Energy harvesting is not a new concept, but is an important concept for IoT. Essentially, any system that represents a change in state (for example, hot to cold, radio signals, light) can convert its form of energy into electrical energy. Some devices use this as their sole form of energy, while others are hybrid systems that use harvesting to augment or extend the life of a battery. In turn, energy harvested can be stored and used (sparingly) to power low-energy devices such as sensors in IoT. Systems must be efficient in capturing energy and storing power. Therefore, advanced power management is needed. For example, if an energy harvesting system uses a piezoelectric mechanical harvesting technique embedded in a sidewalk, it will need to compensate when there is not enough foot traffic to keep the unit charged. Constant communication with energy harvesting systems can further drain the power. Typically, these IoT deployments will use advanced power management techniques to prevent complete loss of functionality. Techniques such as low standby currents, low-leakage circuits, and clock throttling are frequently used. The following figure illustrates the area where energy harvesting is ideal, and the technology that it can power. Care must be taken by the architect to ensure the system is not underpowered, nor overpowered.  

Harvesting systems, in general, have a low energy potential and low conversion efficiency. An architect should consider energy harvesting in situations where there is a large supply of untapped waste energy, such as in industrial settings: