Use MPPT controllers (98% efficiency) for divergent wattages, or parallel-wire identical-voltage panels with 30A fuses. Microinverters enable safest mixing.
Label Inspection: Check the manufacturer's label on the panel's backside. Look for "W" or "Wp" (Watt-peak) values under Standard Test Conditions (STC).
With this data, the calculator will calculate the length of the roof edge and the number of rows of panels in two arrangements: horizontal and vertical.