(Also known as power harvesting or energy scavenging), the process by which energy is captured from a system's environment and converted into usable electrical power. Energy harvesting allows electronics to operate where there is no conventional power source, eliminating the need to run wires or to replace batteries. An energy harvesting system generally includes circuitry to charge a storage capacitor or battery. Energy source examples include light (captured by photovoltaic cells), vibration or pressure (captured by a piezoelectric element or an oscillating mass with a pick-up coil), temperature differentials (captured by a thermo-electric generator or TEG) or radio energy (captured by an antenna).