The use of electric grids for communication purposes may interfere with radio communication services. To offer new directions to avoid electromagnetic interference that reduces the effectiveness of electric power grids as a green and lowcost communication channel, this paper discusses and introduces spectrum sensing techniques for cognitive power line communication (PLC) systems. Additionally, a measurement campaign for monitoring the radio spectrum in the range from 1.7 to 100 MHz is discussed as well as attained results with the spectrum sensing technique. The numerical results indicate the proposed spectrum sensing technique can offer good performance in a cognitive PLC systems.