How Electric Vehicles are Charged Relates to Decrease in Greenhouse Gas Emissions

In the United States, the transport sector contributes the largest amount of greenhouse gas emissions. More attention is given to electric passenger vehicles and their ability to help decrease such emissions.

How Electric Vehicles are Charged Relates to Decrease in Greenhouse Gas Emissions

Image Credit: University of Michigan.

The increase of online shopping behavior and timely shipping has caused the electric delivery fleets to emerge as a bright chance to decrease the environmental impact of the transportation industry.

Electronic vehicles (EVs) form a small fraction of the delivery vehicles at present, but their number is increasing. In 2019, Amazon declared its plan to purchase 100,000 electric delivery vehicles. While UPS has gone for 10,000 of the EVs, FedEx is planning to be completely electric by 2040.

At present, a study performed by the researchers of the University of Michigan (U-M) reveals when, where and how those fleet vehicles are charged can significantly affect their ability to decrease greenhouse gas emissions.

An important feature of the study is that both the emissions directly associated with charging the vehicles and emissions from manufacturing the batteries should be taken into account. Thus, charging practices that reduce the lifetime of the battery will result in early battery replacement, thereby contributing to the total greenhouse gas emissions related to that vehicle.

The scientists at U-M have discovered that 50% – 80% of the lifetime emissions related to the battery of an electric vehicle delivery take place while charging the battery. Thus, making use of a cleaner energy source for charging the vehicle, for example, using the electric grid with lots of renewables is an effective method to decrease the emission of an electric vehicle.

Considering both battery charging and degradation, the team has discovered that greenhouse gas emissions could be decreased by about 37% by improving charging methods.

Also, the researchers found that even in the most carbon-intensive regions of the United States, electric delivery vehicles emitted less greenhouse gas compared to diesel and gasoline vehicles.

Our evaluation strategy leads to two main recommendations for companies investing in fleets of electric vehicles.

Maxwell Woody, Study Lead Author, Center for Sustainable Systems, University of Michigan

The study was published online in the journal Environmental Science & Technology on July 9th, 2021.

“The first is to consider battery degradation when determining when to charge and how much to charge. Some charging strategies can extend battery lifetime, and this will both lower greenhouse gas emissions and protect the company’s investment,” added Woody.

The research team suggested the fleet owners take into account the source of the energy used to charge the vehicles. Charging a vehicle with wind- or solar-generated power and the one charged from a coal or natural gas-fired power will have different effects on the environment.

“Considering the charging source can help companies determine the best places to charge, as local grids vary across the country. Companies should prioritize fleet electrification in regions that provide the greatest carbon-reduction benefits, stated Woody.

Woody recently obtained a master’s degree from the School of Environment and Sustainability at the University of Michigan and is currently working as a research area specialist at the Center for Sustainable Systems.

Through their modeling study, the scientists examined four charging methods and analyzed their lifetime environmental effects. The latest study performed by U-M exceeds previous work by integrating the temporal and regional change in charging emissions with the effect of charging on the degradation of the battery.

The team demonstrated that the baseline charging scenario in which a vehicle becomes fully charged immediately upon arrival to a central depot led to the highest emissions. Using alternative charging techniques resulted in a decrease in emission levels by 8% – 37%.

Charging the vehicle as soon as it returns and charging the vehicle up to 100% result in a lot of time spent sitting at the depot/charging station with a full battery. This extra time spent fully charged will cause the battery to wear out more quickly — so quickly that the battery may need to be replaced sometime in the vehicle’s lifetime. Creating this additional battery produces additional greenhouse gas emissions, as well as additional costs.

Parth Vaishnav, Study Corresponding Author and Assistant Professor, School for Environment and Sustainability, University of Michigan

Charging the battery only sufficient for a day’s purpose, a practice called sufficient charging that, leads to increased battery life and in some cases even doubling it. Thus, emissions associated with battery production were decreased.

On the whole, charging methods that reduce greenhouse gas emissions normally reduce the expense as well. In many cases, postponing charging until the vehicle was close to departure, along with adequate charging, was an ideal method for both emissions and cost.

The most important finding is that there is a big opportunity here to lower emissions. Electric delivery vehicles only make up a small proportion of delivery vehicles right now, but that number is expected to increase in the coming years. Establishing the best practices for charging now, as these vehicles are starting to be deployed in larger numbers, is a critical step toward lowering greenhouse gas emissions.

Greg Keoleian, Study Co-Author, Professor of Environment and Sustainability, and Director, Center for Sustainable Systems, University of Michigan

The additional authors of the study are Michael Craig of the U-M School for Environment and Sustainability and Geoffrey Lewis of the U-M Center for Sustainable Systems. The study was financially supported by the Responsible Battery Coalition.

Journal Reference:

Woody, M., et al. (2021) Charging Strategies to Minimize Greenhouse Gas Emissions of Electrified Delivery Vehicles. Environmental Science & Technology.

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