After registering its millionth light-duty electric vehicle sale in late 2021, California is bracing for millions more to hit the road, and the grid, in coming years.

Electric vehicles' market share is climbing quickly in the world's fifth-largest economy, which intends to sell only emission-free new cars and trucks by 2035. In the first quarter of 2022, amid skyrocketing gasoline prices, battery electric and plug-in hybrid vehicles jumped above 16% of total light-duty sales, up from 12% in 2021 and less than 8% in 2020, according to California Energy Commission data.

To ensure a smooth ride to higher levels of adoption, energy planners, researchers and utilities in the Golden State, by far the largest U.S. market for electrified transportation, are gaming out scenarios for how many EVs Californians will purchase, how much electricity they will need and when they will need it.

"There is a lot of uncertainty," said Siobhan Powell, a PhD candidate at Stanford University's Department of Mechanical Engineering who co-led a recently published study that aims to bring clarity to the variables of future EV charging demand.

"We tend to talk about building scenarios of the future more than forecasting because we don't know exactly how people will charge in 2030," Powell said in an interview. "But if you can study different possibilities of how it might turn out, that's really helpful for grid planning."

The study presented a new framework for estimating large-scale charging demand that PG&E Corp. subsidiary Pacific Gas and Electric Co. and other utilities have begun exploring through a publicly available algorithm. Using the tool, which leverages 16 unique driver types and their charging habits derived from California's already large EV stock, Powell and her colleagues created scenarios of California's peak charging demand in 2030.

Assuming eight million passenger EVs on the road by that time, Stanford ran scenarios that produced peak charging demand between 3.3 GW and 8.7 GW. The highest peak scenario assumes widespread use of home charging controlled by automated timers designed to seek the cheapest electric rates, resulting in a 7-GW spike in demand at 11 p.m.

That is significant considering the state's primary wholesale grid operator, the California ISO, currently experiences peak systemwide loads of between 25 GW and 30 GW for much of the year, topping 40 GW in the summer. Such a sudden jump in charging demand at night "could pose severe challenges to the grid in terms of both ramping at the generation level and damage to equipment at the distribution level," the Stanford study said.

"Everyone right now is trying to do these planning studies of what the grid is going to need for the future for decarbonization and so on, and there was a big question mark on how to capture the load impact of EV charging in a more realistic manner," added Ram Rajagopal, an associate professor in Stanford's Department of Civil & Environmental Engineering and senior author of the study.

The Stanford tool gives utilities and grid planners more flexibility to test out various scenarios based on a greater diversity of EV drivers and behaviors than in other models, according to Rajagopal.

"Getting this piece right of the impact of electric vehicles is important so that the planners can say this is exactly how much generation ... how much resources we will need in the future," he said.

'We really don't know'

The Stanford study comes as other researchers and grid reliability officials, including experts at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the North American Electric Reliability Corp., call for greater collaboration between the auto and utility sectors to prevent EV charging, the fastest-growing load on the grid, from exacerbating increasingly challenging conditions on the power system and leading to blackouts.

The California Energy Commission partly funded the Stanford study in a bid to further refine its understanding of future EV charging demand.

"We have these ambitious policy goals that are one of the things that we need to monitor, but we also need to model for where the market may go on its own," Patty Monahan, a member of the Energy Commission, said during an April 7 discussion on EV charging demand.

While the agency has been focused on quantifying California's need for EV charging infrastructure and transportation electricity demand, "we really don't know, we can't quantify, what's the impact of this charger in this place," Monahan said. "And, you know, maybe we never will be able to do that."

A recent Energy Commission analysis indicates the state's fleet of light-, medium- and heavy-duty zero-emission vehicles could range anywhere from 5.7 million to 15 million by 2035. Those vehicles could require less than 40,000 GWh or more than 80,000 GWh by that time. By midcentury, California's emission-free vehicle stock could jump to between 10.5 million and 32.5 million, according to the analysis, with electricity demand from transportation potentially rising to roughly 190,000 GWh.

That would equal California's total electric generation in 2020.

'Moving utilities'

In some ways, fleets of medium- to heavy-duty vehicles are more challenging to plan for because there is little data available to develop a framework, Stanford's Rajagopal said. On the other hand, fleets represent a "more prescriptive model" with driving and charging patterns that have "a lot less variability," he added.

Zeem Solutions Inc., which in March launched a large-scale charging hub for fleets of trucks and buses near Los Angeles International Airport, is working closely with Edison International subsidiary Southern California Edison Co. to ensure its project, which is designed to serve 10 MW of charging demand, operates fluidly with the grid.

"We're very cognizant, for example, of the peak time here in California between 4 p.m. and 9 p.m., not to be a stress on the grid and maybe utilize some battery storage to ease that," said Zeem Solutions CEO Paul Gioupis. Such a large-scale project "could be a tremendous drain on our community, or we can end up being a tremendous benefit," he added, pointing to possible vehicle-to-grid, or V2G, opportunities in the future.

"We're believers in bidirectional technology," the CEO said. "V2G is just in its earliest stages."

Once the regulatory and technological requirements fall into place, however, Gioupis sees Zeem's business model, based on ownership of electric trucks and buses the company leases, as a perfect fit.

"I don't know a business that's better prepared," he said. "In many cases we see these as moving utilities."

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