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Abstract Microgrids integrating local renewable energy sources at low-voltage level show promising potentials in realizing a reliable, efficient, and clean supply of electricity. Further improvements are expected when such a microgrid is operated based on direct current (dc) instead of alternating current (ac) infrastructure for power distribution commonly in use today. Our study aims to systemically quantify the gap between environmental impacts of microgrids at building level using the case study of power distribution within office buildings. For this purpose, a scalable comparative life cycle assessment (LCA) is conducted based on a technical bottom-up analysis of differences between ac and dc microgrids. Particularly, our approach combines the micro-level assessment of required power electronic components with the macro-level requirements for daily operation derived from a generic grid model. The results indicate that the environmental impacts of employed power electronics are substantially reduced by operating a microgrid based on dc power distribution infrastructure. Our sensitivity analyses show that efficient dc microgrids particularly lead to savings in climate change impact emissions. In addition, our study shows that the state-of-the-art scaling rules of power electronics currently used in LCAs leads to inaccurate results. In contrast, the proposed methodology applies a more technical approach, which enables a detailed analysis of the environmental impacts of power electronic components at system level. Thus, it provides the foundation for an evaluation criterion for a comprehensive assessment of technological changes within the framework of energy policy objectives.

Abstract Public participation is often part of planning and decision-making processes relating to the German energy transformation (Energiewende). Factors influencing the active involvement of individuals have not been fully investigated, although these factors may impact the outcome of participatory decision making. However, a few concepts are discussed relating to what kind of people participate in governance processes: political efficacy, place attachment, value orientation, and sociodemographic characteristics. We further assumed that the aspects of attitudes toward renewable energy technologies, general knowledge about environment and energy, specific knowledge about electricity-generating technologies, personality strength, and living situation might influence people's participation in planning and decision making related to energy issues. In this study, we examine the relevance of these concepts based on a survey for which (n=) 2400 respondents were recruited from an access panel to build up a quota sample on the three crossed characteristics: gender, age, and school education. Many of the respondents are aware of participation options but very few become actively engaged in participation processes. The multivariate analyses conducted showed that attitudes towards renewable energy technologies, value orientation towards nature, political efficacy, personality strength, and individuals' specific knowledge have a strong influence on whether someone becomes actively involved or not.

Digestates from low-tech digesters need to be post-treated to ensure their safe agricultural reuse. This study evaluated, for the first time, vermifiltration as a post-treatment for the digestate from a low-tech digester implemented in a small-scale farm, treating cattle manure and cheese whey under psychrophilic conditions. Vermifiltration performance was monitored in terms of solids, organic matter, nutrients, and pathogens removal efficiency. In addition, the growth of earthworms (Eisenia foetida) and their role in the process was evaluated. Finally, the vermicompost and the effluent of the vermifilter were characterized in order to assess their potential reuse in agriculture. Vermifilters showed high removal efficiency of chemical oxygen demand (55-90%), total solids (60-80%), ammonium nitrogen (83-97%), and phosphate-P (28-49%). Earthworms effectively grew and reproduced on digestate (i.e. earthworms number increased by 183%), enhancing the vermifiltration performance, while reducing clogging and odour-related issues. Both the vermicompost and effluent produced complied with legislation limits established for soil improvers and wastewater for fertigation, respectively. Indeed, there was an absence of pathogens and non-detectable heavy metals concentrations. Vermifiltration may be thus considered a suitable post-treatment option for the digestate from low-tech digesters, allowing for its safe agricultural reuse and boosting the circular bioeconomy in small-scale farms.

