Supplemental Energy Source

Don;
  There are a couple sources for pretty simple homebuilts that you can add to your south walls.  When set up properly, they are like adding window-acreage during the daytime, but without the losses windows can cost you at night.

  The following link is one I'm building, and have the parts to build a few more, but I'm still running on trust, as it's safely in the basement, awaiting the glass and fan..  Very detailed instructions, but pretty cheap materials, and not too hard to make your own variations on, as desired.  (PDF file)  -  The guy is Bill Kreamer, in Belfast, Maine
 http://www.green-trust.org/2000/solar/Homebuilt%20Collector%20Instructions.pdf

You can also see versions in a search of RE articles at Mother Earth News.. (Mostly from the 70's, very simple, with personal testimonials included)

Good Luck!
Bob Fiske