homes are likely to need somewhere between 15 and 22 panels to offset their electricity use, but that's just a baseline. The actual number depends on how much energy you use, where you live and the wattage of the panels you choose. There is no standardized chart that will tell you, for example, “A typical 300-watt solar panel is this long and this wide. ” If you want to calculate how many solar panels you can put on your roof, you will obviously need to know the size of a solar panel. Here's how to figure out your magic number. It's one of the first questions every homeowner asks when they start. Location Impact is Massive: The same home using 1,000 kWh monthly could need just 16 panels in sunny Arizona but 22 panels in Massachusetts due to solar production ratios varying from 1. Future-Proofing Saves Money: Adding panels later costs significantly more due. Modern solar energy development in the United States dates back to 1954 when scientists at Bell Laboratories patented the first silicon solar cell. homes, and the number is expected to climb to 15% by 2030 — about twofold within the next five years. 86 per watt, or $28,600 for a 10kW system.