Open · Deterministic · Reproducible

Run the grid yourself.

GridSim is an open, deterministic simulator of the Great Britain electricity system: half-hourly chronological dispatch over real weather from 1985 to 2024, and swing-equation stability. It is validated against what the grid actually did — and every number it publishes can be regenerated from the source code and a scenario file.

Modelled 2024 gas 73.45TWh

Observed 2024 gas 72.79TWh

Deviation +0.91%

Weather record 1985–2024real

Pinned to ±0.01 TWh in the engine’s regression suite — grid-cli/tests/regression_2024.rs. Method: Validation.

Three doors

EXPLAINThe modelWhat the engine is, how dispatch and stability are computed, and — first-class — exactly what it does not do.

INTERACTIVERun itA gallery of curated reference runs, plus the exact CLI command to reproduce each one on your own machine.

NOTEBOOKInvestigationsDated, reproducible studies. Each ships its scenario, its command, its pinned outputs, and a legal path to the data.

One instrument, three views

GridSim is the third of three instruments on the GB energy system — each isolating one axis of the same question.

Cost
subsidyclock.co.uk — what the settlement costs.

Risk
gridmargin.co.uk — exposure to unreliable supply.

Dynamics
GridSim — how the system behaves, hour by hour, in real weather.

Why you can trust the numbers

Every published figure is a function of three things and nothing else — the scenario file, the data-pack checksum, and the engine’s git hash. No wall-clock, no unseeded randomness. Each quoted number is pinned by a regression test that fails CI if it drifts, so the green tick means the published numbers still regenerate.

  • Validated against reality. The 2024 fleet, run against 2024 weather, reproduces observed gas burn, imports and the generation mix within stated tolerances. See Validation.
  • Official defaults. Parameters default to NESO FES and published official assumptions — the model starts from the system operator’s own numbers.
  • Boundaries stated, not hidden. What the model cannot do is a first-class page, not a footnote.
  • Open data, open code. Engine under MIT / Apache-2.0; the GB reproduction pack under CC-BY-4.0 with full provenance.

The engine is a neutral instrument. Interpretation and argument live only in the Notebook. — About this project.