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About this tool
A practical electronics tool for managing solar panel output workflows efficiently.
The Solar Panel Output Estimator works out daily, monthly and annual generation from array size and peak sun hours using the standard derating chain: kWp multiplied by sun hours multiplied by a performance ratio built from system loss, shading loss, temperature loss and inverter efficiency. It is for homeowners and small businesses sizing a rooftop or balcony array who want to see how each loss eats into the headline panel rating before a vendor quote arrives. With the default 10% system, 4% shading and 8% temperature losses and a 96% inverter, the performance ratio lands near 76%, so a 3 kWp array at 5.1 sun hours produces roughly 11.7 kWh a day rather than the 15.3 kWh the panel label implies.
Open Solar Panel Output Estimator on AltFTool — it loads instantly in your browser.
Under Panel Setup enter "Panel wattage", "Number of panels" and "Peak sun hours / day" — or start from a Quick Preset: Balcony 800W, Home 3kW, Home 5kW, Shop 10kW or Portable 200W.
Under Loss Factors set "System loss %", "Shading loss %", "Temperature loss %" and "Inverter efficiency %"; the four multiply into the performance ratio that is applied to peak kW × sun hours, and "Self-use %", "Tariff INR / kWh" and "Available area sqm" drive the savings and roof-fit checks.
Read Output Result — daily kWh, peak capacity, performance ratio and panel area — with the Monthly Output Curve and the self-used versus exported split; "Copy" takes the summary and "CSV" saves solar-panel-output-estimator.csv.
System, shading, temperature and inverter losses are entered independently and multiplied together, so you can see which one is actually costing you the output.
Generation is divided into the share you use on site and the share exported, because only the self-used part is valued at your retail tariff in the savings figure.
A twelve-month profile scales output between 0.78 and 1.12 of the average, so the monsoon dip and the pre-monsoon peak are visible instead of hidden in an annual number.
Array size in kWp multiplied by peak sun hours multiplied by the performance ratio. Performance ratio here is (1 - system loss) x (1 - shading loss) x (1 - temperature loss) x inverter efficiency, which with the default 10%, 4%, 8% and 96% works out to about 76%.
A well-installed rooftop system typically lands somewhere in the 70-80% range once wiring, soiling, heat and inverter conversion are counted. This tool flags a ratio below 70% as moderate and below 55%, or shading above 25%, as a high loss risk worth investigating before you buy.
The estimator assumes about 2.2 m2 per panel, so ten panels need roughly 22 m2 of clear, unshaded area, and it warns you when the panel area exceeds the roof area you entered. Real installations need extra room for walkways, tilt spacing and edge setbacks, so treat that as a floor rather than a target.
Treat them as an indicative estimate, not a quote. Savings are calculated as generation multiplied by your self-use share multiplied by the tariff you type in, which ignores slab tariffs, net-metering and export rates, subsidies, fixed charges and future price changes — get a site survey and a written quote before committing.
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