South-west report shows low-cost way into renewables

A new study into low-tech, low-cost anaerobic digesters could offer farmers an affordable way into renewable energy projects without investing hundreds of thousands of pounds.


The report, commissioned by Cornwall Agri-food Council and supported by Low Carbon Cornwall, Cornwall County Farms and the Exmoor National Park Authority, considered three low-cost technologies modelled on five real farms in the South West.

The first option is to place a simple impermeable cover over an existing lagoon or above-ground store, capturing the resulting gas and using it to produce energy. Estimated costs for a 4kW system range from £25,000 to £50,000.

A flexible insulated tank used in a lagoon structure is more suited to smaller farms of 100-200 livestock units, costing between £20,000 and £60,000. Farms with fewer than 150 livestock units could suit a fast-rate liquid anaerobic digester, where slurry and manures are separated to produce a high-strength liquor to feed an liquid reactor. This would cost £45,000 to £100,000 for a 4kW system.

“Having carried out an economic study into high-output AD systems, it was clear that an alternative scale of technology would need to be investigated if we were to roll out this technology on the average dairy or livestock farm in the south-west,” said David Rodda from the Cornwall Agri-food Council. With low capital costs, easy-to-use systems and no need for alternative feed materials, these new options could be perfect for many smaller scale farmers.

The five case-study farms ranged from 110 dairy cows in Cornwall to 480 beef cattle on Exmoor. Typical installation costs were £38,000, and in many cases grants are available at up to 50% of the cost, he added. With grant support it was cost-effective to install small AD systems to supply heat and power to two out of the five farms, with a payback period of less than five years.

“This is a report that farmers can use free of charge to help them install low cost AD systems on their farms across the country,” said Mr Rodda. “Two of the farmers involved are very interested in progressing with the model, and we are hoping to set up pilot farms for people to come and see.”