The current consumption is read using an IR reading head.
Most modern electric meter (often identified by the digital display) have an infrared diode for reading the current consumption and other data. The IR reader can be easily set on the top of the infrared diode and keeps using a magnet. It is connected to the server via USB.
Unfortunately, I was not able to read this USB / Serial port with java. So i could not develop a binding for it. In various forums i read that the driver chip used here is especially problematic. If someone knows more about this topic, feel free to contact me.