In calf farms (for meat production) during life time of one calf, so per calf per life time:
1) 2220 KWh (Kilo Watt hour) energy in the form of dung produced, comes in fermentor.
2) Comes out from fermentor (intermediate is BIOGAS):
465 KWh electricity
370 KWh heat
3) Heat needed for fermentor it self 320 KWh
This is good news! Moreover calfs are sometimes in the meadow too, and sometimes in the cowshed, where the dung actual is collected.
In Holland (my country) there is a surplus of cow dung (manure). There is not enough land and meadows to spread the manure as fertilizer for plant growth. Not even when the fermentor has done its work, so derrie comes in, (also) derrie and biogas comes out. Manure is rich in nitrates and phosphates, there is already to much phosphate and nitrate in the soil, this also tends to leak to the underground drinking water storage (so storage in the soil). However the good news is this is a local Dutch problem only, all other countries, or lets say most countries, do not have this problem, there is more than enough land in the world to spread the fermentor treated manure as fertilizer, no phosphate and nitrate problem in the world.
There is 76 billion Kilograms dung produced in 2015 by the life stock in Holland:
82% from cows
16% from pigs
2% from other animals (chicken, goat, sheep etc.)
This can in principle produce 4 billion cubic meters methane (natural gas grade) but actually bio methane (biogas), by anaerobic fermentation.
Good enough for 3.2 million households (families) thats about half the households in The Netherlands.
State of the Art is (2015 statistics say) that anually only 80 million cubic meters biogas is yet produced, good for 64,000 families.
This potential is good news, because farmers can’t handle so much dung, moreover they got to pay enormous taxes to get rid of it, and expanding of the life stock and business is not allowed.
I heard now twice on TV documentaries that Denmark is completely self supporting with respect to energy, only green energy, no fossils. Maybe Holland can go that way too and our biogas (potential) can be a big part of it.
Biogas good be 26.5% of energy demand in 2015.
REFERENCES (In Dutch):
Dutch gas distributors say only anual 1 billion cubic meters biogas can be produced maximal, good for 10% of the housholds (families) in The Netherlands