The size of a rooftop solar installation can vary depending on its purpose. Usually residential systems are smaller compared to commercial rooftop solar plants. Residential rooftop plants are typically in the range of 1-20 KW while commercial and industrial rooftop plants can range from 25 kW to large megawatt-scale rooftop power plants.
The average size of rooftop solar systems for residential rooftops could vary significantly from one country to another. Many residences in developed countries could be sporting solar power plants upwards of 5 kW, as they have the rooftop space, and their electricity requirements could be relatively higher too than residences in developing countries like India, where one can find rooftop solar panels of sizes as small as 100 W.