A useful starting point for solar.
Generation is not the same as savings.
Only electricity that replaces a purchase from the grid saves the avoidable tariff. Surplus generation that you cannot use earns no benefit in this calculator. Your usable percentage should already allow for battery and inverter losses, timing of demand and unused exports.
Use the tariff you can avoid.
Look at the variable per-kWh charge on your own bill. Fixed connection and service charges may continue after installation, so leave them out of the savings rate. Example values are not verified municipal or Eskom tariffs. Export credits are excluded.
Plan for the life of the system.
Generation decreases at your chosen annual loss rate. Upkeep is spread evenly each month. Batteries and inverters may need replacement: this model does not deduct a specific replacement bill, financing cost, or investment opportunity cost. Budget for those separately before deciding.
Daily generation × 365 ÷ 12 estimates the first-year monthly generation. Each subsequent year applies the chosen generation loss. Payback is the first whole month cumulative net savings cover the installed cost. At 10 kWh/day, 100% usable generation and R3/kWh with no upkeep or degradation, a R10,950 system pays back in 12 modelled months.
Simple payback has limits.
This is an undiscounted, constant-price cash model. It does not forecast tariff increases, changes in usage, tax incentives, subsidies, outages or system performance. It is not a system-sizing tool or a promised return. A qualified installer should assess your roof, location, wiring, daytime use and backup needs.
Planning information only. Obtain a detailed installation quote and check all assumptions against your actual bills.
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