GB Grid Stability Digest
The week on the grid — 14–20 September 2026
Issue 2026-w38
The system price went negative in 53 settlement periods, bottoming at −£50/MWh.
The system imbalance price peaked at £275/MWh in settlement period 35 on 2026-09-16.
Frequency left 50 ± 0.2 Hz 15 times for 7 minutes in total, the furthest reading 49.755 Hz at Thu 04:13 — 45 mHz beyond the band.
Vital signs
| This week | vs last week | |
|---|---|---|
| Inertia min / avg / max | 124.9 / 147.2 / 196.7 GVA·s | ▲ +1.2 GVA·s (min) |
| Frequency range | 49.755–50.219 Hz · 49.9 hours beyond ±0.1 Hz | ▲ +0.011 Hz (min) |
| Peak wind + solar share | 77.5% (Sun 13:15) | ▲ +6.9 pp |
| Peak demand | 22.9 GW (Fri 01:15) | ▼ −2.2 GW |
| System price max / min | £275/MWh / −£50/MWh | ▼ −£2/MWh (max) |
Event of the week
RYHPS-1, a VPI Power Limited fossil gas unit, went out unexpectedly at Sat 01:00, taking 715 MW off the system — back after 165 hours. REMIT gives the cause as "Planned Outage"; 4 other unplanned losses over 300 MW were reported in the week.
Learn: The UK electricity market, explained
Every half hour, the system settles at a single imbalance price. That price is the clearest signal of how tight — or oversupplied — the grid is.
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Data: Elexon BMRS · NESO · Carbon Intensity API · Sheffield Solar · All issues
Free to reuse with attribution (CC BY 4.0).