Example result based on the prefilled values.
Annual Generation
3 600,00kWh
Annual Saving
R864.00
Payback
8.10 years
10yr Return
R1 640,00
Continue your plan
Useful next calculations
When to use this calculator
- Before switching supplier, upgrading equipment, or comparing energy-saving changes.
- When you want to test different usage assumptions or price scenarios quickly.
- When you need a simple estimate before requesting installer or supplier quotes.
- When you are evaluating solar panels, a heat pump, or insulation and want to check the payback period before spending.
- When your tariff is about to change and you want to quickly model the impact on your annual energy bill.
A realistic South Africa planning example
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
System Size (kWp)
4.5 kW
Installation Cost (R)
R7,500
Peak Sun Hours Per Year
25 years
Electricity Price (R/kWh)
4.5 kW
After entering these figures, review annual generation, annual saving and payback together rather than in isolation — each metric tells a different part of the story. Then rerun the tool with one input adjusted to see which variable has the biggest effect on all three outputs before you settle on a plan.
How to read your results
Annual Generation
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Annual Saving
This gives you the recurring yearly benefit of the change or upgrade, which is usually the most practical starting point when comparing options. Divide it by 12 to see the monthly equivalent, or multiply by 5 to get a five-year view of the cumulative gain.
Payback
The payback period shows how many months or years it takes to recover the upfront cost through ongoing savings or income. Compare it against how long you plan to stay in the property or use the product before deciding whether the investment makes financial sense.
10yr Return
Use this to compare scenarios over different time horizons and judge whether the projected outcome clears your minimum required target. Remember that real-world returns fluctuate, so also check the result under a more conservative growth assumption.
Method & assumptionsAuthoritative sources
This calculator estimates the financial return from a domestic solar panel installation by modelling three income streams: electricity you generate and use directly (avoiding grid purchases at your unit rate), electricity you export under the Smart Export Guarantee (paid at your entered SEG rate), and any applicable government incentives. It assumes a panel output figure based on the system size you enter, adjusted for typical UK irradiation levels for a south-facing roof. East- or west-facing installations produce roughly 15–20% less annually. The calculator does not account for panel degradation over time, which averages around 0.5% per year for quality panels, nor does it model battery storage independently. Installation costs vary considerably by region and installer, so obtaining at least three quotes is advisable before using this tool for budgeting purposes.
Common mistakes
- !Using an assumption that is not supported by a current local quote, bill, statement or official source.
- !Treating a generic estimate as a lender, provider, payroll or tax authority decision.
- !Mixing monthly and annual inputs without converting them consistently.
- !Forgetting location-specific taxes, fees, eligibility rules or payroll deductions where they apply.
- !Testing only one scenario instead of checking how a cautious assumption changes the result.
What to do next
- Run a second scenario with a cautious assumption so you can see the downside clearly.
- Compare the result with the related calculators below before making a decision.
- Check current local rules, eligibility and provider terms before applying or committing money.
- Keep a record of the assumptions so you can update the estimate when a quote, bill or pay figure changes.
- Use the result to prepare better questions for a lender, provider, adviser or employer rather than treating it as a final answer.
Frequently asked
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