless they say otherwise.
What happened. Thu 2 Jul: London down to −4.4p at 12:00, below zero for 8 hours from 08:00, average 7.8p. Sat 4 Jul: down to −5.2p at 13:30, below zero for 8.5 hours, average 9.1p. All 14 regions went to zero or below on both days.
Likely causes
- 2 Jul was the windiest day for weeks and very sunny with it. Transmission wind averaged 11.9 GW (it had been 2.6 GW on 30 Jun and 3.6 GW on 1 Jul) and solar peaked near 15.0 GW. At 12:00 wind was 13.2 GW, solar 14.5 GW, gas plant was down to 3.5 GW and Britain was exporting about 4 GW over the interconnectors (confirmed by data) Elexon FUELHH 2 Jul, PV_Live 2 Jul
- For 4 Jul, Catalyst's 3 Jul report forecast wind "toward 13.5 GW" and solar "toward 10 GW", with 52% of periods oversupplied; its 6 Jul report shows Friday's day-ahead baseload for the weekend at £52.57/MWh, down from £89.97 (confirmed by source) Catalyst 3 Jul, Catalyst 6 Jul
- On 4 Jul wind averaged 10.8 GW and solar peaked at 11.1 GW; at 13:30 gas plant was at 2.3 GW (confirmed by data) Elexon FUELHH 4 Jul
- 4 Jul was a Saturday, so demand was low. 2 Jul was an ordinary Thursday, which makes it the more unusual of the two: the surplus was big enough to go negative on a working day (inference).
Wider context that week. Gas was at its cheapest of the period (NBP about 104 to 107p), recovering from a late-Jun low after the 17 Jun US–Iran memorandum. The new Ofgem cap period began on 1 Jul. Catalyst's weekly report calls wind "persistently weak" for the week as a whole, which fits the data: 2 Jul and 4 Jul were windy exceptions between calm days Catalyst weekly, 29 Jun to 3 Jul. A heatwave began on 4 Jul and ran to 26 Jul Wikipedia: 2026 UK heatwaves.
Confidence. High for 4 Jul (forecast, price and data agree). High for 2 Jul on the data, but no article discusses that day.
Gaps. No news story, NESO post or Octopus post found about either day. No Catalyst daily exists for 1 or 2 Jul.