Slashdot Mirror
Body Heat Could Charge Your Cellphone
An anonymous reader writes to mention Nature is reporting that scientists have discovered a much more efficient way to use silicon to convert heat into electricity. This offers the possibility of many different applications including possibly charging your portable electronics just by wearing them close to your skin. "The concept of converting waste heat into electricity isn't exactly new, but it never really materialized due to efficiency hurdles. Now, scientists from the U.S. Department of Energy's (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley think they may have found a key [to] increase the conversion efficiency by a factor of 100."
You put a lot of thought into that message, but it is negated by just RTFA which says that the potential applications include "...personal power-jackets that could use heat from the human body to recharge cell-phones...". They aren't talking about the cell phone itself drawing the power, but potentially the entire inner surface of a piece of clothing (which would also have the entire outer surface of the piece of clothing as the cooling surface for differential).
However, this does sound like we will only be recharging cell phones this way in the winter...
You are using the wrong denominator, (T_cold), in your calculation, although it hardly matters in this case because the temperature difference is so small. The formula for maximum theoretical efficiency is:
(T_hot-T_cold)/T_hot
Using your numbers: (305-300)/305 = 1.64%
You did not read the article, did you? Of course you didn't, this is slashdot!
The article is talking about using the technology in the clothes and using the energy from that to power a cellphone. This would give you a lot more surface. And I don't know where you live, but "room temperature" here is not so tropical. So the theoretical maximum according to your calculation would be more like ((305-295)/295) * 120 = about 4 watts. Not a lot, but my telephone charger can provide about 2.2 watts and my battery is charged within 2 hours with that...
Thermoelectric cooling - it's how peltiers work. The effect has been known for a century... don't need to worry about classification! :-p
If the current efficiency rating is .006 then 100 times for efficient would be 60%.