Negative prices (overnight)
Mon 18 Sep · Tue 19 Sep · Wed 20 Sep
Research notes
Figures are for London unless they say otherwise.
What happened
- Mon 18 Sep: London was below zero for half an hour from 23:30, min −1.8p at 23:30; average 17.4p, peak 36.5p at 18:30; all 14 regions at 0p or below; lowest −2.2p in Northern Scotland.
- Tue 19 Sep: London was below zero for 1 hour (longest spell half an hour from 00:30), min −3.7p at 00:30; average 14.3p, peak 32.8p at 18:00; all 14 regions at 0p or below; lowest −4.5p in Northern Scotland.
- Wed 20 Sep: London was below zero for half an hour from 05:00, min −1.6p at 05:00; average 14.1p, peak 34.0p at 18:30; all 14 regions at 0p or below; lowest −1.9p in Northern Scotland.
Likely causes
- Mon 18 Sep, 23:30 (London's lowest half-hour): wind 16GW (60% of supply), solar 0GW, gas 2.5GW (9%), imports 1.7GW, total supply 26.6GW. Over the day wind averaged 13.3GW; the 2023 average was 9GW (29%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
- Tue 19 Sep, 00:30 (London's lowest half-hour): wind 16GW (61% of supply), solar 0GW, gas 2.8GW (11%), imports 1GW, total supply 26.2GW. Over the day wind averaged 16.2GW; the 2023 average was 9GW (29%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
- Wed 20 Sep, 05:00 (London's lowest half-hour): wind 16.3GW (60% of supply), solar 0GW, gas 2.8GW (10%), imports 1.5GW, total supply 27.1GW. Over the day wind averaged 16.2GW; the 2023 average was 9GW (29%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
- Wind was well above its yearly average at the lowest half-hour on Wed 20 Sep (16.3GW, against 9GW for the year). (inference from NESO data)
- The low came overnight on Mon 18 Sep, Tue 19 Sep and Wed 20 Sep, when demand is at its lowest. (inference)
- Elexon market index: Mon 18 Sep averaged £74.18/MWh with a low of −£3.50 at 23:30; Tue 19 Sep averaged £65.31/MWh with a low of −£27.08 at 23:30; Wed 20 Sep averaged £64.45/MWh with a low of −£23.64 at 05:00. Source: Elexon market index, Mon 18 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
Medium. The grid figures fit the prices, but no report found names a cause for 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.