The cost of a solar PV system varies based on the size of the installed system, roof or ground mount variables, local jurisdiction requirements and a variety of other variables but as a rule of thumb if one assumes $3.00/kilowatt of production or an average home needing 7kW (7,000w) system would cost $21,000. The average home needs approximately a 7kw system. If the system is larger, the price/watt goes down, and smaller the price is typically higher.