Just searching the archives because of my similar electric situation so I thought I'd post here.
I'm waiting for my Y due later this summer. I have a detached garage with a 20 amp circuit from a sub panel in my home (my central air at 30 amps is the only other thing on the panel).
Before I attempt any changes, I am going to wait and see if my 20 mile daily commute to and from the garage at the train station can be handled by level 1 charging overnight at home and then another 8-10 hours of free level 1 at the parking garage. I figure I'll likely hit a nearby super charger once every two weeks.
What I'm wondering regarding a possible level 2 install at home if this scenario doesn't work out is perhaps rather than go through the expense of upgrading my 100 amp home Service to 200 amp, and then run a heavier gauge cable out to the detached garage, I just leave my home at 100 amps and add a second 100 amp service to the detached garage and get a full level 2 charge setup.
Thoughts?