Did you know that while you’re sitting down and reading this post, your body can provide about 4-6 watts of power? That’s enough power to run a clock radio. Humans store energy from the food they consumed and some of this energy is then emitted as body heat. This wasted heat can be recovered at about 3-6% efficiency, depending on the difference in body temperature and your surroundings.
To take advantage of this wasted heat, Corey Hewitt a researcher at Wake Forest University in the United States and his colleagues have created a new device that can be use to convert body heat into electricity. The research was published online last week in Nano Letters.
Known as “Power Felt”, the team’s new thermoelectric material consists of multiple layers of carbon nanotubes stacked in between polymer films— resembling a “felt fabric”. The thermoelectric material is flexible and lightweight like fabric as well.
Photo Credit: Wake Forest University
The 72 layer thermoelectric fabric generated a maximum of 137 nanowatts of power. This is not nearly enough power to a wristwatch or any portable electronics. However the device has the potential to be cheaper, lighter, and more easily processed than the more exotic yet commonly used bismuth telluride. Bismuth telluride is used in thermoelectric applications such as seat cooling/heating systems.
Thermoelectric materials are solid-state devices—no moving parts, that directly convert thermal energy into electrical energy. The conversion is based on the “Seekbeck effect”, in which an electrical voltage is produced by a temperature gradient across a material. The opposite of this, a temperature gradient produced by an applied voltage is called the “Peltier effect”.
At the subatomic level, the charge carriers in the thermoelectric material (holes and electrons) can move around, just like gas molecules. When the material senses a temperature difference, the charge carriers at the warmer end move towards the colder end. This movement generates a net charge at the cold end, producing an electrostatic potential (voltage). Eventually, equilibrium is reached between the chemical potential for charge diffusion and the electrostatic repulsion due to the charge build-up.
Hewitt says more work is needed between Power Felt is ready of the market. They will be looking at ways to add more nanotube layers and make the device thinner to increase the power output. He imagines it’ll be possible one day to make a jacket with a completely thermoelectric inside liner to collect body heat and used that to power an iPod.
California Institute of Technology (2012). Brief History of Thermoelectrics. Retrieved February 28, 2012, from http://www.its.caltech.edu/~jsnyder/thermoelectrics/history.html
Neal, K. (2012, February 22). Power Felt gives a charge. Retrieved February 28, 2012, from http://news.wfu.edu/2012/02/22/power-felt-gives-a-charge/
Lawrence Berkley National Laboratory. (2012). Standby Power Summary Table. Retrieved February 28, 2012, from http://standby.lbl.gov/summary-table.html
Hewitt, C., Kaiser, A., Roth, S., Craps, M., Czerw, R., & Carroll, D. (2012). Multilayered Carbon Nanotube/Polymer Composite Based Thermoelectric Fabrics Nano Letters DOI: 10.1021/nl203806q
Snyder, G., & Toberer, E. (2008). Complex thermoelectric materials Nature Materials, 7 (2), 105-114 DOI: 10.1038/nmat2090
Human Generated Power for Mobile Electronics, Starner, T. and Paradiso, J.A., in Piguet, C. (ed), Low-Power Electronics, CRC Press, Chapter 45,2004, pp. 45-1 – 45-35.