A photovoltaic, PV, module level monitoring, MLM, system comprising a base station, BS, connected by means of power cables to module level devices, MLD, which are provided to monitor and/or to control associated photovoltaic modules, PVMs,, wherein the base station, BS, comprises: a base station transmitter adapted to transmit Rapid Shut Down, RSD, control signals, CS, in predefined time slots, TScs, in a downlink channel, DL-CH, through said power cables to said module level devices, MLDs,, wherein the base station transmitter of the base station, BS, is connected to a Rapid Shut Down, RSD, initiator and is adapted to transmit a permission to operate, PTO, signal periodically in the downlink channel, DL-CH, when the Rapid Shut Down, RSD, initiator indicates that rapid shutdown, RSD, is not active and is further adapted to stop transmitting the permission to operate, PTO, signal when the RSD initiator indicates that rapid shutdown, RSD, is active, characterized in that the base station further comprises a base station receiver adapted to receive monitoring signals, MS, generated by said module level devices, MLDs, through said power cables within time slots, TS MS, via an uplink channel, UL-CH, assigned to the module level devices, MLDs,, wherein the time slots, TS MS, of the uplink channel, UL-CH, assigned to module level devices, MLDs, are inside the predefined time slots, TS CS, of the downlink channel, DL-CH, wherein the length of the time slots, TS MS, of the uplink channel, UL-CH, is shorter than the length of the time slots, TS CS, of the downlink channel, DL-CH, wherein frequency division multiplexing, FDM, is used to separate the monitoring signals, MS, and the Rapid Shut Down, RSD, control signal, CS. a base station, BS, connected by means of power cables to module level devices, MLD, which are provided to monitor and/or to control associated photovoltaic modules, PVMs,, wherein the base station, BS, comprises: a base station transmitter adapted to transmit Rapid Shut Down, RSD, control signals, CS, in predefined time slots, TScs, in a downlink channel, DL-CH, through said power cables to said module level devices, MLDs,, wherein the base station transmitter of the base station, BS, is connected to a Rapid Shut Down, RSD, initiator and is adapted to transmit a permission to operate, PTO, signal periodically in the downlink channel, DL-CH, when the Rapid Shut Down, RSD, initiator indicates that rapid shutdown, RSD, is not active and is further adapted to stop transmitting the permission to operate, PTO, signal when the RSD initiator indicates that rapid shutdown, RSD, is active, characterized in that the base station further comprises a base station receiver adapted to receive monitoring signals, MS, generated by said module level devices, MLDs, through said power cables within time slots, TS MS, via an uplink channel, UL-CH, assigned to the module level devices, MLDs,, wherein the time slots, TS MS, of the uplink channel, UL-CH, assigned to module level devices, MLDs, are inside the predefined time slots, TS CS, of the downlink channel, DL-CH, wherein the length of the time slots, TS MS, of the uplink channel, UL-CH, is shorter than the length of the time slots, TS CS, of the downlink channel, DL-CH, wherein frequency division multiplexing, FDM, is used to separate the monitoring signals, MS, and the Rapid Shut Down, RSD, control signal, CS. a base station transmitter adapted to transmit Rapid Shut Down, RSD, control signals, CS, in predefined time slots, TScs, in a downlink channel, DL-CH, through said power cables to said module level devices, MLDs,, wherein the base station transmitter of the base station, BS, is connected to a Rapid Shut Down, RSD, initiator and is adapted to transmit a permission to operate, PTO, signal periodically in the downlink channel, DL-CH, when the Rapid Shut Down, RSD, initiator indicates that rapid shutdown, RSD, is not active and is further adapted to stop transmitting the permission to operate, PTO, signal when the RSD initiator indicates that rapid shutdown, RSD, is active, characterized in that the base station further comprises a base station receiver adapted to receive monitoring signals, MS, generated by said module level devices, MLDs, through said power cables within time slots, TS MS, via an uplink channel, UL-CH, assigned to the module level devices, MLDs,, wherein the time slots, TS MS, of the uplink channel, UL-CH, assigned to module level devices, MLDs, are inside the predefined time slots, TS CS, of the downlink channel, DL-CH, wherein the length of the time slots, TS MS, of the uplink channel, UL-CH, is shorter than the length of the time slots, TS CS, of the downlink channel, DL-CH, wherein frequency division multiplexing, FDM, is used to separate the monitoring signals, MS, and the Rapid Shut Down, RSD, control signal, CS.