Energy was last better‑than‑free: yesterday Next

Research notes

Figures are for London unless they say otherwise.

What happened

• Wed 29 Apr: London fell to −5.2p at 15:00, below zero for 5.5 hours from 10:30. Average 12.4p, evening peak 32.1p.
• Thu 30 Apr: London fell to −7.1p at 13:30, below zero for 6.5 hours from 09:30. Average 10.6p, evening peak 36.2p.

Likely causes

• Wind and sun together on mild weekdays. For Wed 29 Apr the day-ahead baseload "settled sharply lower at 66.52 £/MWh, a 32.22 £/MWh fall on the day, on strong forecast wind and solar contribution into Wednesday", with UK temperatures about 5°C above normal and gas demand some 41 mcm/day below seasonal. (confirmed by source) Prestige, 29 Apr 2026
• For Thu 30 Apr, baseload "settled at just £53.39/MWh, down £13.13", peak "crashed to £26.50/MWh", with N2EX "clearing five hours below zero on Wednesday afternoon" as "combined wind and solar output forced thermal generation off the system". Five hours on the exchange matches the 5.5 hours Agile spent below zero on 29 Apr. (confirmed by source) Prestige, 30 Apr 2026
• On Thu 30 Apr wind was the largest source at 15.6 GW (46.5% of generation) with gas plants down to 1.9 GW. (confirmed by source) Prestige, 1 May 2026
• Peak price well below baseload price is the signature of a solar-driven day. (inference)

Wider context that week

• Geopolitics were pushing the other way. Brent went above $111/bbl and briefly hit a four-year high, a US blockade of the Strait of Hormuz "pushed a renewed risk premium across gas, power, and the wider commodity complex", and NBP day-ahead gas jumped 9.9p to 115p/therm. TTF rose 7.5% on 29 Apr to €46.85/MWh. Prestige, 29 Apr, Prestige, 30 Apr, AleaSoft, 4 May 2026
• Storage: UK at 8%, Germany at 24%, European storage below 35%. Prestige, 30 Apr, AleaSoft, 4 May
• The cheap spell ended abruptly. Day-ahead baseload for Fri 1 May jumped to £101.53/MWh as wind was forecast to fall away over the bank holiday weekend and Torness began a 27-day outage. This is the turn into an expensive May (see the May context section). Prestige, 1 May 2026
• France recorded its all-time lowest daily price that week. AleaSoft, 4 May 2026

Confidence

High for 29 Apr (exchange negative hours reported). Medium to high for 30 Apr (generation mix reported, negative hours not explicitly).

Gaps

• AleaSoft's weekly review reports no negative hourly prices for GB that week, which conflicts with the broker's "five hours below zero" and with the Agile data. AleaSoft's GB coverage is thin, so the broker and the data are more likely right.
• No solar outturn figure for either day.