Insights presented in the Sustainable Energy Authority of Ireland (SEAI) National Heat Report may suggest that the growth potential for the anaerobic digestion (AD) industry in Ireland depends on how much the suckler herd decreases by.
The report published recently stated that based on current herd forecasts, biomethane production resulting from anaerobic digestion of a grass silage, slurry mix, could reach the equivalent of 5% of Ireland’s current gas supply.
This figure could be increased to 10% of current gas supply if pig slurry, other food waste resources and energy crops were also digested this way.
However, this can only be achieved if beef farming declines further, to make more land available to grow energy crops, the report suggests.
Only 7% of the farmed land in Ireland is in tillage use; a decline in this figure is undesirable from a food security point of view.
This means, changing the use of land that is currently farmed for tillage to the growth of energy crops is not encouraged, according to the report.
Although a crop could be grown for AD in a tillage farm’s arable rotation break, to be cost effective, the crop would need to be in the ground for two years which would upset the entire rotation.
“This means that land for bioenergy crops must come from grassland currently used for fodder cultivation. Such land could become available if the number of livestock grazing on the land reduces,” the report stated.
Future for anaerobic digestion
The report presented two hypothetical future scenarios. The first is the ‘Business as Usual scenario’ (BAU).
It would the dairy herd increase by 10% alongside a 23% reduction in the size of the suckler herd by 2030. This would represent an overall reduction in the size of the national herd of 0.5%.
However, in the second scenario, the ‘Land Use Change scenario’ (LUC), the changes are more significant.
The dairy herd increases by the same amount as the BAU by 2030, but within the same timeframe, the suckler herd reduces more dramatically, by 45%.
This scenario was presented under the assumption that a desire to reduce livestock emissions leads to a reduction in suckler herds.
Ultimately, a significant reduction in the suckler herd would create an opportunity for land use change, whereby high energy yielding crops could be planted, or an AD plant could be developed, according to the SEAI.
Location of AD plants
The SEAI report outlined that it would be desirable to have an AD plant close to the slurry producing farms as they are expensive to transport due to their low energy density.
It is possible to have a small scale plant on the farm to overcome these logistical issues although the SEAI report states it is unlikely to be cost effective:
“Larger plants have economies of scale advantages. Even a small scale plant requires slurry from a large number of animas: A 100kWe plant could require slurry from 1,000 dairy cows or 6,000 pigs.”
The report stated that because many smaller farms don’t produce enough slurry to support an AD plant, co-digestion with a feedstock that has a high biogas yield, namely, grass silage, would be desirable.
Ultimately, the report concluded that everyday activity produces a range of sustainable biomass resources that are suitable for energy production, but currently only two thirds of this are being used.
It stated that harnessing the full potential of this resource would help Ireland to reach its greenhouse gas (GHG) requirements as laid out in the Climate Action Plan.