Tesla is much higher priced than others. There are companies that do a lease. My brother in Arvada didn't see any benefit to his electric bill when he did Solar, so cancelled the contract. You should do a lot of research.

I just got a quote of 103k. In the Houston area.

40K would be low, assuming some costs will be shifted to the home’s ”electrical” budget rather than “roofing” budget. BS sales tactics. It also isn’t suited for anywhere that experiences significant snow cover.

You may find that an addition to the main home will be significantly cheaper than a separate ADU. And it won’t be constrained by space limitation requirements.