The impact of sustainability assessment of renewable gas systems on policy implications and optimum end use

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Long, Aoife
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University College Cork
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Ireland has a significant potential resource to decarbonise natural gas through producing green gas for renewable heat and transport. Key resources for anaerobic digestion include food waste, slurry from farming, and grass silage. Gasification and methanation of willow are potential future resources. The 2018 recast European Renewable Energy Directive (RED recast) sets emissions savings criteria for renewable fuels. The criteria are more stringent for use of the fuel as heat, with both a higher specified emissions savings criteria (80% versus 65% for transport) and a lower Fossil Fuel Comparator (80g CO2 MJ-1 versus 94 CO2 MJ-1 for transport). This research aims to determine if Irish feedstocks and conversion pathways can meet the emissions savings criteria of the RED recast. Mono-digestion of grass was initially tested and demonstrated to achieve a greenhouse gas emissions saving of 73% for transport, meeting the 65% emissions saving criteria. For use as heat, the saving achieved is 65% against criteria of 80%. Gasification and methanation of willow were then tested to determine if heat would be a viable end use from a sustainability perspective. Previous land use was shown to have a significant impact on the results of the analysis. Converting land from grassland for cultivation of willow results in greater emissions when compared to conversion from arable land as grassland has a higher rate of carbon sequestration. The gasification methanation pathway was found to meet emissions savings criteria for transport in most cases, and for heat when converting from arable land only. In Ireland, over 90% of agricultural land is grassland. The highest emission saving of 97% was achieved through conversion from arable land for the transport end use. Considering EU and national emissions policies, a transport end use for renewable gas will achieve a greater emission saving towards targets as compared to a heat end use and will contribute (with a weighting of two) to the RED recast 14% renewable energy in transport target. Using biomethane in the Emissions Trading System (ETS) sector will not contribute to national non-ETS targets set by the EU. While the analysis demonstrates a clear policy preference for a transport end use renewable gas has been proposed as a solution to decarbonise industrial processes in Ireland, specifically heat demand (which is part of the ETS sector). As part of this effort, the breast-milk substitutes industry is proposing to use renewable gas as a substitute for fossil natural gas. However, decarbonising the industrial processing of breast-milk substitutes can have potential ethical implications that have not previously been analysed in literature. World Health Organisation nutrition targets aim to increase exclusive breastfeeding to at least 50% globally by 2025 to improve maternal, infant, and young child health and nutrition, a target that will have implications for the energy transition. The analysis in this thesis compares the emissions saved in Ireland from decarbonising the industrial processing of breast-milk substitutes with renewable gas with the emissions saved by an increase in exclusive breastfeeding to 50% in both Ireland and a key export market, China. The emissions saved from achieving the minimum global breastfeeding target are greater than when renewable gas is used to displace natural gas in the production of breast-milk substitutes in Ireland. The decarbonisation of breast-milk substitutes with renewable gas is discussed in relation to the principle of justice as non-maleficence, a principle based on the commitment to avoid harm, a novel application of a principle of justice. Considering this principle it is concluded that breastfeeding support can be considered a demand-side measure for mitigating climate change by reducing the demand for energy services to produce breast-milk substitutes.
Biomethane , Sustainability , Energy policy , Climate justice
Long, A. 2021. The impact of sustainability assessment of renewable gas systems on policy implications and optimum end use. PhD Thesis, University College Cork.