One of today’s most relevant problems in wireless sensor networks is the supply of energy. In several cases the most promising solution could be the energy harvesting based power supply. But hard problems should be answered using that technology, because the available energy for harvesting is usually not constant and out of our control. This paper discusses the development of an energy harvesting power supply for wireless sensors. Both theoretical considerations are discussed and the applications of them are presented using a prototype development example. A solar cell based solution is shown. The proposed power supply was tested and evaluated.