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Economic, environmental, and technical assessment of on-farm anaerobic digestion systems in Ireland
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Date
2024
Authors
Diaz Huerta, Jorge
Journal Title
Journal ISSN
Volume Title
Publisher
University College Cork
Published Version
Abstract
Ireland's pursuit of producing 5.7 TWh of biomethane from anaerobic digestion (AD) plants, to reduce reliance on fossil-derived natural gas, necessitates a thorough examination of viable system configurations. The implementation of AD in Ireland is seen as a targeted approach to achieving emissions reduction of 25% in the agricultural sector. On-farm AD unlocks the opportunity to generate biomethane from indigenous feedstock and curtail emissions from livestock farming. Previous assessments of the mitigation potential of AD systems in agriculture have been undertaken through Marginal Abatement Cost Curves in an Irish context. Although this initial assessment deemed AD as a high-cost of abatement solution, recent uncertainty in energy prices, due to recent geopolitical events, might provide new opportunities for the development of biomethane from on-farm AD. Furthermore, using single values for abatement costs may not encompass or describe the impact of the varying system boundary of an AD system, which can have consequences for the financial and environmental performance. Such variables include the scale of the on-farm AD system, the feedstock used, and the biogas energy end-use. AD systems can vary significantly in terms of scale, design, technology, feedstock, and function.
This thesis delves into the financial and environmental viability of on-farm AD systems, emphasising the need to consider additional inputs and outputs beyond energy sales that lie within the system boundary. The work evaluates different biogas end-use options and varying farm sizes for on-farm AD systems, revealing a wide range of abatement costs, whilst accounting for the uncertainty of external factors.
The findings indicate that, when income from co-products such as biofertilisers are factored into the analysis, as well as the emissions reductions from digestate use, a more optimistic evaluation of AD system viability is attained. Analysis across different scales and process configurations reveals varying mitigation potential, with abatement costs ranging from -7 € tCO2eq-1 to +816 € tCO2eq-1. A key result of the analysis shows that, if a single input variable is changed within the system boundary, the financial and environmental performance of a system can be significantly changed. The efficiency of the AD process emerges as a key determinant, alongside farm conditions such as grass silage yield and synthetic fertiliser use. While heat and electricity production exhibit lower uncertainty, biomethane production faces challenges, necessitating additional incentives for small-scale AD uptake. Novel approaches, such as the integration of microbial electrolysis cell (MEC) technologies, could present an opportunity to enhance small-scale upgrading feasibility, though capital constraints remain Connecting on-farm AD systems through pipelines to centralised upgrading facilities offers a promising alternative to the transportation of materials to a large centralised AD plant, or upgrading biogas at small individual plants, reducing investment requirements. Overall, this research provides insights into enhancing the economic and environmental feasibility of on-farm AD systems, crucial for sustainable agricultural practices and emission reduction goals. Through strategic integration and policy support, on-farm AD holds promise as a key contributor to decarbonisation efforts, offering diversified revenue streams for farmers and addressing emissions from the agricultural sector. Further research and policy development are essential to realise the full potential of on-farm AD in contributing to sustainable development and mitigating climate change impacts.
Description
Keywords
On-farm anaerobic digestion , Techno-economic analysis , Abatement cost , System boundary , Probabilistic analysis
Citation
Diaz Huerta, J. 2024. Economic, environmental, and technical assessment of on-farm anaerobic digestion systems in Ireland. PhD Thesis, University College Cork.