GB grid inertia — live and historical
System inertia for the Great Britain transmission system, measured in gigavolt-ampere-seconds (GVA·s), published free and updated weekly.
System inertia is the kinetic energy stored in the rotating mass of generators and motors synchronised to the grid. It is what resists a change in frequency in the first instants after a generator trips: the more inertia on the system, the slower frequency falls, and the more time automatic reserves have to respond before protection thresholds are reached.
It matters more every year because it is disappearing. Wind and solar connect through power-electronic inverters, which contribute no rotational energy, so a grid running on a high renewable share is a lighter, faster-moving grid. That is why GB inertia is now actively monitored and, when necessary, procured.
For the underlying physics — the swing equation, RoCoF, and frequency nadir — see what is grid inertia and understanding RoCoF. This page is the data.
Observed range
64.1
lowest weekly minimum (GVA·s)
127.0
highest weekly maximum (GVA·s)
3
weeks published
Weekly history
| Week | Min | Mean | Max | Coverage |
|---|---|---|---|---|
| 13–19 July 2026 | 67.8 | 82.0 | 113.5 | 17 / 168 h |
| 6–12 July 2026 | 64.1 | 82.7 | 117.1 | 17 / 168 h |
| 29 June – 5 July 2026 | 69.9 | 91.0 | 127.0 | 17 / 168 h |
All figures in GVA·s. Coverage is the portion of each 168-hour week actually sampled — a minimum drawn from partial coverage is a floor on the sampled data, not necessarily the week’s true low.
Method
Inertia is estimated from live generation by fuel type as E = H × S, where H is the inertia constant in seconds for each plant class and S is rated apparent power in GVA, summed across all synchronised generation. The GB estimate is calibrated against NESO’s published inertia outturn.
Generation data: Elexon BMRS and the Carbon Intensity API. Sampled every 15 minutes; weekly figures are the minimum, mean and maximum across the samples in each Monday–Sunday week (UTC).
Use this data
This series is free to use with attribution. The machine-readable version is at https://gridhz.com/digest/inertia-history.json (JSON, updated weekly).
Suggested citation
GridHz. GB grid inertia: weekly minimum, mean and maximum (GVA·s). Version 2026-07-20. https://gridhz.com/grid-inertia
Updated weekly alongside the GB Grid Stability Digest · live dashboard