Here are the key bits from my SGIP Small-Scale rebate from a non-Tesla certified installer (SF East Bay with PG&E and EBCE).
4kW panels + 1 PW2 installed end of Sept 2019, PTO early Nov 2019
add 2kW panels + 1 PW2 installed end of Dec 2019, PTO early Jun 2020
Declared cost of 2 PW2 on the SGIP...