Thread: Pee power!
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Old 11-13-2012, 06:50 PM   #1 (permalink)
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Pee power!

Teenage Girls from Africa Invent a Urine-Powered

This has been floating around FB lately, and I caught "the bug", so I did the math based on what was being presented. I was as loose as possible with the figures, hoping to give it /any/ chance of being real, but provided I covered all necessary points, it ends up being break-even in a completely perfect environment, if not a net loss of energy.

Anyone care to correct or add something?

Here's my comment on the page and on FB regarding it:
Has anyone actually done the math on this? There isn't enough hydrogen in the water present in 1 liter (volume) of urine to actually make 6kw/h of electricity. Unless they're talking about running at nearly zero load for 6 hours, or we're missing some very large part of the story, there's literally nothing about this that can work.

It takes energy to separate the hydrogen from the urine, which comes from where?

Hydrogen (raw) is 51,500 BTU/lb.

Electricity, given a 100% transfer efficiency, requires 3,413 BTU per kW/h.

In a liter of urine, which for a healthy person, should weigh no more than 8.5 lb/gal, there is about 2.25lb of weight total. Of that, even if it were pure H20, would at best, and not accounting for losses, produce only 420 grams (just under a pound) of H2.

The energy required to maintain electrolysis for a gallon of water = 168,164 BTU.

So, 44488 BTU for 1 liter of water.

Assuming the processes were still 100% efficient at this point (which is not only an exaggeration, but currently impossible), you would be left with 51,500 - 44488 = 7102 BTU of energy to feed the generator to produce electricity, and that's BEFORE losses. So you've basically got 2kW/h of AVAILABLE fuel before accounting for any losses in the entire separation/energy transfer process.

Believe me, the losses would eat that up in a heart beat.

"ʞɐǝɹɟ ɐ ǝɹ,noʎ uǝɥʍ 'ʇı ʇ,usı 'ʎlǝuol s,ʇı"

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