A method for direct current power line communication in a photovoltaic system includes (a) transferring power between a photovoltaic device and a load using a power line, (b) detecting a change in operation of the power line, and (c) in response to the detected change in operation of the power line, decoding operating state of the power line to obtain information. A method for direct current power line communication in a photovoltaic system includes (a) transferring power between a photovoltaic device and a load using a power line, (b) changing operation of the power line, and (c) encoding operating state of the power line to represent information to be communicated.

In a system and method for operating a system, a drive is connectable to a supply-voltage source, especially an AC-voltage source, with the aid of an apparatus, in particular a control unit, via electric lines installed in the system, and information is transmittable between the control unit and the drive, using the lines.