I watched the video as well, and have even visited a 1 megawatt digester, so I know roughly how they work. However it would be pretty difficult to make them really pan out.
The biogas generator on the farm I saw had 1200 dairy cows, producing 250 KW. They kicked it up to 1 megawatt by having
local food companies dump their food waste into hoppers that converted the food waste into biogas. The plant also cost 10 million dollars and still had a lot of problems, namely quality of the gas that kept shutting down the engine driving the generator.
And here lies the rub, while it is possible to get methane out of animal manure, there is not of methane there. I mean, the animals burp and fart getting rid of much of it, and humans are even better at getting rid of it. So Unless you have A LOT of animals, even a meager amount of electrical consumption is going to require a lot of animals on the farm. I figured it around 250 sheep to give me enough methane to do something with (constant 3,000 watts 24/7)
But I mentioned how the biogas generator I saw, bumped production 300% by using food stuffs. This makes sense because the food has not been broken down, burped and farted out. Since I hate hay, and can, and do,
feed my sheep silage, I was thrilled to learn that silage affluent has A LOT of biogas in it. This is basically the
water that is in silage. Since silage consists of 66% water, a silage bunker is normally sloped to drain this water, where it is piped to a leaching field as it is very toxic. My plans were, to redirect this silage affluent to a biodigester where it would be mixed with my sheep manure, then the methane pumped back to a 3 KW gasoline/propane liquid cooled generator I happen to have kicking around. But a few problems arize from that plan.
First, there would have to be significant storage of the silage affluent because just after harvest, the volume would be huge, then taper off over time. The second problem is heat. Before biogas can be produced, it must hit 103 degrees (f) so there must be a way to heat the compost up initially. After that, water circulating through the generators engine goes back to the compost pile to help preheat the pile to keep it at, or above 103 degrees. In other words, there is no radiator on the generator, it gets cooled by trying to heat the compost pile up. But trying to find a small propane powered generator that is liquid colled might be a problem (mine is a 1943 US Navy generator)
But here is where real world numbers get in the way of this otherwise ingenious idea.
While it would be possible for a household to reduce its electrical consumption to a point where a small generator running on biogas would be self-suffecient, obtaining the "fuel" would be a huge problem. I have hundreds of acres of fields in which to tap for this endeavor, however, those same acres produce hay that is sold. Even though I live in a state with one of the highest electrical rates in the country, I do not spend $9000 dollars a year on electricity which is what I get from my hay, so my farm acres are better off used to produce hay and silage and
sell it, then in trying to save $800 a year in elecrical costs.
I do think in the right situation it could be done, and I am close to that. I got the heavy equipment to make the lagoons, the small liquid colled generator, and the
land base to get silage. But even then, the cost of fuel to make the lagoons, all the plumbing, and labor to save $800 a year??? Even to use the biogas for cooking on the kitchen range, for the clothes
dryer, or even boiler for home heating would be questionable. Biogas is not very consistent after all, and not as potent (as many BTU's) as purchased propane, so a person will
experience a lot of flame-outs.
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