Energy collection from the compost pile is something I have researched and wanted to accomplish for quite some time. We have a large wind row that works as a static compost pile, turning and applying it as its aged. A neighbor with a front loader comes and does the machine work, a couple times a year. The livestock create approximately 2 tonne of manure a week; 310,000 lbs a year.
The anaerobic digesters would speed up the process and create multiple outputs such as methane, heat and ready to use fertilizer. The examples are still too big, very expensive initially, and I definitely want to become more knowledgeable about working with methane. I believe there is a lot of potential and really appreciate the work that has been done at the University of New Hampshire.
I think I will try a combination of methods, starting with an aerobic pile to speed things up a little. My goal is to create a space to compost manure closer to the barn over winter months (getting to the wind row is tricky in bad weather); with it closer, heat recovery could warm up our greenhouses for year-round vegetable production. One of the permaculture farms I visited recently had installed subterranean air piping to keep his soil warm, using an old furnace blower.
Ducts along the top collect sun-warmed air in winter blowing it through underground piping and vented in either corner. This is reversed in the summer to cool the greenhouse. I wonder how effective this would be in extreme winter temperatures overnight.
One key step I made recently was to invite a couple of friends over to start bouncing around ideas. We are thinking about ways to include cinderblocks to help retain the heat and run water or air vents under the composting piles. An interesting thing happened when we start looking around at what is already here, the project germinated and now our abandoned cement silo might even work into the plan.