Maximising Regenerative Energy Return from Dynamo-Motor Traction Drives in Solar PV-Powered Electric Vehicles for Long-Haul Operation with Strong Stability

The road to a cleaner future for heavy transport is paved with a difficult paradox: electric trucks need massive batteries to carry heavy loads over long distances, but those batteries add weight that reduces how much cargo the truck can carry. To solve this, engineers look to two sources of free energy that travel with the vehicle: the sun, captured by solar panels on the roof, and the kinetic energy of the truck itself, which can be recaptured when the vehicle slows down or goes downhill. This process of recapturing motion is called regenerative braking. It works by reversing the electric motor so that instead of pushing the wheels, the wheels push the motor, turning the vehicle's momentum back into electricity to store in the battery. The idea is simple and appealing: if a truck could capture enough of its own wasted energy and enough sunlight, it might eventually drive forever without needing to plug in.

However, the laws of physics place strict limits on how much energy can be saved. Every time energy changes form—moving from the battery to the wheels, or from the wheels back to the battery—a small amount is lost as heat. Because of these inevitable losses, a machine cannot simply take energy from a battery, use it to move, and then put the exact same amount back into the battery. To make the math work, an outside source of energy is required to fill the gap. This is where the question becomes critical for the future of freight: just how much of the energy a truck uses can actually be returned to its battery through a combination of solar power and regenerative braking? A new study by researchers at Atlantic International University and several other institutions investigates this precise question for a long-haul electric truck, moving beyond hopeful claims to find the hard numbers that govern what is physically possible.

The researchers built a detailed computer model of a heavy-duty electric truck weighing 3,500 kilograms, designed to travel 450 kilometers on a hilly route in the United Arab Emirates. They equipped this virtual truck with a solar array covering 12.4 square meters of its roof and a powerful electric motor that can act as both a drive and a generator. The team then simulated a full day of driving, tracking every joule of energy the truck took from its battery to move forward and every joule it managed to put back. They found that while the truck could indeed recover energy, the amount was far smaller than the energy it consumed. Over the course of the 450-kilometer journey, the truck required 146.8 kilowatt-hours of energy to overcome air resistance, rolling friction, and the hills. The solar panels contributed 14.4 kilowatt-hours, and the regenerative braking system, which captured energy during descents and braking, returned only 8.3 kilowatt-hours.

When the researchers added the solar and regenerative contributions together, the truck recovered just 15.5 percent of the energy it had used. This means that for every 100 units of energy the truck spent, it got back only about 15. The study explicitly rules out a popular but physically impossible notion: that a motor connected to the drive shaft could somehow sustain the vehicle indefinitely by recirculating its own energy. The researchers demonstrated that if a motor tries to generate power while the vehicle is cruising at a steady speed, it actually forces the main motor to work harder, draining the battery faster than if the generator were not there at all. Regeneration only works when the vehicle is shedding energy that would otherwise be wasted as heat in the brakes, such as when going downhill. Even then, the system is not perfect; due to losses in the gears, the motor, and the battery charging process, only about 75 percent of the energy captured at the wheels makes it back into the battery.

Despite the low recovery percentage, the results showed that these systems are not useless. Without the solar panels and the regenerative braking, the truck would have arrived at its destination with its battery nearly empty, dropping to a level that would damage the battery's long-term health. With the recovery systems active, the truck arrived with enough charge remaining to be considered safe and operational. The combination of solar harvesting and energy recovery reduced the total energy the truck needed to travel each kilometer by 10.4 percent. This small improvement was the difference between a trip that was impossible to complete without stopping to recharge and one that could be finished in a single run.

The study also looked at the electrical stability of the truck's power system. Because the electric motor draws a constant amount of power to maintain speed, it can create a dangerous instability in the electrical circuit, similar to how a heavy load can cause a power line to flicker or fail. The researchers found that without a special control system, the truck's electrical network would become unstable and potentially fail when the motor was working hard. By adding a virtual damping mechanism—a mathematical adjustment in the software that acts like a shock absorber for electricity—they were able to stabilize the system, ensuring it could handle the full range of driving conditions without losing control.

Finally, the researchers asked what it would take for the truck to achieve total energy neutrality, where the energy returned equals the energy used. Their calculations showed that this is theoretically possible, but only under conditions that are not practical for a commercial truck. To reach this balance with the current solar panel size, the truck would have to drive at a crawl of just 10.8 kilometers per hour, turning a long-haul trip into a multi-day journey. Alternatively, to drive at a normal highway speed of 80 kilometers per hour, the truck would need a solar roof covering 91 square meters, which is more than seven times the size of the actual vehicle. The study concludes that while a self-sustaining electric truck is not a realistic goal for long-distance freight, the combination of solar power and regenerative braking provides a vital, real-world benefit: it extends the range enough to make long trips feasible without intermediate charging stops, turning a theoretical impossibility into a practical engineering gain.