There are several factors that play into the generation of a solar array and the overall return on your investment.
Cost of the system
Tax incentives
Renewable energy credits
Kilowatt hour cost
Size and location of the system
Example: A3 Kw system costing $9,000 would currently be eligible for a 30% federal tax credit. Assuming you generate 350 kilowatts on average each month, you could reduce your electric bill about $460 annually. Your investment after tax credits for the above scenario would be $6300.00 and you could get $460.00 value annually for a payback of 13.7 years.