How the calculation works
Yearly usage = monthly bill ÷ price per kWh × 12. System size = usage covered ÷ (sun hours × 365 × 0.8). Payback = system cost ÷ yearly savings.
Frequently asked questions
Are subsidies included?
No. Subtract any subsidy from the installed cost to see a faster payback.
Why is 80% efficiency used?
Real systems lose output to heat, wiring, dust and the inverter, so a figure near 80% is a common planning assumption.