GB Grid Stability Digest
The week on the grid — 28 September – 4 October 2026
Issue 2026-w40
The system imbalance price peaked at £350/MWh in settlement period 37 on 2026-09-28.
Frequency left 50 ± 0.2 Hz 10 times for 4.5 minutes in total, the furthest reading 50.230 Hz at Mon 11:59 — 30 mHz beyond the band.
Wind and solar peaked at 64% of GB generation at Wed 14:15.
Vital signs
| This week | vs last week | |
|---|---|---|
| Inertia min / avg / max | 130.5 / 166.9 / 223.2 GVA·s | ▲ +2.6 GVA·s (min) |
| Frequency range | 49.790–50.230 Hz · 46.3 hours beyond ±0.1 Hz | ▼ −0.006 Hz (min) |
| Peak wind + solar share | 64% (Wed 14:15) | ▼ −8.7 pp |
| Peak demand | 23.1 GW (Wed 01:15) | ▼ −0.1 GW |
| System price max / min | £350/MWh / £0/MWh | ▼ −£244/MWh (max) |
Event of the week
LAGA-1, a EP UK INVESTMENTS LIMITED fossil gas unit, went out unexpectedly at Wed 17:00, taking 865 MW of its 905 MW off the system — back after 90 minutes. REMIT gives the cause as "Turbine"; 4 other unplanned losses over 300 MW were reported in the week.
Balancing auctions
NESO's day-ahead auction bought £6.18m of frequency response and reserve across 7 delivery days this week.
New on GridHz: a daily analysis of this auction. After every clearing we show who set each price, how much capacity sat just above it, and, for any unit, why each offer was rejected and what it would have needed to bid.
| Avg price | |
|---|---|
| Dynamic Containment Low | £5.64/MW/h |
| Dynamic Containment High | £3.22/MW/h |
| Dynamic Moderation Low | £11.22/MW/h |
| Dynamic Moderation High | £0.86/MW/h |
| Dynamic Regulation Low | £21.72/MW/h |
| Dynamic Regulation High | −£11.09/MW/h |
| Positive Quick Reserve | £6.07/MW/h |
| Negative Quick Reserve | £3.61/MW/h |
| Positive Balancing Reserve | £4.11/MW/h |
| Positive Slow Reserve | £3.95/MW/h |
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 →Worth reading
Learn: What is grid inertia?
Inertia is the grid’s stored rotational energy — its resistance to sudden frequency change. Less spinning metal means faster frequency swings when something trips.
Read the explainer →Get this in your inbox
One email every Monday morning: the week on the GB grid, in numbers. No spam, unsubscribe any time.
Data: Elexon BMRS · NESO · Carbon Intensity API · Sheffield Solar · All issues
Free to reuse with attribution (CC BY 4.0).