Solar Photovoltaic panels come in two basic dimension a 60 cell and 72
cell panels. The standard residential 60 cell panel is approx. 38” x 68”
dimensionally, which equates to a surface area of 18 sq./ft. The typical
60 cell panel is rated at 320 watts, so assume 56sq/ft. for every 1000
watts (or 1kWatt) of solar PV required to meet your needs. So in reality
most roofs have plenty of space as a 20’ x 20’ roof is 400 sq./ft.