Abstract: The solar power system for auxiliary-powered brakes and power system for a tractor-trailer is a supplemental electrical system adapted for use with the trailer of a tractor-trailer. The solar power system for auxiliary-powered brakes and power system for a tractor-trailer is designed to: 1) assist in the acceleration of the trailer; 2) use braking energy to generate and store electricity; 3) supplement the stored energy with a renewable source; and, 4) distribute excess energy to the trailer electrical system. In one potential embodiment of the disclosure, the solar power system for auxiliary-powered brakes and power system for a tractor-trailer provides for tapping into the stored electrical energy for external use. The solar power system for auxiliary-powered brakes and power system for a tractor-trailer comprises a plurality of photovoltaic cells, one or more axle assist devices, an electricity storage device, and a distribution system.