Methane Digestion:

Anaerobic digesters convert the energy stored in organic materials present in manure into biogas.  Biogas can be fed directly into a gas-fired combustion turbine.  The type of turbine most often used for small-scale electricity production is the microturbine.  Combustion of biogas converts the energy stored in the bonds of the molecules of the methane contained in the biogas into mechanical energy as it spins a turbine.  The mechanical energy produced by biogas combustion in an engine or microturbine spins a turbine that produces a stream of electrons, or, electricity.  In addition, waste heat from these engines can provide heating or hot water for use on farm.

As a fuel, biogas composed of 65% methane yields about 650 Btu per cubic foot.  Often used when designing systems for the anaerobic digestion of manure, these energy estimates can predict the amount of power production per animal.  General estimates predict one kilowatt of electricity production requires five to eight dairy cows.