Tuesday, January 20, 2009

the concept of Energy Harvesting

For many, the concept of energy harvesting is tightly connected with the 'green' movement.

While that's certainly one aspect, it overlooks a whole range of applications that have less to do with solving the world's energy crisis and more to do with solving the problem of powering remote or embedded devices—indefinitely. That is, without wires and without potentially expensive battery replacement.

Also called energy scavenging, energy harvesting uses piezoelectric, photovoltaic, thermoelectric and inductive devices to convert ambient energy (kinetic, light and thermal) into electrical energy. This energy can then be stored locally to power 'perpetual' devices, usually sensors or other monitoring and control devices with a wireless communications interface. It's this storage that dispels another misconception: that harvested energy is too little to be of practical use. In almost all applications, it's the timed use of accumulated energy that makes the devices practical.

The concept of energy harvesting is clearly not new; the most obvious instantiation is solar-powered cameras used on highways. (For a list of energy-harvesting companies involved in the area, go to www.energyharvesting.net.) However, what is new are the increasingly efficient conversion and power-management ICs, innovative power storage techniques and the availability of low-cost, low-power ICs that are combining to enable greater functionality per millijoule of generated energy.

This has opened up a whole range of truly tether-free applications from wireless sensor networks for structural monitoring of buildings and bridges to battlefield sensors, backpack power generators and communicators, devices embedded within airplane wings and other hard-to-access locations.

In the consumer space, medical applications that take advantage of thermal and kinetic energy are an exciting area of development, while solar-powered Bluetooth headsets and cell-phone chargers are already plentiful. Meanwhile, 'green' automotive designers are looking at perpetual devices to reduce the amount of expensive and weighty harnessing required.

For 2009, consumers can expect a flotilla of devices, particularly in the medical field, as companies such as Texas Instruments Inc. continue seeding the market with kits that combine its low-power MSP430 microcontroller with conversion technologies from the likes of AdaptivEnergy LLC and Perpetuum Ltd., as well as innovative battery technology from Cymbet Corp. Other IC companies also improving the state of the art include National Semiconductor, International Rectifier and Linear Technology.

However, for designers, the space is rife with opportunities. More research is needed for ultra-low-power conversion and power management circuits. Power storage techniques may include ultracapacitors and novel battery chemistries. As innovations are made in those fundamental areas, the system applications for energy-harvesting devices are set to rise exponentially over the coming months.

-Patrick Mannion
EE Times

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