It has been a long time coming, but the State of Illinois is now helping the public finance photovoltaic (electricity) and solar thermal (hot water) panels. The State offers a rebate of 30% of the total cost of the solar system (up to $10,000). The Federal government kicks in an uncapped 30% tax credit. This is obviously most effective when the panels are incorporated into a greater sustainable design renovation or new construction. Simply because it makes more sense to reduce your overall demand, by way of proper orientation and design features, before installing costly energy production systems. This will also substantially shorten the time required to achieve a return on your investment.
As an example, the base cost for a 2-panel solar thermal system is approximately $11,000. After federal and state rebates of 30% each, the total installed costs is reduced to $5,500. A best case payback period would be roughly 2-3 years for this type of system.
A 3kW photovoltaic system (enough to supply the demand for a small house or half of a conventional-sized house) will cost approximately $29,000. After rebates, the installed cost is reduced to $14,000. A best case payback period for PV could be 10 years or less depending on the extent of future electricity rate increases.
There are similar programs for commercial, and even more favorable ones for municipal and non-profit, projects in the form of similar rebates and tax credits.