27kw system!?

Unless you live in a giant mansion, or in a warehouse, there is no way that much solar is going to fit on your roof.

Most houses will max out around 8-10kW, unless they are very large, or have their entire roof area optimally oriented in single large planes.

Even the most advanced panels these days make 20 watts per SF. To get 27,000 watts you would need almost 1,500-2,000 SF of roof area completely covered. Considering most roof profiles have 1/4 to 1/2 of their roof planes pointed away from the sun, you probably need a 4,000+ SF single story house (or 6-8k SF two-story).

Not to mention, a lot of utilities limit the size of residential solar. I've seen as low as 10-15kW limits if you're on a single-phase 240v service.

But if you can get away with it, more power to ya! With a system that size you could probably get bids from commercial contractors who may be a little more cost effective, and won't have to charge as much overhead to cover their army of door-knockers.