Free online solar panel output calculator — estimate daily, monthly, and yearly kWh energy production based on panel wattage, number of panels, sun hours, and system efficiency. Solar irradiance (W/m²) Typical range 200–1000 W/m². Temperature coefficient of Pmax. Caution: Photovoltaic system performance predictions calculated by PVWatts ® include many inherent assumptions and uncertainties and do not reflect variations between PV technologies nor site-specific characteristics except as represented by PVWatts ® inputs. Losses come from inverter efficiency, wiring, temperature, and dirt. That's the wattage; we have 100W, 200W, 300W solar panels, and so on. How much solar energy do you get in your area? That is determined by average peak solar hours. South. The calculation uses solar hours per day for each location using the PV Watts calculator with these design input standards: Actual results will vary for each project. Watch this video to learn how much solar power in kilo-watts or kW is needed to generate the kilo-watt hours or kWh of energy used.