Solar panel roof-fit calculator
Enter your usable roof area, then compare two panels side by side: how many fit, the system size, and a rough yearly output.
1. Your roof
Use only the area free of vents, chimneys, skylights and heavy shade.
2. Two panels to compare
Starting values describe a typical 67.8 × 44.6 in residential panel (the Qcells Q.TRON datasheet size at 430 W). Replace them with the datasheet values of the panels you are quoted.
How the numbers are calculated
Efficiency = watts ÷ (length × width in m² × 1,000 W/m²) Panels = floor(roof area × layout efficiency ÷ one panel's area) System kW = panels × watts ÷ 1,000 Yearly kWh = system kW × peak sun hours × 365 × (1 − system losses)Efficiency here is computed from size and rated watts at standard test conditions, so it will match a datasheet only if you enter the datasheet's exact dimensions. Peak sun hours are full-strength-sun-equivalent hours, not daylight hours, and vary by location and season: much of the US averages about 4 to 6. Layout efficiency allows for fire-code setbacks, spacing and awkward roof shapes. This tool does not model shade, tilt or orientation.
When roof space is the limit, higher-efficiency panels fit more watts. When it is not, compare price per watt and the warranty instead. See the types comparison for documented efficiency ranges.