Occupant behavior can make the difference between an efficient house and a wasteful one. Notorious energy hogs include plasma TVs, old refrigerators or freezers, ice-makers, and dehumidifiers. And don't overlook sneaky items like DVRs, always-on computer and entertainment equipment, etc.
Before installing solar panels, get a home energy audit to find out where you're wasting the most energy. Your house will be more comfortable if you seal leaks and add more insulation, so don't just slap solar panels on the roof without curbing energy use.