Energy harvesting is the process by which energy is captured and stored. Frequently this term is applied when speaking about small autonomous devices, like those used in sensor networks. A variety of different methods exist for harvesting energy, such as solar power, ocean tides, piezoelectricity, thermoelectricity, and physical motion. It will be vital in the future, as fossil fuels run out.

Energy harvesting devices which convert mechanical energy into electrical energy have attracted much interest in both the military and commercial sectors. Some systems convert random motion, such as that of ocean waves, into electricity to be used by oceanographic monitoring sensors for autonomous operation. Future applications may include high power output devices (or arrays of such devices) deployed at remote locations to serve as reliable power stations for large systems. All of these devices must be sufficiently robust to endure long-term exposure to hostile environments and have a broad range of dynamic sensitivity to exploit the entire spectrum of wave motions.

Energy can also be harvested to power small autonomous sensors such as those developed using MEMS technology. These systems are often very small and require little power, but their applications are limited by the reliance on battery power. Scavenging energy from ambient vibrations, heat or light could enable smart sensors to be functional indefinately.

Rockwell Scientific has developed a novel energy harvesting approach based on a breakthrough technology. The core element of this technology is a surface treatment process to reduce the friction between a magnet and a non-magnetic surface to negligible levels - 40 times lower than the friction between two Teflon surfaces. This technology, when implemented into a linear electrical generator, drastically improves its efficiency and enables energy capture from very slight external movements. Prototype devices, which are environmentally acceptable and technologically promising, have been successfully demonstrated.

Other energy harvesting systems convert energy from a button press into radio frequency transmissions to control lighting or building automation systems. Some of these transmitters use piezo technology to generate an electrical pulse from a mechanical click. Another technique harnesses current produced by moving a magnet through a coil to power a radio transmission with a unique identifier to control other aspects of the system. This technology is used in a wireless, batteryless remote light switch produced by EnOcean GmbHand available in the USA from Ad Hoc Electronics.