Photovoltaic panels make sense if your home has the right kind of sun exposure (southern is optimal). You can maximize the energy available to your car by minimizing the energy demands of your home. Solar hot water system usually have the quickest pay back time. Solar-assisted a/c systems are pricy, but can be hyper-efficient.
The payback time for our purchased system was less than 5 years. The out-of-pocket cost for our 3,000 sq. ft. home for the PV panels was $11k after incentives, rebates, tax credits. We currently produce more energy than we use, but will have to reassess after the S arrives. It's MUCH cheaper with solar.