Negative prices (overnight)
Research notes
Figures are for London unless they say otherwise.
What happened
- Fri 27 Sep: London was below zero for 5 hours from 00:30, min −1.7p at 02:30; average 13.5p, peak 33.5p at 18:30; all 14 regions at 0p or below; lowest −2.0p in Northern Scotland.
Likely causes
- Fri 27 Sep, 02:30 (London's lowest half-hour): wind 15.8GW (63% of supply), solar 0GW, gas 3.4GW (13%), imports 0.3GW, total supply 25.2GW. Over the day wind averaged 15.8GW; the 2024 average was 9.4GW (29%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
- The low came overnight on Fri 27 Sep, when demand is at its lowest (total supply as low as 25.2GW, against a 2024 average of 32GW). (inference)
- Elexon market index: Fri 27 Sep averaged £59.84/MWh with a low of −£15.40 at 04:30. Source: Elexon market index, Fri 27 Sep. (confirmed by source; a short-term index, not the day-ahead auction Agile follows)
Wider context that week
- Nothing notable found for that week.
Confidence
Low. Neither the grid figures nor any report found clearly explain this date.
Gaps
- No news report or official write-up found that ties this date to a cause; the causes above are from the data.