Energy harvesting (also known as power harvesting or energy scavenging or ambient power) is a method of generating electrical energy from normally unused energy sources available in the surrounding environment. In other words, it is the process by which energy, coming from alternative energy sources (commonly available in the environment: thermal energy, kinetic energy, chemical energy, potential or solar energy, etc.) is captured and accumulated. This process converts energy into a directly usable electrical current.
Energy harvesting holds great promise for both low-voltage and low-power applications in a wide range of portable or mobile markets such as medical equipment, consumer devices, transportation, industrial controls, and military. Energy conversion takes place in different ways depending on the environmental source. The energy can be captured from a variety of sources deemed wasted or otherwise unusable for any practical purpose.
- Mechanical sources: translational and rotational kinetic and potential energies, inertia, gravitational field, vibrations, elastic energy, piezoelectricity, triboelectric effect, acoustic waves, sea/ocean waves, and wind energy. For example, the conversion of mechanical motion can take place through piezoelectric crystals or particular polymers, which subjected to mechanical deformation stresses, generate small electrical potentials.
- Electromagnetic sources: radio waves, magnetic induction, electromagnetic radiation, photovoltaic, potential energy due to electric fields or magnetic fields. For example, energy from broadcasting or theoretically from any electromagnetic emission can be collected. A typical use of this technique is used to power the RFID (Radio Frequency Identification) identifiers.
- Thermal sources: temperature gradients, pyroelectricity, thermoelectrics. In the presence of thermal gradients, thermoelectric generators can be used.
- Chemical and biological sources: exothermic reactions, potential energy due to chemical bonds, ionization energy, levels of glucose in the blood, salinity gradients, tree-based metabolic energy.