TORONTO, Ont. — In some corners of North America, the idea of adding solar power to a truck or trailer is a no-brainer. You’d be forgiven for thinking that none of those corners are in Canada. That’s mostly true, but it doesn’t necessarily mean that solar has no place here. Just that you must be careful in assessing manufacturer claims about what their solar gizmo can actually do.

Almost all of Canada gets an average of 4.2 hours of solar sunlight a day. Two areas — a small stretch of the southern prairies and a little ribbon of central B.C. — crank that number up to 4.5 hours. Compare that to as many six hours in Arizona, New Mexico, and a patch of southeast California. Doesn’t sound like much of a difference, but it’s a big deal. A 300-watt solar setup that can help to run a tractor’s electric APU in that part of the U.S. would probably have to be a 600- or 800-watt setup for a rig running, say, a Toronto-Montreal-Halifax route.

It also means that manufacturer claims can be rather idealistic if calculations were based on experience in warm and sunny parts of our world. There’s no subterfuge involved here, but “your mileage may vary,” as they say.

According to retired Cummins engineer Kevin Otto, who’s now researching solar options for the North American Council for Freight Efficiency (NACFE), there’s nothing simple about calculating the payback of a solar system on a truck, tractor, or trailer.

The only real no-brainer may be the idea of using a small solar panel to keep the batteries on a van trailer’s telematics or tracking system charged. Otto says that small and simple use of solar is pretty much a given these days, and it’s expanding all the time, no matter your location. The advantages are obvious, given that trailers can sometimes get “lost” for a week or three, more than enough time for batteries to run down with a little assistance.

One provider of asset tracking, Skybitz, has seen its Falcon GXT5000 solar-powered system take off. It recently introduced the next-generation Falcon GXT5002C with built-in cargo sensors and service life lasting the life of the trailer.

“Bottom line,” says company president Henry Popplewell, “solar power is the future of asset management.”

Using a small solar panel to keep a reefer unit’s battery topped up is in the same category, especially if the trailer might sit still for long periods. Both Carrier Transicold and Thermo King offer small panels to serve this purpose.

Thermo King’s ThermoLite solar panels come in three different wattage options (26, 36, and 100 watts) and provide an alternative power source to refrigerated and dry van fleets while offsetting battery drains from parasitic loads. It allows the company’s TracKing or other telematics systems to monitor assets over long periods, even when the refrigeration unit is off and the trailer’s untethered from the tractor. The company says they “work great, even in low-light conditions.”

Carrier Transicold’s Thin Film flexible solar panels maintain the refrigeration unit’s battery charge. They can offset the draw from accessory electrical devices, reducing callout charges related to the battery. Solar panels can also help save fuel by minimizing the need to run a reefer engine to charge the battery.

We’ve heard of a fleet using one of these small panels to keep the refrigerator humming in the bunk, even if the truck’s been shut down, which obviates the need for drivers to empty their fridge at the end of a run.

Powering a liftgate is also a common use of solar panels, and for some fleets it can be an easy decision to go that way. But in this case, the payback calculation isn’t always straightforward because there are so many variables. Assume nothing.

There are many options for this application, but one of the most interesting comes from Purkeys, the well-respected electrical specialist in Arizona. Its Solar Bolt liftgate charging system is a solar-powered battery charger that works with a vehicle’s native electrical system to help keep liftgate and auxiliary batteries charged. It’s a supplemental charging system that keeps batteries charged — whether the vehicle is on or off — by way of a unique, patented controller.

Charging the battery while the vehicle is running reduces the electrical load on the alternator, which reduces the mechanical load on the engine, reducing fuel costs slightly over time. It comes with a standard 90-watt roof-mounted panel, but up to three more panels can be added to increase power to 360 watts.

Then there’s the one that can really save you money on the tractor side — an electric APU running HVAC systems, backed up by solar panels.

The Canadian fleet with the most experience in using such a system seems to be Quebec’s Groupe Robert, though its solar journey began with another purpose. It outfitted its fleet of LNG-fueled tractors with a small solar panel to keep batteries charged on methane detectors. That soon morphed into the replacement of its Thermo King TriPac diesel-fired APUs with Bergstrom NITE Phoenix AC electric units backed up by solar panels to keep drivers comfortable without idling and to keep batteries charged in cold weather. The system is entirely separate from the tractor’s electrical circuits.

At first Robert used one rigid panel, but soon switched to the less-damage-prone flexible type and ended up spec’ing six flexible solar panels on the roof fairing and the hood for 600 watts in total. With four deep-cycle batteries in addition to the standard set of four, drivers now get a full 10-hour rest period of noiseless sleep. The fleet has this arrangement on nearly 200 units and is equipping all new sleeper tractors this way.

Cost wise, it’s a wash in terms of initial purchase price — both the diesel-powered and solar systems are worth $14,000 or so. But the fuel savings start right away.

“By replacing our diesel gen sets with a battery pack located behind the cab and solar panels to power the fully electrical air conditioning unit and in-cab accessories, the purchase cost is comparable, but the elimination of fuel use will result in a 3.5-year return on investment,” says Daniel St-Germain, Robert’s vice-president – material resources.

“The real payback is that solar panels can generate approximately two to four hours more power and help to recharge the battery pack quicker, so the driver can still do everything he’s used to while using no diesel.”

While Robert needs 600 watts out of six solar panels to run its electric HVAC system, New Mexico’s Mesilla Valley Transportation needs only 300 watts from three panels. That’s the difference geography makes, as Mesilla runs mostly southwest routes.

The technologically adventuresome truckload fleet now has several hundred of its Navistar trucks running with eNow’s auxiliary solar system. The result is less idling, longer battery and alternator life, and increased driver satisfaction.

Based in Rhode Island, eNow is arguably the leader in solar panels for trucking use. The International Catalist Super Truck’s trailer roof was festooned with the company’s solar panels, and before you read this article eNow will have introduced a new product. In concert with Great Dane, Carrier, and customer C&S Wholesale Grocers, it will unveil a solar-based all-electric trailer refrigeration system at the ACT Expo in Long Beach, Calif., running April 30 through May 3.

Back with Mesilla Valley, the carrier’s president and CEO Royal Jones is not so clear about payback on its electric/solar APUs as Robert’s St-Germain.

“The big savings for me is getting more hours on your APU,” says Jones, as quoted in Heavy Duty Trucking magazine. “It’s hard to figure the ROI, because it’s not an exact science. But if you save two jump starts a year, that’s $600. If your driver comfort is better, how do you put a price on that? And we used to replace all eight batteries every year, but the trucks with the solar panels have had them for four years.”

As it happens, all those calculations are about to get easier, because Otto is in the midst of helping to prepare a new “confidence report” on solar power for NACFE. Due to be published in May, it will include a payback calculator applicable to several potential solar applications. Broadly, says Otto, the report aims to bring clarity to a niche technology that’s not always well understood — but likely to become much more widespread.