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PurposeBioenergy is increasingly used to help meet greenhouse gas (GHG) and renewable energy targets. However, bioenergy's sustainability has been questioned, resulting in increasing use of life cycle assessment (LCA). Bioenergy systems are global and complex, and market forces can result in significant changes, relevant to LCA and policy. The goal of this paper is to illustrate the complexities associated with LCA, with particular focus on bioenergy and associated policy development, so that its use can more effectively inform policymakers.MethodsThe review is based on the results from a series of workshops focused on bioenergy life cycle assessment. Expert submissions were compiled and categorized within the first two workshops. Over 100 issues emerged. Accounting for redundancies and close similarities in the list, this reduced to around 60 challenges, many of which are deeply interrelated. Some of these issues were then explored further at a policy-facing workshop in London, UK. The authors applied a rigorous approach to categorize the challenges identified to be at the intersection of biofuels/bioenergy LCA and policy.Results and discussionThe credibility of LCA is core to its use in policy. Even LCAs that comply with ISO standards and policy and regulatory instruments leave a great deal of scope for interpretation and flexibility. Within the bioenergy sector, this has led to frustration and at times a lack of obvious direction. This paper identifies the main challenge clusters: overarching issues, application and practice and value and ethical judgments. Many of these are reflective of the transition from application of LCA to assess individual products or systems to the wider approach that is becoming more common. Uncertainty in impact assessment strongly influences planning and compliance due to challenges in assigning accountability, and communicating the inherent complexity and uncertainty within bioenergy is becoming of greater importance.ConclusionsThe emergence of LCA in bioenergy governance is particularly significant because other sectors are likely to transition to similar governance models. LCA is being stretched to accommodate complex and broad policy-relevant questions, seeking to incorporate externalities that have major implications for long-term sustainability. As policy increasingly relies on LCA, the strains placed on the methodology are becoming both clearer and impedimentary. The implications for energy policy, and in particular bioenergy, are large.

Background: Microbial oils – often termed single cell oils (SCOs) – offer an alternative to terrestrial oil crops across the energy, food and chemical industries. In addition to oils, a range of secondary metabolites can be produced from the heterotrophic organisms as part of a biorefinery system. Techno‐economic analysis (TEA) is an important tool for evaluating economic viability, and although TEA is subject to high uncertainties where production is still at the laboratory scale, the tool can play a significant role in directing further research to evaluate suitability of scale‐up. Results: SCO production from the oleaginous yeast Metschnikowia pulcherrima using sucrose, wheat straw and distillery waste feedstocks was evaluated at two production scales. At a scale of 100 t year−1 oil production a minimum estimated selling price (MESP) of €14 000 t–1 was determined for sucrose. This reduced to €4–8000 t–1 on scaling to 10 000 t year−1, with sucrose and wheat straw yielding the lowest MESP. Conclusions: Feedstock price and lipid yield had the greatest impact on overall economic return, though the valorization of co‐products also had a large effect, and further play between feedstock and system productivity strategies could bring the price down to be competitive with terrestrial oils in the future. The novel approach demonstrated here for the first time integrates uncertainty into economic analysis whilst facilitating decision‐support at an early technology development stage. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Energy and exergy analysis is employed to compare the relative thermodynamic performance of low-carbon domestic energy systems based on air source heat pumps and micro-combined heat and power (cogeneration) units. A wide range of current units are modelled under different operating conditions representative of the United Kingdom to determine the energy and exergy flows from primary energy inputs through to low-carbon heating system and then to end use. The resulting performances are then analysed in order to provide insights regarding the relative merits of the systems under the different operating constraints that may be experienced both now and into the future. Although current mid-range systems achieve comparable performance to a condensing gas boiler, the state-of-art offers considerable improvements. Micro-combined heat and power units and air source heat pumps have the technical potential to improve the energy performance of dwellings. The relative performance and potential of the systems is dominated by the electrical characteristics: the grid electrical generation efficiency, the power-to-heat demand ratio and the availability of electrical export. For total power-to-heat demands below 1:1.5, air source heat pumps have greater improvement potential as their energy efficiency is not constrained. At higher power-to-heat ratios, micro-combined heat and power units offer the potential for higher overall efficiency and this generally occurs irrespective of whether or not the thermal energy from them is used effectively. [ABSTRACT FROM AUTHOR]