If you are interested in checking into incentives for Photovoltaics (solar electric panels or thermal) see:
http://www.dsireusa.org/
They list all available rebates/grants/tax credits by state.
Right now the Feds (US) are offering a tax credit of 30% of the installed cost of your system ($2k cap for residential) On grid or off! This credit can be spread over several years. I'm not an accountant but I understand that you can also apply an accelerated depreciation schedule to increase your tax savings.
As far how much power can you produce:
When the sun is directly overhead (Noon sun) it has an intensity of about 1000 watts/sq meter at sea level.
Photovoltaic systems can deliver +/- 12% to the grid.
A good rule of thumb for your system size is to figure on harvesting about 10 watts/sq foot per noon sun hour per day. Many places in North America get around 5 noon sun hrs per day. A system that can produce 3kW will take up approx 300 sq', (+/- $27k before incentives) and can produce 15 kWh daily.
The cost savings depends on how much you pay/kWh. Check your utility bill.
Thermal collectors (water or air) can harvest as much as 40% of the noon sun energy. It's a little tougher to get a hard number on your cost savings but it usually has a better return than PV. (Solar Electric)
Another "incentive" is that once you have installed a renewable power system, you have locked in your energy costs for the life of the system. Compare that to utility rate inflation of 3-5% per year in many areas.
If you want to learn more about Solar check out NABCEP.org
North American Board of Certified Energy Practicioners.
They have a downloadable study guide with many references.
Enjoy