I took the 30% credit and my electrical service,Oncor had rebate which I used.
$9K is all I paid after those two items.
My system is 28 panels,generating 7KW.
Green Mountain energy,which isn't available everywhere, pays 100% retail rate what you put back to the grid. So far this year they owe me $400 in credits . I have a 7KW system on my roof. My house is over 2,000 SqFt.