For the eco-conscious EV driver, an electric vehicle is only as clean and green as the source of electricity charging its battery.
That’s because EVs plugged into the grid can either be powered by “dirty” sources such as fossil fuels such as coal, or from “clean” renewable energy that comes from sources such as solar, hydro or wind power. With many utilities, it’s likely to be a mix of renewables and fossil fuels. The best way to ensure your EV is actually powered by renewable energy is to connect your home’s EV charger to a solar energy system or use a public charger also sourced by solar panels.
With spiking gas and electric prices and an intensifying climate crisis, it’s no wonder the solar and electric vehicle industries are gaining in popularity each year. Rooftop solar panel installations are breaking records, and US EV adoption is expected to accelerate — predicted to reach 40% of passenger car sales by 2030, according to the US Bureau of Labor and Statistics.
Forget the statistics, it’s in plain sight and we can’t ignore it. EV charging stations are becoming the norm, automakers are making headlines as they invest in new EV technology, and rooftop solar panels are also becoming commonplace to see.
Even with the upswing in EVs and home solar systems, switching from a combustion car to an electric vehicle, however, can be a complicated decision with considerations conventional car drivers don’t have to worry about, like installing a charger in your garage. Adding solar panels to the equation adds even more layers of complexity to an already significant investment.
Here’s what you need to know about powering your home and EV with solar panels and how many you’ll need if you do.
Why use solar panels to charge an electric vehicle (EV)?
There are some less obvious benefits to home solar charging in addition to watching free, clean electrons pulled from the sky streaming into your car’s battery.
Most home EV chargers treat your car like any other appliance that needs to be plugged in and charged overnight. Actually, it’s more like a quite needy appliance that requires a particular current (DC) and lots of it as quickly as possible, which can mean operating at high voltage.
All of this increases strain on the grid and can add a load to your home’s electrical system, especially if your wiring is older or in need of upgrading. In the worst cases of neglect or poor electrical work, it can even be dangerous.
Using solar panels to charge an EV actually streamlines the charging process because both systems speak the same electrical language, in a way.
As Wyldon Fishman, founder of the New York Solar Energy Society, explained, solar panels and electric vehicles both operate with direct current (DC), meaning there’s no need to install an inverter between your panels and EV, although a charge controller is still imperative to have in the circuit. DC can also run at lower, safer voltages.
Relying on solar panels rather than the grid to charge your electric vehicle also means not having to worry about being stuck at home with a dead battery if the power goes out, especially if you opt to pair your panels with a battery or other solar storage.
How much energy is needed to charge your EV at home?
First, consider your goals for your solar charging system. Do you want to charge your car using your solar panels, and will you primarily be charging overnight? If so, you’re going to need to install a battery or other storage system.
In most cases, you’re likely to have a solar system that’s hooked into the grid as well as your home, perhaps with a connected battery for emergency backup, or not.
If this is your scenario, it could be helpful to know how much of your existing solar output the rest of your home is consuming. If you never pay a utility bill or your utility bill is primarily for nighttime or cloudy days (when your solar panels aren’t at work), this means your existing solar system is probably producing more than you need and the extra is being fed into the grid or a battery or both. Some of this excess energy could be used to charge your EV, meaning you will need fewer solar panels to drive a fully solar-powered car.
Once you’ve got an idea of whether you’re running a solar surplus, the next step is determining how much additional demand an EV will add to your system.
How many solar panels will I need to charge just my EV?
First, consider how much you typically drive in a day. Put simply, the more you drive, the more wattage you’re likely to need in panels.
Here’s the steps to figuring out how your average daily energy needs to power an EV.
Step 1. Determine how many kilowatt-hours your EV uses per mile. The EPA and US Department of Energy’s fueleconomy.gov site lists the estimated efficiency of all electric cars in kWh per 100 miles; simply divide by 100 for a per-mile estimate.
Step 2. Multiply your EV’s kWh/mi by the number of miles you anticipate you drive on an average day. (You can get your average daily miles by observing your driving habits for a few days or by dividing your annual observed mileage by 365). This gets you the total number of kilowatt-hours you’ll need to produce to power your daily driving.
Step 3. You can then divide the EVs needed kilowatt-hours by the number of peak sun hours you can expect to receive at your location each day.
Step 4. The final figure should give you the size of your ideal EV-charging solar array in kilowatts.
Step 5. To calculate the number of panels you’ll need, the wattage of the solar panel comes into play. The most efficient solar panel wattage can range from 370 to 465 watts. After you choose your best solar panel brand, convert the panel wattage of the panel to kilowatts by dividing by 1,000.
