Solar Payback Calculator Australia
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Work out the payback period and lifetime savings of a rooftop solar system on your home in Australia. This calculator uses your system size, daily usage, self-consumption rate, retail rate and feed-in tariff to project net savings over a 25-year system life — and shows the year you break even.
System and household
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Your solar payback
Payback period
—
to fully recover system cost
Year-1 savings
—
bill offset + feed-in revenue
Net at 10 years
—
cumulative savings minus cost
Lifetime net (25 yrs)
—
total benefit over system life
Net cumulative position (savings minus system cost)
Year-by-year savings table
| Year | Generation | Annual savings | Cumulative savings | Net position |
|---|
How to use this calculator
- Enter the system size in kilowatts. The Australian residential standard is between 6.6 kW and 10 kW.
- Enter the system cost — this is the out-of-pocket price quoted by your installer after the federal STC discount.
- Use your last electricity bill to estimate average daily household usage in kWh.
- Set self-consumption realistically — without a battery, most households use 25–35% of what their solar generates. Pool pumps, electric hot water on a daytime timer and home offices push this higher.
- Use your retailer's current retail rate and feed-in tariff. The bigger the gap between them, the more important self-consumption becomes.
Key assumptions
- Production factor: 4.0 kWh per kilowatt of capacity per day for an unshaded north-facing array — a national average across Australian capital cities.
- Orientation factors: north 1.00, east/west 0.88, south 0.72.
- Generation declines each year by the degradation rate you set (0.5% per year by default).
- Retail electricity rates and feed-in tariffs stay constant for the 25-year projection. In practice both move over time; if you expect rates to keep rising, the result is conservative.
- No batteries, no inverter replacements, no rebates beyond the STC already netted off the system cost.
- Self-consumption is capped at total household usage so the model never claims to offset bills you don't have.
Frequently asked questions
How does the calculator estimate solar generation?
It uses a national average of 4.0 kWh per kWp per day for an unshaded north-facing array — broadly consistent with ARENA and Clean Energy Council guidance for Australian capital cities. Orientation reduces this for east/west (88%) and south (72%) arrays. Generation falls each year by the degradation rate you set.
What's a realistic feed-in tariff to use?
Most retailers now pay 4–7 cents per kWh for exported solar. A handful of legacy and special-offer plans pay more for a capped daily volume. Check your current retailer's plan; the calculator's 5 c/kWh default is a sensible starting point for 2025–26.
Should I model a battery?
This calculator is solar-only by design. The simplest way to model a battery is to push self-consumption upward (commonly to 60–80%) and add the battery's installed cost to the system cost. Whether the result still pays back depends heavily on the gap between retail and feed-in rates.
Why is self-consumption more important than export?
Self-consumed solar saves you the retail rate (28–35 c/kWh). Exported solar earns the feed-in tariff (4–7 c/kWh). The five- to seven-fold gap means a smaller system that matches daytime usage usually beats a bigger system that exports the surplus.
Are STCs already included in the system cost?
Yes — the cost field is the out-of-pocket price you'll pay after Small-scale Technology Certificates have been netted off by your installer. Australian installers almost always quote the discounted price, but ask if it isn't clear from your quote.
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Read article →This calculator provides general estimates only and is not financial, energy or product advice. Always obtain a written quote from an accredited solar installer before purchasing.