Work out how many panels of a given wattage are needed for a target output.
Each panel produces its rated wattage times sun hours, reduced by system losses. Rounding up means actual output slightly exceeds the target, which provides useful margin. Panel wattage has risen steadily, so a modern array needs far fewer panels and less roof area than an equivalent system from a decade ago.
Solar Panel Size
Panels = daily kWh ÷ (panel watts × sun hours × derate ÷ 1,000)
Panels = daily kWh ÷ (panel watts × sun hours × derate ÷ 1,000) Each panel produces its rated wattage times sun hours, reduced by system losses. Rounding up means actual output slightly exceeds the target, which provides useful margin.
Panel wattage has risen steadily, so a modern array needs far fewer panels and less roof area than an equivalent system from a decade ago.
This calculator takes 4 inputs: Daily energy needed, Panel rated power, Peak sun hours per day, System losses. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.