Custom calculators › Solar home batteries
Solar home battery calculators
A calculator for your own website that answers the three questions every battery enquiry starts with: is a battery worth it, what size, and what will it save. The visitor enters their postcode, their power bill, their panels and their roof, and gets a payback, a model from your range and the rebates they qualify for, in about a second.
We build these for battery manufacturers, distributors and energy retailers, embedded on your own site in your own branding and around your own range. The working example below runs on a brand-neutral product range. Change anything and the whole year re-runs.
Seeded from Representative market offer against the Victorian Default Offer 2026; export rate per Essential Services Commission 2025-26 minimum and prevailing market offers. Overwrite them with the numbers off your own bill. Daily supply charges are left out because the battery does not change them.
Generating 9,666 kWh a year, 1465 kWh per kWp, with 28 kWh clipped at the inverter. A west-facing array generates less in total and more of it in the evening peak, which changes what the battery is worth. Try it.
Saving, year one
$951
Bill goes from $1,224 to $273
Simple payback
8.6 yr
11.5 yr discounted
Cost after rebates
$8,103
$11,500 installed, less $3,397 in incentives
15-year net benefit
$5,928
$1,630 present value, 7.9 % return
One day, half hour by half hour
Left axis is kWh in each half hour, right axis is the battery's state of charge. Every figure above is the sum of 17,520 of these steps. The filled bands are what meets the household's demand in each half hour, and they add up to the demand line. The dashed line is total solar generation, so the gap above the orange band is what charges the battery and then exports. The solid green line is the battery's state of charge on the right axis. Switch to a cloudy day and it does not fill, which is the case an annual average cannot represent.
Solar self-consumed
72%
28 % without the battery
Demand met on site
84%
36 % without the battery
Full cycles a year
282
3,813 kWh through the battery
Throughput to year 15
50 MWh
Against a 48 MWh warranty — exceeded
Where the energy goes
Year one, 9,666 kWh generated against 7,500 kWh used from 6.6 kWp.
| Solar used in the house directly | 2,726 kWh |
| Solar stored in the battery | 4,235 kWh |
| Solar exported | 2,705 kWh |
| Solar lost to clipping and the export limit | 28 kWh |
| Battery discharged to the house | 3,813 kWh |
| Imported from the grid | 1,180 kWh |
Across the year
The bars are how this household's demand is met each month, and they add up to the demand line. The orange line is total generation at Melbourne. Where it falls below the demand line, usually mid-winter, the battery cannot be filled from solar however large it is, and that is what decides whether extra capacity is worth buying.
What size actually pays
The same simulation run at fourteen capacities, priced at $3,200 fixed plus $640 per usable kWh. Payback improves as the battery starts covering the evening, then turns as the extra capacity stops being filled. Best payback here is 14 kWh; best present value is 16 kWh. The change of slope at 14 kWh is the federal rebate tier boundary, not an artefact. Sizes under 5 kWh earn no federal rebate at all, which is why the smallest battery on the chart can cost more after rebates than the next one up.
The rebate stack
| Cheaper Home Batteries Program92 STCs at $37, from 13.5 kWh usable at 6.8 STCs/kWh, tiered above 14 kWh | $3,397 |
| Total off the purchase price | $3,397 |
Solar Victoria’s interest-free battery loan closed in May 2025. The $1,400 solar panel rebate and its matching loan continue but do not apply to batteries, so a Victorian battery gets the federal discount and nothing else.
Example Energy Storage is not a real company and the five products above are not real products. This demonstration exists to show the calculation, not to represent any manufacturer. Figures are modelled estimates from a synthesised weather year and a synthesised load profile, on representative tariffs and indicative prices. They are not a quote, a performance guarantee or a recommendation for a specific installation.
What is doing the calculating
A battery earns the difference between what a kilowatt-hour costs to import at 7 pm and what the same kilowatt-hour earns as an export at 1 pm. That difference is a property of a tariff structure and a load shape, so a model built on annual averages cannot see it at all. This one is built on the half hour.
A real time step
17,520 half-hourly steps a year, re-run for every year of the asset life and again at fourteen capacities for the sizing chart. Half-hourly is what Australian and New Zealand interval meters report, which makes it the finest step at which a result can be checked against a customer's own data. Peer-reviewed work on time resolution found hourly models over-estimate battery state of charge by up to 10 % against 5-minute resolution, and shift self-consumption volumes by 5 to 8 % on the choice of step alone.
Validated, not asserted
The solar chain runs published correlations: Erbs for the daily beam and diffuse split, Collares-Pereira and Rabl and Liu and Jordan for the half-hourly distribution, the Perez anisotropic sky for the tilted plane, Martin and Ruiz for angular reflectance, the Faiman model for module temperature and the Huld relation for module efficiency, both with the coefficient set for the panel type and the mounting. Across all 39 climate sites, from Darwin to Invercargill, it reproduces PVGIS in-plane irradiation to a mean absolute error of 1.0 % and PVGIS annual yield to 0.8 %, worst site 2.2 %. Automated tests hold it there on every build.
The whole incentive stack
The Cheaper Home Batteries discount is tiered by usable capacity, so it is not a rate times a size. Several states add a capacity payment or a virtual-power-plant payment on top, and in Western Australia and South Australia the state money is conditional on joining a VPP, which then changes how the battery is dispatched. The tool prices the stack for the postcode and shows the tier boundary in the sizing curve.
Your calculator, on your own site
The example above is the engine on a generic product range and representative tariffs. A build for your brand is the same engine with your data behind it and your styling on top, delivered as something you own rather than a page you link out to.
