With 487 electric-vehicle makers in China, according to the latest official count, the country is looking to electric vehicles to reverse record air pollution, but the environmental impact of China's electric vehicles may not be altogether beneficial - it depends on how they are charged.


Traffic jam in Beijing, China (Photo by Li Lou / World Bank)



With the majority of China's electricity still coming from coal-fired power plants, there are questions about how effective the EVs will be against air pollution.


Now, new research from Harvard University and Tsinghua University in Beijing found that private electric vehicles in China can have a positive effect on carbon dioxide (CO2) reduction if EV owners will charge vehicles slowly  during off-peak hours, allowing for more effective use of wind power.


Quickly charging vehicles in the higher energy "fast mode," can use more energy, and more fossil fuel than it saves.


Meanwhile, buses and taxis in China contribute to nitrogen oxide (NOX) emissions, a major precursor of air pollution. The team determined that electrifying the bus and taxi fleet offers the most effective option for improving air quality.


"This research offers a more nuanced strategy for reducing CO2 emissions and improving air quality in China," said co-author Michael McElroy, a professor of Environmental Studies at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Department of Earth and Planetary Sciences.


"Electrifying the public fleet and introducing incentives to charge personal electric vehicles at off-peak times would be the most effective strategy to reduce NOX and CO2 emissions in Beijing," said McElroy. "This strategy could also be applied to cities across the world that have a significant source of electricity from coal."


"It is critically important that electric vehicle charging is managed properly to maximize the benefits of renewables," said co-author Xinyu Chen, a research associate in Environmental Science and Engineering at SEAS.


The researchers used real-time power demand data and driving patterns for Beijing and its suburbs to develop a comprehensive model of the energy system.


They found that how electric vehicles are charged - whether in the low-energy slow mode or high-energy fast mode - plays an important role in the integration of wind energy.


Typically, vehicle charging in the fast mode, 30-minutes or less, occurs during hours of peak power demand, so demand is pushed even higher, triggering additional coal generators to come . With these generators operational at night, the opportunity to take advantage of available wind power is reduced.


"If people were incentivized to wait until evening and charge their vehicles in the slow-charge mode, which takes hours, the power load could take advantage of wind energy available during off-peak hours," said co-author Chris Nielsen, executive director of the Harvard China Project.


In terms of lowering air pollution, the researchers found that the gas-powered or diesel-fueled fleet of public vehicles in Beijing - about 30,000 buses and 66,000 taxis - is responsible for nearly 20 percent of total NOX emissions, equivalent to the contribution from 8.2 million private vehicles.


Electrifying Beijing's fleet of buses and taxis would reduce total NOX emissions and increase air quality, the study concludes.


Supported in part by the Harvard Global Institute and the Hui Fund of the Ash Center of the Harvard Kennedy School of Government, the research is published in the journal "Nature Energy."



By Sunny Lewis

Environment News Service (ENS)


September 4, 2018