The size of your solar install depends on what your average electrical usage is for your home, and how much electrical offset you want your system to produce. For most installs, 100-115% offset is ideal to cover all your electrical energy needs. For an average residential home in the U.S., that is 11 kilowatts.
The investment tax credit (ITC), or the federal solar tax credit, allows you to deduct 26 percent of the cost of installing a solar energy system from your federal taxes. The ITC applies to both residential and commercial systems, and there is no cap on the amount.
Solar will save you between 30-50% on your monthly electrical expenses, as well as help save the planet.