Evacuated Tube Boosts Performance of Thermoelectric Device
Gang Chen and Daniel
Kraemer of MIT show off
The solid-state thermoelectric generator (TEG) holds the promise of generating useful electric urrent from waste heat. For instance, a layer of
TEG material laminated to an engine exhaust could help
to charge the batteries in a hybrid vehicle. Laminated to
the back of a hot photovoltaic module, the TEG current
could significantly boost the output of the module.
TEG semiconductors work by using the motion of
atoms within the crystal lattice to drive electron flow. The
effect is amplified when atoms can be induced to oscillate
in unison, as a wave called a phonon, and the efficiency
of the process depends on maintaining a large difference
in temperature between the hot side and the cold side of
the device. As early as 1954, Maria Telkes achieved 3. 35
percent conversion efficiency with a tracking solar concentrator focused on a TEG. Recent work by Gang Chen
at the Massachusetts Institute of Technology (MIT) and
Zhifeng Ren at Boston College showed that including
carbon nanotubes can greatly improve the efficiency of
electron flow and capture.
Now a team led by Chen, and working at labs at MIT,
Boston College and GMZ Energy, has combined a nanotube
TEG with a vacuum chamber to produce 4. 6 percent conversion efficiency in a non-tracking, non-concentrating device.
Chen, professor of power engineering at MIT and director of the Pappalardo Micro and Nano Engineering Laboratories, with his doctoral student Dan Kraemer, put their
TEG inside an evacuated glass tube, resembling a tube from
an evacuated-tube water-heating module. The back of the
TEG is bonded to the wall of the tube so as to be cooled by
an ambient-temperature mass on the other side of the glass.
The front side is bonded to a copper-plate collector. Exposed
to sun, the device produces a temperature gradient of about
380°F (200°C). Chen suggests that the device could be a
useful low-cost adjunct to solar water-heating arrays.
The work is funded by the Solid-State Solar-Thermal
Energy Conversion Center, an Energy Frontier Research
Center at the U.S. Department of Energy, and was published online in the May 1 edition of Nature Materials
( nature.com/naturematerials). —SETH MASIA
16 July/August 2011 SOLAR TODAY solartoday.org
Copyright © 2011 by the American Solar Energy Society Inc. All rights reserved.