Draft Animal Power – Draft animals and sustainable land stewardship › Forums › Sustainable Living and Land use › Sustainable Energy › Crunching numbers for energy planning
- May 23, 2011 at 3:09 pm #67399FELLMANParticipant
@Countymouse 27151 wrote:
Another possibility is the use of methane from anaerobic digesters. They are usually used for cattle manure, although I suppose they could be used for other manure as well. If a cow (or steer) produces 60 lb of manure per day, a good digester will produce 60 cubic feet of methane from this which will yield 36000 BTUs per cow per day (60*600 BTU/cubic foot) (from http://www.habmigern2003.info/biogas/methane-digester.html). 36000 BTUs is equal to about 10 KWH if the conversion to electrical power was 100% efficient. Of course is wouldn’t be, and would probably have a loss of 50% or more, yielding maybe 5 KWH per cow per day. That said, some household appliances could be run off of the gas itself (which is similar to natural gas) and not incure the loss from conversion to electrical power. Even if it all the methane was used to make electrical power and a 50% loss was incured in the process, that would make 1825 KWH per cow per year (5 KWHx365days). At $0.15 a KWH, this would yield a savings of $273 per cow per year, so 4 cattle might pay your electrical bill if you watched your consumption closely… It’s still alot of investment in the digester and generator, but thought I would throw this idea out there as well.
This analysis doesn’t include (of course) the “fringe benefits” of money from the sale of milk or meat from cattle. It also doesn’t include the monetary value of the work oxen could do.
I personally find it fascinating that the power excreted out the rear of an animal seems to be close to (and maybe greater than) the amount of power they are able to produce with thier muscles. In this scenario, they essentially become roaming collectors of the solar power that is captured by the plants thoughout the farm. This essentially turns the entire farm into a solar panel. Although this biological system is surely less efficient at producing electrical power than a solar panel (with energy passing through various forms and losses are incured at each step) the mammoth size of the “panel” and it’s relative cheapness, would likely make the system competative. Not to mention the fringe benefits…
I am lead to believe digesters that are up and running are running at a loss financially at the moment but who knows about the future .May 23, 2011 at 4:03 pm #67393Andy CarsonModerator
A look at another source might be a good answer as to why this system is not used more commonly… Apparently, the conversion of biogas into electricity is only 20% efficient (WOW!) and it takes about 35% of the total methane produced to keep the reactor warm. Probably not as good of a system as I had previously thought, but it still seems to have potential. The authors quote a cost of $90,000 for a lagoon, so it would likely be most useful if one could find a way to use the biogas directly instead of loosing 80% to electrical conversion. Interesting read…May 23, 2011 at 7:33 pm #67385goodcompanionParticipant
There’s the rub. All that energy in the pasture, a gigantic solar panel, as you put it, but how to run our gizmo-heavy lives with it. There’s probably no way.
I had a brief burst of optimism on reading Andy’s first post but upon closer review the word does seem to be that the methane digester is largely a creature of the CAFO. The nice thing about using an animal’s muscle power instead of trying to chemically disassemble its poop is that the muscle power is easy and cheap to tap into.
I figured out that my annual hay crop is about 70 million kilocalories. Wow! If only people had rumens, we’d be all set. My fuel and infrastructure to get that hay baled and stacked in the barn amounts to maybe a couple million kcal at most. Still, a major caloric surplus! We’re producing energy, whee!
But when I feed those bales out to my horses and my beef cows, much of the energy is dissipated as movement, body heat, gas, and so on. I produce a surplus of about 7 market animals weighing out at 550 lbs each, of which maybe 300 lbs is eaten. 7 x 300 = 2100 lbs of beef. The beef has about 1000 kcal to the pound so we are at 2.1 kcal of beef.
Of course there is the horse muscle energy as well but let’s set that aside for the time being.
Hey, wait a minute! I put up 70 million kcal of hay using just 2 million or so kcal of inputs and I thought I was doing a damn good job. But the end result is about the same caloric value in food as I put into the haying process, to say nothing of maintaining the barns and fences and the energy cost of processing. Maybe I’m not doing such a good job after all.
So, there it is, that great big green solar panel. I’m farming grass and creating food. Yet in the end analysis I’m breaking even on energy. I guess at that I should still pat myself on the back since most american farming burns up 10 calories for each produced in food. Still, it’s hard to get too cocky.
Let alone any hope of tapping that big green solar panel somehow to power the rest of my lifestyle. Add in the utility costs and the road vehicles and we are back at a hopelessly imbalanced energy equation.
It’s a worthy goal to strive not to waste energy, and to effectively convert solar power to food. If that’s not the farmer’s job, then what is? But with cheap energy flooding the culture it is damn near impossible to have a net energy gain from farming. Only a handful of “labor saving devices” seems to torpedo the energy math.
I’m hoping my rice equation will look better than the beef equation. Supposedly rice has one of the highest caloric net productivity of any food system.May 24, 2011 at 12:24 pm #67381Carl RussellModerator
So a few thoughts about these last few comments.
