The quintessential question of how long will it take to break even on the investment in a PV solar system varies, but it is typically in the range of 8-11 years for residential and 4-7 years for commercial. Some of the variable factors affecting the payback are: a larger system costs less per kilowatt installed than a smaller system; multi-faced roofs add complexity and some cost; specialty systems add cost and extend payback time; A ground-mount while typically more efficient will cost more than a roof-mounted system due to the need to build the structure to mount to; Older homes or commercial properties with electrical systems that do not meet current safety standards may add cost to the installation of a solar system as electrical systems need upgrades.  The best way to determine what the ROI (return on investment) is to have a solar PV installer provide an accurate bid to build an appropriately sized system for your desired address.