Vehicle-to-grid charging: What you need to know

Solar and storage continue to increase in popularity throughout the country, and why not: Pairing a solar battery with a solar panel installation provides an affordable, clean, reliable power supply for your home. At the same time, electric vehicles continue to become more and more mainstream: in 2019, the millionth electric vehicle hit the road in the US, and EVs were even heavily featured in Super Bowl ads.

With more homeowners than ever considering solar + storage solutions and with more car purchasers than ever opting for electric vehicles, the natural next question is: can I use the battery parked in my driveway to back up my whole home? Enter vehicle-to-grid technology.

At its core, vehicle-to-grid technology (or V2G) is what allows you to take the electricity stored in your electric vehicle's (EV) battery and either use it to power your home or send it back to the grid, as you would with a net-metered solar panel system.

So far, the functionality of EV batteries and chargers has only worked in one direction: you can put electricity into your car, but you can't take it out. In practice, this makes sense, as it is exactly the same way that a traditional internal combustion engine, gasoline-powered car functions: you wouldn't (or at least shouldn't!) take the gas out of your car after you've filled the tank.

However, batteries have many technological advantages over static fuel tanks, including the ability to both charge and discharge. V2G takes advantage of this capability by allowing you to not only accept electricity from the electrical grid but also to send it back to the grid or your home.

EV batteries are typically 5 to 10 times the size of a home solar battery: most EVs contain a battery with between 75 kilowatt-hours (kWh) and 100 kWh of capacity, while the most frequently installed home batteries–the LG Chem RESU 10H and the Tesla Powerwall 2–store 9.3 kWh and 13.5 kWh, respectively.

At a residential level, V2G technology could allow you to back up your entire home without needing to install a solar battery or in addition to a solar battery. Given that your EV's battery is so much larger than a standard home battery, you may even be able to avoid a critical load panel and power appliances like an HVAC that would otherwise be difficult or impossible to power with a single solar battery. Additionally, in places with time-of-use rates or that don't have one-to-one net metering (i.e., where every unit of electricity you put onto the grid is credited as one full unit of electricity you can use from the grid later), V2G technology allows you to improve the financials of going solar.

At a larger scale, the implications of V2G technology are exciting and seemingly limitless. For instance, imagine a future where you drive your EV to work and park it in a parking lot covered by solar canopies, where it charges during the day along with all of your coworkers' EVs. When prices on the grid increase in the mid-day summer heat, all of these EVs respond and pump that stored, clean solar energy back onto the grid and get paid to do so. And your EV knows that, since it's a Wednesday, you go to the grocery store and lead pickup from after-school activities, so it stops discharging to the grid to leave more than enough charge in your battery to run your errands and keep you moving if any unexpected additional errands arise.

In both cases, V2G technology allows you–and the electrical grid as a whole–to better integrate more and more renewable energy, acting as a mobile storage device on wheels.

At present, V2G technology is only just gaining traction. Two separate articles add some hope that bi-directional chargers (and batteries) for EVs will be available in the US promptly.

In 2019, international manufacturer Wallbox introduced their EV charging system in the US market, with plans to rollout their bi-directional platform in 2020 and beyond. This charger is a 7.4 kilowatt (kW), bi-directional charger that opens up access to the benefits described above to any EV owner when they install this Level 2 charger.

More recently, reports emerged that Tesla may be actively preparing their vehicle fleet for bi-directional charging and discharging functionality with the electrical components already included in standard Tesla vehicles. This type of technology would be important because it would allow a Tesla owner to receive the benefits of V2G technology with the EV charger they already have. Note: subsequent analysis and an update to the media reports indicate that this is not the case and that Tesla's onboard inverters are not capable of bidirectional charging and discharging.

Interested in the benefits of vehicle-to-grid technology but can't wait for it to become more commercially available? A great place to start is by checking out solar + storage on EnergySage. Investing in a solar + storage solution for your home is a great way to provide backup power in the event of outages that is cleaner and, in the long run, more affordable than a backup generator. Additionally, installing solar–alone or with storage–is a great way to generate financial savings for 25+ years. To see how much solar can save you, check out EnergySage's Solar Calculator. To receive no-cost, no-risk custom solar and storage quotes for your home, register for an account on the EnergySage Marketplace.