Reference in now made to FIGS. 4, which illustrate system 40, according to an embodiment of the present invention. For simplicity, a single string 423 is shown of distributed power sources, e.g. solar panels 101a-101d connected to respective power modules 405a-d. Serial string 423 is input to conventional inverter 104 through wires 412 and 410. The output of inverter 104 is connected to and supplies electrical power to the electrical grid. At the input of inverter 104, is connected a signaling mechanism 420 which superimposes a signal on serial string 423 through wires 412 and 410 when inverter 104 is converting power to the grid.