Shingle your roof with conventional shingles for $10,000 as opposed to $76,700, then take the              $66,700 you saved and invest it.   Use the annual dividend to pay your energy bills or save it up to replace your roof with a brand new one in 30 years and have plenty left over for a nice vacation.  Any way you look at it, a $76,700 solar roof is not a rational business decision even with the economic argument posed by Musk.  The only reason to buy such a roof is because you wish to make your friends jealous or because you want to lower your environmental impact.