Energy was last better‑than‑free: yesterday Next

Research notes

Figures are for London unless they say otherwise.

What happened

• Wed 10 Apr: London was below zero for half an hour from 23:30, min −0.2p at 23:30; average 11.7p, peak 29.5p at 18:00; all 14 regions at 0p or below; lowest −0.2p in Northern Scotland.
• Thu 11 Apr: London was below zero for 3 hours from 00:00, min −2.1p at 01:00; average 10.7p, peak 29.2p at 17:30; all 14 regions at 0p or below; lowest −2.5p in Northern Scotland.
• Fri 12 Apr: London was below zero for 1.5 hours (longest spell 1 hour from 15:00), min −1.5p at 13:30; average 7.1p, peak 25.2p at 18:00; all 14 regions at 0p or below; lowest −1.8p in Northern Scotland.
• Sat 13 Apr: London was below zero for 6 hours (longest spell 5.5 hours from 10:30), min −8.4p at 14:00; average 4.2p, peak 19.5p at 18:30; all 14 regions at 0p or below; lowest −10.1p in Northern Scotland.
• Sun 14 Apr: London was below zero for 7 hours (longest spell 1.5 hours from 00:00), min −3.9p at 13:30; average 5.1p, peak 29.9p at 18:00; all 14 regions at 0p or below; lowest −4.7p in Northern Scotland.

Likely causes

• Wed 10 Apr, 23:30 (London's lowest half-hour): wind 18.8GW (62% of supply), solar 0GW, gas 2.6GW (9%), imports 1.1GW, total supply 30.2GW. Over the day wind averaged 15.1GW; the 2024 average was 9.4GW (29%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
• Thu 11 Apr, 01:00 (London's lowest half-hour): wind 18.5GW (64% of supply), solar 0GW, gas 2.5GW (9%), imports 0.5GW, total supply 29.1GW. Over the day wind averaged 14.6GW; the 2024 average was 9.4GW (29%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
• Fri 12 Apr, 13:30 (London's lowest half-hour): wind 15.5GW (42% of supply), solar 7.8GW, gas 1.1GW (3%), imports 4.3GW, total supply 37.1GW. Over the day wind averaged 15.6GW; the 2024 average was 9.4GW (29%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
• Sat 13 Apr, 14:00 (London's lowest half-hour): wind 15.4GW (46% of supply), solar 7.1GW, gas 1.5GW (4%), imports 2.8GW, total supply 33.8GW. Over the day wind averaged 14.5GW; the 2024 average was 9.4GW (29%). Source: NESO historic generation mix. (figures confirmed by source; link to prices is inference)
• Sun 14 Apr, 13:30 (London's lowest half-hour): wind 10.3GW (31% of supply), solar 8.4GW, gas 1.5GW (4%), imports 5.4GW, total supply 32.9GW. Over the day wind averaged 12.2GW; the 2024 average was 9.4GW (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 10 Apr and Thu 11 Apr (18.8GW and 18.5GW, against 9.4GW for the year). (inference from NESO data)
• The low came around midday on Fri 12 Apr, Sat 13 Apr and Sun 14 Apr, with solar at 7.8GW, 7.1GW and 8.4GW. (inference from NESO data)
• The low came overnight on Wed 10 Apr and Thu 11 Apr, when demand is at its lowest. (inference)
• Sat 13 Apr and Sun 14 Apr were at the weekend, when demand is lower. (inference)
• Elexon market index: Wed 10 Apr averaged £49.31/MWh with a low of £0.21 at 23:30; Thu 11 Apr averaged £47.76/MWh with a low of −£3.30 at 02:30; Fri 12 Apr averaged £19.39/MWh with a low of −£5.61 at 12:30; Sat 13 Apr averaged £6.75/MWh with a low of −£33.02 at 14:30; Sun 14 Apr averaged £7.45/MWh with a low of −£48.78 at 14:30. Source: Elexon market index, Wed 10 Apr. (confirmed by source; a short-term index, not the day-ahead auction Agile follows)

Wider context that week

• Storm Kathleen (Sat 6 Apr to Sun 7 Apr) was within a few days of it. Source: Met Office, UK storm season 2023/24. (confirmed by source; its effect on these prices is inference)

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.