Methodology & data sources — Australia
No black box. Here is exactly how every Australian estimate is built, every assumption behind it, and where each number comes from.
The formula
- Your monthly bill becomes annual kilowatt-hours at your state's electricity rate.
- A system is sized to cover the share of that usage you choose, using your state's solar yield.
- Gross cost = system size × your installed $/W.
- The STC rebate is worked out on that system size and taken off the price, along with any other rebate you enter.
- Annual saving values the power you generate realistically: the share you use as you make it is worth your full retail rate, and the surplus you export is worth your state's feed-in tariff.
- Payback is the year your cumulative savings overtake that net cost, with power prices rising ~2.5%/yr and panels losing ~0.5%/yr over a 25-year horizon.
That is the same engine the US pages use. What changes between the two countries is not the arithmetic — it is the incentive, the export regime and who publishes the inputs.
Why exporting barely counts here
This is the single most important thing on the page. Across the states we cover, a feed-in tariff is worth 4–37% of what the same kilowatt-hour costs to buy back. So a kilowatt-hour you use as you generate it is worth several times one you sell.
AER Consumer Data Right, 294 feed-in offers across 18 retailers, as at 2026-08-24
We assume a home without a battery uses 40% of what it generates on
site and exports the rest. Each generated kilowatt-hour is therefore valued at
0.40 × retail + 0.60 × feed-in, not at the retail rate. That is a
deliberately conservative choice: it lowers every payback figure on the site, and it
is why a battery — or simply shifting your washing to the middle of the day — changes
the answer so much.
Annual savings are also capped at your annual bill. You cannot avoid buying more power than you actually buy, and we do not count export income beyond that.
The STC rebate
Australia's Small-scale Renewable Energy Scheme is a discount applied at the quote, not a credit claimed later: the installer creates the certificates and takes the money off your price. The calculation is:
certificates = floor(system kW × zone rating × deeming years)
- Zone rating — the Clean Energy Regulator's deemed figure for your postcode, from the Renewable Energy (Electricity) (Zone Ratings and Zones for Solar (Photovoltaic) Systems) Instrument 2019. We use the capital city's zone for each state, because that is where the population is; several states span more than one zone, and each state page says so.
- Deeming years — the scheme closes on 31 December 2030 and a system is deemed for the years remaining. A system installed in 2026 is deemed 5 years. This is why the rebate shrinks every January.
- Certificate price — we assume $38. Certificates trade on an open market; the Clearing House sets a fixed $40 price but runs a queue, so the traded price sits below it. Quoting the $40 ceiling would flatter every payback figure on this site, so we do not.
- The Regulator rounds down to whole certificates, and so do we.
Because the rebate depends on system size, and system size depends on your bill, rate and coverage, it is recalculated every time you touch an input. It is shown as a worked-out field rather than an editable one — it is not a number you get to choose.
What we deliberately do not model
Batteries. There is a national battery discount — the Cheaper Home Batteries Program, worth about 30% off an installed system of 5 to 100 kWh, delivered through the same certificate mechanism as the panel rebate, with only the first 50 kWh of usable capacity eligible and tiering by size since 1 May 2026. We describe it and we do not calculate it. What a battery earns depends almost entirely on the shape of a particular household's load through the day, and a state median cannot stand in for that. Publishing a battery payback derived from an assumed load curve would be a guess wearing the same clothes as our measured figures, which is the one thing this site is built not to do.
Sources: DCCEEW — Cheaper Home Batteries Program · Clean Energy Regulator — solar batteries
Where the numbers come from
Electricity rates and feed-in tariffs
Both come from the Australian Energy Regulator — Consumer Data Right, Product Reference Data — the retail plans energy companies are required to publish, which is to say the offers you could actually sign up to today, not a national average computed after the fact. Current snapshot: 129 single-rate residential offers and 294 feed-in offers from 18 retailers across the six states, as at 2026-08-23.
