I did get some information like, an efficient yak dung stove can produce heat at a rate of 17198 kJ/kg (of dried yak dung). And that it burns at 400 degrees Celcius, which works out to a Carnot efficiency of about 60% presuming the outside environment is the Qinghai-Tibet Pleateau at 0 degrees Celcius. Okay, a little optimistic, I grant. An iPad battery is rated at 24.8 W-hr, which is like 89.28 kJ of energy, and that means it just takes 9 grams of dried yak dung to do a full charge. Incredible, at first glance.

Then I realized that an iPad doesn’t take much power to run at all. Even more of a killjoy to my nascent yak dung entrepreneurial instincts is HP Labs, which already designed a megawatt datacenter fueled by dung. They say that a single dairy cow produces 125W in recoverable electricity in dung alone (yes, I did the math). That’s not even counting making cows run circles to generate more electricity from kinetic motion. Alas.

But something useful can be done. Instead of straight heating elements, I suggest a server farm. Maybe box it up like an electric heater, sell the CPU cycles back while still getting the same heat out.

LED light bulbs coming, but incandescents being phased out by mandate in January, 2012? What?! Time to stockpile bulbs. I like my black-body radiation.

Speaking of black-body radiation, suppose I have an enclosed system with a single aperture for light and only light to pass through. Do I now have a system for converting heat to light, and therefore to electricity via bandgaps? Doesn’t that violate some law of thermodynamics?

Okay, I guess the temperature of the photovoltaic converter (the heat sink) matters also, since photons incident on it need to find a site where the electron is in a low-energy state, so unless the converter is at absolute zero, there is some probability the photon will not be captured, which becomes waste heat.

Now what if we enclose the photovoltaic converter, too, so photons cannot escape? That won’t work, either, since at thermal equilbrium, the converter radiates as many photons as it captures, so no voltage develops. The converter just becomes hotter.

But wait, if the converter’s temperature rises above that of the radiating source, doesn’t that imply that the enclosed converter receives some kind of energy, even if it isn’t converted to electricity? Doesn’t that also violate a law of thermodynamics? Ah, but the radiating source and the converter are in optical contact. That must mean that no passive one-way optical material can exist, in which one side is totally opaque and absorptive and another side is totally transparent and reflective. Sounds like Kirchhoff’s law…

Yet, there are transparent optical interfaces that use total internal reflection on one side to achieve exactly this one-way effect, is there not? Okay, the optics also radiate, so no free lunch here.