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All OEMs have developed electric units that meet current CARB regulations and can be plugged in at the dock. (Great Dane)

Transport refrigeration unit technology for temperature-controlled trailers has expanded beyond conventional diesel-powered refrigeration units to a growing number of greener alternatives, including diesel-electric hybrids and, in some cases, entirely electric options.

Hybrid TRUs can run on diesel over the road and plug into an electric power source when they are loading, unloading or being used for storage to enhance energy efficiency and reduce emissions.

, through a joint venture with , offers single-temperature and multi-temperature hybrid TRUs, powered by diesel or shore power, for its 3000R line of refrigerated trailers.

“Demand for hybrid has been strong, especially in California,” said Steve Bennett, Utility’s president and chief operating officer.

Hybrid systems meet the California Air Resources Board’s ultralow emissions standard, he added.

“Running the TRU on shore power cuts the noise dramatically, so if a trailer is parked at a grocery store dock in a residential neighborhood, neighbors aren’t disturbed when the TRU is plugged in,” Bennett said.

At the same time, running the unit on shore power is generally half the cost of diesel, he said, adding that grocery and food service customers including Kroger, Albertsons, Golden State Foods and H-E-B have been adding 480-volt plugs to docks at their warehouses and stores.

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The Kroger Co. operates 175 Cargobull hybrid TRUs, including 125 in its private fleet for Ralphs, its supermarket chain in California.

“We are getting some good feedback from our warehouses on how quiet they are to operate and no complaints from drivers or our shops,” said Dan Umphress, Kroger’s manager of fleet services.

Kroger also has reserved 10 battery-electric Tesla Semis and is working to take delivery of the first two zero-emission tractors, Umphress said.

The Tesla Semi features electric power takeoff, giving it the capability to run refrigerated trailers.

Cargobull TRUs and the Tesla Semi are compatible, Utility’s Bennett said. “Utility will supply Cargobull TRUs [to Kroger] that can be powered via ePTO.”

Dan Priestley, senior manager of the Tesla Semi program, highlighted the vehicle’s ePTO feature during a presentation in April at the 2025 Advanced Clean Transportation Expo in Anaheim, Calif.

Electric Units Show Strong Performance

, a refrigerated trailer leasing provider with more than 15,000 temperature-controlled trailers, began using some electric TRUs more than five years ago and today has about 86 electric units from a mix of manufacturers and featuring various technologies, including solar, battery pack and wheel regenerative technology, said Alan Gassler, national account support and zero-emission operations and sales analyst at the company.

“We make sure we’re diversified,” he said. “This way as technologies change and improve, we can pivot when necessary.”

Asked about the pros and cons, Gassler said, “What we’re seeing in regard to cooling is it’s mimicking the diesel counterparts. There aren’t really load loss issues that we’ve run into.”

The units record slightly higher uptime, too, which he attributed to fewer components requiring maintenance.

“We’re seeing a lot of upfront cost savings once these units get into running day-to-day routes,” Gassler added, noting the advantage of fixed kilowatt prices.

Manufacturers have developed electric units that meet current CARB regulations and can be plugged in at the dock, “but since there’s not enough infrastructure for that to happen, this is not necessarily being enforced,” observed Joel Bishop, regional sales director at Great Dane.

California-based refrigerated carriers are required to register their refrigeration units with CARB, Bishop and others noted.

“They receive a number that must be displayed on the unit,” he added. “It is not required of out-of-state carriers, but is strongly recommended.”

Compliance officers from CARB conduct inspections directly at shipper locations and check all the units for compliance. In addition, trucking companies are required to keep current logs for when they get inspected and to be 100% in compliance.

’s Vector trailer TRU incorporates a small diesel engine that drives a generator that produces electricity for electric refrigeration. Carrier’s line of hybrid equipment includes single-temp and multi-temp reefer units.

At ACT Expo, Carrier Transicold exhibited its new Vector 8200, which it described as an “all-electric, engineless TRU for single or multi-temperature trailer storage” with options to cool one-, two- or three-compartment trailers.

Carrier also introduced Vector eCool, a “power management architecture that maximizes energy efficiency from regenerative and grid-supplied electricity.” In-wheel electric motors generate up to 160 kilowatt-hour peak power, the company said.

Last year, announced an integration of its hybrid trailer refrigeration units and electric TRUs with Range Energy’s eTrailer system. Range’s system, which equips trailers with a high-voltage battery and an electric axle, can provide zero-emission electric power for trailer refrigeration.

“Although the pace of electrification has decelerated at large, we’re seeing steady interest in our hybrid and electric TRU options,” said Chris Tanaka, vice president of product management at Thermo King Americas.

Fleets operating in urban environments or states with more aggressive emissions regulations are among the most curious, he added.

Infrastructure, Training Challenges Remain

As customers explore pilot programs or transition a portion of their fleet to hybrid or electric TRUs, infrastructure and total cost of ownership remain key considerations, Tanaka said.

“Charging infrastructure is limited, particularly at common route stops like truck terminals and distribution centers, which can make consistent access to power difficult,” he explained. “Transitioning between power sources may also require additional driver training or changes to operational workflows.”

Electric TRUs also can add weight, reducing overall payload capacity and influencing route planning and load strategies, Tanaka added.

Gassler of PLM noted that battery health is another challenge.

“With the eTRUs you really have to start monitoring battery voltage and overall kilowatt output to ensure that your batteries are in good health, as well as to make sure there’s enough power to run these routes without the risk of the unit going down,” he said.

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(John Sommers II for Transport Topics)

Utility Trailer’s telematics system, TrailerConnect, which is standard on 3000R models with Cargobull TRUs, monitors components such as the compressor and electric fan motors. The system also monitors trailer health, including the trailer electrical system, antilock braking system and tire inflation, and sends notifications, Bennett said.

Carrier Transicold’s Lynx Fleet telematics platform is integrated with the TRU, tracking locations and monitoring temperatures, delivering analytics and remote diagnostic capabilities, and providing “data and intelligence” to fleet managers, the company said. For electric TRUs, it tracks battery voltage, temperatures, charging cycles and overall battery health.

In May, Carrier acquired Addvolt, which specializes in battery-electric and power management technologies for electric refrigeration systems.

Deploying hybrid or electric units demands operational adjustments and training, vendors and fleet managers said.

“You have to be very tight in the standard operating procedures you put in place because it could change how you’re loading,” PLM’s Gassler said. “At the end of the day, if you’re not charging these things, they’re not going to run.”

Gassler recommended a holistic approach when evaluating operations and making sure everyone is trained up.

“A big success for us was putting together ‘one-pagers’ — step-by-step guidance for drivers and operations personnel,” he explained. “The one-pagers, tailored to each customer, have been big wins for us.”

Fleets can also partner with electric utilities. Grants for infrastructure assistance are available in California. For example, The Carl Moyer Program, a partnership between CARB and California’s 35 local air districts, provides grant funding for “cleaner-than-required” engines and equipment.

The Bay Area Air District, based in San Francisco, periodically offers grants for zero-emission transport refrigeration units. It most recently was taking applications for grants that could provide $100,000 per TRU or 80% of the cost of the TRU, whichever is lower.

“It can’t be done overnight,” Gassler noted. “Especially if you have to work with municipalities or utilities. Some projects can take years before you’re even able to plug in a unit.”