For many electric vehicle (EV) drivers, it’s only a matter of time before this idea pops up: Why don’t I install PV modules so I can run my car on sunshine?
Our research suggests that approximately one in three EV owners has a home grid-tied PV system. The one-two punch of EV and PV can break the ties between driving and burning fossil fuels—including the coal, natural gas, or other nonrenewable energy sources used by utilities to produce electricity.
At first, you might think of putting PV modules on top of your car—but due to the efficiency of PV modules and the limited size of a car’s roof, the amount of energy that can be produced isn’t going to help much. Even if you covered the 16 or so square feet of your EV’s roof with PV, on a day of full sun, the energy would cover only a couple miles of driving. The small PV spoiler on the Nissan Leaf is good only for recharging the car’s 12-volt accessory battery. And you’ve probably seen lightweight, low-speed solar concept cars with huge roofs to increase PV surface area.
But a more realistic approach is to use a large-enough grid-tied PV system to offset the daily energy you’re using to charge your EV. When your home PV system is producing power during the day, any appliance that’s running in the house—lighting, television, or an EV charging station—is directly fed by solar power.
Even when you charge at night—as you should, because it’s often cheaper and greener (see “Utility Power Can Be Greener at Night” sidebar)—your electric car can benefit from clean home-produced electricity. Here’s the reason: the PV system is tied into the grid—pumping excess electrons out to be shared by all utility users. Think of the grid as an energy bank, where you deposit green power when the sun is shining, and withdraw those energy credits when you need them.
In many regions of the country, electric utilities rely heavily on fossil fuel as a source. This inspires one viewpoint that EVs are not much greener than a Prius-like hybrid or a small fuel-efficient internal combustion engine-powered car like a Ford Fiesta. Having a grid-tied PV system can put a quick end to this concern.
But even if the environmental question is somewhat settled, debates on the economics of EV and PV are less easily resolved. The traditional argument against both PV systems and electric cars is that you are paying more upfront—on expenses that might take years or decades to pay back through reduced energy and gasoline expenditures.
Arguments for or against these investments are elusive. As usual, the devil is in the details—with a broad set of variables, including:
Now add all the uncertainties regarding financing plans for both your car and PV installation—and add in unpredictable and unstable oil and electricity prices. Finally, don’t forget to include the resale value of an electric car. Even if upfront costs are not recovered during the period of ownership—by cheaper fueling and maintenance—any difference is commonly recouped upon sale of the car. Similarly, the value of your home is often increased after adding a PV system. It’s a home amenity (like granite countertops), but one that saves money each month.