Negative prices (the night the clocks went back)
Research notes
Figures are for London unless they say otherwise.
What happened
- Sun 25 Oct: London was below zero for 6 hours from 00:30, min −8.2p at 01:00; average 7.2p, peak 29.4p at 18:00; all 14 regions at 0p or below; lowest −9.9p in Northern Scotland.
Likely causes
- The clocks went back at 2am that morning (the last Sunday in October), so the night had an extra hour. Source: GOV.UK, when do the clocks change. (confirmed by source; any effect on prices is not established)
- Negative hourly prices were seen across much of north-west Europe on 24 and 25 Oct 2020 as weekly European wind output reached its highest since March. Source: S&P Global, 26 Oct 2020. (confirmed by source for Europe; the article doesn't mention Britain)
- Sun 25 Oct, 01:00 (London's lowest half-hour): wind 11.6GW (46% of supply), solar 0GW, gas 4.4GW (18%), imports 1.4GW, total supply 25.2GW. Over the day wind averaged 12GW; the 2020 average was 7.8GW (25%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
- The low came overnight on Sun 25 Oct, when demand is at its lowest. (inference)
- Sun 25 Oct was at the weekend, when demand is lower. (inference)
- Elexon market index: Sun 25 Oct averaged £28.83/MWh with a low of −£18.79 at 04:30. Source: Elexon market index, Sun 25 Oct. (confirmed by source; a short-term index, not the day-ahead auction Agile follows)
Wider context that week
- Storm Barbara (21 Oct) came before and Storm Aiden (31 Oct) after. Source: Met Office, UK storm season 2020/21.
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.
- Elexon's system warnings feed has no entries before mid-2023, so warnings for these days couldn't be checked there.