In deciding which energy harvesting technology to utilize, one needs to review the various energy sources available. These potential energy sources are light, thermal, vibration, and RF. Out of the various technologies available for energy harvesting, solar is most widely used and has the highest estimated potential energy for harvesting, from 100 mW/cm2 outdoors to 0.1 mW/cm2 using indoor lighting. Thermal energy is the next highest potential energy generation source and can be acquired from sources such as our bodies, or the heat generated by appliances and machines. Vibrational energy is a potential source as well, but it’s potential energy generation is less then light and thermal sources. Even though there are discussions of being able to retrieve energy from electrical signals transmitted wirelessly, estimates of harvested energy are low and likely not a viable energy harvesting source presently.