Solar panels are sending power into electrical grids and supplying juice directly to buildings, but do they make sense for commercial vehicles? Yes, says the North American Council for Freight Efficiency in its latest Confidence Report, “Solar for Tractors and Trailers,” issued June 28.

Solar panels’ cost has come down and efficiency has increased to where they can pay for themselves in roughly three years, said NACFE’s executive director, Mike Roeth, and two researchers, Jessie Lund, of the Rocky Mountain Institute, and Kevin Otto, a retired Cummins electronics engineer. They briefed reporters during a call-in press conference upon issuance of the report.

Panels are now thin and flexible enough to mount on curved surfaces, so can be affixed to roof air deflectors and even on hoods of tractors.

There’s much more room on van and reefer trailers to place panels, and they are used primarily to charge batteries in reefer units and for liftgates and pallet jacks. Reefer unit makers offer panels that help keep batteries charged so engines can start every time they’re needed to run refrigeration equipment.

“Liftgates use a very large amount of power for a very short amount of time,” Otto said.  “There are different sizes and capacities, and you need to size your batteries to the lift gate.”

(Many delivery trucks operate on urban routes where distances between stops are too short for the tractor’s alternator to sufficiently charge the trailer’s batteries, said Derry Stuart, a fleet consultant who discussed the topic at an industry meeting a few years ago. But solar panels on the trailer keep batteries charged and the liftgate ready to work every time.)

The job of solar panels on trailers differs greatly according to application, Otto said.  So the number and output of a panel complement needs to be carefully planned.

Cost of a 300-watt installation, including panels and control apparatus, is about $2,000, Otto said. The recent Trump-imposed tariffs on foreign metals and products might add only $40 to $50 to that, said Lund, the other researcher.

A 100-watt panel ideally will produce 7 to 8 amperes, but various real-life conditions will often reduce that by 30%, he added. So that panel might make 1 amp at dawn and 5 to 6 amps at noon.

“Solar” implies sunlight, whose intensity varies due to weather conditions and geographic region, Otto said. “In the dark East, you get two-thirds of the output compared to when you’re in areas like Phoenix.”

Solar power can run electric HVAC systems in sleepers, thus reducing engine idling during overnight breaks. But they don’t save a lot of fuel, Roeth said.

“The minimum savings we see with these panels in most applications, and in particular with tractors, is battery health,” Roeth said. “Panels can extend the life of the battery and the cost of replacement, as well as reduce service calls” on the road.

NACFE’s report includes a payback calculator for tractors and a “confidence matrix” for tractors and trailers that users can employ to gauge the financial feasibility of installations. The report is available at  www.nacfe.org/technology/solar-panels-2/?cf_id=1033.

Related: How Fleets are Using Solar Power