Be aware that you can still get solar power benefits even if you live in a chilly, overcast area. It doesn't need to be like Florida all year round for it to be a big part of your energy savings goals. Great solar power output can come on poor weather days.
You should always have a lease transfer option if you lease the solar energy system versus purchasing it outright. If your home is sold, you will need to have this option handy. If you can transfer it to the new owners, you'll be fine.
Solar Energy Technology by Prof. V.V. Satyamurty, Department of Mechanical Engineering, IIT Kharagpur. For more details on NPTEL visit http://nptel.iitm.ac.in.
Keep your solar panels out of the shade. It might seem obvious, but your solar panels do need sun. Make sure that you are not installing them in the shade. Trim back the branches on surrounding trees if you need to. Failing to do so could cost you more than half your energy output.