>> Is there any limit on the size of the Tax Credit?
No, the tax credit is now unlimited. If you buy a million dollar system you will get a $300,000 tax credit from the IRS. It used to have limitation on size but that was removed in 2009 or so. These rules and wind and solar tax credit as law is in place through 2016.
Would you like to buy a million dollar system? <just kidding>