Tesla has been erroneously charging sales tax in MA for the powerwall portion of solar systems. @TORQU3 and I have found that the state considers powerwalls part of the solar system and therefore exempt from sales tax. If you’ve paid sales tax on your MA solar system you should contact Tesla for a refund. If you are getting a system installed in the future, make sure there is no MA sales tax added. I just got my sales tax refund.