Battery Sizing Optimiser / Simulator – SolarPlus Help Centre

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The Battery Optimiser is a tool on the Design map page that tests battery sizes and dispatch strategies against a site's own consumption and solar profile — so instead of guessing a battery size, you can compare the cost, payback, and self-consumption impact of going smaller, bigger, or with the battery you've already chosen, and even generate a month-by-month peak-shaving plan.

Before you start

A consumption profile must already be built for the system on the Energy tab. The simulation form only appears once the system has one — without it, opening the Battery Optimiser shows just the manual battery selector, not the sizing tool.
(Recommended) A tariff loaded on the Energy tab. Cost, payback, and demand-saving figures are only as accurate as the tariff behind them, and Peak Shaving specifically relies on demand-period pricing to model savings.
To test the Selected Battery option, add a battery to the design first. This mode measures the specific battery you've already picked rather than a range of possible sizes.
This article covers the Battery Optimiser widget itself. Picking a specific battery brand/model is done in the Battery Selector panel of the same widget — see the separate Battery Selector help article. Longer-term dispatch settings saved against a system live on its Energy Control Profile, covered in a separate article.

Video Walkthrough

1. Open the Battery Optimiser

On a system's Design map page, select the amber battery icon in the left-hand tool column (tooltip: Battery Optimiser). This opens a panel over the map with the sizing form at the top and a battery selector list below it.

Selecting the icon again toggles the panel closed. It sits alongside the other design tools on that same toolbar (Shading & Obstructions, System Inverters, Surface Settings, and so on).
If the sizing form doesn't appear and you only see the battery selector list, the system doesn't have a consumption profile yet — build one on the Energy tab first, then reopen the widget.

2. Choose what you're testing

The Analysis Basis dropdown at the top of the form controls what the optimiser actually compares:

Recommended Size — tests a range of battery capacities around the calculated optimum and reports back an Undersize, Optimal, and Oversize option side by side, so you can see the trade-off of going smaller or bigger than what's recommended.
Selected Battery — skips the range and analyses only the battery already added to the design. The C-Rate field is disabled in this mode because the real battery's own C-rate is used automatically instead of an assumed value.

3. Set your cost assumptions

These fields drive the investment and payback figures in the results — they don't change the physical battery, just the financial modelling around it.

Battery Lifetime — the number of years used to annualise the battery's cost (default 10).
Battery Cost per kWh — the incremental cost added for every kWh of battery capacity tested (default $650/kWh).
Rebate per kWh — any battery rebate value, deducted per kWh from the cost above (default $0).
Fixed Solar Cost and Fixed Battery Cost — flat costs added on top of the per-kWh figure, regardless of the size tested (defaults $5,000 and $2,000). Fixed Solar Cost is only added to the total investment if Include Solar Capex is switched on.
C-Rate — how fast the battery can charge or discharge relative to its size (default 0.5). Ignored when Analysis Basis is set to Selected Battery, since the real battery's own rate is used instead.

4. Pick an optimisation goal

The Optimisation Mode dropdown tells the optimiser what it's trying to maximise when it picks the "Optimal" result:

Lowest Cost — the size with the lowest net cost over the battery's lifetime.
Fastest Payback — the size that pays for itself soonest.
Maximise Self-Consumption — the size that keeps the most solar on-site rather than exported.

5. Turn on Peak Shaving (optional)

Switch on Peak Shaving to have the optimiser also model reducing the site's peak grid demand, not just its energy costs. Two extra toggles appear once it's on:

Grid Charge Battery — allows the battery to top up from the grid (in addition to solar) so it has enough charge to shave the next demand peak.
Self-Consume During Peak Period — when on, the battery targets zero grid import during self-consumption (peak tariff) periods, and only enforces a fixed kW ceiling during the remaining periods. When off, the same kW ceiling is applied across every billing period instead.

Include Solar Capex is on by default. Turn it off if you only want the battery's own cost and payback isolated from the solar system's cost.

6. Run the simulation and read the results

Select Run Simulation. SolarPlus saves the current design first, then runs the analysis — a spinner shows on the button while it's working, and the results open as a panel alongside the form.

The comparison table lines up Solar Only against Undersize / Optimal (badged "best") / Oversize — or, in Selected Battery mode, just Solar Only against your Selected Battery, since there's no range to show either side of it.
Rows cover battery size, time-of-use strategy, simple payback, year-1 rate of return, renewable fraction, PV self-consumption, battery utilisation, solar-to-battery and battery-to-load ratios, investment, annualised capex, annual bill, annual savings, and net cost per year. If Peak Shaving was on, a Demand Savings row is added and the strategy row instead shows the modelled peak-shaving target range in kW.
Alongside the table, an hourly chart compares average load, solar, and battery discharge, a monthly chart shows average daily solar, and a small stats card summarises average daily load, average daily solar, peak demand, and the share of load met directly by solar.
If Peak Shaving produced month-by-month modelling, a Monthly Peak Shaving Breakdown table appears below, broken out by billing period (Peak/Shoulder/Off-Peak) per month, with demand and cost before and after, and the saving. A warning icon next to Demand After means the target kW ceiling for that period wasn't fully achievable — hover it to see what was actually achieved.
If the run only returns a solar-only snapshot (no full battery modelling — for example a quick solar-only check), you'll see a Solar Performance Snapshot instead: just the charts and daily averages, with no comparison table or Save option.

