Back in the late 1970’s I was very absorbed in learning all I could about alternate energy technologies to ascertain their practicality. A friend of mine had 1,000 acres of cow pasture with unlimited supplies of, ahem, natural resources, so I calculated how much manure it would take to generate the methane needed to power a generator and run everything in a very large house including air conditioning. After a long string of calculations, I realized it would require a digestion tank the size of a swimming pool and a ton of manure per day. My ultimate conclusion was that alternate energy sources are too diffuse to be practical for sustaining our standards of living. I gained new respect for the number of BTU’s packed into a gallon of petroleum.
Dairy farms do it - after milking, they flush the barn into a tank...