Negative prices (overnight)
Research notes
Figures are for London unless they say otherwise.
What happened
- Fri 21 May: London was below zero for half an hour from 03:30, min −1.1p at 03:30; average 13.3p, peak 29.4p at 18:00; all 14 regions at 0p or below; lowest −1.3p in Northern Scotland.
Likely causes
- Fri 21 May, 03:30 (London's lowest half-hour): wind 16.5GW (63% of supply), solar 0GW, gas 3.4GW (13%), imports 0.5GW, total supply 26.4GW. Over the day wind averaged 16.6GW; the 2021 average was 7.1GW (22%). 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 Fri 21 May (16.5GW, against 7.1GW for the year). (inference from NESO data)
- The low came overnight on Fri 21 May, when demand is at its lowest. (inference)
- Elexon market index: Fri 21 May averaged £56.26/MWh with a low of −£39.28 at 04:30. Source: Elexon market index, Fri 21 May. (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.
- Elexon's system warnings feed has no entries before mid-2023, so warnings for these days couldn't be checked there.