Single-panel voltage zeroing system for safe access on PV plants

In this paper, an effective circuit for both voltage and current zeroing of single solar panels embedded in a solar field is presented. The circuit interrupts the panel current by means of a solid-state power switch and zeros the panel voltage by means of an electromechanical relay. Each solar panel can be either connected or disconnected from the string independently from each other. The circuit is connected to the existing junction box and does not require additional wiring, neither for its power supply, which is always derived from the solar panel, nor for its data transmission, which is achieved through a special suited power line communication scheme exploiting the existing dc power bus. Experiments performed on a test solar field equipped with in-housemade circuit prototypes evidence the reliability of the proposed approach