From the British debate on the depletion of coal in 1865 to the First World Power Conference held in London in 1924, scientists, engineers, industrialists, and politicians produced new interpretations of the past, present, and future in terms of the mobilisation of energy resources. This thesis identifies an emerging ‘energy developmentalism’, which called for maximising energy use to maintain or improve a nation’s place in international competition. Energy developmentalism was not a marginal worldview confined to ‘energeticists’, but a coherent set of claims, measurements, and arguments that informed energy governance on an international scale. Rather than focusing on a single resource, energy developmentalism applied a unified schema to all energy sources, including those like solar and tidal energy that were still mostly theoretical. Drawing on sources from across Europe, while staying grounded in political changes in Britain and France, makes it possible to understand how a general formula for transforming raw materials with maximum efficiency was applied differently depending on specific political contexts. This period saw the articulation of problems like the depletion of resources, the difference between renewable and nonrenewable energy, the intermittency of renewables, the overreliance on a single source of energy, and the centrality of energy to modern economies – problems that are often associated with later periods. Scientific measurements of efficiency, horsepower, and kilowatts became operators in political debates centred on questions of national standing and progress. Even as oil became increasingly important in the world economy, the delegates at the First World Power Conference transformed a vision of a renewable energy future into one of a general expansion of energy consumption as the basis of progress. In so doing, they downplayed the continued importance of fossil fuels and equated ‘conservation’ with the fullest possible use of all energy sources, renewable or not.

Cryptocurrencies have gained a lot of attention in recent years, mostly due to their decentralized manner of operation and their growth in value. However, a major drawback most of them possess is their high energy consumption. Current solutions to this problem have significant l imitations: bringing back centralization and/or substituting the required energy with, e. g., storage space. This paper aims to address the problem by investigating the use of a two-level deep reinforcement learning (RL) model to design incentive policies for green mining in cryptocurrencies. This is done by modeling one such energy-intensive cryptocurrency system and creating an RL environment. Finally, by running simulations in an RL environment, we develop and test incentive policies, according to which cryptocurrency participants who primarily use renewable energy for their mining operations are more likely to add new blocks to the blockchain. Our results show that even when the green score of each crypto miner (determined by their use of green energy sources) has relatively small importance (up to 0.3) in their selection probability, miners still shift towards green mining in order to increase their chance of being picked to validate cryptocurrency transactions and receive the corresponding rewards.

Redox flow batteries (RFBs) are a promising technology for grid-level energy storage. The ability to decouple energy and power, as well as the potential for low-cost and safe materials, make them particularly suited to this application. However, there is a lack of viable organic catholytes for RFBs and research thus far has primarily focussed on anolytes. Research in this thesis focuses on novel catholytes, degradation studies and electrolyte optimisation for aqueous organic redox flow batteries (AORFBs), the most challenging and yet the most promising area of this technology. In the first results chapter (Chapter 3), a series of triarylamines was synthesised. Initial electrochemical testing (using cyclic voltammetry) revealed one of these candidates, amino-functionalised 4-amino-trisphenyl amine, proved to be the most promising. However, battery cycling with this as the catholyte results in extensive polymerisation, leading to rapid capacity fade. This rapid capacity fade was improved by electrolyte optimisation, and utilising a mixed-salt system of 0.5 M HCl and 0.5 M H3PO4 it was possible to decrease capacity fade, increase coulombic efficiency and access more theoretical capacity. Chapter 4 explores commercially available phenothiazine dyes. Nicotinamide (NA) was used to increase solubility, specifically, the solubility of the most promising candidate explored, azure-a (AA), was doubled from 1 M to ca. 2 M. When cycled with NA in the supporting electrolyte, AA, had relatively stable cycling performance, though only half of the theoretical capacity was reached. Evidence suggests that this is the result of dimerisation of AA-based redox species. An extensive study using electrochemical impedance spectroscopy (EIS) showed that NA prevents a thick, charge-transfer blocking, film from forming on interphases in the cell (i.e. the electrode or membrane), thus improving the cycling performance. Chapter 5 further investigated both the dimerisation of AA-based species and their interaction with NA which leads to the observed improved performance. Through spectroscopic studies (NMR, EPR and UV/vis) it was found that there are at least four dimeric AA-based species in solution (most likely different dimer conformations). The role of pH on AA aggregation is also explored here for the first time. Finally, the origin of the improvement in battery performance using AA is shown to be preferential hydrogen-bonding with NA which intercepts AA aggregate, therefore reducing dimerisation and subsequent polymerisation. The final research chapter (Chapter 6) explores synthetic modification of phenothiazine, which is otherwise insoluble in aqueous conditions. A sulfonated propyl chain was found to improve solubility up to 1.15 M in 1 M HCl. However, upon cycling the sulfonate group was lost and an emulsion formed, leading to rapid capacity loss. This was improved by utilising NA as an additive (as shown previously in Chapters 4 and 5). Overall, this thesis has found that synthesising novel compounds presents many challenges, especially as the performance of candidate catholytes cannot be accurately predicted before experimental cycling. Ultimately the greatest improvements in cycling performance were achieved through electrolyte optimisation rather than synthetic changes in a particular catholyte family. It is therefore recommended to focus future research efforts on optimisation of the supporting electrolyte as the means for improving battery performance.

