Sensor networks are emerging in many applications with the availability of the spreading IoT (Internet of Things) technologies. These applications having sensor networks generally do not require big data transfers, but instead, they need to send a small amount of data from time to time. Long-range wide area network (LoRaWAN) is a very good solution for this kind of communication since LoRaWAN offers long-range transmission with deep-sleep mechanism between the transmissions. However, these networks must be reliable, and from the point of energy supply for a long period of time, they should be sustainable. Since the nature of sensor-based IoT devices is being small and placable anywhere, they are generally battery-powered. With the usage of batteries, many disadvantages including limited power, cost of replacement of the dead battery, especially in rural areas, environmental concerns, etc. arise. Therefore, energy harvesting from different sources depending on the application and location of the sensor network may eliminate these problems. In this study, firstly, we focused on how the energy is consumed by the LoRAWAN communication systems by analyzing the power consumption during the transmit phase and providing necessary formulas. Secondly, by looking at the formulas, a possible optimization is recommended on the power consumption in LoRAWAN systems in order to have longer battery life. Thirdly, we have searched and analyzed energy harvesting methods and applications used by the researchers in recent years, as well as elaborating power consumptions, in typical microcontroller-controlled sensor nodes with LoRaWAN communication ability in order to provide comparative information on energy-harvesting battery-less LoRAWAN nodes.