If my rough calculations are right, the Medium sized system will cover all of our South-facing roof surfaces and offset 90% of our usage. Depending on when Tesla gets back to me, we might have enough savings to upgrade to a Large system which would cover 125% of our usage, but it would have to extend onto the Northeast roof. So it's a 47% increase in installation cost for a 38% increase in production.
Not sure if Tesla is creating systems in between Medium and Large, but I'll update the thread with Tesla's design docs when they get back to me.
My personal opinion is the same as
@charlesj on this. Size it for at least 100% of your electricity usage, since people tend to start using more electricity when they get solar. The goal would be to be like 101% of your yearly usage, counting your model 3, AND any future plans for another EV in the home, etc.
When I got my system in 2015, solar city tried to size me for 80-85% ( i have a solar lease actually) and I said I wasnt signing anything until they could get me to 100% of my usage. In order to get SCE to agree to that usage, I had to tell them I was buying an EV within the next year / 12 months (thereby increasing my energy usage).
I signed the paperwork, because I planned to do that, but life happened, and I didnt buy the Model 3 until end of 2018. Because my system was sized at like 105% in 2015, prior to me making energy improvements like swapping all my lighting to LEDs, getting a more energy efficient fridge, Dishwasher, washer / dryer, etc etc, my solar production WITH my model 3 in the usage is roughly 99% of my yearly usage.
I drive my model 3 about 18k miles a year, so this is a fairly significant thing. I wish I had more solar, actually, but really cant fit any more panels on my roof.
I have (34) panels, that are like 260w or something. I would love to just put better panels and a larger inverter on my roof, because I see being a two ev household when my wifes X3 comes off lease in a year or so.
