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Batteries and fuel cells would overhaul emissions from semis and other heavy vehicles

Although electrified versions of vans, buses and semis cost more upfront on average than their diesel-powered counterparts, the overall calculus behind adopting greener vehicles is currently in flux.

A new life cycle analysis shows that electric and hydrogen fuel cell vehicles significantly reduce lifetime greenhouse gas emissions compared with diesel vehicles. So much so that if a medium- or heavy-duty battery electric vehicle were powered completely by renewable energy, there would be around a 90% reduction in lifetime emissions compared with the diesel equivalent.

The research team was led by Maxwell Woody and Greg Keoleian of the University of Michigan School for Environment and Sustainability (SEAS) Center for Sustainable Systems (CSS). SEAS doctoral student Spencer Checkoway also contributed to the research, as did Robert De Kleine, Hyung Chul Kim and James Anderson at Ford Motor Co.

“There’s an urgency for climate action and to reduce greenhouse gas emissions from the transportation sector,” said Keoleian, a professor at SEAS and co-director of CSS. “There’s a disproportionate amount of emissions from these heavy- and medium-duty vehicles compared to the rest of the vehicles on the road.”

The cost of diesel fuel is skyrocketing. California, where the new Tesla Semi is establishing a toehold, has also unveiled a rebate program to help companies purchase electric medium- and heavy-duty trucks. Plus, even as the federal government embraces fossil fuels, some companies remain committed to their sustainability goals, as evidenced by Amazon's ever-growing fleet of electric delivery vehicles.

Heavy trucks carry an outsized burden...Now, research from the University of Michigan shows just how big a difference switching from diesel to fuel cells or batteries can make when it comes to greenhouse gas emissions. If a medium- or heavy-duty battery-electric vehicle were to be powered completely by renewable energy, it would offer around a 90% reduction in lifetime greenhouse gas emissions compared to its diesel equivalent.

The research team, led by Maxwell Woody and Greg Keoleian, has published its results in the journal Nature Energy.

"There's an urgency for climate action and to reduce greenhouse gas emissions from the transportation sector," said Keoleian, a professor at the U-M School for Environment and Sustainability. "There's a disproportionate amount of emissions from these heavy- and medium-duty vehicles compared to the rest of the vehicles on the road."

Medium- and heavy-duty vehicles account for nearly 30% of road vehicle emissions despite making up just about 5% of traffic on U.S. roadways, according to the U.S. Department of Energy.

"Moving to battery electric vehicles and even hydrogen fuel cell vehicles provides a significant reduction in emissions," said Keoleian, who is also co-director of U-M's Center for Sustainable Systems.

This study, focusing on larger vehicles, follows a comprehensive study from the team showing that electrified sedans, SUVs and light-duty pickups reduced lifetime emissions from noncommercial vehicles across the U.S.

Comparing powertrains and fuel sources...In the new study, the team performed life cycle analyses for Class 3 vehicles weighing between 10,001 and 14,000 pounds (4,536 and 6,350 kilograms) up to Class 8 vehicles that can weigh up to 80,000 pounds (36,287 kilograms).

They modeled different powertrains, including internal combustion engines, hybrids, battery-powered EVs and fuel cell electric vehicles, accounting for a variety of other factors. That included variables like how a vehicle was driven—for example, with the frequent starts and stops of urban delivery up to the long-haul drives of trucks with sleeper cabs.

The researchers also examined how hydrogen and electrons for fuel cells and batteries, respectively, were sourced, comparing established methods to newer, greener options.

In the case of fuel cells, this meant analyzing and sourcing hydrogen from the standard process known as steam methane reforming, versus greener hydrogen from the electrolysis of water powered by renewables. For battery electric vehicles, the standard is simply plugging into the current grid versus charging from renewables alone.

Cleaner energy sharpens the gains...Though there were variations due to these factors, a clear takeaway emerged: Hydrogen fuel cells and battery-electric powertrains offered the largest lifetime emissions reductions compared with diesel-powered vehicles.

-Battery electric vehicles cut emissions by 72%–82% using the current grid and by 87%–92% using renewables only.

-Fuel cells offered 12%-51% reductions using steam methane reforming and 44%–68% reductions with electrolysis powered by renewables.

-Hybrid powertrains offered 1%-26% emission reductions.

"Basically, we see across all the different vehicle sizes the same general pattern of the conventional diesel having the highest emissions, then the hybrid, then the fuel cell with conventional hydrogen production, then the battery electric with grid electricity, then fuel cell with green hydrogen, and then the battery electric vehicle with renewable electricity," said Woody, a postdoctoral researcher with CSS. "That pattern held across everything that we investigated, from the Class 3 van to the Class 8 truck."

Provided by University of Michigan