A safety shutoff system for protecting a photovoltaic system, the photovoltaic system comprising an inverter connected via a DC power line to a plurality of photovoltaic modules connected in series, the safety shutoff system comprising: - a control signal generator comprising: ∘ an oscillator for generating a time-varying control signal; and ∘ a DC-signal separator for transmitting the time-varying control signal via the DC power line; ∘ wherein the DC-signal separator provides a first low impedance path for DC current generated by the PV modules between the series of the PV modules and the inverter and a second low impedance path for the time-varying control signal between the control signal generator and the series of the PV modules; characterized in that it further comprises: - a plurality of switching modules, each configured to be connected between a dedicated PV module and the DC power line and comprising: ∘ a DC-signal separator for receiving the time-varying control signal from the DC power line, ∘ a rectifier and power storage block configured to store power of the time-varying control signal and to supply the stored power to other components of the switching module; ∘ a control signal detector for determining a presence of the time-varying control signal; and ∘ a switch connectable between terminals of the dedicated PV module, wherein the switch is a normally-open switch; ∘ wherein the control signal detector, when powered by the power storage block, is configured to close the switch upon detecting an absence of the time-varying control signal. - a control signal generator comprising: ∘ an oscillator for generating a time-varying control signal; and ∘ a DC-signal separator for transmitting the time-varying control signal via the DC power line; ∘ wherein the DC-signal separator provides a first low impedance path for DC current generated by the PV modules between the series of the PV modules and the inverter and a second low impedance path for the time-varying control signal between the control signal generator and the series of the PV modules; ∘ an oscillator for generating a time-varying control signal; and ∘ a DC-signal separator for transmitting the time-varying control signal via the DC power line; ∘ wherein the DC-signal separator provides a first low impedance path for DC current generated by the PV modules between the series of the PV modules and the inverter and a second low impedance path for the time-varying control signal between the control signal generator and the series of the PV modules; - a plurality of switching modules, each configured to be connected between a dedicated PV module and the DC power line and comprising: ∘ a DC-signal separator for receiving the time-varying control signal from the DC power line, ∘ a rectifier and power storage block configured to store power of the time-varying control signal and to supply the stored power to other components of the switching module; ∘ a control signal detector for determining a presence of the time-varying control signal; and ∘ a switch connectable between terminals of the dedicated PV module, wherein the switch is a normally-open switch; ∘ wherein the control signal detector, when powered by the power storage block, is configured to close the switch upon detecting an absence of the time-varying control signal. ∘ a DC-signal separator for receiving the time-varying control signal from the DC power line, ∘ a rectifier and power storage block configured to store power of the time-varying control signal and to supply the stored power to other components of the switching module; ∘ a control signal detector for determining a presence of the time-varying control signal; and ∘ a switch connectable between terminals of the dedicated PV module, wherein the switch is a normally-open switch; ∘ wherein the control signal detector, when powered by the power storage block, is configured to close the switch upon detecting an absence of the time-varying control signal.