Anaerobic Digestion

Charlesfield Farms

After overcoming initial scepticism, a £10m anaerobic digestion plant is providing both eco-friendly power for local homes and a guaranteed source of income for nearby farmers.

When Charlesfield Farms wanted to diversify its business, the estate decided to join the green revolution. The result was a new £10 million anaerobic digestion (AD) plant that produces eco-friendly methane gas from locally grown feedstock, then feeds it directly into the nearby energy grid.

Running since 2015, the plant in St Boswells in the Borders now generates enough energy to supply up to 4,000 homes, reducing reliance on non-renewable natural gas. The AD site has proved such a success that more local farmers are now queuing up to join.

The plant – only the second of its kind in Scotland – was opened in 2015, with funding from Iona Capital, an investor in renewable energy projects.

One initial hurdle was getting buy-in from local farmers willing to commit arable land to grow feedstock for the plant. But helped by CKD Galbraith, a 10-year contract was developed that gave farmers payment based on the cost of production, plus a margin of £150 per acre. This now offers security for both sides, with the plant enjoying guaranteed supply, and the farmer knowing what price he will get for his harvested crop and budgeting accordingly.

Trevor Jackson, whose family has been farming at Charlesfield for four generations, said: “People worked out that they could do it at little risk to themselves and would get an enhanced profit. So it took a bit of hard work, but once they realised the benefits, they settled down and accepted it.”

The plant uses natural fermentation to break down plant and animal materials using micro-organisms in an airtight tank. The resulting methane-rich gas can then be used to generate heat and power or injected into the supply grid. It cuts the amount of greenhouse gases that would be released into the atmosphere if the materials were left to decompose in landfill.

And one of the leftovers from the process – a digestate high in nutrients – is also returned to the farmers for use as an organic fertiliser.

Such a set-up is now benefiting the local economy too, as Trevor explained: “Because the plant purchases feedstock, it benefits the farmers. Plus there’s all the people involved with contracting and maintenance – and we use quite a lot of local maintenance folk.

“Running the farming operation plus the plant has actually created more jobs than we expected and we’ve taken on the equivalent of five to six full-time staff. We reckon it puts about £1.5m back into the local economy every year.”