• Quick note - the problem with Youtube videos not embedding on the forum appears to have been fixed, thanks to ZiprHead. If you do still see problems let me know.

Electriciy from manure

Brian-M

Daydreamer
Brian-M
Joined
Jul 22, 2008
Messages
8,044
How much electricity can you produce from a small amount of manure?

I've recently been watching some old episodes of "The Good Life", a BBC sitcom about a couple who decide to go self sufficient and live off the land from their home in the suburbs.

I've just watched the episode where they get their power disconnected and start producing enough electricity to run a few lights and a freezer from the methane created from manure provided by their livestock; two pigs, a goat, and a dozen chickens.

I can't help but think that this can't be anywhere near enough manure to do the job.

Can anyone knowledgeable about this tell me if it actually is a realistic setup or just complete... manure?

I found a clip from the episode on YouTube. The explanation of the setup begins around 4:30...
 
A single pigpen was able to power all of Bartertown, so it seems reasonable to me.
 
steve s said:
Quite a few dairy farmers are turning manure into electricity. Here's one...
http://science.kqed.org/quest/2013/08/29/harnessing-the-hidden-power-of-cow-manure/

Do a Google search on dairy farm generates electricity from cow manure and you'll find a lot of others. It helps prevent methane from getting into the atmosphere. And the byproduct is fertilizer.

Steve S
Click to expand...

I'm not asking if you can generate usable methane that way (I already know it can be done), I'm asking if you can generate enough methane from the amount of manure the animals in their backyard would be producing to continuously run a small generator.

Although, the further thought occurs... how much usable methane would they get if they put their own manure in the effluence digestor along with the animal manure?
 
According to this site - https://www.extension.purdue.edu/extmedia/ae/ae-105.html
Engine-driven devices are not very efficient when operated directly from a methane generator. For example, an electric generator (driven by a gas engine) operating at variable torque has a poor efficiency, because the hourly gas production and consumption are nearly the same, regardless of the amount of loading on the system. About 16-18 cubic feet of digester gas are required per horsepower-hour, assuming an energy value of 650 BTU's per cubic foot., assuming an energy value of 650 BTU's per cubic foot.
Click to expand...
Daily output of methane per 1000 lbs of swine and beef is about 18 to 19 cuft (dairy is about 50% more), with an energy content of 650 BTU/cuft.

If we assume that the output of the livestock mentioned above is equivalent to 1000# of swine (probably quite a bit too high), then they'll have about 12,000 BTU a day to use (about enough to run one cooking burner for an hour).
 
Could they be using an absorption refrigerator, instead of a generator and electric fridge? Seems better suited to a small biogas supply.
 
ben m said:
Could they be using an absorption refrigerator, instead of a generator and electric fridge? Seems better suited to a small biogas supply.
Click to expand...

Yeah, a few hours of lighting, especially energy efficient lighting is no problem at all, the 'fridge might be stretching it depending upon how well insulated it is, its power requirements and how often it is opened.
 
Attach a paddle wheel to a generator, and you can generate as much power from manure as you want, as long as you keep shoveling the manure back onto the top of the wheel.


ETA: I think I've just inadvertently deepened my understanding of the 9/11 truth movement.
 
Last edited:
Old man said:
According to this site - https://www.extension.purdue.edu/extmedia/ae/ae-105.html

Daily output of methane per 1000 lbs of swine and beef is about 18 to 19 cuft (dairy is about 50% more), with an energy content of 650 BTU/cuft.

If we assume that the output of the livestock mentioned above is equivalent to 1000# of swine (probably quite a bit too high), then they'll have about 12,000 BTU a day to use (about enough to run one cooking burner for an hour).
Click to expand...


Let's see... 1 BTU = 1.055 KJ ... 1.055*12000 BTU = 12,660 KJ = 3517 Watt-hours, about 146 watts continuously. Which would be more than enough...

... assuming lossless power generation and animals that produce more than half their bodyweight in manure per day (I agree that 1000 lbs is probably quite a bit too high).

Looking up freezer power consumption, they'd need about 2600 Watt-hours per day, so a more realistic amount of manure production or a plausible level of generator efficiency would mean not enough power.

ben m said:
Could they be using an absorption refrigerator, instead of a generator and electric fridge? Seems better suited to a small biogas supply.
Click to expand...

In the series, it's an electric deep-freezer they already owned before starting to produce their own power and an old diesel generator converted to run on methane. (It's a sitcom, not reality-TV.)
 
Last edited:
Brian-M said:
I'm not asking if you can generate usable methane that way (I already know it can be done), I'm asking if you can generate enough methane from the amount of manure the animals in their backyard would be producing to continuously run a small generator.

Although, the further thought occurs... how much usable methane would they get if they put their own manure in the effluence digestor along with the animal manure?
Click to expand...

Just a note... in the clip he said he had 50 gallons of manure ready for his contraption. I would assume that this wouldn't be daily production, but he could conceivably have collected that much while making the machine.

Would that amount of animals produce enough poo on a daily basis to keep it running? I suspect not.
 
Last edited:
Brian-M said:
I'm not asking if you can generate usable methane that way (I already know it can be done), I'm asking if you can generate enough methane from the amount of manure the animals in their backyard would be producing to continuously run a small generator.

Although, the further thought occurs... how much usable methane would they get if they put their own manure in the effluence digestor along with the animal manure?
Click to expand...
Read all about these things here. http://www.oecd.org/env/outreach/36203835.pdf. I suppose they could do the cooking and lighting using biogas stoves and lamps, and generate only the small amount of electricity required for electronic devices. A gas powered iPad would be wonderful, but perhaps not yet on the market.
 
You can also generate manure from electricity. Just depends on the voltage and sphincter control of who you hook it up to.
 
Brian-M said:
Let's see... 1 BTU = 1.055 KJ ... 1.055*12000 BTU = 12,660 KJ = 3517 Watt-hours, about 146 watts continuously. Which would be more than enough...

... assuming lossless power generation and animals that produce more than half their bodyweight in manure per day (I agree that 1000 lbs is probably quite a bit too high).
Click to expand...
Those figures are 1000# of animal, not manure.

More realistically, if they're keeping each pig for 8 months (250#), their average daily weight of hogs will be 290 lbs (call it 300). We'll be generous and say that the goat is 200 lbs, and the chicken manure is the equivalent of 100 lbs of goat.

So, all of the animals together produce (on an average day) the methane that would be produced by less than 750 lbs of hogs.

.75 X 18 cuft = 13.5 cuft. 13.5 cuft X 650 BTU /cuft = 8,775 BTU.

Running a generator to power electrical devices is not trivial. The generator would need to either run constantly (regardless of wattage being consumed) or started every time you need power. The generator would also have to produce enough power to start the freezer compressor motor (typically 150% to 200% of running wattage).

Yes, theoretically (with a lossless system), you might think that you could produce 100 watts continuously, but in the real world it's closer to 25.

So, no, this would not work.
 
Craig B said:
Read all about these things here. http://www.oecd.org/env/outreach/36203835.pdf. I suppose they could do the cooking and lighting using biogas stoves and lamps, and generate only the small amount of electricity required for electronic devices. A gas powered iPad would be wonderful, but perhaps not yet on the market.
Click to expand...

Here's a miniature butane fuel cell, methane shouldn't be that far removed.
http://www.gizmag.com/usb-charger-butane-fuel-cell-nectar-lilliputian-systems-brookstone/28281/
 
You must log in or register to reply here.

Back
Top Bottom