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  • (1995) Heiser, Gernot; Altermatt, Peter; Williams, Angela-Margaret; Sproul, Alistair; Green, Martin
    Conference Paper
    This paper describes the use of three-dimensional (3D) device modelling for the optimisation of the rear contact geometry of high-efficiency silicon solar cells. We describe the techniques and models used as well as their limitations. Our approach is contrasted with previously published 3D studies of high-efficiency silicon solar cells. Results show that the optimum spacing is about 2/3 of that predicted by 2D simulations, and exhibits a much stronger dependence on contact spacing. The optimal value found is about 60% of that of the present UNSW PERL cells, however, the possible efficiency gain is only about 0.1% absolute.

  • (2022) Nguyen, Minh Triet
    Singlet fission is a photo-physical process that generates two triplet excitons from one singlet exciton and can potentially enhance efficiency in photovoltaic systems. The combination of photovoltaics and singlet fission is a novel field for solar energy conversion when there is much interest in renewable, non-destructive, and continuously available energy sources. Singlet fission can also overcome thermalization losses in photovoltaics, which happens in traditional cells when the incident photon energy is higher than the silicon bandgap energy, using a carrier multiplication mechanism. This thesis will design, construct, and characterize photovoltaic devices incorporating singlet fission materials to study singlet fission in practical application. The research focuses on materials characterization, spin dynamics, and electron transfers between acene and the semiconductor layer in Au/TiO2 ballistic cells, and the incorporation of singlet fission layers on silicon-based cell structures. In detail, a set of investigations was developed and summarized by implementing singlet fission materials into a state-of-the-art ballistic photovoltaic device and silicon-based solar cell. The studies demonstrate proof of concept and rationally explain the process. The first part of the thesis investigates thin films of pentacene, TIPS-pentacene, and tetracene via crystallinity, morphology, absorption, and thickness characterization. Additionally, Au and TiO2 layers in Schottky device structures were optimized to achieve the best performance for energy transfer from an applied dye layer (merbromin). The drop-casted dye layer influences the device performance by increasing short-circuit current and open-circuit voltage, demonstrating the ability of charge transfer between the device and the applied film. This device structure provides a test bed for studying charge and energy transfer from singlet fission films. The latter part of the thesis describes several investigations to understand singlet fission in a thin film using this architecture. Magneto-photoconductivity measurements were primarily used to observe the spin dynamics via photoconductivity under an external magnetic field. Control experiments with bare Au/TiO2 devices showed no observable magneto-photoconductivity signal. In contrast, devices with pentacene and tetracene singlet fission layers showed a strong magnetoconductivity effect caused by ballistic electron transfer from the singlet fission layer into the TiO2 n-type semiconductor through an ultra-thin gold layer inserted between the layers. A qualitatively different behavior is seen between the pentacene and tetracene, which reveals that the energy alignment plays a crucial part in the charge transfer between the singlet fission layer and the device. The last section investigates the application of pentacene and tetracene evaporated thin-films as sensitizer layers to a silicon-based solar cell. The optimized Si cell structure with the annealing treatment improved the cell's performance by increasing short-circuit current and open-circuit voltage. The deposition of pentacene and tetracene as sensitizer layers into the device showed some results but posed several challenges that need to be addressed. As the current-voltage and external quantum efficiency measurements were taken, it was observed that material interfaces need to be designed to fully achieve the singlet fission of the acene layer into the Si devices.

  • (2020) O'Neill, Daniel
    This thesis examines the impacts of Electric Vehicles (EVs) and Vehicle-to-Grid (V2G) technology on residential microgrid environments. EVs are rapidly growing technology which play a major role in lowering Greenhouse-gas emissions in the transport sector. Additionally, EVs can also reduce emissions in the energy sector while also improving grid stability. This can be implemented by V2G technology supporting variable renewable generation (as additional storage) and by providing ancillary services. While some studies have presented specific instances of V2G implementation, long-term operation of the technology is still not well researched. Past research indicated financial barriers and availability as concerns which deter the implementation of V2G. Recent advancements in battery technology present new opportunities to make the technology viable. Using current and predicted EV technology trends, new EV load and V2G availability profiles were developed and used to evaluate the long-term operation and benefits of EVs and V2G in a residential microgrid environment. Simulation results indicate that the operation of V2G in a microgrid environment improves the economic operation of the system and reduces the levelized cost of energy by up to 5.7%. These results suggest the latest advancements in EV technology have improved the economic viability of V2G as well as its potential for further improving grid efficiency by providing energy services like peak demand shaving and additional storage capacity.

