The wireless transmission of process data is a widely discussed topic in the field of automation. A lot of semi-wireless sensors or sensor hosts can be found in today's markets using radio transmission. However, using a wireless data transmission is one necessary step in realising wireless sensors. A further important step is the use of a maintenance-free wireless power supply. Energy Harvesting methods may be a solution. Measurements in a real system environment shows the usable environmental power which can be converted into electrical energy.