Joan Helen wrote:
It is my understanding that a small human family cannot generate enough waste, that you must have animals involved as well. What do you think?
Hmmm. Well, strictly using their own urine and feces, then, yes, we do not generate enough wastes to produce enough biogas to be practical for very much.
However, people generate far more organic waste from their kitchen than they do... directly. Likewise, we can use lawn cuttings or other ag wastes, or even restaurant garbage. So, yes, it would be good to have animals, but no, it is not required to have animals to be able to generate enough biogas for cooking and lighting, and maybe even space and water heating.
What we have to do, however, is have good information, fact-based. We need to understand simple math and physics. We have to have some insight into biology and the like. The very real physical process of making biogas depends entirely on our educating ourselves about these issues. The most potent ecological and evolutionary adaptation is abstract thought.
Mark Clouse wrote:
Thanks David and I'm so thankful to discover the availability of your book. I made a cursory investigation of biodigestors/biogas last spring when I was trying to find a benifical solution to my critter waste disposal of my small dog kennel. [...] I gave up on this solution based on the amount of manpower effort the systems I found would take to process the waste and other factors like bringing the effluent to optimal temperature in winter months.
Given that this is a permaculture forum, it should come as no surprise that I would say that one has to take a systems approach to biogas, particularly where animals are concerned. Dogs...? I don't recall hearing about a digester using dog manure, and I've not thought the matter through with specific regard to dogs, but my point is that if the kennel (barn, stall, etc.) is well-designed, it will reduce or eliminate the work required to get the wastes into the digester. If you have to shovel it together, pick it up, put it in a wheelbarrow and trundle it to the digester, then it is far less likely that the digester will continue to function, because, like Audrey (2) in The Little Shop of Horrors, the digester will eventually be seen as a gaping maw saying "Feed me! Feed me!" What you need, by contrast, is to have the digester downslope from or underneath the manure, so that it either falls in or can be easily pushed that direction.
As far as keeping the digester warm, again systems pertain. Since the digester is a box filled with water, it not only is difficult to heat because it takes so much energy to warm water, but as well for precisely the same reason, when heated, it serves as thermal mass. As such, one great place for a small digester is in a greenhouse, where it should be arranged to have whatever heat there is, directed toward it. When the sun goes down, all that nice, warm water will tend to keep the greenhouse warmer, and the greenhouse will prevent the heat from escaping to the Great Outdoors, so both plants and digester will be happier.
(As well, where the carbon dioxide is removed from the biogas in a manner that allows its subsequent release-- as it would by scrubbing via water-- then the CO2 can be released into the greenhouse, again making the plants happy...)
But on Sunday night, I was watching 60 minutes and they has a piece on Fuel Cell Electric Generators and the inventor remarked that a scaled down model for home use should be available in 3+ years for about $3000 that would make electricity from natural gas or BIOGAS. This could really change the equation and complement home electric generation by other means than expensive PV modules.
I didn't see it. We have Sunday dinner with as much of the family that can gather, and it seems to cut into my TV time. Should I kick them out and watch TV? Hmmmm....
What the heck. They're family. Besides, it looks like the show is available at http://www.cbs.com/primetime/60_minutes/ , at least for the time being.
I am new here but wanted to comment on your post.
Really you don't have to produce enough there are so many ways to get free feed stock.
Lawn services, tree trimmers, mowing your grass to tree bark, sawdust, wood chips from a chippers
cutting corn stalks behind a picker garden or greenhouse waste.
It all depends on how you will use it will you generate all your electric for your home or farm?
Will you run all your vehicles and farm machinery off of it?
Or will you use it just for cooking?
Joan Helen wrote:It is my understanding that a small human family cannot
generate enough waste, that you must have animals involved as
well. What do you think?
It depends. In most cases, a small family will not generate enough waste to make it practical. Besides, most food waste seems better fed to chickens for egg and meat production. I've seen most small biogas systems used for cooking, but it's easier to use a small rocket or gasifier furnace - or solar cooking might be done. Photovoltaics is actually practical for this purpose in many cases. Bottom line is I don't see biogas production as practical unless one happens to have a great supply of waste that can be easily converted.
On photovoltaics, the most practical way to achieve energy self-reliance today is with a combination of photovoltaics and biomass. The cost for PV panels have come down dramatically in recent years. The combination of (1) greatly minimizing electricity requirements, (2) large PV array, (3) modest battery system, (4) opportunity loading, (5) biomass for heating applications, and (6) small back up generator for those periods of very poor solar production - this the most practical way to go.
On (4) opportunity loading, since the cost for PV panels is low today, then a larger array can be had. Make hay while the sun is shining. A modest battery is likely to be full early in the day, so surprisingly large electric loads can be operated at this time without taxing the battery system, including cooking.
In Canada, many households use gas for heating, and the average household uses 7 cubic meters of gas per day. There seems to be a lot of variables involved in calculating biogas production, but it seems that for an average Canadian household to switch over from natural gas, they would need quite a few more cows than three. I think it was in the order of ten but don't quote me on that.
Now switching over like that isn't exactly a very smart move, and if you were going to go to the trouble of building your own biogas plant, you probably have better sources of heating, and smarter building design that the average Canadian house!
I ran the numbers out of curiosity rather than a practical endeavour.
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