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As a historic 10-day heat wave threatened brownouts across California last summer, a small San Diego County school district did its part to help: It captured excess power from its electric school buses and sent it back to the state’s overwhelmed grid.

The eight school buses provided enough power for 452 homes each day of the heat wave, and the buses were recharged only during off hours when the grid was not strained.

California energy officials have high hopes that this new power source, called bidirectional charging, will boost California’s power supply as it ramps up its ambitious agenda of electrifying its cars, trucks and buses while switching to 100% clean energy.

Gov. Gavin Newsom called two-way charging technology a “game changer,” saying “this is the future” during a speech last September, about a week after the heat wave ended.

This year, a bill already approved by the state Senate in a 29-9 vote would require all new electric cars sold in California to be equipped with bidirectional technology by 2030. In the Assembly, two committees approved the bill earlier this month and it is now under consideration by a third.

This two-way charging has big potential — but also faces big obstacles. By 2035, California expects to have 12.5 million electric cars on the road, but it’s an open question how much California can rely on them to feed the grid. Automakers say the technology would add thousands of dollars to the cost of an electric car, and California’s utilities are still sorting out how to pay ratepayers for selling them the kilowatt hours.

The ability to use electric cars, trucks and buses to feed energy back into the grid would be especially helpful during peak times for energy use, such as heatwaves. But relying on vehicles as a year-round power source may not be practical — at least not yet.

“It’s a great idea conceptually…but we haven’t had the time to flesh out the details of what needs to happen for California to be able to power itself on electric vehicles,” said Orville Thomas, state policy director for CALSTART, a sustainable energy nonprofit.

“It should be on the menu of options that California has. Is it going to be the number one option? Definitely not.”

So far, its use has been limited in California. Pacific Gas and Electric has a pilot program — the first in the nation — that lets up to 1,000 residential customers with bidirectional chargers sell power back to the utility. Some school districts also are experimenting with it.

Only about half a dozen electric car models currently are equipped with bidirectional capabilities, including the Hyundai Ioniq 5, Nissan Leaf and Ford F-150 Lightning. Tesla announced recently that all its models will have it by 2025.

Electric vehicles convert one type of energy, alternating current electricity, into another, direct current, which is stored in a battery. Bidirectional charging means that an electric vehicle can convert the energy it has stored in its battery and send it to other sources, such as home appliances or back to the grid.

Willett M. Kempton, a University of Delaware professor who has studied bidirectional charging for more than two decades, said the vast majority of the time a vehicle is parked and not using electricity.

“Five percent of the time you’re using the car and you want to have enough energy — electricity or gasoline — to get to where you’re going and back. But most of the time, it’s just sitting there and some other use could be made of it,” he said.

Kempton said these vehicles, properly managed, could be sources of reserve energy, supplanting backup sources that burn fossil fuels. 

Gregory Poilasne, co-founder and CEO of Nuvve Holding Corp., which sells electric fleet charging services, said a big challenge is that cars are unreliable energy assets. “At any time, somebody might come in and unplug the car,” he said. But he added, as the technology becomes more reliable and affordable, bidirectional cars and fleets should increase. 

The cost: $3,700 per car

In Denmark, bidirectional charging earns electric vehicle fleet owners who sell power to the grid $3,000 per vehicle a year, Poilasne said, adding that this reduces the average total cost of electric car ownership by about 40%.

But citing the high cost, automakers oppose the Senate bill that would mandate the chargers for all new cars sold in California by 2030. It would increase the average cost of an electric car by $3,700, according to an opposition letter written by Curt Augustine of the Alliance for Automotive Innovation, which represents General Motors, Ford and other major auto companies.

About $3,000 of that cost would be adding battery capacity to meet warranty requirements, while other costs are for hardware and software.

“This technology is a competitive matter between vehicle manufacturers and should remain that way,” Augustine wrote. “Not all customers will see an advantage of bidirectional charging, and therefore, should not have to pay more for a technology that they will not use.”

Thomas of CALSTART agreed, saying it should be optional.

