Negative prices (overnight, weekend)
Sat 12 Oct · Sun 13 Oct
Research notes
Figures are for London unless they say otherwise.
What happened
- Sat 12 Oct: London dipped to −1.1p for one half-hour at 23:30; daily average 16.8p. All 14 regions at or below zero.
- Sun 13 Oct: London below zero for 2.5 hours in the small hours (longest spell 1.5h from 02:00), min −1.1p at 03:00, then a 39.9p evening peak.
Likely causes
- A band of strong wind passed through overnight Saturday into Sunday. NESO data: wind reached 18.5GW at 21:30 on Sat and was 17.8GW (64% of total supply) at 23:30 when the price went negative. At 03:00 Sun it was 16.1GW (63%) against total supply of only 25.5GW. Source: NESO historic generation mix. Wind figures (confirmed by source); link to the negative prices (inference).
- Weekend night, so demand was at its weekly low. Total supply bottomed at 23.3GW at 03:30 Sat and 24.0GW at 05:30 Sun. Source: NESO historic generation mix. (inference)
- The wind then collapsed through Sunday: 17.7GW at midnight down to 1.2GW by 16:30, which is why Sunday evening was already pricey (39.9p) and why Monday 14 Oct spiked. Source: NESO historic generation mix. (inference)
Wider context that week
- NESO had only existed for a fortnight: it took over from National Grid ESO on 1 Oct 2024. Wikipedia: National Energy System Operator
- The Ofgem price cap had just risen to £1,717 a year for a typical household from 1 Oct. Ofgem
- The Met Office summary for the month says only that "slow-moving weather fronts" brought widespread rain to England and Wales after clear conditions on 10 and 11 Oct. Met Office October 2024 summary
Confidence
Medium. The generation data shows plainly that it was very windy at exactly the negative half-hours, on a weekend night. No news report ties these particular prices to a cause.
Gaps
Looked for a named storm, a Met Office wind warning, and any press coverage of negative day-ahead prices for 12 or 13 Oct. Found none. No named storm was active (Storm Ashley, a week later, was the season's first).