electric vehicle charging in front of solar panels

Solar energy and electric vehicles (EVs) are a winning combination. If you drive an EV, but charge with power that has a lot of coal in the energy mix, it boosts the climate impact of driving. Thus, charging your EV with renewable energy is a great choice. Also, charging with solar panels is an excellent way to reduce your fuel costs and get the greatest value out of your solar PV system.

Most solar panels on the market are around 15%-20% efficient in converting sunlight into electricity. This means that fewer solar panels are needed to produce the same amount of energy compared to solar panels from a decade ago. Because PV modules are more efficient than ever, many houses have enough roof space to provide power for the home and charge a vehicle.

Whether your roof is able to fully power both your home and your EV depends on the following factors.

  • Solar equipment efficiency: The solar panels, inverter, and optional batteries are all factors
  • Solar potential of the property: If there is shade from buildings, trees, house features, etc.
  • Size of the south-facing roof: Most solar panels are installed facing south and sometimes installed facing east or west
  • Energy use of the home: Look for information on your utility bills of kilowatt-hour (kWh) usage
  • Efficiency of the EV: The average EV needs 30 kWh per 100 miles
  • How much you drive: The average EV owner drives 5,300 miles per year
  • Where you charge: If there is a robust charging infrastructure in your area or you only charge at home
  • Your local climate: The amount of available sunlight where you live throughout the year

Before installing a solar energy system on your home, it’s good to examine energy efficiency. Do you have energy-hogging appliances or electronics that should be replaced? Do you have energy-efficient lighting? Can you make minor adjustments to consume less energy, such as rinsing dishes in cold water, installing an energy-saving showerhead, or reducing the use of your air conditioning?

How much power does your electric vehicle consume?

In general, EVs can consume about 25 to 35 kWh per 100 miles. The exact efficiency of an EV depends a bit on your driving style, the outdoor temperature, and the type of driving you are doing. Unfortunately, efficiency declines in cold weather. Also, the model of the car you drive is a big factor in how much electricity your EV will use. The U.S. Department of Energy has information on the efficiency of specific models.

Where do you charge your EV?

Another big factor in sizing your solar system is considering where you charge your car. Do you only charge at home or do you charge on the go a lot? As the network of electric vehicle charging stations increases, you might start charging on the go more often, in shopping malls, friends’ homes, or at work. How appealing this option is might also depend on the cost of charging and if the energy comes from renewable sources of energy.

How many solar panels will you need to charge your car?

Once you know roughly how much you drive, where you charge, and the efficiency of your car, you can begin plugging in some numbers. Let’s assume you drive about 10,000 miles a year, only charge at home, have a sunny south-facing roof, and live in Chicago or Portland, Maine. Then, you’ll need about eight 350-watt solar panels to charge your EV.

Let’s say you drive just 5,000 miles, only charge at home, and you live in San Diego, California, without any shade. Then, you’ll only need about 3 solar panels to keep your car charged. If you had the same set-up but the home is located in Seattle, you would need an extra panel or so.

What if you don’t have enough roof space for solar panels?

Some properties are shaded or don’t have much south-facing roof space. Other EV owners may rent, so it doesn’t make sense to go solar. Another option is to join a community solar farm. Although models vary, most community solar farms follow a subscription model. This means that you can buy discounted power from a solar farm and pay no upfront investment.

The community solar market varies widely by state and its policies. Currently, CA, CO, CT, DE, HI, IL, MA, MD, ME, MN, NC, NH, NJ, NY, OR, RI, SC, VT, and WA are the best states for community solar installations.

By Sarah Lozanova

Sarah Lozanova is an environmental journalist and copywriter and has worked as a consultant to help large corporations become more sustainable. She is the author of Humane Home: Easy Steps for Sustainable & Green Living, and her renewable energy experience includes residential and commercial solar energy installations. She teaches green business classes to graduate students at Unity College and holds an MBA in sustainable management from the Presidio Graduate School.