Negative prices (overnight, weekend)
Research notes
Figures are for London unless they say otherwise.
What happened
- Sat 25 Mar: London was below zero for half an hour from 05:00, min −0.3p at 05:00; average 18.2p, peak 35.8p at 16:30; all 14 regions at 0p or below; lowest −0.4p in Northern Scotland.
Likely causes
- Sat 25 Mar, 05:00 (London's lowest half-hour): wind 15.7GW (59% of supply), solar 0GW, gas 3.3GW (13%), imports 1.9GW, total supply 26.4GW. Over the day wind averaged 11.3GW; the 2023 average was 9GW (29%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
- The low came overnight on Sat 25 Mar, when demand is at its lowest. (inference)
- Sat 25 Mar was at the weekend, when demand is lower. (inference)
- Elexon market index: Sat 25 Mar averaged £43.36/MWh with a low of −£27.27 at 04:30. Source: Elexon market index, Sat 25 Mar. (confirmed by source; a short-term index, not the day-ahead auction Agile follows)
Wider context that week
- The Energy Price Guarantee began on 1 Oct 2022, setting household electricity unit rates at 34.0p/kWh. Source: Solar Power Portal, 2022. Octopus applied it to Agile by charging 34p for any half-hour priced 34p to 52p before VAT and taking 17p off anything above, which is why so many half-hours from then to 30 Jun 2023 sit at exactly 35.8p (34p with VAT) and the highest at 82.1p. (confirmed by data in the site's store; see
src/lib/events.mjs) - Electric Insights: output from all fossil fuels fell below 4GW for the first time on 24 Mar 2023, the day before. Source: Electric Insights, Power system records (Q1 2023). (confirmed by source)
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.