Why this can differ from the figure you saw elsewhere. Comparison sites usually quote a blended average that mixes single-rate and time-of-use plans, and feed-in figures that lag the market. Both pull the headline toward the middle. We publish the median of what is actually on offer today under one plan type, which in a state like South Australia lands several cents higher than a blended average — and, on feed-in tariffs, well below the numbers that were current a couple of years ago. Neither construction is dishonest; they answer different questions. Ours answers "what would I sign up to this week".
We publish the median, not the mean — one outlier plan should not move a state's headline figure. We use only single-rate plans: 211 time-of-use offers were set aside, because a time-of-use plan cannot be compared to a flat rate without knowing when a particular household actually uses power. Including them would make the figures tidier and wronger. Feed-in tariffs are treated the same way — flat rates only, time-varying ones excluded.
Recorded confidence: measured for both rates and feed-in tariffs — these are published figures, not modelled ones. The exact offer counts and the retailers sampled differ by state and are printed on each state page.
Solar yield
From the Clean Energy Regulator — postcode zone ratings for solar PV systems. An important caveat we would rather state than bury: this is a deemed radiation-based figure used to work out certificate entitlements — it is not a measured output or a simulation of your roof. It takes no account of your orientation, pitch, shading or inverter. Real output varies, and a quote based on your actual roof will be better than this number. We use it because it is the published, checkable figure that the rebate itself is calculated from, and because using one consistent basis for both the yield and the rebate keeps the two halves of the estimate honest with each other.
Confidence: modelled. Zone ratings as at 2020-01-01.
What we assume, and what we do not know
Two inputs on these pages are assumptions, not measurements, and we would rather say so plainly than dress them up:
- $1.00 per watt installed, before the rebate. A plausible current figure for a straightforward residential install. There is no authoritative published dataset of Australian install prices that we can use, so this is a starting point, not a quote — edit it to match what an installer has actually offered you.
- A $180/month power bill as the pre-filled example. We do not hold a licensed Australian household-consumption dataset, so rather than derive a bill from a figure we cannot source, we use one plausible number consistently across every Australian page. Type in your own — it is the single input that most changes the system size you are shown.
Neither figure changes the payback period much on its own: payback is driven by your rate, your sunshine and the cost per watt, not by how big your bill is.
Why Western Australia and the Northern Territory are missing
Both sit outside the National Energy Customer Framework, so their retail plans are not published through the Consumer Data Right that every rate on these pages rests on. We could estimate them. We would rather not: an estimate presented with the same confidence as a measured figure is exactly the failure this site exists to avoid. They are not covered rather than guessed, and a state only gets a page here at all if it has the measurements its calculator needs.
How the data is licensed
Every figure carries its source, date, method, confidence level and licence, and a build-time validator refuses to publish a number that is missing any of them or whose licence forbids commercial use. This is not a formality — it has already changed what we could build. OpenElectricity is the obvious Australian energy dataset and it is published CC BY-NC, which makes it unusable on a site carrying affiliate links, so it is not used here at all.
- Clean Energy Regulator zone ratings — CC BY. Attribution: Clean Energy Regulator, Commonwealth of Australia.
- AER Consumer Data Right product reference data — used under the terms of the CDR API. Attribution: Australian Energy Regulator and the Victorian Department of Energy, Environment and Climate Action.
What this is — and isn't
A fast, transparent estimate to help you decide whether solar is worth pursuing where you live. It is not a quote, a guarantee, or financial advice. Real costs depend on your roof, shading, equipment and installer. Always get itemised quotes before you buy.
Honesty policy
We use medians of real offers and label them as such. We never invent precise rebates or fake "average savings", and there is no lead-capture form — nothing you type leaves your browser, and we do not sell your details. We are not an installer and take no solar-industry funding. If a number here is wrong or out of date, that is a bug — tell us.
Data current as of 2026-08-24. Feed-in tariff figures as at 2026-08-23.