Solar photovoltaic (PV) panels are the most cost effective renewable energy source for most zero energy homes. Installing a PV system is the last step to take to reach the net zero energy goal, since PV panels are the most costly of all strategies. The amount of solar PV panels required to reach the zero energy goal should be calculated only after all other energy-saving measures – outlined in the Twelve Steps to Affordable Zero Energy Home Construction and Design – have been modeled to minimize energy use. The goal is to minimize the use of solar panels as much as possible to cover the remaining energy needs of the home at the lowest cost possible. Since the price of solar photovoltaic systems is dropping rapidly, this is something of a moving target.