How It Works
AD can utilise a wide variety of feed stocks from both farm production and from external sources. A farm based digester on arable land might use some of the following:

• Maize and/or grass silage

• Cash crops such as potatoes, turnips, alfalfa etc

• Bio-Glycerol – a by-product of the creation of bio-diesel

The amount of biogas produced depends on the type and quality of feedstock, in particular the amount of dry organic solids present.

To produce one kilowatt of electricity continuously in an 8,200 hour a year operation requires around:

• 1.1 acres of Maize or,

• 4.5 tonnes of glycerol, or

• a combination of the above

The plants are largely automated with computers controlling the gas engine and digester feeds. The only requirement of the plant operator is to fill a hopper with silage or energy crops once a day.

Specialist plant maintenance is carried out by expert external technicians, although operators can carry out some basic work. Plant sizes around 500kW are common in Germany, however the plant size is tailored to the size of the farm - or co-operative of farms.