How the solar payback calculator works
Last updated 10 November 2026
A solar system replaces electricity you would have bought. The saving each year is the energy it supplies, times your tariff. Payback is when the total saving reaches what the system cost.
How it works
- Saving in a year = energy used from the system in the year × the tariff for that year.
- The tariff rises by the yearly percentage you enter.
- Payback is the point where the savings add up to the cost, in years.
Worked example
With the starting figures:
- In the first year the system saves R 18 000.
- It pays for itself after about 6.0 years.
- Over the whole period the savings come to R 374 113, which is R 254 113 more than the cost.
How to read your result
The headline is the simple payback time: the number of years until your total savings equal the cost of the system. With the starting figures, the first-year saving is R 18 000.
The chart shows the savings building up year by year against a dashed line for the system cost. Where the lines meet is the payback point. After that, the savings are a gain.
The last row, saving minus system cost, shows where you stand at the end of the period you chose. A negative number means the system had not paid for itself by then.
A closer look at the energy figure
The calculator multiplies the energy you use from the system by your tariff. The energy figure is the biggest driver of the answer, so it is worth getting right.
Count only the energy you use yourself. Power that a system makes but you cannot use at that moment does not reduce your bill, unless your municipality or supplier pays you for it. The calculator does not assume any payment for exported power.
Ask the installer how the estimate was made, and compare it with your own use. The electricity usage calculator can help you see what you use in a month.
A closer look at the tariff
Your bill may be made up of more than one rate. Some tariffs have steps, where the price per kWh rises as you use more. Some have time-of-use prices, and some add fixed monthly charges that solar does not remove.
A single number cannot show all of that. For the tariff box, use the price per kWh you would avoid paying, which you can work out from a recent bill. The yearly increase is an assumption. Try a lower value to see how sensitive the payback is to it.
What this does not cover
The result is a simple payback. It does not discount future savings, so a rand saved in year ten counts the same as a rand saved today. It also leaves out battery replacement, panel ageing, maintenance, insurance, and the interest on any loan used to pay for the system. Keep those in mind when you compare quotes.
Things to watch
- Batteries have a shorter life than panels and may need replacing.
- Tariff increases are uncertain. Test a lower number.
- Rules for feeding power back and for tax allowances may change. Check the current rules before you buy.
Start with the electricity usage calculator to see what you use. Read the full disclaimer.