Nanotechnology Made Clear

Dressing Up: Thermoelectric Nanowires vs. Nano Solar Cells

Thermoelectric devices can convert heat into electricity. Many temperature sensing devices take advantage of this effect by using electricity to measure temperature in devices called thermocouples. Various researchers are working to produce inexpensive and efficient thermoelectric materials that can change waste heat into electricity.

Recently there was an announcement that researchers at Berkeley had made silicon nanowires that convert heat into electricity using a thermoelectric effect. One possible use of these is to charge portable devices. The wires could be simply be embedded in fabric, so that your jacket could become a charging station, using your body heat to generate the electricity.

Other researchers have made thermoelectric nanowires. The difference with Berkeley’s work is that they have reduced the diameter of the wires and modified the surface texture to reduce the thermal conductivity while maintaining the electrical conductivity, a key requirement of thermoelectric materials.

It is, in fact, the combination of the wire diameter, the roughness of the surface texture, and doping the silicon with boron that reduce the thermal conductivity without having serious impact on the electrical conductivity.

This concept can be applied in other ways as well. One possibility for this research is that cars could be set up to use their own waste heat to run the radio and other electrical devices in the car. Siphoning off and making use of heat from power plants would be another logical use. All that heat your laptop computer generates that now scorches your thighs could be used to power the laptop up.

This got me thinking about the folks who are working on a parallel track to embed solar cells in fabric. Konarka Technologies, for example, is currently selling solar cell material to Sky Shades, a maker of awnings. By embedding nanoparticles in plastic film they produce a lightweight, flexible photovoltaic material called Power Plastic®. The process involves printing or coating nanoparticles (such as quantum dots or nanocrystals) onto other material using a process similar to printing ink on newspaper.

That’s when I started wondering, why would you need both of these technologies? Then a light went off in my brain—solar doesn’t work in the dark, or in regions of the country where it’s cloudy many days of the year. That’s why the combination of these two solutions could work to ensure that you’re inexpensively charged up, 24/7.

The jacket of the future might have thermo electric nanowires in strategic places (under your arms is a logical hot spot) with solar cells embedded on the shoulders. Imagine how handy a military jacket with both thermo-electric nanowires and solar cells would be. Lighter weight batteries that can be constantly recharged could be carried onto the battlefield to power communications or other equipment.

When will you find such a juiced up jacket in your local department store? You’re probably looking about ten years lead time till you make that shopping trip. In the meantime keep that cell phone charger handy and check my Nanotechnology and Energy Web page for updates.   


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