Negative prices (overnight)
Research notes
Figures are for London unless they say otherwise.
What happened
- Wed 4 Jan: London was below zero for 1 hour (longest spell half an hour from 02:30), min −2.1p at 03:30; average 23.0p, peak 35.8p at 16:00; all 14 regions at 0p or below; lowest −2.5p in Northern Scotland.
Likely causes
- Wed 4 Jan, 03:30 (London's lowest half-hour): wind 18.7GW (65% of supply), solar 0GW, gas 2.8GW (10%), imports 0.7GW, total supply 29GW. Over the day wind averaged 18.4GW; 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 4 Jan (18.7GW, against 9GW for the year). (inference from NESO data)
- The low came overnight on Wed 4 Jan, when demand is at its lowest. (inference)
- Elexon market index: Wed 4 Jan averaged £73.61/MWh with a low of −£49.75 at 04:00. Source: Elexon market index, Wed 4 Jan. (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)
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.