The Role of Electric Trailers in Trucking’s More Sustainable Future

The Role of Electric Trailers

Investing in more sustainable logistics efforts didn’t always make financial sense in the past, but today zero-emissions trucking isn’t just trending, it’s beginning to deliver on business expectations. While industry electrification endeavors so far have focused mostly on the tractor, all-electric trailers— particularly Transportation Refrigeration Units (TRUs)—are beginning to show promise as well.

Semi-trailers, for the most part, already have an array of electric devices onboard, like those designed to protect the driver and those sharing the highway. Other devices, like electric liftgates and platforms, are used throughout the day as products are moved both to and from the trailer. There are also easily overlooked devices such as interior and exterior lights, locks, telematics, and other components that rely on battery power. Reefers not only use all the above, but require the need for a small diesel engine to run its TRU.

Great Dane Electrification Product Manager Colby White believes it won’t be long for all-electric TRUs to become more commonplace in the transportation industry. With fuel prices on the rise and not expected to drop any time soon, he says an all-electric TRU will no doubt garner more attention by fleet owners as the economic benefits begin to outweigh those of their diesel-powered counterparts.

“Another notable benefit of an engineless TRU is that it boasts zero emissions and zero pollutants as the refrigeration unit is 100% electric. A zero-emissions trailer will travel freely throughout the U.S. without concern of any state-imposed restrictions for idle run-time, pollutants, or noise,” White says. “Less obvious benefits, but just as important for the win column, include longer service intervals and less downtime than traditional TRUs due to fewer parts to wear out.”

The Viability of All-Electric Trailers Today

Unfortunately, White says, there are many uphill challenges ahead for all-electric reefer early adopters. For example, the initial cost for an all-electric TRU may cause sticker shock for fleet owners. Much of this cost comes from the battery and onboard recharging systems such as regenerative braking or solar energy panels. These charging systems play an important role in that a battery may not have enough stored energy for a full day of deliveries. Weight is another concern, as the combined electric equipment can weigh hundreds of pounds more than diesel equivalents.

White says these are issues that will likely be overcome through innovations, industry collaboration, and regulatory mandates. However, one of the most glaring hurdles for fleets today is infrastructure—particularly, the inability to charge batteries away from the home office.

“Cities and populated rural areas are adding charging stations at a fast rate. However, these are generally intended for automobiles and not exactly designed to handle anything larger than a Class 4 truck body,” White says. “It’s important for buyers to know early on that the number of charging stations outside metropolitan areas are few in numbers.”

For this reason, White believes all-electric trailers will first be used in urban areas for delivery where the tractor trailer can return to its home site to charge after deliveries are made. There are also service and maintenance limitations to consider, he says.

“Tractor and trailer repair centers have not ramped up to service high-voltage battery systems just yet,” White says.

Technologies Worth Keeping an Eye On

White says regenerative braking and solar harvesting are two technologies that show promise today in the right circumstances.

Regenerative braking is already common within the automotive sector to extend an electric car’s range, and this technology can also be found on electric semi-tractors and electric buses at an industrial level. Manufacturers like ConMet, Meritor, SAF Holland, and Hyllion have already debuted new products under the banner of eMobility.

“As trailers are passively pulled by a tractor, adding regenerative braking to one of its axles to charge an onboard battery or the tractor’s battery seems possible,” White says. “Truck bodies may have different challenges due to available space and loads placed on a single-axle chassis.”

Solar power, with all its advancements, cannot generate enough power to run a system as demanding as today’s electric TRU with the usable rooftop space of a semi-trailer, White says. But it can supplement power to the battery, effectively increasing its capacity much like regenerative braking.

“A problem that has always plagued solar energy harvesting is the role weather and seasonal changes play on energy generation,” White says. “There are regions of North America that get an abundance of sun during the year. In these areas, solar energy harvesting would provide the greatest amount of energy. However, as you travel northward, and with the onset of winter, days get shorter and the sun hangs lower in the sky, all impacting the performance of solar harvesting.”

White further cautions that, due to the mobile nature of trailers, finding sunlight not hindered by tall buildings in urban areas may be challenging depending on the time of day or season. This reduces the effectiveness of solar harvesting and the ability to add power to the battery.

“Unfortunately for solar, it still faces hurdles of rainy days or dense overcast, further impacting its potential to provide added power to the battery,” he says.

All-Electric Trailers of Tomorrow

White says the trucking industry isn’t that far off—perhaps 10 years or so—from all-electric tractors pulling all-electric trailers behind them being commonplace on our roadways. And, many of these trucks will likely be autonomous.

“In fact, several manufacturers have already started work on driverless tractors,” he says. “As tractor manufacturers approach this goal, trailer manufacturers wanting acceptance into this market will need to either partner with a tractor manufacturer or have a smart trailer ready to interface with the tractor. This is not an easy task as protocols and standards have yet to be established.”

White says within the next few years advancements in trailer electrification will give way to an engineless TRU for both last-mile delivery and long-haul trucking. As these semi-trailers grow in sophistication, fleets would be wise to find partners in this space—including OEMs, suppliers, and utilities—to accomplish their sustainability goals together.

Are Fleets Investing in Electrification Playing with Fire?

There are plenty of examples of electric vehicle fires in the media and on the internet, but does this mean they are more prone to catch fire or burn than other types of vehicles?

“The number of incidents may seem high, but when looked at more closely, the number of EV fires to car gasoline fires is far less,” says Great Dane Electrification Product Manager Colby White.

According to a July 2021 article from Forbes, between 2012-2020, there has been approximately one Tesla vehicle fire for every 205 million miles traveled. By comparison, data from the National Fire Protection Association and U.S. Department of Transportation shows that in the U.S. there is a vehicle fire for every 19 million miles traveled.

There are several ways an EV battery can catch fire, but most are preventable. White noted that a fire may result due to something missed or done incorrectly during the manufacturing process, or it can be due to an external force such as abuse or mishandling the battery where it is physically damaged.

Fires have also been started when something has punctured the case exposing the battery to foreign matter.

“Of course, the same can be said for other vessels that store energy, including gasoline tanks and oil containers. And like gasoline and oil products, EV batteries can catch fire if safeguards are bypassed or ignored,” White says. “However, unlike gas and oils, EV batteries rarely start with an explosion. They often have indicators of a problem before something more catastrophic happens.”