Abstract <p>For the autonomous power supply system of a passenger car, the use of photovoltaic panels and a supercapacitor is considered in order to prevent deep discharge and reduce fluctuations in battery power. An electrical connection diagram of a supercapacitor and a solar panel, a method for calculating the uncompensated battery power and the principle of its compensation by a supercapacitor based on transistor control of a bidirectional step-down converter are presented. An algorithm for tracking the maximum power point of a photovoltaic panel using a step-up semiconductor converter has been developed. The calculation of the circuit elements using domestic components and verification of its operability based on computer modeling are performed.</p>