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Environmental researchers warn against charging electric cars at home overnight

[June 28, 2023: Staff Writer, The Brighter Side of News]

The vast majority of electric vehicle owners charge their cars at home in the evening or overnight. (CREDIT: Creative Commons)

According to a recent research conducted by Stanford University, most electric vehicle (EV) owners tend to charge their vehicles at home during the evening or overnight, leading to significant costs for the electricity grid. To address this issue, the study suggests a shift towards daytime charging at public charging stations or workplaces.

The study, which was published in the journal Nature Energy, focused on the increasing number of EV ownership in the western United States and the potential strain on the electric grid by 2035.


The study found that the rapid growth of electric vehicles (EVs) and their continued reliance on residential, nighttime charging could lead to a 25% increase in peak electricity demand within a little over a decade. However, if more people charged their vehicles during the day at work or public charging stations, it could reduce greenhouse gas emissions and avoid the added costs of generating and storing electricity.

Ram Rajagopal, an associate professor of civil and environmental engineering at Stanford and co-senior author of the study, suggested that policymakers consider utility rates that incentivize daytime charging and investment in charging infrastructure that encourages drivers to shift from home to work for charging. The study's implications may also impact utilities in the region, especially after California's decision to ban sales of gasoline-powered cars and light trucks by 2035.


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The study encompassed the entire Western US region, taking into account California's heavy reliance on imported electricity from other western states. Siobhan Powell, the lead author of the study, emphasized that the consequences of EV charging and other electricity uses extend to the entire Western region, given the interconnected nature of the electric grid. She further noted that all states may need to reconsider their electricity pricing structures as their EV charging needs grow and their grid evolves.

At present, California experiences a surplus of electricity during late mornings and early afternoons, primarily due to its solar capacity.


According to the researchers, utilizing cheap electricity during periods of low demand by charging most electric vehicles (EVs) can prevent wastage of energy. However, if the majority of EV charging continues to occur at night, then the state will have to construct additional generators that may rely on natural gas or invest in expensive energy storage on a massive scale. A massive battery first receiving electricity and then transmitting it to an EV battery can lead to power loss due to the additional step.

Overview of the methods for evaluating grid impacts and modelling EV charging demand. (CREDIT: Nature Energy)

In addition to this, the current pricing model for electricity poses another issue. Large commercial and industrial customers are charged substantial fees based on their peak electricity usage. This method of pricing can act as a disincentive for employers to install charging stations, particularly when half or more of their employees own EVs.


In the study, various charging infrastructure availability scenarios were compared with different residential time-of-use rates and commercial demand charges. Several rate adjustments resulted in a negative impact on the grid level, while some led to improvements. The scenario that showed the greatest benefits was one that encouraged more daytime charging and less home charging.

Profile of aggregate EV charging demand illustrated for each infrastructure and control scenario. (CREDIT: Nature Energy)

Additionally, the study found that if the Western US reaches a point where 50% of cars on the road are electric, more than 5.4 gigawatts of energy storage would be necessary, equivalent to the capacity of five large nuclear reactors. However, if people shift towards charging their vehicles at work instead of at home, the storage needed for EVs would decrease to 4.2 gigawatts. Nonetheless, constructing the required infrastructure would demand significant lead time and could not be accomplished immediately.


The transportation sector is responsible for most of California's emissions, so it's crucial to decarbonize it quickly, according to Ines Azevedo, an associate professor of energy science and engineering at Stanford. She believes that the study provides valuable insights into how to achieve this goal.

The study's authors emphasized the importance of not only incentivizing daytime charging but also investing in charging infrastructure at workplaces and public areas. By encouraging employers to install chargers and making public charging stations more accessible, the transition to daytime charging could be facilitated.

Shifting charging times to coincide with peak renewable energy production periods could significantly reduce greenhouse gas emissions. If EVs are charged when solar and wind energy is most abundant, it could reduce reliance on natural gas-fired power plants and other sources of carbon-intensive electricity.

The study's implications are particularly significant for California, which has set an ambitious target of having five million EVs on the road by 2030 and banning gasoline-powered cars and light trucks by 2035. Achieving these goals will require significant investments in charging infrastructure and changes in consumer behavior. Policymakers can encourage more daytime charging and incentivize employers to install chargers to ensure that the transition to EVs is sustainable and cost-effective.

As the researchers note, rapid decarbonization of the transportation sector is essential, and the study provides valuable insights into how to achieve this goal. Policymakers must invest in charging infrastructure and encourage more daytime charging while also incentivizing employers to install chargers. By doing so, they can help reduce greenhouse gas emissions and make the transition to EVs as sustainable and cost-effective as possible, particularly in California.


The study accentuates the significance of recognizing the grid-level effects of EV charging and advocates for coordinated policy and investment schemes to ensure a seamless transition to EVs. The authors contend that with the right policies and investments, it is possible to create a more sustainable and durable energy system that is beneficial for both consumers and the environment.

This work was funded by the California Energy Commission, by the National Science Foundation, and by the Bits & Watts Initiative with support from Volkswagen.

For more science news stories check out our New Innovations section at The Brighter Side of News.


Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.


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