NemSim
NemSim is an hourly grid dispatch model for Australia's National Electricity Market.
You describe a set of regions, each with its demand, its generation assets and its storage, and NemSim dispatches them hour by hour across a modelled year. Where the reliability standard you declared is not met, it grows storage until either the standard is met or the search reports what stopped it. The result is a set of technical and economic figures: what was generated, what was curtailed, what was left unserved, how much storage the system needed, and what the whole thing costs per MWh served.
The model is deterministic. The same inputs at the same commit produce identical results, every
modelled value to the last decimal place, and every published result carries the SHA-256 of the
exact input bytes it was built from. Dispatch artifacts are not quite byte-identical across reruns,
because each run stamps a fresh runId, which identifies the run rather than describing its
contents.
That is the property the rest of this site is built around: if a number moves, something you changed moved it.
Where to start
| If you want to… | Go to |
|---|---|
| Install it and run your first scenario | Guide |
| Understand what the model actually does | Concepts |
| Know what it assumes, and where it will mislead you | Assumptions |
| Design a study, or drive it with an LLM | Exploring |
| Look up a type, a field, or a published JSON schema | API reference |
What it is for
The published work so far uses NemSim for one question: what happens to system cost and reliability as large new loads are added to the grid, and at what point does new storage become necessary. The published study frames those loads as data centres, but any load increase behaves the same way. You can see the results on the results site.
That is one slice of a much larger space. Because the model is deterministic and every assumption is either a scenario input or a documented constant, the same framework answers questions it was never specifically built for:
- Generation mix. Replace coal with wind, or wind with solar, and read the storage and curtailment consequences rather than guessing at them.
- Economics. Vary the discount rate, capital costs, fuel prices or technical lives and watch which conclusions survive and which were artefacts of one cost assumption.
- Reliability. Ask what a stricter or looser standard costs, in storage and in dollars.
- Sensitivity analysis. Sweep any single input across a range and publish every run with its provenance, so the shape of the response is inspectable rather than asserted.
Exploring the scenario space covers how to design those studies, including how to hand the machine-readable schemas to an LLM and have it generate sweeps for you.
What it is not
NemSim is a system-planning model, not a market simulator and not a forecast.
- It does not model bidding, prices, settlement, or any market behaviour. Generation is dispatched in merit order by short-run marginal cost.
- The cost it reports is the cost of building and running the system, not a retail bill.
- It models a single year against a single weather year, with no stochastic draws, so it reports a realised outcome rather than an expectation over a distribution.
Those are load-bearing limitations, not disclaimers. Read Limitations before you quote a number from it.
Project status
NemSim is being built in public, one validated layer at a time. The results site shows the current state of that work, and the repository carries the model, the CLI that produces the artifacts, and the committed inputs those artifacts were built from.