How dispatch works

Every run of ▶ Simulate or ⚙ Optimise works through a full year of the plant's operation, one 15-minute step at a time. This page is that model: the step it takes, the rule that decides what the battery does at each one, and how a single run becomes the year-by-year result on the 💹 Financials tab.

One year, in 15-minute steps

The dispatch model advances in fixed 15-minute steps through the whole year — 0.25 hours each, 35,040 steps in total. Its input series comes from one of two places: the generation CSV loaded on the 📂 Data tab, auto-upsampled to 15 minutes if it was recorded coarser; or, for a 4. Standalone BESS (grid-charged) project, a full year's calendar the application builds internally, since there's no generation profile to read. See Generation data.

At every step, generation has first claim on the battery: solar and wind output are totalled first, and the grid may only supply what that combined total can't. That holds across every rule below — the grid is always the last resort, never the first source.

Two things apply uniformly, whichever rule governs a given run: round-trip efficiency (RTE — the share of energy recovered over one full charge/discharge cycle, including auxiliary losses) and the pack's usable capacity — nameplate energy scaled by depth of discharge (DoD, the fraction usable per cycle) and state of health (SOH, the battery's remaining capacity relative to nameplate as it ages). A third property, C-rate — the battery's power-to-energy sizing ratio — caps how fast it can move that energy in or out. See The battery model for how all three combine. The battery itself starts every run at 100% state of charge.

The five dispatch rules

Exactly one rule governs a run, chosen from the project type, the Peak-Shift checkbox, the Peak tab's hour selection, and the Battery EOL basis.

Peak and off-peak (the default)

This is the rule that applies when none of the other four conditions on this page are met.

On Peak hours the battery is a deficit-filler only: it stays idle whenever generation already covers the Contracted Capacity (CC — the firm load the plant is obligated to serve), and discharges exactly the shortfall when it doesn't. It never charges on a Peak hour. On Off-Peak hours the roles flip: the battery is a surplus-absorber only. The CC is met from generation first, and the battery charges only from whatever generation is left over above that — it never discharges Off-Peak.

Generation-charged Peak-Shift

Ticking the Peak-Shift dispatch checkbox — its exact label depends on the project type, see Choosing a project type — changes the roles again. Inside the Peak window, the battery, together with any generation available at that moment, discharges to meet the CC, and anything beyond that is exported. Outside the window, generation charges the battery first and the balance is exported; there's no load obligation, and so no shortfall against the Delivery Fulfilment Ratio (DFR — the share of required energy actually delivered) outside the window at all.

An optional grid backup — used only as a worst case — can additionally top the battery up inside the Peak window, but only with whatever the window's remaining generation can't cover on its own.

The empty peak set: CC-firming

Untick every one of the 24 Peak-tab hours and the dispatch switches to CC-firming: instead of a discharge window, the CC is firmed every hour of the day. When generation meets or exceeds the CC, the CC is served from generation, the surplus charges the battery, and only what the — now full — battery can't absorb is exported. When generation falls short of the CC, the battery discharges to fill the gap, and whatever the battery itself can't cover becomes a shortfall. See An empty peak set for the exception a Standalone project makes to this.

Standalone: grid charging only

A 4. Standalone BESS (grid-charged) project has no generation to draw on, so the battery's energy comes entirely from the grid. On Peak hours it discharges to meet the CC; on Off-Peak hours it recharges from the grid, capped by both its C-rate ceiling and however much headroom the pack has left. That grid import is tracked separately from everything else, as the basis for the cost set on Grid charging.

Cycle-mode

This is the rule that applies when Battery EOL (End-of-Life) is set to In Total Cycles on the 🔋 BESS tab. Dispatch follows a fixed schedule instead: discharge, day-charge, night-charge (wind-only projects) and grid-charge hour windows, set in the ⚙ Configure Cycles & Charge/Discharge Windows… dialog — independent of whatever the Peak tab's hours are set to. See Battery end-of-life and Degradation, EOL and augmentation.

From one run to a year-by-year result

A single ▶ Simulate click doesn't just run the dispatch model once. The financial model behind both ▶ Simulate and ⚙ Optimise re-runs the whole 15-minute year — dispatch and all — once per project year, each time at that year's own degraded battery health and generation output, together with that year's DFR result. Only once every project year has been run this way is the discounted cash flow assembled from the per-year results — which is why a run reports its progress year by year rather than finishing instantly. See Your first analysis for what that run looks like end to end.

Where to go next