Table of Contents

Scenario parameters

Everything on this page is a value you supply in a scenario configuration. NemSim does not assert any of it. It takes what you give it, dispatches accordingly, and reports the consequence.

That distinction matters. The constants in Model assumptions are the model's claims and we defend them there. The values below are the user's claims, and the committed scenarios/nem-fy2026-all-regions.json is one person's set of them: a starting point to argue with, not a reference case to cite.

For the exact field names, types and validation rules, see Scenario configuration. This page is about what the values mean and how sensitive results are to each.

Why we are not publishing a sourced cost deck

A costing deck that claims authority invites a reader to accept the output without examining the input. NemSim's whole proposition is the opposite: change a number, rerun, and see what moves.

So the committed scenario carries no citations, and none of its economic values should be treated as ours. If you need defensible numbers, bring your own. CSIRO's GenCost and AEMO's Integrated System Plan inputs are the usual Australian starting points. Then sweep them, because the point is not to find the right value but to learn which conclusions depend on it.

Cost basis

Parameter Unit What it means
costBasis.year year The real-dollar year every cost in the scenario is stated in. Purely a label: no deflator is applied, so all your inputs must already be in this year's dollars.
costBasis.realDiscountRate fraction The real discount rate used to annuitise capital. 0.07 is 7%. Real, not nominal: applying an inflation-inclusive rate to real-dollar costs double-counts inflation.

Sensitivity: high, and asymmetric. The discount rate is applied to every capital cost in the system, and capital-heavy technologies feel it hardest. Raising it favours low-capital, high-fuel-cost plant; lowering it favours renewables and storage. If you sweep one economic parameter, sweep this one. A conclusion that flips between 5% and 9% was never a conclusion about the technology.

Generation fleets

Parameter Unit What it means
nameplateCapacityMw MW Installed capacity. For Solar and Wind this scales the resource trace; for dispatchable plant it is the per-interval ceiling.
costParameters.capitalCostAudPerMw AUD/MW One-off build cost, annuitised over the technical life at the real discount rate.
costParameters.fixedOperatingCostAudPerMwYear AUD/MW/year Charged on installed capacity whether or not the plant runs.
costParameters.variableOperatingCostAudPerMwh AUD/MWh generated Charged on gross generation, including generation used to charge storage.
costParameters.fuelPriceAudPerGj AUD/GJ Multiplied by heat rate to give a fuel cost per MWh generated.
technologyProfile.heatRateGjPerMwh GJ/MWh Thermal energy consumed per MWh generated, on the same gross basis as variable operating cost. With fuel price this sets the fleet's short-run marginal cost, which is what decides merit order.
technologyProfile.technicalLifeYears years Annuitisation period for capital cost.
monthlyCapacityFactors fraction per month An energy budget rather than a capacity limit. Used by Hydro, whose output is limited by inflow.

Sensitivity: fuel price and heat rate change dispatch, not just cost. Together they set short-run marginal cost, which sets merit order. Change them enough and plant swaps position in the stack, which changes what is generated, what is curtailed and how much storage is needed, not merely what the same dispatch costs. Capital cost and fixed operating cost, by contrast, change the bill without changing a single MWh.

Storage fleets

Parameter Unit What it means
initialEnergyCapacityMwh MWh Installed storage energy. Zero means no fleet is built, but the cost and technology assumptions on the plan still govern any capacity storage sizing adds.
initialPowerCapacityMw MW Installed charge and discharge power. Must be zero exactly when energy is zero.
costParameters.powerCapitalCostAudPerMw AUD/MW Build cost scaling with power rating: inverters, connection.
costParameters.energyCapitalCostAudPerMwh AUD/MWh of capacity Build cost scaling with storage size: cells, reservoir. One-off, not annual.
costParameters.fixedOperatingCostAudPerMwYear AUD/MW/year Charged on installed power.
technologyProfile.roundTripEfficiency fraction, 0–1 Applied once, on charging. A full cycle loses 1 − efficiency of the grid energy used to charge.
technologyProfile.technicalLifeYears years Annuitisation period. Batteries and pumped hydro differ by decades here, which is most of why their levelised costs differ.

Sensitivity: these costs price the answer, they do not choose it. The sizing search never reads a cost parameter. It probes power and energy separately and ranks the probes purely on unserved energy and peak shortfall, so the MW and MWh it settles on are the same whatever these two costs are; what changes is the bill attached to them. That is the same point Limitations §5 makes: the result is a near-frontier point, not a cost-optimal one, so the power and energy costs are worth sweeping to price the shape the search chose, not to steer it.

A scenario with a zero-capacity Battery plan is how you tell NemSim "build whatever storage this needs, and price it at these economics". That is the normal way to use the sizing loop.

Storage sizing block

Parameter Unit What it means
targetUsePercentage % of demand energy The reliability standard this scenario is sized against. Defaults to the NER standard if omitted.
maximumPowerMw MW Largest Battery power the search may consider, per region.
maximumEnergyMwh MWh Largest Battery energy the search may consider, per region. Must support four hours at the power maximum.
maximumPasses count Cap on whole-system dispatch passes. Each pass re-dispatches every region for the full year, so this bounds run time.
reliabilityStandardName text A label carried through to published results.

The maxima are commercial limits you assert, not physical ones. Reaching one is a reportable outcome, not a failure: "no battery within these bounds meets the standard" is a result. It is not a proof that no battery could, which only the energyLimited outcome gives.

Interconnectors

Parameter Unit What it means
fromRegionId, toRegionId region A directed path. A reciprocal corridor is two entries.
capacityMw MW Directed transfer capacity, metered at the sending end.
capitalCostAudPerKmPerMw AUD/km/MW Build cost, scaling with both route length and capacity.
fixedOperatingCostAudPerKmPerMwYear AUD/km/MW/year Fixed operating cost on the same basis. There is no variable term.
technicalLifeYears years Annuitisation period.

Route length is not a parameter. It is derived from the endpoint regions' weather-site coordinates. Two consequences are worth knowing before you quote a transmission cost, both covered in Limitations §6: route length runs long, and declaring a corridor in both directions charges its full length twice.

Demand

Parameter Unit What it means
demandFile path The operational-demand artifact for this region. Per region, not top-level.
weatherFile path The weather artifact for this region. Also supplies the region's location.
dataCentreNameplateMw MW An additive demand component at full load factor, on top of base demand.

dataCentreNameplateMw is named for the study it was built for, but nothing about it is data-centre-specific: it is a flat, always-on load increase. Use it for any load you want to add without a shape.

Where the committed scenario's values came from

scenarios/nem-fy2026-all-regions.json uses a 7% real discount rate, Battery round-trip efficiency 0.87 over a 20-year life, pumped hydro 0.80 over 80 years, and 3,860 AUD/km/MW transmission capital cost over 50 years, among others.

None of these carry a citation, and the scenario schema has no field for one. They are plausible planning figures chosen to make a working example, and they are exactly the values you should be replacing with your own and sweeping.

Next

Edit this page