A typical home solar panel is about 3 feet wide by 5. 5 feet long, occupying an area of roughly 17. So, how much space do you need for an effective solar panel system, and how will your roof's square footage affect the size of your array? Join us for a complete guide to roof space for solar panels, as well as a few alternatives for those without suitable rooftops. Are 72-cell panels better than 60-cell panels? 72-cell panels produce more power per panel but are. We have calculated how many of either 100-watt, 300-watt, or 400-watt solar panels you can put on roofs ranging from very little 300 sq ft roof to huge 5,000 sq ft roof, and summarized the results in a neat chart. This is a standard 10kW solar system, consisting of 25 400-watt solar panels.