electric vehicle in winter charging

Electric vehicles need to be charged in the right way to maximise carbon benefits

Image credit: Dreamstime

The potential for electric vehicles (EVs) to reduce greenhouse gas emissions is highly dependent on where, how and when those vehicles are charged, a University of Michigan study has found.

The researchers looked at the emerging use of EVs in delivery fleets, which are getting larger due to the rise of online shopping and just-in-time shipping.

Though EVs represent a small fraction of delivery vehicles today, the number is growing. In 2019, Amazon announced plans to obtain 100,000 electric delivery vehicles. UPS has ordered 10,000 of them and FedEx plans to be fully electric by 2040.

The study found that the emissions directly tied to charging the vehicles and emissions that result from manufacturing the batteries must be considered to maximise their environmental benefits.

For example, charging practices that shorten a battery’s lifetime will lead to early battery replacement, adding to the total greenhouse gas emissions associated with that vehicle.

The researchers found that 50 to 80 per cent of the lifetime emissions associated with an electric delivery vehicle’s battery occur during charging. Therefore, charging from a cleaner energy source, such as an electrical grid with lots of renewables, is one of the most impactful ways to lower the emissions of an electric vehicle.

When both charging and battery degradation were considered, it was estimated that greenhouse gas emissions could be lowered by as much as 37 per cent by optimising charging strategies.

Nevertheless, even in the most carbon-intensive regions of the United States, electric delivery vehicles resulted in fewer greenhouse gas emissions than their gasoline or diesel counterparts.

“Our evaluation strategy leads to two main recommendations for companies investing in fleets of electric vehicles,” said Maxwell Woody, lead author of the study.

“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.”

The second recommendation to fleet owners is to consider where the energy charging the vehicle comes from. A vehicle charged from solar or wind energy and a vehicle charged from a coal- or natural gas-fired power plant will have very different environmental impacts.

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

The study found that fully charging a vehicle upon returning to a central depot resulted in the highest emissions, whereas employing alternative charging methods led to emissions reductions of up to 37 per cent.

“Charging the vehicle as soon as it returns and charging the vehicle up to 100 per cent 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,” said study corresponding author Parth Vaishnav.

“Creating this additional battery produces additional greenhouse gas emissions, as well as additional costs.”

Charging the battery only enough to complete the day’s route, a practice the researchers called sufficient charging, led to a large increase in battery lifetime – in some cases more than doubling it. As a result, emissions tied to battery production were reduced.

Charging strategies that minimised greenhouse gas emissions typically lowered costs as well. In most cases, delaying charging until the vehicle was close to departure, combined with sufficient charging, was the optimal strategy for both cost and emissions.

Earlier this month, the RAC Foundation said that the average car or van in England is driven just 4 per cent of the time, giving ample time for it to be charged in the most environmentally beneficial way.

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