Is there a CAP on the federal solar tax credit?

Hi, I saw your FAQs on the 30% tax credit for solar and still have a question.  A solar company is quoting me over $63k for our system, so the 30% would be about $21k.  But is there a CAP on the federal tax credit for solar?  That install cost is high, and I'm not sure the $21k would even be real.