Abstract Automated vehicles have become a popular topic of conversation. Initially, these conversations were limited to technology developers, innovators and engineers, as they worked to progressed the various technologies and systems that are required to create automated vehicles. Then, over time, these conversations extended to other communities; lawyers, insurers, planners, policymakers, social scientists, and various publics all began hearing, and talking about automated vehicles – also known as ‘driverless’, ‘self-driving’, and ‘autonomous’ vehicles. Levels of automation emerged as a way to depict gradations or categories of autonomy, with tasks divided between those for the machine and those for humans. In this paper, we critically reflect upon the dominance of levels of automation – up to seven sequential ‘steps’ - proposed by a number of industry organisations. Focusing on the Society of Automotive Engineers (SAE) Standard J3016, we signal the intended and unintended performative effects of these levels. We argue that current discourses on automated vehicles have been underpinned by a techno-centric, expert-dominated logic, and point to the benefits of more dispersed, geographically contingent, and socio-technical perspectives in re-framing the dominant discourse and allowing for more nuanced spatial and temporal understandings on future systems of (automated) mobility.

The production of sustainable fuels for transportation and energy represents an essential technology enabling the transition away from fossil fuel use. Over the past two decades several biological routes for the production of chemically identical molecules to those in fossil fuels (‘drop-in’ fuels) have been discovered and characterized. These have held promise as breakthrough technologies but have yet to reach commercial viability. Industrial scale bioprocess development for drop-in fuel production has been held back by high feedstock prices and inadequate process efficiencies. Currently, bioethanol and biodiesel are produced using crop-derived sugars and oils, so called ‘1st generation’ biofuels. Although their use positively impacts net CO2 emissions, their derivatization from food crops means they compete for arable land. To avoid this ‘food vs. fuel’ issue, alternative carbon sources for bioproduction must be explored. In this thesis the use of two non-sugar substrates, acetate and ethanol, were explored as carbon sources for hydrocarbon biosynthesis. Either carbon source enabled the production of these compounds at titres and product/substrate yields similar to that of glucose. The rate and efficiency of substrate conversion to product largely governs the viability of a bioprocess. These properties are in part defined by the enzymes that make up the relevant metabolic pathways. One of these pathways is the cyanobacterial alkane biosynthesis pathway discovered in 2010, consisting of acyl-ACP reductase (AAR) and aldehyde deformylating oxygenase (ADO). The terminal ADO enzyme is known for its low catalytic efficiency, and as a result many enzyme engineering efforts have targeted this enzyme. This thesis describes the design of growth-coupled approaches for engineering ADO. Growth-coupling involves linking enzyme activity to cell fitness and taking advantage of the principles of directed evolution to select for improved enzyme variants. Several growth-coupling approaches were assessed in this work through a combination of in silico flux balance analysis and experimental work, mostly focussing on the byproduct of ADO – formate. These efforts resulted in functional growth-coupling of ADO activity via the reductive glycine pathway. Another approach to growth-couple ADO activity was based on redox cofactor auxotrophy. An E. coli strain lacking all central metabolic pathways for NAD+ reduction was constructed, dubbed NADHaux, and its growth could be tightly linked to NADH generation by formate oxidation. Taken together, this thesis provides insights into the extremes of E. coli redox metabolism and presents hopeful results regarding the use of non-sugar carbon sources for bioproduction. In addition, it describes valuable novel methodologies for the evolutionary engineering of alkane biosynthesis.