I think the biggest killer is if you are going to run A/C. In the midwest, it is almost a requirement. It is really difficult (actually not difficult but price prohibitive!) to size a system to handle a/c. I originally installedy my system so I could run a dock de-icer in the winter (I use a compressor type system from "dockbubbler.com" - it uses little juice compared to blade types). I had to size the panels based on the amount of daylight I get in the winter. I actually have 2 more solar panels that I only use in the winter to provide additional juice. I will try to find my folder with all the calcs in the next couple of days and post up the basics.
Nick
PS - is there anyway to run a spell check on these posts?