Negative prices all weekend
Sat 11 Apr · Sun 12 Apr
Research notes
Figures are for London unless they say otherwise.
What happened
- Sat 11 Apr: London averaged −2.3p across the whole day, the only day in the half-year with a negative average. Minimum −10.9p at 14:30, below zero for 18 hours (16 hours straight from midnight), maximum only 14.6p.
- Sun 12 Apr: minimum −4.2p at 01:00, below zero for 14 hours (longest spell 7 hours from 09:00), average 6.0p, with a 31.1p evening peak.
Likely causes
- Strong weekend wind and low demand: "UK day-ahead baseload settled at just £17.79/MWh on Friday, reflecting strong weekend wind and low demand". The day before, the same broker had forecast weekend wind "to lift materially above seasonal norms". (confirmed by source) Prestige, 13 Apr 2026, Prestige, 10 Apr 2026
- Warm weather cut demand further. UK temperatures were forecast about 5°C above the seasonal average that week and gas demand was running well below normal. (confirmed by source) Prestige, 14 Apr 2026
- Saturday's deepest price was at 14:30 and Sunday's long negative spell ran 09:00 to 16:00, both daylight hours, so solar was adding to the wind. Solar had set records on 6 and 7 Apr. (inference)
- AleaSoft later described 13 Jun as the GB market's "lowest price since April 12", which confirms 12 Apr as a very low day on the wholesale market. (confirmed by source) AleaSoft, 15 Jun 2026
- April as a whole: a widely repeated figure says 16.9% of midday half-hours in GB cleared below zero in Apr 2026, up from 11.3% in summer 2025. I could only find this on low-quality aggregator sites and could not trace the original, so treat it as unverified. (not confirmed) el-balad.com
Wider context that week
- US-Iran peace talks in Pakistan collapsed over the weekend and the US announced a naval blockade of the Strait of Hormuz. Markets opened sharply higher on Mon 13 Apr, with NBP gas back to about 120p/therm. Prestige, 13 Apr 2026
- The system was not slack throughout: system buy prices spiked to £215.32/MWh in the early hours of Sun 12 Apr, and by Mon 13 Apr wind had dropped to 4.9 GW (about 15% of demand) with gas at 34.5% of the mix. Prestige, 13 Apr, Prestige, 14 Apr
- TTF gas settled at €43.64/MWh on Fri 10 Apr, the lowest since 28 Feb, on the ceasefire and warmer weather. AleaSoft, 13 Apr 2026
Confidence
Medium to high. The cause is sourced, but only from one broker, and there is no GB generation data for the two days.
Gaps
- No wind or solar outturn for 11 or 12 Apr, and no press coverage found of what looks like the most negative day of the period. Bloomberg may have covered it but could not be opened.
- The broker's £17.79/MWh looks high against an Agile daily average below zero. It may be a blended weekend figure rather than Saturday alone. Not resolved.