When I was comparing Solar providers, I found that each of them, including Tesla, have 'canned' packages... small, medium, large, with or without batteries (Tesla only with batteries). All of them could give me a canned 'design' in a day. But it wasn't a detailed design. My detailed design is a 7 sheet drawing of exactly how the system would be installed on my house including the calculation of current on conductors right down to the labels. It also has data sheets for each piece of equipment. The design has to meet the specific city building codes which can vary from city to city, and of course which electric company owns the power line to the house. The Three Line drawing is the document that is eventually sent to the city to get a permit and is used during inspection and also to the power company for the interconnect agreement. I'm not making excuses for Tesla, but maybe the level of design you are getting from the local company is not a detailed design but a canned package. The local company might have a better handle on the city's codes and the power company. But the reality is, Tesla is over subscribed and they do seem to be slow. The other thing you will learn is that if you want to change the design it will cost you some money. I added some additional panels to my design. It cost me $200 plus the additional cost of the panels. It was worth it... actually I wished I had gone bigger! A 3-house deal with a local company might be worth it even at a slighter higher cost. They will be more responsive if things go wrong than Telsa will be.
