With the widespread use of wireless sensors, the management of their energy resources has become a topic of research. Wireless sensors usually use batteries as their power supply but in some applications battery replacement can be cumbersome and require considerable amount of time which can affect the process being monitored. It is possible to harvest energy from the sources in nature for wireless sensors. In this article, a review of current alternative energy sources has been demonstrated in order to address the feasibility of their integration with wireless sensor networks.