  • (2024) Liang, Jiaxing
    Electrochemical energy systems (EESs), like supercapacitors (SCs) and batteries, are essential for sustainable societies. Nanofluidic two-dimensional conjugated polymers (2D CPs) as functional materials advance charge transport and storage in SCs and batteries, utilizing their in-plane conjugated networks and interlayer nanoconfined fluids as charge carriers’ paths. Their persistent lamellar structures further promote durability. Integrating nanofluidic 2D CPs with quasi-solid-state (QSS) device configurations is promising to synergistically enhance the functionalities of SCs and batteries with efficient charge transport in electrodes. Meanwhile, such study is lacking. This thesis explores the applications and kinetics of nanofluidic 2D CPs in QSS SCs and batteries. Recent advancements of 2D CPs in SCs and batteries are reviewed. Layered tungstate anion-linked polyaniline (TALP), featuring in-plane electronic conductive network and intrinsic nanoconfined fluids as ionic transport path, is selected as a model material for QSS SCs and batteries. The methodologies employed in this research are outlined, and the reproducibility of TALP is examined. The research first investigates TALP-based nanofluidic 2D CPs as active materials in low-temperature QSS zinc-ion hybrid capacitors (ZIHCs). Utilizing nanoconfined supercooled water, TALP exhibits superior ionic conduction and storage at sub-zero degrees, promoting the performance of as-obtained iced ZIHCs with a maximum areal energy of 580.0 µWh cm−2 at 43.3 mW cm−2. The following chapter describes the design of miniatured QSS lithium-ion batteries (LIBs) electrodes with TALP-based 2D CPs as nanofluidic fillers. The nanofillers with confined organic solvents endow rapid cation diffusion in ultracompact electrodes for QSS LIBs, rendering high volumetric capacity (266.7 mAh cm−3). The final session reports TALP-based nanofluidic 2D CPs as artificial cathode-electrolyte interphase (CEI) for QSS dual-ion batteries (DIBs). The layered artificial CEI permits efficient anion transport on graphite cathode while accommodating its large volume change and minimizing side reactions. These enable the development of sustainable QSS DIBs with high areal performance (1.78 mAh cm−2) and long lifespan (94% capacity retention after 2000 cycles). The versatile capabilities of TALP highlight the immense potential of nanofluidic 2D CPs in QSS SCs and batteries, revealing promising avenues for their future research and development.

  • (2023) Bell, Nicholas
    Zero energy building targets offer a pathway for significant potential emissions and cost reduction within the built environment. However, achieving zero energy building (ZEB) targets for existing office buildings can be challenging, given limitations on potential retrofits and on-site renewable energy generation opportunities. While retrofits can improve the performance of existing buildings, it is now certain that climate change will lead to more severe and frequent extreme weather events, and its impact on the optimal selection of retrofits to future-proof building’s improvements remains unexplored. This research investigates using extreme weather datasets in HVAC building simulation to test traditional HVAC system sizing methods under extreme conditions, quantify the impact of climate change on energy use, peak demand, and thermal comfort, for a typical commercial building in the four most-populated climate types. Viable retrofit selection strategies for the building envelope, on-site equipment and generation, and HVAC refurbishments are reviewed against purchasing off-site renewable electricity, to determine the viability of retrofit-only ZEBs across five building performance levels (different NABERs star ratings) in six key Australian climates under current and future conditions. The results show the extreme weather datasets have higher variability and increase peak cooling demand (35%) and unmet cooling hours (189%). A methodology including extreme hot and cold weather and typical conditions and datasets is proposed to future-proof HVAC system design against the impacts of climate change. To overcome increased energy demands because of climate change, a marginal abatement approach to retrofit selection highlights that some retrofits (HVAC refurbishment, rooftop solar, more efficient lighting and office equipment) are cost-effective compared to Renewable Energy Certificate (REC) use only and provide greater marginal abatement. A combined review of retrofit selection under existing and future conditions in thirty energy-performance/climate scenarios showed office buildings were able to achieve a 32% average energy reduction. While building energy retrofitting for commercial office buildings are unlikely to make ZEB targets achievable for most buildings, they can drive significant energy reduction (13-45%) and reduce the need for REC use.

