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Obtaining Energy from the Environment
Converting the energy available from vibration, heat and solar sources gains momentum
Design News Staff -- Design News, October 6, 2008
Portable products and remote mounted units pose a challenge for users. While these products can have wireless connectivity, battery life can be a problem. To eliminate the need for frequent battery changes, many suppliers have developed energy converters to produce electrical power from the energy available from vibration, heat and solar sources. Combinations of these approaches and ultracapacitors as alternate storage technology are some of the changes that are occurring for sourcing power. Here is an example of each technology.
HEAT ENERGY
Using the Seebeck Effect, where electricity is produced from a temperature differential applied across the device, Nextreme developed a miniature, thin-film thermoelectric generator (eTEG). With a form factor of 3.5 x 3.5 mm, the eTEG has demonstrated output power levels in excess of 10 mW at a delta-T of 70K and greater than 300 mW at a delta-T of 120K. This corresponds to an output power density of approximately 1 to 3 W/cm2. In contrast to conventional bulk thermoelectric units that are limited to heat fluxes less than 20 W/cm2 even with an order of magnitude greater area, the eTEG has exceeded the 20 W/cm2 level. In addition, the form factor that can be as much as 20x thinner than bulk material alternatives. The solid-state energy harvesting technique is ideal for waste heat conversion from the combustion process in turbines and engines.
SOLAR AND VIBRATION ENERGY
The Midé Volture Solar-Hybrid Energy Harvester (HeH) integrates a solar panel with the standard electronics for its Volture piezoelectric energy harvester. A vibration-only unit, like the company’s PEH20W, uses one stack of two piezoelectric elements operating in the 50 to 150 Hz range with a 3 Hz energy harvesting bandwidth. In addition to the ability to obtain energy from vibration energy, solar energy provides another power source for greater power. Already under development, the next generation will combine solar and piezoelectric power with a power management technique that will enable intelligent battery charging. The Volture Hybrid solar module is the first step toward incorporating other energy harvesting methods, as well.
VIBRATION ENERGY
Using Piezoelectric’s Ceramic Fiber Composite (PFC), Advanced Cerametrics Inc. (ACI) has developed its HARVESTOR™ line of power supply products. The patented flexible ceramic fibers are lighter yet more robust than bulk piezoelectric ceramics. The PFC transducers produce 500V peak to peak at a resonant frequency of 35 Hz, 0.9 lbf that can charge a 400 µF capacitor to 50V in less than 4 sec. They have been configured to yield a continuous 145 mW of power. With these active fibers, up to 70 percent of the ambient vibration can be converted to electrical power. Weighing grams not ounces, the thickness of the energy harvesting element can be less than 0.4 mm. Specifically developed for capturing, storing and delivering power to wireless sensors and transmitters, micro circuits, smartcards, cell phones and other handheld devices, the HARVESTOR™ technology can be used in monitoring equipment, machine health condition systems, building controls and process controls.
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