Wireless sensor nodes are usually powered by batteries or accumulators, which have a limited operation time and need to be recharged. Energy harvesting therefore offers the possibility to supply a system with freely available energy for making it autark. This work presents current approaches of using energy extracted from the environment to power microelectronic devices. In the first part the main focus is, to determine the amount of energy produced by different energy harvesters using measurements. As a second step, the operation of a micro energy harvesting system is explained and has been tested with a laboratory demonstrator. This demonstrator has been redesigned for an internal demo system of a micro energy harvesting system which shall visualize the effectiveness of the harvesters.