4.2.1. Biogas production
The biogas production rate, in Nm3/animal-day, embodies both the potential biogas production from an animal’s manure
and the availability of that manure. Thus, changing the value of biogas production rate in this analysis implies either changing the amount of gas that is produced per animal or changing the availability of the manure. Changing the biogas production rate had the greatest effect on the profitability criteria for both dairy and beef farms and, therefore, is the most important value to determine accurately. If the biogas production per animal was constant, the overall biogas production rate used as the lower bound for dairy farms would represent a change in manureทavailability from 80% to approximately 40%. Therefore, if much
of the dairy manure was “lost” in the fields due to animal
grazing no dairy farms would have favourable profitability
criteria for a small-scale biogas plant. Although changes in
biogas production affected the profitability criteria for beef
farms more significantly than the other parameters, the effects
were not as big as for dairy farms. This is due to the fact that
beef farms already have a low manure availability.