No matter where or when they are charged, electric vehicles (EVs) are cleaner than gasoline cars. Using electricity from the electric power grid, though, is associated with some emissions. For a truly emissions-free experience, many EV owners are turning to renewable energy to charge their vehicles. According to one 2019 survey, more than 30% of U.S. EV drivers have solar arrays.
Adding solar to your house produces environmental improvements and can provide financial benefits as well, but as with any home improvement project, it is important to do your research before diving in. Below, we provide some items to consider and steps to take as you work through the process.
One note before we get started: There are two ways to think about charging on solar. If you purchase a photovoltaic (PV) system that is completely independent of the grid, you will always and exclusively be home charging on sunshine. Even when the sun isn’t shining, stored solar energy from a battery bank can be called upon. Likewise, some public charging stations have this setup.
Alternatively, and more likely, you will use solar to offset how much electricity your EV (or home) uses. Even if the grid is supplying the real-time power you use to charge (if you’re charging overnight, for example), your array will generate enough energy during other parts of the day to account for some or all of your charging.
Sizing Your Array
One of the first things to think about when deciding to install solar is whether you want your array to cover just your EV charging, your home’s entire electricity usage or something in between.
An initial goal should be to look at your past electricity usage in monthly and annual kilowatt-hour (kWh) consumption. For your home, this information should be available on your electric utility’s account portal; for your EV charging, it may be accessible through your home charging station or can be calculated. For example, let’s say your EV uses 290 watt-hours per mile, or travels 3.45 miles per kWh. If you drive 12,000 miles each year, your EV would consume approximately 3,480 kWh of electricity, or 290 kWh per month. Depending on how much charging you do at home, you might consider an array that produces around that much solar energy. (Keep in mind that your driving, and home energy use, habits may have changed due to the COVID-19 pandemic.)
Knowing your usage information is useful for determining what percentage of your energy consumption you want to supplement with solar, and in general, it is helpful to have an idea of your preferred system size before talking to installation companies. They can help you determine what you ultimately need, but this knowledge will allow you to better participate in the process.
Choosing Your System
You have a few setups to choose from, each with its own pros and cons, costs and use cases. For all types, however, it is useful to ensure that your home is energy efficient, which can help you save money when purchasing the array and may allow you to go with a smaller array size.
Grid-connected Systems: Grid-connected systems are the most common and cheapest to install. With this setup, the solar energy produced is either used in your home or captured by your utility through a meter before it goes onto the grid. Because your home is connected to the grid, if the solar array does not supply all of your energy needs, the grid is there to fill in. If, on the other hand, your array produces more energy than you need, you may receive a credit from your utility that can be applied later.
Hybrid Grid-connected Systems with Battery Backup: This design is similar to a grid-connected system but has a small battery bank that can be called on to power your home or critical appliances, including your EV charging station, when your array is not producing. How long your appliances, or entire home, stay powered depends on the size of your battery bank.
Off-grid Systems: These systems are completely independent of the grid. In other words, even if there were a citywide outage, your home would still have power. Off-grid systems are the most expensive but offer complete energy independence. A larger battery bank is needed that is typically able to power your home for 3-5 days and meet your energy demands through nights, cloudy days and storms. Off-grid-type configurations also exist specifically for EV charging, allowing you to power your EV solely with your solar array.
Locating Your Array
Rooftop: This is the most common placement. Because roof space is typically not used for anything else, locating the array here leaves real estate open for other purposes. There is also generally less shading to worry about and minimal aesthetic impact, as most people install the array flush with their roof.
Ground-mounted: Ground-mounted systems make it easier to perform maintenance or replace modules because they are more accessible. If there is a lot of shading around your house, the system can be installed in a location that captures more sunlight. However, the farther away the system is from the home, the greater the losses and the lower the performance.
Custom Design: Custom designs are least common but available to fit particular needs. The biggest downside is price, as they will cost more than other systems.
Finding an Installation Company
There are a few ways to go about finding a solar installation company. If you have neighbors or friends who have added solar, ask them about their installer and experience. In addition, you can reach out to your electric utility for recommendations and search online for companies in your area.
Focus on local companies who are likely more familiar with your utility and ordinances. Their proximity will also bring down the price of the system, and companies located farther away may be hesitant to perform the installation because of travel time.
Be sure to research companies before reaching out. Check reviews and look at previous installations, how long they’ve been in business and their licensing. When you are ready to move forward, get bids from at least three installers. Bids should come after the company performs a site assessment at your home.
Be wary of contractors who say you’ll have no more power costs, and keep in mind that the cheapest bid may not be the best. A low price could signify inexperience or poor construction practices. Quality should be considered over price, and before signing a contract, have an attorney or lawyer read over it if possible.
Other considerations that arise when pursuing solar include the array’s layout and orientation, your utility’s policies and programs, potential additional costs (such as electric service upgrades), and financing and incentive options. For information on these topics and more information on the topics discussed above, check out these two articles from Advanced Energy: What to Know Before Installing Solar at Home and Deciding “Yes” on Solar.
EVs and PVs in Action
To hear about EVs and solar PV systems in action, we reached out to a few of our Plug-in NC ambassadors to learn about their experiences.
Chris, who lives in Raleigh, has been driving on sunshine since 2016, when he got his first EV and installed his solar array. Chris’s rooftop system is 4.3 kilowatts (kW), which has met about 80% of his home charging over the past four years.
In 2019, Chris’s fleet of EVs — he has a BMW i3, an Energica Eva motorcycle and a Hyundai Ioniq — consumed just over 5,000 kWh of energy, and his solar array generated 4,429 kWh, good for over 88% of his charging and savings of close to $500. In the first half of 2020, his solar offsetting reached 107%, meaning his array produced more energy than his EVs consumed. Chris said that in the last four years, he has spent less money to charge at home than he would have spent on gasoline in just four months of owning a gas-powered car.
Asheville-based Dave has a 6-kW solar array that meets the home charging needs (and more) of his Tesla Model 3 and Chevrolet Spark EV. In 2019, Dave’s two vehicles consumed 5,636 kWh of solar energy, and he reported savings of over $600.
Ben, located in Charlotte, got his 10.5-kW solar array in March 2019 and his EV — a Tesla Model 3 — in August 2018. So far, Ben is able to complete about 95% of his home charging with solar energy and is seeing savings of around $20 per month.
David, from High Point, has been charging his EVs on solar since 2015, when he had his array installed. David’s system is the biggest of the bunch — at over 20 kW (along with battery storage), it covers nearly all of his home electricity use outside of December and January, when solar production tends to be lowest.
David computes his savings by taking into account his reduced electric bills and the amount of gasoline he avoids purchasing, which is a lot considering he drives over 30,000 miles each year. Altogether, David paid just $297 to his utility in 2019 — on a total home energy usage of 20,186 kWh — and saved around a whopping $3,000.
It’s no surprise that so many EV owners are exploring solar. The perks of driving and charging on sunshine can be significant, and as prices for both technologies continue to drop, we expect we’ll see even more emissions-free travel.