In Xcel Energy and Aquila service territories of Colorado, Rebates and Renewable Energy Credits (REC) are offered. The Rebate can be as high as $200,000. REC payments for the energy produced by a 100,000 Watt Array can reach $18,400 each year of the 20 year contract. Outside of those areas the REC's may be sold on the market, just like futures.
Together with the above, the currently effective accelerated five year depreciation (MACAR) can provide a Return on Investment (ROI) of under 3 years. with the remaining depreciation reducing your Tax Burden for 3 more years. Those companies with large incomes, and the associated tax burdens, can approach 2 years for the ROI.
Additionally, the installation of this equipment increases the value of your property in three ways. First, directly as a value for the cost of the system. Second, the value of the property is increased by the Energy Cost Avoided. Third, as you are aware, the reduction of your environmental impact is of value both for future generations, and as a market sales tool.