Negative prices (weekdays)
Mon 15 Sep · Tue 16 Sep
Research notes
Figures are for London unless they say otherwise.
What happened
- Mon 15 Sep: very cheap all day, London average 4.8p, maximum only 20.4p, two negative half-hours (low −0.5p at 22:30).
- Tue 16 Sep: below zero for 4 hours, mostly overnight (longest spell 1.5 hours from 03:30), low −0.4p. All 14 regions negative both days.
Likely causes
- A deep low crossed the country. The Met Office issued a yellow wind warning from 20:00 Sun 14 Sep to 18:00 Mon 15 Sep for most of England and Wales, with gusts of 45 to 55mph inland and 60 to 70mph on coasts and hills. (confirmed by source: Met Office, published 12 Sep)
- Elexon-metered wind jumped from 2.2GW on Sun morning to 16.7GW by Sun evening, then averaged 14.6GW on Mon (never below 11.8GW) and 13.3GW on Tue. Gas averaged 3.1GW on Mon and never exceeded 4.2GW, which is why even the Monday evening peak stayed cheap. (confirmed by source: Elexon FUELHH, 14 to 16 Sep)
- The Met Office's week-ahead blog on 16 Sep said winds would "pick up again through Tuesday evening" with another Atlantic system, and the low would keep things "blustery through midweek". (confirmed by source: Met Office week ahead, 16 Sep)
Wider context that week
- Nuclear output dropped from about 3.3GW to about 2.5GW from 15 Sep and stayed there into Oct (same Elexon query). I did not find which reactor went off. Less nuclear would normally support prices, so it makes the low prices more notable, not less. (inference)
Confidence
High. A named Met Office wind warning, plus generation data, plus the shape of the prices all agree.
Gaps
No market report for these dates. The cause of the nuclear drop on 15 Sep was not identified.