With electronic circuits now capable of operating at microwatt power levels, it is feasible to power them from non-traditional sources. Hence, the rise of energy harvesting, which provides the power to charge, supplement or replace batteries in systems where battery use is inconvenient, impractical, expensive or dangerous.
Energy harvesting can eliminate the need for wires to carry power or to transmit data. It can power smart wireless sensor networks to monitor and optimize complex industrial processes, remote field installations and building HVAC systems. And otherwise wasted energy from industrial processes, solar panels and internal combustion engines can be harvested for useful purposes.
Ambient energy sources include light, heat differentials, vibrating beams, transmitted RF signals and any source that can produce an electrical charge through a transducer. Such "free" energy sources can be converted into electrical energy by using a suitable transducer, such as thermoelectric generator (TEG) for heat, a piezoelectric element for vibration, a photovoltaic cell for sunlight (or indoor lighting) and even galvanic energy from moisture. These energy sources can be used to power electronic components and systems autonomously.
Despite their complexity, energy-harvesting systems have already been deployed in transportation infrastructure, wireless medical devices, tire pressure sensing and building automation. In building automation systems, elements such as occupancy sensors, thermostats and light switches can eliminate the power or control wiring normally associated with their installation and instead use localized energy harvesting. A wireless network using an energy-harvesting technique can link sensors in a building to reduce HVAC and lighting costs by turning off power to nonessential areas when the building is vacant. The cost of enabling energy-harvesting electronics is often lower than that for running supply wires, so there is an economic gain to be had by adopting a harvested power technique.
Many of the advantages of a wireless sensor network disappear if each node requires its own external power source. Through power management developments have enabled electronic circuits to operate longer for a given power supply, that approach has its limitations. Energy harvesting provides a complementary approach, powering wireless sensors nodes by converting ambient energy into usable electricity.