“There might be a situation where there are people that want to do it and will pay a little extra for a car that is bidirectional, but there will also be people that just want to use a vehicle for driving,” he said. “Do we raise the price of electric vehicles for everybody?”

But Sen. Nancy Skinner, a Democrat from Oakland who authored SB 233, said she wants to ensure that automakers don’t reserve the technology for only their higher-end models. She said since the relatively affordable Nissan Leaf has it, it can be widely available.

Skinner said all consumers would benefit from the technology by selling energy to the grid or using the energy in emergencies. But she said another important reason is that it could end reliance on diesel generators during power emergencies like during wildfires.

“If you have an EV you don’t need that diesel generator,” Skinner said. “Why would we want to encourage diesel generators? They’re extremely polluting.”

Jeffrey Lu, an air pollution specialist with the California Energy Commission’s vehicle-grid integration unit, said the state is working with owners to identify the best times to charge — called smart charging — to protect the grid. Bidirectional charging takes the concept a step further, he said.

The Energy Commission is not yet ready to say how reliant California will be on bidirectional charging to provide sufficient power and meet the state’s 2045 mandate for carbon-free electricity.

“We’re fairly early in this process. California is very committed to load flexibility broadly, but where that load flexibility specifically comes from, how many megawatts or gigawatts are coming from any particular kind of resource? We’re working on that,” he said.

California’s utilities are running pilot projects and studying how bidirectional charging might work and how electric car owners could be compensated for selling energy to the grid.

The California Public Utilities Commission has studied the issue for more than a decade, said spokesperson Terrie D. Prosper, including funding pilot projects and establishing two working groups.

Last year many utilities signed a “Vehicle to Everything” memorandum of understanding with car manufacturers, state agencies, the federal government and others seeking to accelerate all aspects of bidirectional charging.

Southern California Edison, which serves about 5 million businesses and residences, wants to go beyond using bidirectional charging as just an emergency backup. 

Chanel Parson, Edison’s director of electrification, said the utility is working on a rate program that would allow customers to sell their power back to the grid every day of the year. 

“By selling it back to the grid when our rates are more expensive, then that actually helps reduce customers’ energy bills. And it could be so economically attractive that they’re actually making money,” she said.

Pacific Gas and Electric, which serves 5.5 million electric customers in Northern California, said it is aggressively looking to build what it calls a robust vehicle-to-grid-integration. It has partnerships with BMW of North America, Ford Motor Company and General Motors exploring bidirectional charging.

The utility last year launched the nation’s first bidirectional charging pilot available to residential customers, offering up to 1,000 customers $2,500 for enrolling and up to an additional $2,175, depending on their participation.

The Los Angeles Department of Water and Power also is conducting a pilot project using a small fleet of its Nissan Leafs. The utility hopes the technology will eventually provide power during peak load times. 

“Five years is definitely within reach,” said José María Paz, the utility’s project manager for vehicle-to-grid integration. “Technology is advancing quite fast.”

School buses are a test case

The electric school buses at the Cajon Valley Union School District in San Diego County are among a number of school district pilot projects in California. Experts see school buses as a good option for two-way charging because they have set routes and are often parked during peak load times between 4 p.m. and 9 p.m.

Nationally, Nuvve has about 350 school buses connected to its platform.

At the Cajon Valley district, eight electric buses sent 767 kilowatt hours of power back to the grid during the heat wave between Aug. 17 and Sept. 9, according to Nuvve.

Working with Nuvve, the buses power up when energy is less expensive, said Tysen Brodwolf, the district’s transportation director. Brodwolf said there are still several quirks, including the chargers not communicating properly with the grid or someone improperly plugging in a bus.

“But we’re getting there every day,” Brodwolf said. “We’re working through all those bumps and obviously, when you take on a pilot project, you have to take that into consideration that things aren’t necessarily going to go smoothly.”

How California’s electric cars can feed the grid and help avoid brownouts is an article from Energy News Network, a nonprofit news service covering the clean energy transition. If you would like to support us please make a donation.