Solar savings calculator
Work out what a rooftop solar system would cost, what the PM Surya Ghar subsidy takes off it, and how long it takes to pay for itself. Enter a monthly KSEB bill, a unit count from a recent bill, or the usable roof area — whichever number you have.
Cost breakdown
Bill mode assumes the bill goes to zero — annual savings here are exactly twelve times the monthly bill. The tariff sets the system size; it does not independently derive the savings.
This system out-produces their consumption. Savings are capped at what they actually use — export credit is not modelled.
Estimate only, at 1,460 kWh/kW/year and a flat ₹60,000/kW. Actual generation varies with shading, tilt and weather; confirm against a site survey before quoting.
How this estimate is worked out
Sizing starts from how much electricity you actually use. A one-kilowatt rooftop system in Kerala generates roughly 1,460 units a year — about four units a day — so the calculator divides your annual consumption by that figure and rounds to the nearest half kilowatt. If you enter a bill rather than units, it converts the bill to units at the tariff you give.
Cost is estimated at ₹60,000 per kilowatt installed, before subsidy, and each kilowatt needs about 100 sq ft of shade-free roof. Systems are capped at 10 kW for a home and 50 kW for a business.
Subsidy. Residential installations qualify for the MNRE / PM Surya Ghar central subsidy — up to ₹78,000 for a system of 3 kW or more, less below that. Commercial installations get nothing, which is why the payback period differs sharply between the two. Payback is simply the net cost after subsidy divided by the annual saving.
What the estimate assumes
These are real limits of the model, not disclaimers. We would rather you know them before you spend money.
Bill mode assumes your bill goes to zero. The annual saving in bill mode is your monthly bill times twelve — the tariff cancels out of the arithmetic. It is a statement of what a full offset is worth, not an independent calculation of it.
Roof mode never learns your actual consumption. It sizes the system from area alone, so it always reports a 100% offset — the system is being compared against itself. If you know your usage, bill or units mode gives a truer answer.
Cost is flat per kilowatt. There is no economy of scale in the model, so a large commercial quote is a straight multiple of a small one. Real quotes usually improve with size.
Generation figures use Kerala irradiance and assume an unshaded, reasonably south-facing roof. Shading, roof pitch, panel choice and the age of your wiring all move the real number. For an exact figure, call us on +91 75105 00080 and we will survey the roof.
This calculator is part of docsun.
If you install solar for a living, the same estimate runs inside docsun alongside the customer record — so you can size a system, show payback, and then generate the KSEB and PM Surya Ghar paperwork for the job from one place.