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Sustainable Energy

Can Tractor-Trailers Go Electric Along with Cars?

Petroleum-free trucks and other heavy vehicles are coming, but making diesel engines more efficient offers a better chance at short-term improvements.

While battery-powered cars are on the road to mass adoption, freeing big-rig trucks and trash haulers from their reliance on petroleum fuels is a far bigger challenge. Because big trucks need more energy than cars to move their mass and cargo, it’s harder for them to rely on batteries, which are less energy-dense than diesel fuel.

Big trucks are an important nut to crack. Because of their brawn, they average just five to six miles per gallon and thus have an outsize climate impact. Trucks weighing over 8,500 pounds account for more than one-fifth of greenhouse-gas emissions from transportation in the United States, and from 1990 to 2012 their carbon footprint grew five times faster than emissions from light vehicles, according to the U.S. Environmental Protection Agency.

However, petroleum-free options are in the wings. Here’s a look at some of them and the challenges they face.

Big weight, high costs

Switching to battery power can work for trucks. But they require big batteries, which are themselves heavy, reducing a truck’s capacity to carry or tow cargo and equipment.

And big batteries are expensive—enough to more than double the price of a new medium- or heavy-duty vehicle, according to a study of electric trucks in the Los Angeles area. The study, by the West Coast Collaborative, a research consortium coördinated by the EPA, predicted that the extra investment would pay off in less than five years, assuming fuel savings of $12,770 per year, plus government incentives and lower maintenance costs.

But the estimate was based on a diesel price of $4.40 per gallon. Since 2011, diesel prices have crashed to less than $3 per gallon, and electric-truck innovators are booking few sales. Perhaps reflecting this reality, the EPA now projects that no more than 3 percent of heavy trucks will be fully electrified by 2025.

The use of plug-in hybrid-electric drivetrains—the combination battery- and engine-powered design Chevrolet uses in the Volt car—will infiltrate the market more quickly. The EPA projects that they will account for up to 36 percent of some types of heavy trucks by 2025. The hybrid design reduces the size and cost of the batteries required. Wrightspeed, the heavy-EV startup launched by Tesla cofounder Ian Wright, is retrofitting $500,000 garbage trucks with plug-in hybrid drives for roughly $150,000 to $200,000.

Plug-in hybrids are not petroleum-free. Wrightspeed’s trucks, for example, can travel only 30 miles on their battery alone and then rely on diesel or natural gas to power their motors. But their adoption could bring down the cost of the large motors and other equipment required for purely battery-powered trucks.

Overhead wires

Some applications, such as long-haul trucking, may never be viable for battery-driven vehicles. Biofuels could be part of the solution there, according to an R&D road map for medium- and heavy-duty trucks prepared in 2013 by the California Hybrid, Efficient and Advanced Truck Research Center (CalHEAT). But biofuels must overcome their high cost and concerns over their environmental impact.

CalHEAT’s road map also foresees corridors in which electric trucks travel electrified rails or wires, as electric buses and trains do today. In Germany, Siemens has tested diesel-electric hybrid trucks designed to switch over to grid power where overhead lines are available, and last year the company was selected to create a demonstration of its “eHighway” concept in Southern California.

Siemens’s $13 million demonstration, scheduled to be completed this summer, will see two miles of overhead catenary wires installed on a trucking route between the ports of Los Angeles and Long Beach. CalHEAT’s road map envisions a more ambitious electrified truck corridor linking those ports to Oakland and Stockton in Northern California. Last month Siemens signed a deal to install a similar demonstration in Sweden, which aims to have a fossil-fuel-free transportation sector by 2030.

The takeaway:

The easiest way to cut carbon emissions from trucks is to make diesel vehicles more efficient by using better engines, low-resistance tires, and aerodynamic trailers. Such upgrades are expected to cut heavy-truck emissions by about 20 percent by 2021. A second wave of mandates, proposed this summer by the EPA and the National Highway Transportation Safety Agency, is projected to cut emissions and fuel consumption by another 24 percent by 2027.

Thanks to Jason Bell for this week’s question. If you have one, let us know at questionoftheweek@technologyreview.com.

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