One line of embed code
A single script tag on your own page, in your typography, your colours and your layout. It works on WordPress, Shopify, Squarespace, Webflow, HubSpot or a hand-built site, because it is an embed rather than a plugin. If you would rather not touch your site at all, we host it on a subdomain of your domain instead.
Your product range, with the specs that matter
Usable against nominal capacity, continuous charge and discharge power, round-trip efficiency, standby draw, and the warranted retention and throughput. The last two are the ones nobody publishes and everybody needs: 25 W of standby is 220 kWh a year, and a battery that holds 13.5 kWh but only delivers 3.3 kW cannot cover a 4 kW winter evening. Sizing on energy alone misses both.
The tariffs your customers are actually on
Your own retail plans if you are a retailer, or the published plan set for the distribution zones you sell into. The Consumer Data Right energy API carries every published plan in the National Electricity Market, and we can read it live so the tool never quotes a rate that has moved.
Interval data where the customer has it
A synthesised load profile has the right shape and the right annual total. A customer's own half-hourly NMI data has their actual shape, and for a household with a pool pump, a workshop or shift work that is the largest single uncertainty in the answer. An upload path turns the tool from an estimate into something an installer can quote from.
Leads with the working attached
Optional capture on the result, delivered to whichever inbox or CRM you use. You receive the postcode, the tariff, the load, the roof, the model the tool recommended and the payback it returned, so the first call is about a specific system rather than about what a battery is.
Dealer and installer instances
One engine, many front ends. Each dealer gets the tool on their own site with their own pricing and their own lead routing, and you keep one set of product data and one set of assumptions behind all of them. Changing a spec or a price updates every instance at once.
Why this gap exists
Australia installed around 220,000 to 270,000 home batteries in 2025, roughly triple the year before, and the federal discount has since taken the program past 350,000 systems. The public calculators grew with that market and several are good. SolarQuotes offers interval-data upload. Battery IQ pulls wholesale prices, certificate rates and retail plan data through live APIs. Amber grounds its estimate in twelve months of its own customers' behaviour.
Each of those tools was built to feed its owner's funnel. SolarQuotes routes to its installer network, Amber sells its own retail plan, and Battery IQ's most sophisticated assessment sits behind an email form and a callback. None of them is a tool a battery brand can put on its own product pages.
The Clean Energy Council's approved battery list carries more than 1,000 products. Very few of those brands run a rigorous calculator of their own, which is the same pattern we already see in hot water: brands want one, and building it in-house means building a simulation engine.
The export rate is where the gap shows most. Western Australia's buyback scheme pays 10 c/kWh for exports between 3 pm and 9 pm and 2 c/kWh at every other hour. New Zealand retailers pay up to 24 c/kWh for exports in the winter morning and evening peaks. Under both, part of a battery's return comes from shifting exports rather than from self-consumption. Switch the market to New Zealand above and select the peak-export plan: the payback moves by more than two years on the same house, array and battery.
Why the array is not a side input
Start with the rule that decides several thousand dollars of the answer: the Cheaper Home Batteries Program does not cover a battery installed without solar PV. A battery that only stores grid energy is ineligible, however large it is. Nothing about a battery's own specification reveals that, so a calculator which does not ask about the array can hand a customer a rebate they will never receive.
A battery only earns on the surplus the array actually delivers, at the hours it delivers it. Two houses on the same street with the same annual generation give completely different battery answers if one has its panels on a single north face and the other has them split east and west. The split generates less over the year and more of it early and late, which flattens the midday surplus and raises the generation that already meets demand. Both effects change what a battery is worth, in opposite directions.
The panels themselves matter more than most tools admit. Modern n-type silicon has roughly half the temperature sensitivity of the older p-type fleet, which is worth several percent a year in Brisbane or Perth and almost nothing in Hobart. A roof-mounted array runs about 10 K hotter than the same modules on a ground frame. A ten-year-old array has lost about 6 % of its output. This tool asks for all three, because a battery is usually retrofitted to an array that is already up there.
Two results fall out rather than being assumed. Inverter clipping is far smaller than the nameplate ratio suggests: the very common 6.6 kWp array on a 5 kW inverter loses about 0.1 % of its output, because a hot roof-mounted array never reaches its rating. At 10 kWp on the same inverter it is 8 to 14 %, and only a DC-coupled battery can recover any of it. The other is the network export limit, which caps what leaves the property and turns spilled solar into something a battery can capture.
What we would need from you
A first build takes about three to four weeks from receiving the data. Most of that is scoping the calculation and validating it against cases you already know the answer to, rather than the front end.
Your product table
Model code, nominal and usable capacity, continuous and peak charge and discharge power, round-trip efficiency, standby consumption, warranted years, warranted retention, warranted throughput, backup capability, whether each model is AC or DC coupled, and either a price list or a price field the installer fills in. If you sell panels or inverters as well, their specifications feed the same engine.
The markets it covers
Which states or regions, and whether it needs New Zealand. Each Australian state carries a different incentive stack and a different set of tariff structures, so the states you sell into set the configuration work rather than the engine work.
Cases you can check
Two or three real installations where you know the array, the tariff, the battery and roughly what the customer's bill did. We validate against those before the tool goes live, and you get the comparison. A calculator that disagrees with your own installed base is worse than no calculator.
Want one for your battery range?
Send your model table and tell us which markets the tool needs to cover. We will scope a build against them and come back with a fixed quote.
Request a quoteThe calculator above is a demonstration. Example Energy Storage is not a real company and its five products are not real products. Figures come from a synthesised weather year and a synthesised load profile on representative tariffs and indicative prices, and are not a quote, a performance guarantee or a recommendation for a specific installation. Incentive rules are current as at September 2026 and the federal certificate rate is scheduled to step down on 1 January 2027.