How battery-powered trailers could transform trucking

Semi-trucks move over 11 billion tons of freight in the US each year, spewing greenhouse-gas emissions and other pollutants along the highways as they go.

Shifting these and other heavy-duty trucks to zero-emissions technologies will be a challenge-even more so than for smaller vehicles, since larger vehicles require bigger batteries and more powerful chargers. One company thinks the key to progress is hiding behind rigs inside its trailers.

Range Energy is building battery-powered trailers that can help pull their own weight. By adding batteries to trailers, the company says, it can make a sizable cut in emissions, even while using existing diesel vehicles. The trailers could also be used with zero-emissions technologies like hydrogen- or battery-powered trucks to extend their range and efficiency as they hit the roads.

While there's a growing wave of innovation in zero-emissions trucking, few companies have considered looking at trailers, says Ali Javidan, founder and CEO of Range Energy. Essentially, it's still just a dumb box on wheels," Javidan says.

Range Energy, founded in 2021, is looking to make trailers smarter, adding batteries and a motor. The newest version of the company's product incorporates between 200 and 300 kilowatt-hours' worth of batteries. That's more than what might be inside a passenger electric vehicle-battery packs in SUVs and pickups can be up to 100 kWh. But it's significantly less than the batteries needed to power an entirely electric semi-truck, currently estimated around 800 kWh or more.

In Range's trailers, the battery pack and the systems that manage it are connected to an e-axle at the rear, which delivers the power and helps move the trailer. The whole assembly is connected to the truck by the kingpin, or hitch, which helps sense the truck's movement and controls how the trailer responds. The goal isn't to drive the trailer from the back, Javidan says, but to help make the trailer feel weightless to the truck pulling it.

Adding an electric trailer onto a diesel truck turns the rig into something of a hybrid vehicle. The result can significantly improve both greenhouse-gas emissions and other pollution, like nitrogen oxide (NOx) emissions, Javidan says.

The company tested out an earlier version of its trailer that included a smaller battery of 100 kWh on a route with a mix of both flat highway and stop-and-go urban conditions. The trailer was able to improve gas mileage by about 36% over the whole route. That translates to cutting greenhouse-gas emissions by around a quarter.

Range's newer trailers with larger batteries should improve gas mileage even more, and in certain conditions they could double the fuel economy, cutting emissions by up to half, Javidan says.

While semi-trucks only make up about 5% of vehicles on the road, they're responsible for about a quarter of greenhouse-gas emissions from transportation. Finding options to help clean up emissions from heavy-duty trucks will be a major piece of cleaning up the transportation sector while making sure we have the products we need and use every day.

Range trailers can also significantly improve emissions of NOx pollutants, which are harmful for human health. In fact, they can have an outsize impact, since NOx emissions tend to be highest during specific operating conditions like when an engine is shifting. Range's trailers are able to ramp their contribution up when it's most needed, so the newest models could cut NOx emissions by up to 70%, Javidan says.

As they hit the roads, battery-powered trailers might face some of the same challenges that fully electrified rigs are running into.

In the US, trucks can't be heavier than 80,000 pounds (40 US tons). Zero-emissions vehicles get a small buffer of an additional 2,000-pound allowance, but battery-powered rigs can run something like 5,000 pounds heavier than their diesel counterparts. That's a major concern for operators, since the amount they can haul can be limited by those restrictions.

However, many loads reach the volume limits of a trailer before hitting the weight limit. This is called cubing out" in the industry, and it's common when hauling packages, for example. (Think of the last package you ordered from Amazon-if it was a box that had one or two items inside and a whole lot of air, you get the picture.) Those are the loads Range trailers will likely be most useful for at first, Javidan says.

Another concern is that electric trailers will rely on the same charging infrastructure that's in short supply for trucks today, says Stephanie Ly, a researcher at the World Resources Institute.

Large trucks could take hours to charge even on the fastest chargers available today-a problem for drivers, who often face pressure to complete deliveries quickly. And installing more powerful chargers could require significant planning and investment from utilities.

But trailers tend to have more downtime than tractors, because many companies own more trailers than trucks. And a 200-kWh battery would take less than an hour to charge on one of the fast chargers commonly available today, so the problem might be more surmountable than it is for fully electric trucks.

Range Energy has one of its newest trailers running pilot tests in California and will launch several more this year, Javidan says. Then, the company plans to start building the next batch, which it will begin delivering to customers in early 2025.

Javidan declined to share how much the company charges for each of its trailers but says an up-front investment in one could pay for itself through fuel savings in just five or six years on average. And if trailers are driven for more miles, or in places where charging is cheap or fuel is particularly expensive, that payoff could be even faster, a potentially appealing prospect for companies with large fleets.

Still, getting fleet operators on board with new technologies may be a challenge-one that will be crucial to improving the climate results from trucking, says Thomas Walker, transportation manager at the Clean Air Task Force.

It's a multi-segmented problem," Walker says. It's not just the vehicle. It's not just the grid. It's all of it."