Solar Payback Calculator: Formula, Example and What the Result Means
Estimates how long a rooftop solar system takes to pay for itself. This guide walks through what each input means, the formula behind the answer and a worked example using typical Australian figures. You can follow along in the free Solar Payback Calculator.
Why it matters
Some of the most useful calculations are the small everyday ones: how much a road trip costs in fuel, what an appliance adds to the power bill, or how many working days are left until a deadline.
What you need to enter
The calculator asks for 6 inputs. The table shows each one with the example value used later in this guide.
| Input | Example value |
|---|---|
| System cost after rebates ($) | 6000 |
| System size (kW) | 6.6 |
| Daily output per kW (kWh) | 4 |
| Self-consumed (%) | 50 |
| Grid tariff (cents per kWh) | 32 |
| Feed-in tariff (cents per kWh) | 5 |
The formula
Savings = self-used kWh × grid tariff + exported kWh × feed-in tariff. Payback = cost ÷ annual savings.
Worked example
Entering the example values above gives these results:
| Result | Value |
|---|---|
| Payback period | 3.4 years |
| Annual generation | 9,636 kWh |
| Annual savings | $1,782.66 |
The headline figure is 3.4 years (payback period). Change any input in the calculator and every result updates instantly, so you can test different scenarios side by side.
How the payback period changes with system cost after rebates
The table below keeps every other input at the example value and moves only “System cost after rebates ($)” up and down by 10% and 20%. It shows how sensitive the payback period is to that one figure.
| System cost after rebates ($) | Payback period |
|---|---|
| 4,800 | 2.7 years |
| 5,400 | 3 years |
| 6,000 | 3.4 years |
| 6,600 | 3.7 years |
| 7,200 | 4 years |
At 4,800 the result is 2.7 years; at 7,200 it is 4 years. If a small change in this input moves the answer a lot, it is worth double-checking that figure before you rely on the result.
A practical tip
Feed-in tariffs have fallen, so using solar power yourself during the day is worth far more than exporting it.
Keep going
Before relying on the number, read Solar Payback: What to Check Before You Trust the Number. You might also find these guides useful:
- Using a Age Calculator in Australia: A Step-by-Step Guide
- Days Between Dates Calculator Explained for Australians
- Using a Percentage Calculator in Australia: A Step-by-Step Guide
Frequently asked questions
- Are the results exact?
- Maths calculations are exact. Cost calculations depend on the prices and usage you enter.
- Do the date calculators handle leap years?
- Yes. They use real calendar dates.
- Can I suggest a calculator?
- Yes. Use the contact page to request one.
Run your own numbers in the Solar Payback Calculator.
Open the calculatorGeneral information only. Rates and thresholds change, usually on 1 July. Confirm current figures with the ATO or the relevant authority, and get personal advice for decisions about your situation.