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