Devices, systems and methods for operating, monitoring and diagnosing photovoltaic arrays used for solar energy collection. The system preferably includes capabilities for monitoring or diagnosing an array by automatically disconnecting portions of the array during normal service (when load is not maximum, and observing the resulting change in electrical characteristics. More intensive diagnostic procedures can be launched if needed. One embodiment provides for performing monitoring or diagnostic operations on the array in daylight or at night. Another embodiment allows monitoring or diagnostic operations to be performed on a portion of the array while other parts of the array continue to collect energy. Yet another embodiment provides a safety mode for an array for maintenance or during emergencies.