To solve the problem of a high string direct-current voltage in a rooftop photovoltaic (PV) system during a string-level rapid shutdown and to reduce the risk of high-voltage electric shock for firefighters working in and around the PV array, this paper introduces a rapid-shutdown system for a rooftop PV at panel level. This system includes a shutdown controller and shutdown modules installed inside each junction box of the PV modules, whose communication protocol complies with the SunSpec standard protocol. First, the shutdown controller continuously sends a cyclic code sequence using a power-line carrier. Second, the shutdown module receives the codes, decodes the frequency shift keying (FSK) signal, and controls the opening and closing of the PV modules according to the command code. Experimental results show that the voltage within the rooftop PV array is limited to that at the module level (80 V) in 30 s in the case of emergency shutdown. This solution is useful for improving the safety performance and reducing fire hazards and is more portable. Furthermore, it does not require additional wiring and significantly decreases system costs.