Distillery by-products, livestock feed and bio-energy use: report

Appendix 4 - Feedstock requirement of Anaerobic Digestion plants in Scotland

63. Anaerobic Digestion plants use a range of feedstocks including wastes and also potential animal feeds such as distillery by-products, rejected potatoes and vegetables and purpose grown energy crops. There is a lack of comprehensive official usage data for AD feedstock usage in Scotland which meant it was not possible to determine usage quantities through official data sources. Instead SRUC has prepared estimates of plant capacity based on a range of industry data sources such as; ADBA, NNFCC, REA and others.

64. SRUC has used these information sources coupled to existing industry knowledge to estimate the potential capacity of AD plants in Scotland by sector. These are not official statistics (of which there are none) and should only be considered as indicative estimates.

65. There are a wide range of AD plant types and final uses for the energy produced. Energy can be in the form of; heat, electricity or bio-methane (~96% methane). End uses can be as part of the operation of the AD plant, in an adjoining process (such as a distillery) or exported off-site onto the national electricity or gas network.

66. Making direct comparisons between different types of plants and end uses is not straightforward. SRUC has instead attempted to convert the available information on capacity into a single estimate of bio-methane output capacity per hour since all AD plants produce methane. SRUC estimates indicate that the total bio-methane capacity of Scottish AD plants in 2018 was equivalent to 21,545m³ per hour of which the largest sector was agricultural at 36.6% of capacity and distilling at 31.5% of capacity.

Table A4. Estimates of Scottish AD plant capacity by sector in m³ bio-methane

Source: SRUC

67. Capacity does not equal output as plants are not always running at full capacity. In general AD plant operators will seek to maximise running time (to improve payback on capital investment) and it has been assumed for these estimates that AD plants will run for 8,500 hours on average per year (out of 8,760 hrs available). On that basis, energy value of feedstock required to run these plants for the entire year can be calculated. SRUC estimate this as 4,771,013 GJ of energy.