Negative prices (the first day of the Energy Price Guarantee)
Research notes
Figures are for London unless they say otherwise.
What happened
- Sat 1 Oct: London was below zero for 3.5 hours (longest spell 3 hours from 02:30), min −8.4p at 03:30; average 19.9p, peak 38.8p at 18:30; all 14 regions at 0p or below; lowest −10.1p in Northern Scotland.
Likely causes
- Sat 1 Oct, 03:30 (London's lowest half-hour): wind 13.4GW (56% of supply), solar 0GW, gas 3.7GW (16%), imports 1.2GW, total supply 23.7GW. Over the day wind averaged 15.4GW; the 2022 average was 8.8GW (27%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
- The low came overnight on Sat 1 Oct, when demand is at its lowest (total supply as low as 23.7GW, against a 2022 average of 33.1GW). (inference)
- Sat 1 Oct was at the weekend, when demand is lower. (inference)
- Elexon market index: Sat 1 Oct averaged £121.58/MWh with a low of £13.26 at 15:00. Source: Elexon market index, Sat 1 Oct. (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: wholesale gas prices fell from £194/MWh in August "to a low of just £8/MWh in October". Source: Electric Insights, Power prices ease going into winter (Q3 2022). (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.