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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 GeneratorEndAllDisease.com

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.

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Old 11-13-2012, 07:01 PM   #2 (permalink)
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I saw something kind of like that on discovery channel where in Indina people were taking apart dead alkaline batteries and sticking the electrodes in cow poop, they got enough power out of 6 or 8 poo cells to charge a cell phone battery.
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Old 11-13-2012, 07:14 PM   #3 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
I saw something kind of like that on discovery channel where in Indina people were taking apart dead alkaline batteries and sticking the electrodes in cow poop, they got enough power out of 6 or 8 poo cells to charge a cell phone battery.
Did you read the article? They're attempting to electrolyze human urine into "brown's gas" (not really, but close enough) to burn in a generator.

They're suggesting it will provide "6 hours of electricity" (their words), which one can only assume means 6kW/h, from one liter of urine.
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Old 11-13-2012, 07:22 PM   #4 (permalink)
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Here, I was looking at that too:
http://ecomodder.com/forum/showthrea...tml#post339605
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Old 11-13-2012, 07:35 PM   #5 (permalink)
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Yeah, basically what that article is saying is exactly what I was thinking. It's valid for a waste-stream, but to actually power anything, they're violating the in/out principles.
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Old 11-13-2012, 07:39 PM   #6 (permalink)
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Old 11-13-2012, 07:45 PM   #7 (permalink)
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Quote:
Originally Posted by Christ View Post
Did you read the article? They're attempting to electrolyze human urine into "brown's gas" (not really, but close enough) to burn in a generator.

They're suggesting it will provide "6 hours of electricity" (their words), which one can only assume means 6kW/h, from one liter of urine.
I think the 6 hours is just idling the generator. But you should read the link in the article "cracks the urea" You'll need to redo your math.

There they say that the energy to electrolyze urea is about 1/3 of that required for water. Of course a liter of urine only contains a few grams of urea.
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Old 11-13-2012, 07:52 PM   #8 (permalink)
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Quote:
Originally Posted by mort View Post
I think the 6 hours is just idling the generator. But you should read the link in the article "cracks the urea" You'll need to redo your math.

There they say that the energy to electrolyze urea is about 1/3 of that required for water. Of course a liter of urine only contains a few grams of urea.
-mort
Like I said, I was being REALLY LAX on the numbers in hopes that it could SOMEHOW work.

Urine is like 97 percent water by volume. Ergo, water would be the best candidate to remove the maximum volume of hydrogen per unit energy invested from that particular medium.

Actually leaving the urea in the water lessens the electrolytic load necessary to separate the hydrogen from the oxygen, but it's still completely unrealistic.
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Old 11-13-2012, 09:02 PM   #9 (permalink)
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water would be the best candidate to remove the maximum volume of hydrogen per unit energy invested from that particular medium..
No, really, read the link. The urea electrolyzes at a much lower voltage than water. The water doesn't participate in the energy equation in this case.
-m
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Old 11-14-2012, 10:04 PM   #10 (permalink)
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No, really, read the link. The urea electrolyzes at a much lower voltage than water. The water doesn't participate in the energy equation in this case.
-m
I'm aware. Like I said, I was trying to give them the absolute best chance of success. The amount of urea salts in urine wouldn't be able to produce the amount of hydrogen necessary to do what they were claiming, so I went the other way with it.

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