A system comprising an array of solar panels, each panel including an electronic control module, wherein the panels are all connected in electrical series with each other and to a switch and to a string inverter, may be signaled to power down each panel to a safe output at its output terminals. The method includes sensing output wave forms of a module to be the result of its own DC-DC converter output or to be at variance with the expected output. Output wave forms at variance indicate that the control module is connected in electrical series with the input capacitance of the string inverter. If the output is as expected, the control module is deemed to not be connected to the capacitance of the string inverter as a result of the electrical series switch being open. The module then immediately drives its output to a safe level.