...I am having a hard time seeing how it is more efficient overall than other biofuels.
1) The stuff on ethanol vs biogas doesn't include hi output crops like Jerusalem Artichokes (900 gallons ethanol per acre) or cattails (3,000 gallons ethanol per acre), both of which are far more efficient than corn (200-300 gallons ethanol per acre). [...]
What sort of biogas output are we looking at for the same feedstocks? By my calculations, you need about 1 lb biomass per cubit foot of biogas (this can vary, but at an average). So, with that average, if we take the Jerusalem Artichoke example above, we could potentially produce about 100K cubic feet of biogas per acre of JA.
But, right now, I have a hard time seeing how biogas on its own would be easier to use as some of the other biofuels. Definitely solid and liquid fuels are easier to handle, and nothing is easier to produce [than] wood gas.
Thanks for your great information. It looks my first numbers were off on the biogas from JA. I am glad you cleared that up. One thing, where do you get 900+- BTU per cubic foot of biogas? I had always seen 600 BTU per cubic ft, if it was only 65-75% methane. That is a good thing if it contains more BTU per cubic foot.
David House wrote:
...912 BTU per cu ft for methane (and assuming 65% methane in the biogas)...
In those studies comparing the ethanol, did they take into account the energy required to keep the digester up to proper temps (90 degrees or so), because those temps are very similar to ethanol fermentation temps. The difference being, of course, that ethanol fermentation is maybe a week long, whereas biogas is continuous. I definitely see where net/net of biogas could be higher, though I do think for both systems solar heat is the only reasonable way to go.
The next thing I am thinking is how much energy is required to compress methane into a transportable form? I think that is where ethanol gets a lot of attention, because it is liquid. But maybe it doesn't take much to get to 3500 psi. Do you know?
In my area, transportation fuel is the big issue. Electric vehicles are not feasible here for 2 main reasons. 1. distances - the large city, which is the source of the majority of goods and manufacturing is just over 100 miles away, making it a 200 mile roundtrip 2. roads - many of our ranch and rural roads are dirt and require trucks or high clearance vehicles (I am not saying a truck can't be electric). Cars are not viable here.
About compressing biogas, I'm not talking about liquefying it, I'm talking about compressing it to a stage where it is feasible to travel. I think that is like 2500-3500 psi, something like that. CNG, basically.
...I am not looking for the solution for the world. I am looking for a solution for my home, and possibly, for my village at a later time. We do not have a standard American petrol diet, which makes a conversion easier. Most households average less than 300 gallons of petrol a year, and many are well below that average....
With ethanol, we are looking at about 1/2 acre or less per household (less than 100 households) for transportation fuels. If biogas can do better per acre at lower required energy, maybe we should consider it.
Do you have resources for converting fuel injected vehicles to CNG? A lot of vehicles in our are use propane, so I imagine kits are available, but I think most of the trucks I have seen using propane are carburetor systems.
I didn't realize that 3500 psi would liquify methane. What pressures are the normal CNG working at?
yup - all those rice farmers across the world should be imprisoned - how dare they disturb mud-dwellers ?
Yes, I have seen wetlands harvested sustainably, and have seen this in a lot of the non developed countries that depend on wetlands.
I don't think mono crops are sustainable, and I don't recommend them at all
I think Ernie was talking more about natural wetlands being distrubed rather than a system of rice culture, though rice culture in many areas could be used as an example of sustainably harvested wetlans, as many are very old and have been cultivated over time