Sustainable Engineering

Aug. 7, 2008
Electricity from waste heat

Nextreme Thermal Solutions Inc. has gotten a grant from the North Carolina Green Business Fund to boost the efficiency of thin-film thermoelectrics used to convert waste heat into electricity.

The Fund is directed by the N.C. Board of Science and Technology. Nextreme’s thin-film embedded thermoelectric generator (eTEG) generates electricity via the Seebeck effect, where electricity is produced from a temperature differential applied across the device. The devices use a superthin, nanoengineered material that delivers a Seebeck coefficient 150% greater than conventional thermoelectric material. The grant will be used to optimize the thin-film growth process with the goal of doubling the power output of a single device from 250 to 500 mW.

The resulting small size will help address applications that standard bulk thermoelectric devices and other energy harvesting or reclamation systems cannot manage. The company is currently working with customers to harvest waste heat for powering remote sensors that can monitor equipment and human activities. Other applications include thermal batteries that can power implantable medical devices and devices that capture waste heat from exhaust manifolds to improve fuel efficiency in automobiles.

A sensor for natural refrigerant
Schneider Electric’s Kavlico unit recently developed a combined pressure/ temperature sensor for use with the natural refrigerant R744 (C02) for mobile airconditioning systems. The idea behind replacing ozone-depleting refrigerants with R744 is to reduce global greenhouse-gas emissions.

The sensor has a 17-4 PH hermetically sealed stainless metalinjection- molded housing and uses a sense element based on TiON (Titanium OxyNitride) thinfilm technology capable of withstanding high (–40 to 180°C) media temperatures. Operating pressure range is 0 to 150 bar with a proof pressure of 210 bar and a burst pressure of 320 bar. Outputs can be analog, SPI, LIN2.0, or CANbus formats. The sensor also meets EU directives for electrical and electronic equipment.

Mercury limits for CFLs
The National Electrical Manufacturers Association (NEMA) has published LL 8-2008 Limits on Mercury Content in Self-ballasted Compac t Fluores cent Lamps. NEMA’s Lamp Section produced the new standard, which is voluntary, based on discussions with representatives of the U.S. Environmental Protection Agency (EPA), the Dept. of Energy, and the Natural Resources Defense Council. It covers limited integral, self-ballasted compactfluorescent lamps of all base types, such as E26 and GU24, generally referred to as compactfluorescent lamps (CFLs).

Ed Yandek, chair of the NEMA Lamp Section Technical Committee, says LL8 responds to utilities, environmental groups, energy-efficiency consortia, the EPA, and other stakeholders, including retailers, that have all expressed a desire to limit the amount of mercury used in selfballasted compact-fluorescent lamps. All CFL manufacturers and suppliers, not just NEMA members, can participate in LL8. “It is to the lighting industry’s advantage to limit the total mercury content of CFLs and to work with all stakeholders so that CFLs are managed in an environmentally responsible manner at end-of-life,” says Yandek.

LL8 provides an industry process by which manufacturers can commit to a voluntary maximum mercury dose level per lamp. It applies only to integral, self-ballasted CFLs manufactured or imported after April 15, 2007, so that manufacturers have enough time to manage their supply chains. An electronic copy of LL8- 2008 may be downloaded at no charge or a hard copy may be purchased for $28 at NEMA’s Web site.

More juice from solar arrays
Problem: The output of solar arrays tied into the utility grid can be impacted by nonuniformities caused by shading, panel mismatches, or accumulated dirt. Even a small amount of shading on the array can halve the energy harvest. Shading conditions can even invalidate local utility and governmental incentives, making certain installations costprohibitive.

National Semiconductor Corp. claims its SolarMagic technology helps solve this problem by recouping up to 50% of the lost energy. It is compatible with today’s solar architectures regardless of the underlying solar-cell technology.

National won’t say much about SolarMagic internals. The technology is now in field trials with REgrid Power Inc., one of the largest solar installers in California. REgrid officials say they’ve observed energy output improvements of up to 44% in the shade and 12% overall compared to the same system running without SolarMagic technology. Later this year, National plans to have SolarMagic products ready for solar installers.


Nextreme’s Thermal Copper Pillar Bump process integrates thinfilm thermoelectric material into solder-bumped interconnects that provide mechanical and electrical connections. Unlike conventional solder bumps, thermal bumps function as solidstate heat pumps on a microscale. The stack-up of a thermal bump, including the thin-film material, solder and electrical traces, is only 100 microns high and has a diameter of 238 microns.

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