Slightly negative at midday, record zero-carbon share
Research notes
Figures are for London unless they say otherwise.
What happened
London dipped to −1.4p at 13:30 and was below zero for 4 hours from 11:30. Average 13.9p, evening peak 32.0p. The lowest regional price was also −1.4p, in the East Midlands.
Likely causes
- NESO recorded two records that day: solar hit 14.8 GW between 12:30 and 13:00, and the grid ran at a record 98.8% zero-carbon between 15:30 and 16:00 (previous record 97.7% on 1 Apr 2025). At that moment the mix was wind 50.1%, nuclear 34.4%, biomass 9.8%, solar 2.2%, hydro 1.5% and gas just 1.2%, a record low for gas. (confirmed by source) NESO, 24 Apr 2026, pv magazine, 24 Apr 2026
- The day before, renewables had met more than 58% of demand and pushed midday system sell prices to −£83.99/MWh. (confirmed by source) Prestige, 22 Apr 2026
- A minimum of exactly −1.4p, lowest in the East Midlands rather than Northern Scotland, suggests the wholesale price bottomed at about zero rather than below it, with the post-1 Apr Agile reduction taking the retail price just under zero. The same −1.4p floor appears on 4 Jun and 27 Jun. On properly negative days Northern Scotland is always lowest, because its multiplier is largest. (inference, supported by the 4 Jun wholesale figure in that section)
Wider context that week
- The next day, Thu 23 Apr, solar went above 15 GW for the first time (NESO: 15.4 GW at 12:30 to 13:00; Montel: 15.42 GW). Agile did not go negative that day: day-ahead baseload for 23 Apr was £94.00/MWh as wind fell to about 7 GW. NESO, Prestige, 23 Apr 2026
- Washington extended the US-Iran ceasefire indefinitely overnight on 21 to 22 Apr, but the naval blockade stayed and Iran seized vessels in the Strait of Hormuz. Brent was back near $99/bbl and TTF rose 16% over the week. Prestige, 22 Apr, AleaSoft, 27 Apr 2026
- UK gas storage was nearly empty going into summer: Rough at 0%, Hornsea at 13%. Prestige, 22 Apr 2026
Confidence
High. NESO records on the day, at the right times.
Gaps
- No day-ahead hourly prices for 22 Apr to confirm the "wholesale stopped at zero" reading.