How is solar panel size calculated?
A solar system is generally sized from the amount of electricity you want the system to generate, the solar resource available at the site and the expected system performance.
For example, if a home uses 300 kWh per month and the assumed peak sun hours are 4.5 hours per day with an 80% performance factor, the calculation estimates the DC system capacity needed to produce roughly that amount of energy.
Why does the calculator use performance losses?
Solar modules do not deliver their nameplate output continuously. Temperature, wiring, inverter conversion, dust, mismatch, shading and other system effects can reduce the usable energy compared with a simple nameplate-capacity calculation.
How many panels will I need?
Once the estimated system capacity is calculated, the tool divides it by your selected panel wattage and rounds up to a whole panel. Actual string design and final panel count can differ because installers must also consider inverter voltage/current limits, roof geometry and the specific module being used.
How much roof area does solar need?
India's National Portal for Rooftop Solar says a 1 kW rooftop system generally requires about 10 square metres of shadow-free area, while noting that the actual requirement varies with module efficiency and placement.