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Energy harvesting is also known as power harvesting or energy scavenging. It's the process whereby ambient energy is stored and captured. Ambient energy is energy that is natural, non-electrical in nature, and is self-regenerating or renewable. Sources of ambient energy include wind, solar, biomass, hydro, geothermal, and tides. Windmills are a centuries old form of ambient energy, though they are still being improved upon or innovated.
Energy harvesting takes advantage of these sources to provide energy that is renewable and more environmentally friendly than that derived from fossil fuels. It is most often used to generate electricity, but can generate other energy forms as well.
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Why Energy Harvesting?
Convenience - Consumers wouldn't have to worry about changing or recharging batteries for devices such as laptops or cell phones or other electronic devices.
Backup Energy Sources - Such devices can serve as backups to primary power sources. This would increase their reliability, as a backup energy harvesting source would prevent power interruptions. This is important to operations such as hospitals that need energy even in emergencies such as blackouts.
Mobility - Wireless sensor networks can have secure mobile nodes, which is a useful feature for firefighters, the military, and law enforcement. By the same token, equipment that takes advantage of the networks would also be secure and mobile. One popular wireless network protocol is that from the ZigBee Alliance, which is developing a Green Power spec specifically for energy harvesting. This will allow devices such as sensors, switches, and detectors to harvest energy from solar cells, thereby precluding the need for batteries or connections to power lines.
Business Practices - Business costs for consumers would be reduced in terms of the packaging, development, disposal, longevity, and reuse of certain products. Product installation and maintenance would also have a reduced cost. An example is that of the costs that would be saved with the elimination of chemical batteries and rechargers, along with the extensive wiring they normally require, in the use of cell phones. There would be an automatic streamlining in their design, development, and packaging as a result.
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In addition to the types listed here, other sources include mechanical, biological, and chemical energy, and additionally complex amalgamation that is the human body. The three most popular types of energy harvesting are photonic, which has to do with light; thermal which has to do with heat; and vibrational, which is concerned with harvesting energy from oscillations. These different types may be combined to form hybrids that increase energy output and stability.
Energy harvesters are considered to be "free" forms of energy in comparison to fossil fuels, especially if they are captured near the location where they are to be used.