Price spike (at the cap)
Research notes
Figures are for London unless they say otherwise.
What happened
- Fri 17 Dec: London peaked at 35.0p at 00:00 (Agile's 35p cap), average 35.0p, lowest 35.0p at 00:00; highest anywhere 35.0p in Eastern England.
Likely causes
- Every half-hour that day was at Agile's 35p cap. (confirmed by data) See the 11 to 16 Dec 2021 event for the European gas and French nuclear context. (confirmed by source)
- Fri 17 Dec, 00:00 (London's peak): wind 2.4GW (8% of supply), solar 0GW, gas 15.6GW (52%), imports 2.9GW, total supply 29.7GW. Over the day wind averaged 1.8GW; the 2021 average was 7.1GW (22%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
- Wind was less than half its yearly average at the peak on Fri 17 Dec (2.4GW, against 7.1GW for the year), so gas made up the gap. (inference from NESO data)
- Elexon market index: Fri 17 Dec averaged £298.70/MWh with a high of £379.02 at 16:30. Source: Elexon market index, Fri 17 Dec. (confirmed by source; a short-term index, not the day-ahead auction Agile follows)
Wider context that week
- Agile was capped at 35p per kWh for new customers until 22 Jul 2022 (the version Agile launched with, AGILE-18-02-21; see
src/lib/products.mjs), so a "high" day before then is one where the evening peak reached that cap. (confirmed by data: the capped half-hours sit at exactly 35.0p)
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.