Adding additional panels is the approach they took with us, and I was a bit concerned because our main panel was full, and it is a split-bus panel, which is not something you can install these days (or for like 4 decades, from what I've read.) So now, we have new boxes and disconnects everywhere - a service disconnect breaker on the TEG to kill only grid power, a firemen's disconnect outside to kill solar+PWs, a generation panel with breakers for the solar and each PW, and a new main breaker that kills everything (wired between the TEG and our existing main panel.) Fortunately it is in the basement, but one thing that I would love for the future is one integrated box that has the TEG, main panel and all the disconnects (except the required external disconnect) in it just to make things look cleaner.
As others have said, none of it is free, but they did review our electrical ahead of time (as I recall, though they did not send anybody out to check out our roof, they did send an electrician to review that portion) and everything was accounted for in the contract. That is really all I would expect - that Tesla is upfront about what electrical work is required and how much it will cost. They presumably know better than most of us (certainly me) what is needed to add the solar/PW and what is required to meet code.
