Energy was last better‑than‑free: yesterday Next

Research notes

Figures are for London unless they say otherwise.

What happened

• Mon 26 Dec: London was below zero for half an hour from 03:30, min −1.6p at 03:30; average 20.1p, peak 36.8p at 18:00; all 14 regions at 0p or below; lowest −1.9p in Northern Scotland.
• Wed 28 Dec: London was below zero for half an hour from 23:30, min −2.5p at 23:30; average 22.2p, peak 35.8p at 09:00; all 14 regions at 0p or below; lowest −3.0p in Northern Scotland.
• Thu 29 Dec: London was below zero for 6 hours (longest spell 5 hours from 01:30), min −8.0p at 04:30; average 14.6p, peak 35.8p at 16:00; all 14 regions at 0p or below; lowest −9.6p in Northern Scotland.
• Fri 30 Dec: London was below zero for half an hour from 01:30, min −2.6p at 01:30; average 19.2p, peak 35.8p at 09:30; all 14 regions at 0p or below; lowest −3.1p in Northern Scotland.
• Sun 1 Jan: London was below zero for 2.5 hours (longest spell 2 hours from 04:30), min −4.9p at 03:30; average 21.8p, peak 35.8p at 16:00; all 14 regions at 0p or below; lowest −5.8p in Northern Scotland.

Likely causes

• Mon 26 Dec 2022 was the Boxing Day bank holiday, and the week between Christmas and New Year has low demand. Source: GOV.UK bank holidays. (confirmed by source for the date; demand is inference)
• Electric Insights: "5 AM on 30 December" saw "a record of 3 GW of surplus clean power produced", and on the 30th "two-thirds of the country’s electricity came from wind power alone". Sources: Electric Insights, 100% low carbon (Q4 2022), Electric Insights, Power system records (Q4 2022). (confirmed by source)
• Mon 26 Dec, 03:30 (London's lowest half-hour): wind 15.6GW (61% of supply), solar 0GW, gas 3GW (12%), imports 0.1GW, total supply 25.8GW. Over the day wind averaged 16.6GW; the 2022 average was 8.8GW (27%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
• Wed 28 Dec, 23:30 (London's lowest half-hour): wind 18.4GW (59% of supply), solar 0GW, gas 2.3GW (7%), imports 2.6GW, total supply 31GW. Over the day wind averaged 15.7GW; the 2022 average was 8.8GW (27%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
• Thu 29 Dec, 04:30 (London's lowest half-hour): wind 17.7GW (63% of supply), solar 0GW, gas 2.5GW (9%), imports 0.3GW, total supply 28GW. Over the day wind averaged 18.2GW; the 2022 average was 8.8GW (27%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
• Fri 30 Dec, 01:30 (London's lowest half-hour): wind 17.4GW (62% of supply), solar 0GW, gas 2.3GW (8%), imports 1.1GW, total supply 27.9GW. Over the day wind averaged 19.3GW; the 2022 average was 8.8GW (27%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
• Sun 1 Jan, 03:30 (London's lowest half-hour): wind 13.2GW (51% of supply), solar 0GW, gas 2.7GW (11%), imports 2.8GW, total supply 25.7GW. Over the day wind averaged 10.8GW; 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 28 Dec, Thu 29 Dec and Fri 30 Dec (18.4GW, 17.7GW and 17.4GW, against 8.8GW for the year). (inference from NESO data)
• The low came overnight on Mon 26 Dec, Wed 28 Dec, Thu 29 Dec, Fri 30 Dec and Sun 1 Jan, when demand is at its lowest (total supply as low as 25.7GW, against a 2022 average of 33.1GW). (inference)
• Mon 26 Dec was a bank holiday (Boxing Day) and Sun 1 Jan was at the weekend, when demand is lower. (inference)
• Elexon market index: Mon 26 Dec averaged £67.14/MWh with a low of −£6.00 at 05:30; Wed 28 Dec averaged £73.16/MWh with a low of −£51.51 at 03:00; Thu 29 Dec averaged £88.62/MWh with a low of −£16.70 at 02:30; Fri 30 Dec averaged £38.84/MWh with a low of −£46.76 at 05:00; Sun 1 Jan averaged £112.68/MWh with a low of −£31.60 at 03:30. Source: Elexon market index, Mon 26 Dec. (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

High. Holiday demand and published wind records for 29 and 30 Dec.

Gaps

• Elexon's system warnings feed has no entries before mid-2023, so warnings for these days couldn't be checked there.