Solar payback period: how it is actually calculated
Payback is the number of years until your accumulated savings equal what the system cost you after rebates. For most Australian households a solar-only system lands between five and nine years. The figure is highly sensitive to three assumptions that are rarely stated: the price you actually pay per system, how much generation you use on site, and whether electricity prices are assumed to rise.
The calculation, in plain terms
Payback is simple arithmetic on top of one hard estimate. The arithmetic is:
To get the annual saving you need to know how much the system generates, how much of that you use yourself rather than export, what you pay per unit, and what you are paid for the units you export. Get any of those wrong and the payback figure moves by years, not months.
Why two quotes give wildly different paybacks
1. The price they used
The same 6.6kW array can be quoted anywhere across a several-thousand-dollar range. A payback calculated on the cheapest end of the market and presented next to a mid-market quote is not comparable. When you see a payback figure, ask which price it used.
2. The self-consumption assumption
This is the big one, and it is almost never stated. If a calculator assumes you use 50 per cent of your generation on site and you actually use 25 per cent, its saving figure is roughly a third too high, because the other units are only earning the feed-in rate. Occupancy is what drives this: home during the day, home sometimes, out all day.
3. Whether prices are assumed to rise
Assuming electricity gets more expensive every year makes payback shorter, because the power you avoid buying is worth more each year. That is a defensible assumption, but it is an assumption, and a projection that quietly bakes in a large annual increase will always look better than one that does not.
What a fair projection looks like
A projection worth trusting states its assumptions on the same page as its answer. Ours uses a modest annual electricity price rise, a small annual panel degradation, and self-consumption derived from the occupancy you actually reported rather than a flattering default. The full set is published in the methodology.
| What moves payback | Effect |
|---|---|
| Home during the day | Shortens it |
| Out during the day | Lengthens it |
| Heavy roof shading | Lengthens it |
| Higher retail rate | Shortens it |
| Adding a battery | Usually lengthens it |
| Paying a premium price | Lengthens it |
Payback is not the only thing you are buying
It is the cleanest number to compare options with, because it is the only one that accounts for what the thing costs. But it is not the whole decision. A battery usually pays back more slowly than panels alone and still buys you something real: more of your bill gone, and the lights staying on in an outage. That is a legitimate reason to choose the slower option, as long as you are choosing it knowingly rather than being sold it.
Get your own payback, with the assumptions shown
A ten-year projection built from your bill, your roof and your occupancy, with every assumption published.
Check my home, freeCommon questions
What is a good solar payback period in Australia?
Anything under about seven years is strong, seven to ten is reasonable, and beyond ten deserves a hard look at whether the system is sized right or the price is competitive.
Does a battery pay for itself?
Usually more slowly than panels alone. A battery increases how much of your bill disappears but costs considerably more upfront, so the payback typically lengthens even as the annual saving grows.
Why is my quoted payback shorter than an online calculator says?
The most common reasons are an optimistic self-consumption assumption, a large assumed annual electricity price rise, or a payback calculated on a cheaper system than the one being quoted.
Does solar increase the value of my house?
It can, but not reliably and rarely by the full installed cost. Treat any resale uplift as a bonus rather than part of the payback calculation.
How accurate are solar payback estimates?
They are estimates built from the answers you give. A figure derived from your actual bill rate and usage is materially tighter than one built from a state average and a bill bracket, which is why supplying real numbers is worth the thirty seconds.
Last reviewed 27 August 2026. Rebate amounts, feed-in tariffs and retail prices change; figures here are checked against the calculator's own state data, which is published in the methodology.