As people increasingly turn to electric vehicles as a means to go green, a new study aims to address a growing concern: Can the grid handle the strain associated with charging those vehicles?
Nearly 200,000 electric vehicles were sold in the U.S. last year, an increase of more than 25 percent compared with sales in 2016. At current adoption rates, more than one million electric vehicles will be on the road across the country by 2020.
Using data from 200 houses with 348 passenger vehicles in the Midwest, researchers from the National Renewable Energy Laboratory simulated the electrical demand associated with increased electric vehicle adoption. The simulation found that a market share of up to 3 percent – or 7.5 million vehicles – would not significantly impact aggregate residential power demand.
However, when researchers examined the impact of charging electric vehicles on a more local level, they found reason for concern.
Excess demand on equipment
Specifically, a problem presented itself in a scenario where there was a high concentration of electric vehicle adoption in a neighborhood, and the owners of those vehicles engaged in “uncoordinated charging” – in other words, plugging the vehicles in to recharge upon returning home each day.
This clustering effect could significantly increase the load on residential distribution transformers and potentially decrease their lifespan, according to the researchers. The problem is exacerbated when electric vehicle owners use the faster, more powerful Level 2 charging option (240 volt) as opposed to Level 1 (120 volt).
When the researchers simulated a distribution transformer connected to six households and 11 vehicles, they found the transformer could handle charging up to six vehicles with Level 1 charging; however, when a vehicle with Level 2 charging was added to the group, they observed demand in excess of nominal capacity.
“Whether consumers choose one [charging option] or the other has a great impact on how much extra load there is on transformers,” said Dr. Matteo Muratori, a transportation and energy systems engineer at the NREL and author of the study published in Nature Energy.
Muratori cited previous research that found the expected lifespan of transformer equipment can decrease by two orders of magnitude when the transformer experiences demand 50 percent above its nominal capacity.
“The problem is … electric vehicles are a new technology that didn’t use to be present, so transformers that are being deployed today may not account for them,” he said. This means utilities may need to upgrade or replace their equipment more often as transformers cripple under the unexpected load.
Incentivizing good behaviors
Muratori said the finding highlights the need to study the charging behavior of electric vehicle owners – in terms of when they charge their vehicles and which charging option they use – and find ways to incentivize charging behaviors that lessen the strain on transformers.
While Muratori notes the worst time of day to charge electric vehicles can vary depending on season and location, he said owners who want to lessen their impact should consider “instead of charging from 5 PM to midnight, would you be willing to charge from 1 AM to 8 AM?”
“It’s still seven hours, but instead of adding load in the late afternoon while using other household appliances … you’re postponing the load to the middle of the night when almost nothing else is running in the house,” he said.
According to Muratori, the onus falls on utilities as well to find ways to incentivize favorable charging behaviors that may be less appealing to vehicle owners. Charging vehicles in the afternoon “maximizes convenience” and owners who have Level 2 charging stations installed “have shiny, faster equipment they paid for – they want to use it,” he explained.
Utilities could implement a demand-response program, he suggested, in which they offer cheaper charging for customers who participate and charge their vehicles at designated times.
Additionally, utilities could push for charging stations to be installed in more locations, so there is less need to charge vehicles at home. In Maryland, for example, utilities have proposed partnering with state and local governments to provide public charging stations for residents.
Beyond influencing charging behaviors, Muratori said utilities also must take local electric vehicle adoption into account when planning infrastructure upgrades to ensure they can handle the additional strain going forward.
Alex Crees is a writer covering issues related to energy, the environment and politics. Her work has appeared in Fox News and Prevention. Alex earned a bachelor’s degree in journalism from New York University.