What if we could use the energy stored in electric vehicles (EVs) to supplement power on the national grid when local sources of renewable energy like solar and wind become unavailable? Or to help commercial buildings reduce their demand for electricity from fossil-fuel-burning power plants? Or even to power a commercial building following a public safety power shutoff by the local utility?
Actually, that day is already here for an increasing number of owners of fleets of electric-powered vehicles including cars, vans, school buses, and light- and heavy-duty vehicles.
Unfortunately, most U.S. consumers do not currently have easy access to this vehicle-to-grid (V2G) integration process. But the good news is that costs are coming down, state energy commissions are focused on shaping relevant power-sharing standards, and increasing numbers of auto original equipment manufacturers (OEMs) and EV charging station manufacturers are planning how best to incorporate V2G capabilities into current or future models.
Driving in a One-Way World
Today, most electric EVs and EV charging stations in the U.S. are set up for unidirectional (one-way) charging: Power flows only from the charging station to the battery of the vehicle.
Some vehicles, such as the 2021 Ford F-150 Hybrid pickup, feature multiple 120-volt power outlets in the bed of the truck for powering tools and small appliances. And many utilities offer incentive programs to EV owners to use “smart charging” (V1G) technologies to automatically charge their cars during off-peak hours when electricity rates are lowest. But neither of these approaches allows power from an EV’s battery to be shared with the electric grid.
V2G at a Glance
V2G operations require two things: an automobile with bidirectional charging capabilities (one that can both charge and discharge its battery) and an EV charging station that can both charge car batteries and send power back to the grid. The only consumer car currently available in the U.S. with bidirectional charging is the Nissan Leaf. Other auto manufacturers such as Mitsubishi, Toyota and Volkswagen are building models with bidirectional charging, but none that are available for purchase in the U.S.
V2G chargers come in two varieties: AC (alternating current) and DC (direct current). An AC V2G charger — the less expensive of the two — supplies AC power from the grid to the EV, which converts that power to DC using an onboard converter, then sends the DC power to its battery. Upon discharge, the EV pulls DC power from its battery, converts the DC back to AC using an onboard inverter, then returns the AC power to the charging station, which delivers the power to the grid.
By contrast, a DC V2G charging station converts grid-supplied AC power to DC, then sends it directly to the EV’s battery. Upon discharge, DC power flows from the battery back to the charging station where an inverter changes the DC power back to AC, which then flows back to the grid.
Changing the Rules
In the U.S., energy “aggregators” such as San Diego-based Nuvve work with owners of fleets of medium to large electric vehicles to participate in the V2G power-sharing market. Nuvve uses proprietary software to control via the Internet the times and rates at which V2G charging stations charge fleet vehicles or deliver power from those vehicles back to the grid. The V2G software allows vehicles to be charged when demand for (and cost of) electricity is lowest.
“We’re able to directly access the controls of the vehicles and the charging stations and control that rate of charge,” explained Marc Trahand, Nuvve’s executive vice president of marketing. “With our software, we can combine the power from batteries from all of these vehicles on a regional basis, creating what we call a virtual power plant, or one big virtual battery.”
That aggregated level of energy, he continued, is a source of high value to fleet owners.
“With our virtual power plant, we can sell energy to local or system-level energy markets and share that value with the owners of the batteries,” said Trahand.
Increasingly, energy stored in EV batteries is being sold into energy markets to help compensate for second-to-second power fluctuations that occur because the grid is being powered increasingly by renewable energy.
“Solar and wind power have natural, built-in-variability, so when you use them to replace the power from a stable, natural gas-burning power plant, you get minor disturbances on the grid,” Trahand explained. “We can smooth out those disturbances with energy storage, and V2G is a perfect way to provide that extra storage.”
He added that V2G can also become a valuable grid ally in states such as California that generate immense amounts of renewable energy during the day but then have to rely on other, often “dirty” greenhouse-gas-producing sources of power to meet the spike in demand when consumers come home and start turning on their appliances.
“With V2G, we can charge cars during the day using clean solar energy, then push any energy left in the EVs back into homes to help minimize the demand peak in the evening,” explained Trahand. “By charging these cars late at night, after the peak load is gone, we can help EV owners make optimum use of their car batteries.”
Easing Peak Demand
Another application for storing and managing EV energy with V2G is called vehicle-to-building, or V2B.
“Once we’ve got control of a battery, there are lots of things we can do with its power,” Trahand noted, “including sending it back to a building.”
Depending on the size of the building and number of EV batteries available, he continued, V2G could be used to minimize a building’s peak energy demands or minimize its “time of use” energy charges.
Putting Fleets to Work
Nuvve is working to mature and speed the deployment of V2G technology by partnering with OEMs of electric school buses, such as Lion Electric in Quebec, Canada, and Blue Bird Corporation in Fort Valley, Georgia. The goal is to include bidirectional charging and V2G compatibility in as many new electric school buses as possible.
Electric school buses are an ideal application of V2G because the vehicles spend just a few hours per day delivering students to or from school and the rest of the day waiting in a school bus yard. This midday waiting period is ideal for charging the buses, storing energy or sharing energy with the grid.
However, Trahand is quick to point out that the company’s grid integration software will never leave a vehicle with insufficient power to perform its transportation duties.
“We know the drive patterns of each bus, we know how much energy should be in that bus before it’s time to drive out of the yard,” he emphasized. “Having sufficient charge for a vehicle’s daily driving duties is our number one priority.”
Educating the Regulators
V2G research and development is also taking place at the other end of the educational spectrum, thanks to grants provided by the California Energy Commission (CEC).
“We want our policies to send the right signals to the marketplace to encourage smart use of the grid,” suggested California Energy Commissioner Patty Monahan. “We’d like to see charging happening at times of the day that are optimal for the grid. We think that aggregators, with their work in the medium- and heavy-duty electrification space, will play an important role in shaping the behavior and performance of that future grid.”
In 2017, CEC provided a $4.2 million grant to help fund a three-year demonstration of V2G chargers on the UC San Diego campus. Under the Intelligent Electric Vehicle Integration (INVENT) program, 50 owners of EVs drove their cars normally during the day but then connected to V2G chargers at night to demonstrate how the energy from their EV batteries could be shared with the grid with positive effects without hindering the day-to-day operation of the vehicle.
In Trahand’s perfect future, fleets of Amazon, UPS and FedEx trucks would also be electrified and connected to V2G networks — thereby reducing the release of greenhouse gases in metropolitan areas while adding resilience and stability to the grid.
Bringing the Future Closer
And while prospects for consumer-sized, consumer-priced V2G technology remain limited in the near term, the world is definitely changing.
“Until now, the V2G chargers we’ve been using have been the size of a refrigerator,” explained Trahand, “and no one wants that in their driveway.”
The next generation of chargers, he believes, will be much smaller, wall-mounted boxes that would allow consumers to start participating in the V2G market. And regulators’ understanding of the technology and where it fits on the spectrum of grid operations is continuing to evolve.
Trahand equates V2G technology today to the early days of cell phones “where phones were big and you needed a suitcase for your battery.”
“Bit by bit, this technology is getting better, it’s getting smaller, and it will eventually be integrated inside every electric vehicle,” he said.
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