I'm in California where solar is mandatory on new homes so I had to either lease it or buy the system. It has helped cut the cost of air conditioning for me by quite a lot.
Wing Commander mentioned insulating the walls in cold areas. I'd add do this in hot areas also. The exterior of my house is insulated with foam sheets walls are fiberglass insulated and I have insulation in the roof. I think this is all required by law around here. It makes a huge difference. The temperature inside the house isn't affected near as much by the outside temperature as the last house I was in that had no wall insulation. BTW on some days it can get over 120 degrees around here in the summertime.