Solar power makes sense for many commercial trucks, and in many applications, an investment in the right equipment can be paid back in roughly three years, 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, and they are especially useful for sleeper-cab tractors, 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.

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.

Solar power helps a truck’s alternator keeps batteries charged and ready for use to operate heating, air conditioning and “house” loads from dusk to dawn, they said. And drivers report that the panels begin generating electricity first thing in the morning. 

 “You do take some wear off the alternator as you’re going down the road charging,” Otto said. “A 300-watt panel during an 8- or 9-hour period is worth an extra battery (in power storage). You can figure that batteries will have a couple of hours more (operating) life… So there are fewer call-outs for batteries and you do get longer battery life.”

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.”

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

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 lift gates 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.

“Lift gates 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 liftgate.”

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.

The report has four main conclusions:

• Technology has progressed and fleets are adopting to do work

• Fuel savings are generally quite small. Depends on where you’re operating and how intense the energy is. Calculator on line

• Installation should be designed expressly for the application. They come in standard sizes, but it’s important to understand what problem it’s trying to overcome.

• Manufacturers’ claims are close to the real world, but numbers from fleet users are lacking.

“We found some comments from drivers and fleet managers that told the story about solar very well,” Roeth said. “We don’t know, but we think it will help with attraction and retention of drivers” because solar addresses their needs for heating and air conditioning.

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 here.

Related: Real-World Fuel-Economy Lessons From NACFE Run on Less