Just let me say that I don’t think the job of a farmer is to convert solar energy into food. I think our job is to protect the ecological integrity of the biological systems that we interact with while we procure a livelihood from our environment. That said, I think that the ideal to work toward is one in which we employ as many natural processes as possible, as the entropy inherent in these systems is all accounted for by other energy consuming organisms in those biological communities.
Although Methane has real value for heat, etc., there are a few more problems other than just the inefficiencies. In real terms of biological energy, manure has other values, that in my mind, trump anything derived from digesting it into energy components.
First the infrastructure investment like so many other alternatives is a big drawback, as it can only be used for that purpose, locking into perpetuity that method of manure management. Then there are decisions of scale to provide enough manure to keep the system running as efficient as possible. There are also other infrastructure investments such as barns and manure handling systems, which also contribute to increasing scale.
Second, the biological relationships between soil bacteria and other organisms, and the plants, and the way those plants deliver nutrients to the animals raised on that soil go far beyond measure. These relationships are in place without any investment from the farmer. Utilizing the animals to disperse the manure while at the same time harvesting the feed in a way that best supports regrowth saves all of those infrastructure investments that go along with Methane digesting and manure management. This scenario is independent of scale, working with 1 cow – 1000.
The trap of considering these natural resources as a supply for conventional energy is seductive. Biomass energy is the same. The energy that goes into harvesting and processing, the cost of machinery and infrastructure, and the inherent inefficiencies just make these systems short-term at best.
Looking at Erik’s first post about using a treadmill with horses, pumping water into an elevated cistern would be a very efficient system, especially if it uses a direct-drive pump.
Thanks for posting about the ram pumps. I was just at the hardware store looking for components to build one for my own farm.
I also just outfitted one of my fields with a water system based on a 12’x4″ PVC set in the brook with a reduction to 1/2″ black plastic pipeline running through the field. It doesn’t have much pressure but it fills the water tank. This will significantly improve the effectiveness of the grazing, by providing water without having to keep giving them access to a limited section of the brook, keeping them out of the water, and allowing me to make smaller paddocks and moving them more often, AND I won’t need to transport water as an alternative.
CarlMay 24, 2011 at 3:35 pm #67389near horseParticipant
It’s pretty easy to point out the inefficiencies in power generation – including conventional methods (example – power losses in transmitting electricity over distance). So those current limitations are not exclusive to “alternative” energy production.
Also, sometimes “efficiency” isn’t necessarily the right measure of usefulness or viability. An example might be Erik’s mention of HP treadmill to pump water. We could argue that solar energy converted into horse flesh and then power to drive a treadmill/PTO to then move water has many “inefficiencies” but the benefit to Erik’s operation, IMO, far outweigh those. He’s sort of paying his horse (in terms of keep etc) for the power rather than the power company. One other thought, if he pumped the water uphill to a holding tank and then, as it was used downhill (for watering horses, garden, rice) it turned a Pelton wheel to generate some power ……. That’s what I like about smaller scale is the diversity of options and synergies available if we look.
Methane production has/is being used/developed on a small scale. If I recall the right acronym, a group in the 70s – VISTA(?) worked on small, cheap methane production/storage for developing countries. Also, there was an effort to use it in Nepal/Tibet where firewood gathering for cooking denuded the sparse number of trees to the point where women spent the whole day searching for wood to cook. They had a rudimentary concrete basin in which they made a manure slurry (I think it was only from their animals but maybe not) – I don’t recall how they captured/stored the gas but they had a single pipe on the ground feeding a single burner in their “hut” so to speak. Heck, I saw where one group in India was using truck or tractor inner tubes to store the gas.
In the north, I think maintaining the temp for keeping the fermentation/digestion going would be the challenge for us small scale producers but perhaps more of a seasonal production – like composting.
The “ram pumps” have and are being employed to do just as Carl mentioned – move water away from the streams and keep stock out of the streams themselves.
Lastly, years ago I visited a small producer in the mtns of north Idaho who make a living off their market garden. They have no electricity, so to speak, except for what they generate from their gravity fed garden watering setup. They dug a holding pond well upslope from their garden(s) – the water runs downhill, past the elevation of the garden, runs a little pelton wheel and then is forced back uphill (still lower than the pond) and through their T-tape setup. It’s incredible what level of production these folks achieve.
BUT – transportation is the issue for them (and for many of us). It’s dang hard to get around that one.June 19, 2011 at 7:47 pm #67391blue80Participant
Fellman, thanks for posting the ram pumps. I came across one of those in Indiana a few years back while remodelling a vintage log home. It ran 1/2 mile from the creek to a summer kitchen, then on the ground, then through a stock watering trough, then through the garden.
I have more water rights than land below our fast flowing canal canal and was hoping to find one of these pumps to load a tank and drip some acreage above the canal, so again, thanks!
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