GB Grid Stability Digest
The week on the grid — 19–25 October 2026
Issue 2026-w43
The system imbalance price peaked at £275/MWh in settlement period 32 on 2026-10-19.
Frequency left 50 ± 0.2 Hz 13 times for 5.3 minutes in total, the furthest reading 49.757 Hz at Mon 16:59 — 43 mHz beyond the band.
The system price went negative in 7 settlement periods, bottoming at −£16/MWh.
Vital signs
| This week | vs last week | |
|---|---|---|
| Inertia min / avg / max | 128.6 / 159.3 / 220.7 GVA·s | ▲ +1.0 GVA·s (min) |
| Frequency range | 49.757–50.194 Hz · 49.4 hours beyond ±0.1 Hz | ▲ +0.006 Hz (min) |
| Peak wind + solar share | 58.5% (Sun 11:46) | ▼ −12.8 pp |
| Peak demand | 22.9 GW (Thu 01:00) | ▲ +0.4 GW |
| System price max / min | £275/MWh / −£16/MWh | ▲ +£12/MWh (max) |
Event of the week
HUMR-1, a VPI Immingham LLP fossil gas unit, went out unexpectedly at Fri 16:30, taking 842 MW of its 1230 MW off the system — back after 60 minutes. REMIT gives the cause as "2026 Outage"; 4 other unplanned losses over 300 MW were reported in the week.
Balancing auctions
NESO's day-ahead auction bought £4.01m of frequency response and reserve across 7 delivery days this week.
| Avg price | vs last week | |
|---|---|---|
| Dynamic Containment Low | £4.08/MW/h | ▼ £0.85 |
| Dynamic Containment High | £2.37/MW/h | ▼ £1.04 |
| Dynamic Moderation Low | £9.20/MW/h | ▼ £1.28 |
| Dynamic Moderation High | £0.47/MW/h | ▲ £0.03 |
| Dynamic Regulation Low | £16.03/MW/h | ▼ £2.11 |
| Dynamic Regulation High | −£11.01/MW/h | ▲ £1.62 |
| Positive Quick Reserve | £4.61/MW/h | ▼ £0.75 |
| Negative Quick Reserve | £3.57/MW/h | ▼ £1.24 |
| Positive Balancing Reserve | £1.83/MW/h | ▲ £0.25 |
| Positive Slow Reserve | £1.54/MW/h | ▲ £0.19 |
Dynamic Regulation High cleared below zero: providers pay to deliver it, because absorbing energy from the grid charges their batteries for free.
Daily auction analysis →Demand flexibility
NESO called 10 Demand Flexibility Service events this week (2 turn-down and 8 turn-up) and bought 398 MWh of flexibility for £84k. That is 2% of the 26,000 MWh it asked for.
| This week | vs last week | |
|---|---|---|
| Events | 10 | ▼ 2 |
| Cost | £84k | ▼ £31k |
| Avg accepted price | £212.30/MWh | ▲ £14.11 |
| Largest provider | Infinis Limited (42% of MWh) |
Worth reading
Learn: How wind power affects grid stability
Wind turbines connect through inverters, so they don’t naturally add inertia. High wind output means cheap, clean power — and a lighter, faster-moving grid.
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Data: Elexon BMRS · NESO · Carbon Intensity API · Sheffield Solar · All issues
Free to reuse with attribution (CC BY 4.0).