So I was looking into how many yak dung pies are required to charge an iPad once, but I couldn’t find how much a dried yak dung pie weighs.

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.

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