Frequently Asked Questions

What is anaerobic digestion?

Anaerobic digestion is the biological degradation of organic matter in the absence of oxygen. The process takes in organic materials such as animal slurry, silage, farmyard manure and other farm wastes, and digests it in a tank to produce biogas and digestate.

What is biogas?

Biogas is produced from anaerobic digestion and is comprised of approximately 60% methane and 40% carbon dioxide. It can be used to fuel a combined heat and power (CHP) engine which produces electricity and heat.

The electricity generated is eligible for the Feed-in-Tariff (FiT) and the heat is eligible for the Renewable Heat Incentive (RHI) scheme. Both the electricity and heat can also be used on site on the farm.

What is digestate?

Digestate is a by-product of the anaerobic digestion process and can be separated into liquid and solid fractions in order to reduce liquid storage space and target nutrients for different crops. Unlike composting, the volume of the input feedstock is not reduced by any appreciable amount during the anaerobic digestion process.

The liquid part of the digestate is a high nutrient fertiliser containing nitrogen, phosphorous, potassium, as well as other significant and essential trace elements. Fertiliser performance is superior as nutrients are more readily available for uptake by plants.

How much could a plant cost?

Depending upon the feedstocks envisaged, the size of the plant and individual characteristics of the site, the plant can cost between £1,500 to £5,500/kWe.

What kind of feedstocks can be used with the de-gritting system?

The usual organic feedstocks such as slurries, manures, crops, weed toppings and local wasted organics can all be fed to these digesters. Other organic feedstocks, which are normally excluded from AD without considerable pre-processing, can also go into the digester. These include slurry from cows bedded on sand, woodchip or ash, unwashed fodder or sugar beet and crops grown on sandy soils.

How long would it take to install an AD plant?

Before a plant can be installed the site will need to have planning permission. Once this has been acquired the build time is approximately 6 to 12 months depending on the size of the plant.

How much income would a plant give?
An AD plant will generate income from 4 main sources.

Feed-in-Tariff (FiT) – government payment for each kWh of electricity generated. Current tariff levels; plants below 250kW receive 10.13 p/kWh, between 250kW and 500kW receive 9.36 p/kWh. These are current figures for FiT Year 6, from 1 April 2015 to 31 March 2016

Export Rate – generated electricity which is not used on site and is exported back to the grid is approximately worth 4.5p/kWh

Renewable Heat Incentive (RHI) – for heat generated from biogas the current tariff levels are; below 200kWth (kW thermal) receive 7.62 p/kWh, between 200kWth and 600kWth 5.99 p/kWh.

Energy Savings – utilising the electricity and heat available from the CHP engine will reduce the farm’s energy bills.



If you have further questions, please do not hesitate to contact us.