Energy derivation from external or manmade resources and natural resources such as sun, wind, thermal power is termed as energy harvesting. Wireless sensor networks possesses many autonomous objects or devices that make use of sensors for monitoring the physical and environmental conditions. The efficient working of wireless sensor networks needs a continuous supply of energy and therefore different energy harvesting techniques is therefore a good solution for eliminating the different limitations of energy related to the wireless sensor networks. The different energy acquiring or harvesting techniques include the use of different natural and manmade resources for harvesting the energy. The different energy harvesting techniques include RF energy, solar energy, thermal energy and so on. Energy harvesting is a must need for wireless sensor networks as it need a continuous supply of energy. In case an energy sensor node suffers depletion, it fails to perform its responsibility in the network any further until it is replaced by proper energy resources. Therefore, it is an effective idea to implement different energy harvesting techniques to eliminate the energy problems associated with wireless sensor networks. The longevity of the wireless sensor networks can be increased by increasing the life of the sensor nodes. Many energy harvesting techniques can be employed in ensuring a continuous supply of power to the sensor nodes, which will in turn increase the lifetime of WSNs. Thus, the need of energy harvesting becomes more essential for WSNs in order to reduce the use of conventional energy resources (Shaikh & Zeadally, 2016).
The primary energy source of WSNs are power from a battery source, but it consists of different problems. However, there are certain problems with this power source, which includes current leakage even when the battery is not in use thus resulting in a huge loss of power and energy (Ulukus et al., 2015). Therefore, a continuous energy supply is necessary to be considered for wireless sensor networks that can be obtained by efficient energy harvesting techniques. There are different energy harvestinh techniques that can be strategically used in wireless senor networks. These processes and techniques are listed below (Shaikh & Zeadally, 2016)-
1) Energy harvesting using radio frequency: This is an efficient energy harvesting methodology that deals with harvesting the radio waves, which is then transformed or converted into electricity.
2) Harvesting solar energy: the energy of the sun is harvested and can be used as an efficient source of energy. This energy harvesting techniques can be used in wireless sensor networks to eliminate the associated energy problems.
3) Thermal based Energy: Thermal energy harvesting deals with conversion of heat energy or thermal energy to electrical energy. Seebeck effect is mainly used for conversion, transformation of thermal, or heat energy to electrical energy.
4) Flow based Energy: the rotational movement of the turbines and rotors is harvested to and converted into electrical energy to be used in WSNs.
5) Wind energy harvesting: The wind energy is captured for generation of electricity.
6) Hydro power energy: Hydropower energy harvesting process is used to harness the energy of falling water, which is then converted into electricity.
Shaikh, F. K., & Zeadally, S. (2016). Energy harvesting in wireless sensor networks: A comprehensive review. Renewable and Sustainable Energy Reviews, 55, 1041-1054.
Ulukus, S., Yener, A., Erkip, E., Simeone, O., Zorzi, M., Grover, P., & Huang, K. (2015). Energy harvesting wireless communications: A review of recent advances. IEEE Journal on Selected Areas in Communications, 33(3), 360-381.