Free solar calculators for installers in India

Free calculators for solar installers and their customers: system size from a monthly bill, an indicative subsidy, a GST split into CGST, SGST or IGST, payback on the net cost, a sample quotation and a rupee amount in words. Each page shows its formula and assumptions, and a result can be shared as a link.

Last updated 10 Oct 2026

• Solar system size calculator

  Estimate the rooftop solar size in kW from a monthly electricity bill. Every constant is shown, and you can change the tariff to match the customer.

• Solar subsidy calculator

  Estimate the central and state rooftop solar subsidy for a system size. Each line is labelled verified or unverified, and the result is indicative only.

• Solar GST calculator

  Work out GST on a solar quotation line by line. You enter every rate, and the calculator splits CGST and SGST or IGST from the two states you choose.

• Amount in words (Indian)

  Convert a rupee amount into words using the Indian lakh and crore system, ready to copy onto a quotation, cheque or invoice. Free, with no sign-up.

• Solar ROI and payback calculator

  Work out how long a rooftop solar system takes to pay for itself. You enter the cost, the savings and any subsidy, and a sensitivity table shows what-if cases.

• Solar quotation generator (sample)

  Fill a sample solar quotation with your own figures and see the layout, GST split and total in words. A watermarked demo with fictional customer details.