Crop materials are fed into large airtight tanks called anaerobic digesters. These are known as the “concrete cow” as the process is similar to what goes on in a cow’s stomach. Bacteria are added and the mixture is kept at 42°C. As the crops break down, methane is produced which can be used in gas engines. The engines make heat, which can be used to keep the digesters or adjacent sewage works at their most efficient temperatures, and electricity, to use on-site or export to the National Grid.

We use a combination of maize, wheat, rye and energy beet in the digesters. Energy beet is a special hybrid form of sugar beet which produces a large amount of gas in digesters. When the crops are harvested they pickle in their own juices to produce a product known as silage. This is the form in which crops are fed into the concrete cow. We grow our own crops on Severn Trent land adjacent to the concrete cow. In the past, contaminated materials were added to this land which means it cannot be used for food production in the next 900 years! The process is especially sustainable because crop digestion also produces fertilizer as a by-product, which is used to help grow our crops. Some other crops are also bought in to ensure enough feed for the digester.