Long-term, truck operators are eyeing fleet electrification or use of renewable liquid fuel, such as hydrogen, to eliminate diesel-related greenhouse gas emissions. New solar and battery pairings adapted for tractor and trailer installations are beginning to address driver comfort and fuel use—maybe not solving either issue, but at least adding a potentially valuable tool for addressing both concerns while helping to cut fuel and servicing expenses.
Semi-trucks burn through a lot of diesel—on average, their fuel efficiency runs 6.5 to 7 mpg, though that can top 10 mpg, depending on the tractor model and how drivers operate their vehicles. While most of that energy goes to running the tractor and the freight it’s hauling, a fair amount is also required when the vehicle is standing still. The tractor uses power to support cab operations and driver comfort during loading, unloading and “hoteling” (the time drivers spend relaxing and sleeping in their cabs during mandatory rest breaks). Heating or air conditioning keep running during these times. The tractors also have their own energy demands for liftgates and, in the case of refrigerated units, to keep their contents cold or frozen.
In the past, drivers simply idled their engines to perform many of these functions—or put up with inadequate temperature control. More recently, auxiliary power units have eliminated idling needs, but many of these are diesel-powered, so emissions still result. Battery-based solutions don’t produce emissions themselves, but they can force tractor engines to auto-start when they begin to run out of juice to recharge batteries using the tractor’s alternator. Many of these batteries are also lead-acid based, meaning they can only be discharged down to 50% without experiencing damage.
Today, onboard solar panels are beginning to help support trucks’ energy needs, in combination with lithium-ion batteries capable of frequent, full discharge and recharge. The panels are fabricated using flexible backings that can be attached to tractors’ roof fairings, the sloped surfaces above the cab that create a more aerodynamic profile. According to a 2018 report by the North American Council for Freight Efficiency (NACFE), such panel/battery pairings offer multiple opportunities for reducing diesel consumption and ongoing maintenance expenses while also ensuring driver comfort. The report identified two primary applications for tractor-trailers:
- Battery-based HVAC systems: These operate independently from the tractor’s engine, but they’re connected to enable automatic engine starting if their charge runs low. These systems can have issues with dying batteries, leading to calls for roadside assistance. Solar panels provide a way to extend battery life by reducing discharge levels. They also protect vehicle alternators by reducing battery recharging needs after a full night of operation.
- Hotel loads: Today’s semi cabs are like studio apartments on wheels, fitted out with small refrigerators, microwave ovens, coffee pots and televisions. According to NACFE researchers, batteries alone might only be able to support these devices for 8–10 hours at a time. Solar panels can help batteries remain at a higher rate of charge, prolonging their lifespans as a result.
The trailers being hauled also have become big energy users and need support for liftgates, refrigeration units and the telematics that allow fleet operators to track trailer locations remotely. Their flat rooftops offer ample space to install flexible solar panels to support those capabilities.
Electrical contractors, of course, are likely more interested in stationary trucking-related solar opportunities, such as solar canopies for larger truck dealerships. One example is the system installed at Rush Enterprises’ Peterbilt dealership in Converse, Texas. Called the largest solar carport in Texas when it was installed in June 2020, it incorporates more than 3,500 solar panels and was developed as a community solar project by the local company Big Sun Solar.
While the dealership gets a monthly break on its electric bill from the local utility CPS for hosting the massive carport, it’s saving even more money on its insurance bills. The new installation now provides shelter for up to 181 Class 8 commercial vehicles, which includes semi-trucks. The area around San Antonio is known for frequent, severe hailstorms, which obviously pose a major risk to vehicles on an exposed lot. Just last spring, the National Weather Service (NWS) documented that Texas’ largest-ever hailstone fell in nearby Hondo, measuring 6.4 inches across and weighing more than a pound.
An even larger hailstone was posted on social media that night, but—in typical Texas style—was blended into a batch of margaritas before the NWS team could document its size.