Step 6. Final math is to divide the EV kWh requirements by the solar panel efficiency in kWh to get the number of panels needed to charge the EV.
The formula:
- kWh/mi for your EV x average miles driven in a day = total kWh production for the EV
- Total kWh production needed for EV / local peak sun hours = size of ideal solar system (in kW)
- Convert the solar panel wattage of the brand of choice to kilowatts by dividing by 1,000.
- EV production needed (in kWh per day) / panel efficiency (in kWh) = number of solar panels needed
Example math:
Take the example of the Hyundai Ioniq 6, the most energy efficient electric sedan on the road today:
Step 1. According to fueleconomy.gov, it averages 24 kWh/100 mi or 0.24 kWh/mi.
Step 2. We’ll also use the EPA’s average mileage estimate of 15,000 annual miles, which works out to around 41 miles per day.
Step 3. 0.24 kWh/mi x 41 miles = 9.86 kWh daily power EV usage
Step 4. 9.86 kWh / 4 peak sun hours = 2.4 kW (This is how much solar energy in kW you will need to charge your EV).
Step 5. We will use a solar panel wattage of 410W, such as the Q.PEAK Duo Black from Qcells, to calculate the number of panels needed for the Hyundai Ioniq 6. Convert the 410W to kilowatts by dividing by 1,000 (0.41 kW).
Step 6. EV production needed to charge the Hyundai Ioniq 6 (in kWh per day) / energy needed per Q.PEAK Qcells solar panel) = number of solar panels needed. 2.4 kW / 0.41 kW = 5.85 solar panels
In this example, six Qcells solar panels are needed to accommodate the energy needs of the Hyundai Ioniq 6 with average driving habits. Six Qcells solar panels don’t accommodate the rest of the home’s energy consumption.
Meanwhile, at the other extreme, dropping the Ford F-150 Lightning’s 48 kWh/100 mi into the same formula yields a daily energy use of 19.68 kWh and a 4.9 kW solar requirement, doubling the Qcells solar panels needed to 12 panels.
If that’s too much math, Fishman simply recommends putting around eight to 12 solar modules on a canopy that you can use as a solar carport.
“It’s about 2.5 kilowatts that you need for a canopy. You might go a little more, but that’s all you need,” Fishman said.
We’ve seen others in the industry put the figure at closer to 3 kW, but if you’re unsure, you can run through all the math for your situation.
How many solar panels will I need to power my whole home?
This basically comes down to figuring out your home’s total energy needs and then designing a solar array that can meet those needs.
To calculate how many solar panels your home will need: Desired energy production (kW) / Solar panel wattage (kW) = Number of solar panels needed
There’s a lot of things to consider to determine both sides of this equation, and CNET goes into further detail on the subject here. Adding EV chargers to your home simply means adding more energy use to both sides of the equation.
Most reputable solar companies will help you work out your energy needs and propose a solution that they will surely be willing to install for you. But doing the math on your own as well can help you make the most informed choice when it comes to picking an installer and assisting in designing a system that meets your needs best.
Don’t forget that there are other things you might want to do before even beginning to consider solar for your home. Making energy efficiency improvements can go a long way toward shrinking your overall needs and thereby shrinking the size of the solar system you require.
Is it worth it to add more solar panels to accommodate an EV?
Adding more panels to your existing solar system or to one that you’re planning is one way to power all your home’s energy needs, including your EV. But it isn’t necessarily the only way to charge your EV. You can also build a stand-alone off-grid system that’s dedicated to just your car.
Fishman recommends building a carport topped with solar panels at just the right tilt to get a good amount of sun on average, based on your location on the globe.
“A carport is fixed at latitude,” she explained. “So if you’re at 42 degrees above the Equator, then your tilt for your solar modules is 42 degrees.”
Which comes first: A solar panel or EV purchase?
If you’re dedicated to renewable energy and kicking fossil fuels to the curb, it makes sense to have your solar system all setup before you spring for the EV so you never have to worry about charging your car from dirtier energy sources that mix with renewables on the grid.
But the reality for many people will be that an EV and home solar energy are two very costly investments. A car or EV tends to be a personal purchase that we spend a lot of time in, whereas energy is a readily available commodity that we tend to think about less. So it wouldn’t be surprising for people to prioritize a flashy new EV over adding solar panels to a home that already has access to electricity via the grid.
Ultimately, it comes down to your priorities and your situation. Maybe your utility is good about incorporating solar into its energy mix via its own solar farm systems, renewable energy credits or offering a community solar program. If so, you might have fewer qualms with plugging in your car at night, no matter how many panels are on the roof.
