We just got 21x250w (5.25kw) panels and a Goodwe inverter from True Value Solar for $3794 installed. For example, today was a nice clear day and we got just under 25kwh (7.135c/kwh so $1.80ish). Not bad for the middle of winter! Still take awhile to pay for itself though obviously.

You give examples from 3-5kw. It's not much more for the larger system so I'd be going as big as you can on the north facing roof space.

__________________
No more GC8, sad face.
[SIGPIC][/SIGPIC]