7. Apply the monthly plan to your battery

When the Monthly Peak Shaving Breakdown table is showing, select Save in its header to write the modelled plan onto the system.

The suggested kW setpoint for each month is saved onto the battery system already on the design. This needs an actual battery system saved on the design — if there isn't one (and no grid-charge plan to save either), you'll see a "No battery system found" message instead.
If the simulation also recommended a monthly grid-charging schedule, Save additionally updates (or creates) the system's Energy Control Profile grid-charge settings, charging the battery to 95–100% state of charge overnight between 00:00 and 04:00.
A success toast confirms once the setpoints are saved. From there, the values live on the battery system and energy control profile like any other saved setting — you can review or adjust them later outside this widget.

Limits & rules

The working rules behind the Battery Optimiser, for quick reference.

Access to the simulation form
No consumption profile on the system	form hidden, selector list only
Running a simulation	auto-saves the design first; cancelled if that save fails
Analysis basis
Selected Battery	C-Rate field disabled; no Undersize/Oversize columns
Recommended Size	shows Undersize / Optimal / Oversize columns
Peak Shaving
Grid Charge Battery / Self-Consume toggles	only shown once Peak Shaving is on
Self-Consume During Peak Period on	targets 0 grid import in peak periods; kW ceiling elsewhere
Self-Consume During Peak Period off	same kW ceiling enforced in every period
Results & saving
Solar-only / fast run	Solar Performance Snapshot only, no comparison table
Monthly Peak Shaving Breakdown table	only shown when month-by-month modelling is returned
Saving the monthly plan	requires a battery system already saved on the design

Cost fields don't change the design

Battery Lifetime, Battery/Solar Cost, and Rebate per kWh only feed the optimiser's financial modelling — they don't add a rebate to the quote or change any pricing elsewhere in SolarPlus. Rebates and pricing are configured separately on the Tax and Rebates and Pricing tabs.

FAQ & troubleshooting

I opened the Battery Optimiser and only see a list of batteries — where's the sizing form?

The sizing form only appears once the system has a consumption profile. Build one on the Energy tab, then reopen the Battery Optimiser — the form should now show above the battery selector list.

What's the difference between "Recommended Size" and "Selected Battery"?

Recommended Size tests a range of capacities and shows you an Undersize, Optimal, and Oversize option to compare. Selected Battery instead analyses only the specific battery already added to the design — useful once you've locked in a battery and just want to see how it performs, without SolarPlus suggesting a different size.

Why is the C-Rate field greyed out?

C-Rate is only editable when Analysis Basis is set to Recommended Size, where it's an assumption used across the tested range. In Selected Battery mode, the real battery's own C-rate is used automatically, so the field is disabled.

What do the three Optimisation Mode options actually optimise for?

Lowest Cost picks the size with the lowest net cost over the battery's lifetime. Fastest Payback picks whichever size pays for itself soonest. Maximise Self-Consumption picks the size that keeps the most solar on-site rather than exported to the grid. Whichever you choose determines which size is badged "best" in the results table.

Why don't I see Undersize/Oversize columns in my results?

Those columns only appear for a Recommended Size analysis, where a range of sizes is tested. A Selected Battery analysis only compares Solar Only against the one battery you've picked, so there's nothing to show either side of it.

I only got charts, not a comparison table or Save button. Why?

That means the run only produced a solar-only snapshot rather than full battery modelling — you'll see a Solar Performance Snapshot with just the hourly/monthly charts and daily averages. Run the full simulation from the Battery Optimiser form (with a battery size or selected battery to test) to get the comparison table, financial rows, and the option to save a monthly plan.

What do Grid Charge Battery and Self-Consume During Peak Period do?

Grid Charge Battery lets the battery top up from the grid (as well as solar) so it has enough charge to shave the next demand peak. Self-Consume During Peak Period changes how the target is applied: on, the battery aims for zero grid import specifically during self-consumption (peak) periods and only enforces a fixed kW ceiling during the rest of the day; off, the same kW ceiling applies across every billing period. Both only appear once Peak Shaving itself is switched on.

What does the warning icon next to "Demand After" mean?

It flags a month/period where the modelled kW target couldn't be fully met — for example the battery ran out of charge before the peak ended. Hover the icon to see the target you set against what was actually achieved for that period.

What happens when I select Save on the Monthly Peak Shaving Breakdown table?

It writes the modelled per-month kW setpoints onto the battery system already saved on the design, and — if a grid-charging schedule was also recommended — updates or creates the system's Energy Control Profile grid-charge settings (targeting 95–100% state of charge overnight). You'll need a battery system already saved on the design for this to work.

Where do I actually pick a battery brand or model?

That's the Battery Selector panel underneath the sizing form in the same widget (or from the Design tab directly) — it's always available regardless of whether the sizing form is showing. See the separate Battery Selector help article for details.

Do the cost fields (Battery Lifetime, Cost per kWh, Rebate) change my quote?

No — they only feed the optimiser's own financial modelling to compare sizes and strategies. They don't apply a rebate or change pricing anywhere else in SolarPlus. Rebates and pricing are set up separately on the Tax and Rebates and Pricing tabs.