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Milking the most from the ‘concrete cow’ Anaerobic digestion may operate like a cow’s insides but, as Charlotte Maclean reports, it can generate strong financial returns. designed around the feedstocks which grow well in the area. For example, maize is fast becoming the established front-runner in terms of energy crop for AD, but there is little point designing a west-coast plant to run on maize, as the climate is unsuitable for this crop. The plant is therefore being designed to run primarily off grass silage, supplemented with whole crop cereals and rye, together with manure and energy beet, where these can be sourced locally. In essence, the plant operates in much the same way as the digestive system of a cow – AD is often referred to as a “concrete cow” system. As with cattle, the fuel can be varied throughout the year, provided new feedstock is introduced gradually, so that the bacteria inside the digester (as with a cow’s stomach) can adjust accordingly. One key issue to consider is the degression in both Renewable Heat Incentive (RHI) and Feed-in Tariff (FIT). This is the regular decrease in the subsidy rate offered for each scheme, according to the level of uptake of that particular technology in the preceding period. It is

essential to account for degression when considering the financial returns from AD, particularly given that the time from feasibility to commissioning can be fairly lengthy for AD plants. Once accredited however, the tariff rates are fixed (indexlinked) for 20 years. Another important consideration is the introduction in February this year of new sustainability criteria under the RHI. These take effect from September and require evidence to be provided on both land use and greenhouse gas (GHG) emissions for each consignment of crop

feedstock, though waste feedstock, such as slurry or manure, will be exempt from the criteria. If an energy producer is unable to demonstrate both criteria have been met, RHI subsidy can be withheld. Default figures produced by Ofgem can be used for GHG emissions, but the suggestion is that these have been set at a level which makes the Governmentimposed limits unachievable if default figures alone are used. So keeping accurate records and reporting on feedstock production will be increasingly important in the AD sector. Charlotte Maclean is an Associate Rural Surveyor, in the Stirling office of CKD Galbraith. charlotte.maclean@ckdgalbraith.co.uk 01786 434 603

What is Anaerobic Digestion? Anaerobic digestion is a series of biological processes in which microorganisms break down biodegradable material in the absence of oxygen. The result is a mixture of methane and carbon dioxide gases (biogas), some organic material (digestate) and water. l Biogas can be burned to produce both heat and electricity, while methane can be used as vehicle fuel or injected into the gas grid.

l Digestate is a stable, nutrient-rich substance and can be used for a range of products and purposes: most usefully as a fertiliser, rich in nutrients, but also as feedstock for ethanol production, and in low-grade building materials like fibreboard. l Water, after treatment within the AD process, may be returned to the watercourses.

www.ckdgalbraith.co.uk | Twitter: @CKDGEnergy | Energy Matters Autumn 2015 | Page 5

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Galbraith Energy Matters Autumn 2015  

Energy Matters Autumn 2015 News and views from Galbraith on the current issues affecting the Renewable Energy Industry. Autumn 2015.

Galbraith Energy Matters Autumn 2015  

Energy Matters Autumn 2015 News and views from Galbraith on the current issues affecting the Renewable Energy Industry. Autumn 2015.