  • (2022) Marshall, Luke
    Globally, energy systems are expected to undergo a complete transition from fossil- fuelled generation to renewable energy in the coming decades, with a majority of energy supplied by wind and solar in many countries. In much of the developed world, this transition will take place in the context of restructured electricity markets. This thesis examines whether electricity markets, which are intended to be the key drivers of electricity industry operation and investment, are suitably designed and implemented for transitioning to high penetrations of renewable energy. Of particular interest is the role of competition in delivering efficient market outcomes, the potential for exertion of market power in high-penetration renewable energy scenarios, and whether current auction designs to incentivise efficient behaviour will be effective in the context of energy delivered at near-zero marginal cost. Previous work on electricity market competition in Australia has focused on measuring market concentration, a commonly used indicator of competitiveness, on short-term time horizons, based on historical data. However, competitiveness in Australia’s National Electricity Market (NEM) in the long term has not been assessed, nor how it might change as a result of the transition to high penetrations of variable renewable energy (VRE). This may be due in part to lack of suitable measures of competition in markets with multiple interconnected regions, but also the theory and evidence around VRE bidding patterns now and into the future has not yet been confirmed. Assessing competitiveness of future markets requires new methods for modelling and assessing potential market dynamics that affect market power. While capacity expansion modelling has been used for understanding the future technical and economic performance of electricity systems with different generation technologies, there have been very few attempts to relate these models back to the concepts of competition and market concentration. Machine learning techniques may also have the potential to provide new insights into the strategic behaviour of participants in future energy systems and have been used for modelling and solving many other complex multi-agent interactions, but to date a straightforward method for applying modern machine learning techniques to models of competitive electricity markets has not been proposed. Furthermore, significant changes that are under consideration to facilitate the energy transition, such as the introduction of a new two-sided market design in the NEM that would require all demand-side participants to submit bids, have not been considered in modelling to date. This thesis aims to investigate competition and market power in restructured electricity markets as well as their role in the clean energy transition. It investigates whether the Australian NEM has been and will continue to be a competitive market through the transition to renewable energy and how renewable generators participate in electricity auctions now and into the future. Additionally, it examines the way new tools and frameworks might further understandings of incentives and behaviour to enable more efficient and stable market designs. In order to establish a theoretical base and explore what causes market mechanism failure, a literature review and case study are undertaken into episodes of the exercise of market power globally, with a specific focus on the Californian electricity crisis. To establish how well market mechanisms are currently working, a range of competition metrics are applied to historical datasets in order to study the level of competitiveness of the Australian National Electricity Market. This leads to new answers to the question of whether the NEM is currently a competitive market, showing that current market concentration indicators provide conflicting results depending on how they are applied. A new measure of competition is provided which demonstrates that most regions are generally competitive, but some, such as Queensland, have notable periods of constraint. In order to determine how the transition to renewables might impact competition in the NEM, new indicators of competitiveness are also applied to simulations of future high-penetration renewable energy scenarios. These analyses demonstrate that swings between surplus and constraint can lead to an increase in the frequency of opportunities to exercise market power. This is an important result that shows how high-penetration renewables may significantly disrupt the function of wholesale electricity spot markets. To understand both the underlying incentives acting on renewable generators in the NEM and the current bidding strategies of these generators a case study of these generators in the NEM is undertaken. It is seen that these participants generally offer energy at or below $0/MWh, but are occasionally seen to bid at very high prices, possibly in an attempt to push up the spot price. Following this analysis, in order to examine what strategic incentives might be present in future high-penetration renewable energy grids, new equilibria for near-zero marginal cost generators are proposed. Following on from these investigations, the performance of a two-sided market in a 99% renewable energy grid is explored. In a two-sided market, flexible demand-side participants would be required to enter bids into the wholesale market. Based on forecasts of flexible demand response and renewable energy performance in a 99% renewable energy scenario, this modelling showed that demand response was, counterintuitively, less likely to be present in a two-sided market; additionally, the two-sided market was seen to mitigate the impacts of the exercise of market power because the more elastic supply curve placed upper limits on strategic generator offers. In order to develop a new modelling framework for renewable bidding behaviour in recognition of the difficulties in modelling competitive equilibria for future high- penetration renewable electricity market conditions, a market simulator is developed for the OpenAI platform that can be used to train deep learning models of electricity market bidding. Such models may be extremely useful in the context of the transition to high-penetration renewables, because competitive dynamics could be accurately predicted and understood before new capacity is built and operated. There are several key contributions of this work; it presents a new method for calculating and estimating levels of competition in electricity markets such as the NEM, which are comprised of multiple regions with constrained interconnectors, provides and applies a new methodology for exploring thresholds of competitiveness in simulations of future energy systems, develops the first long-term exploration of renewable bidding behaviour in Australia’s NEM, gives a new tool for running market behaviour experiments with emerging AI tools, and provides an early analysis of the impact of implementing a two-sided market mechanism, as proposed by Australia’s Energy Security Board. Together, these contributions may help to significantly enhance current understandings of the opportunities and challenges associated with transitioning to high-penetration renewable energy within a wholesale electricity market.