Beach‐cast kelp (principally Laminaria spp.), known as macroalgal wrack, has been suggested as a feedstock for biofuel. However, to be extracted sustainably it is necessary to understand its ecological role and predict the impacts of its removal. Field‐based observations combined with food web modelling were used to predict the ecosystem effects of removing wrack from beaches of the Uists, western Scotland. Beaches with wrack were associated with enriched benthic infauna (polychaetes) on the lower shore, and wrack mounds supported abundant macroinvertebrates (mainly Diptera larvae and oligochaetes); with some of the highest biomasses reported globally for beaches. These fauna are valuable prey to shorebirds, as demonstrated by a strong positive relationship (R2 = 0.82) between wader abundances and the percentage cover of wrack on beaches. Inshore, drifting macroalgae was associated with elevated abundances of detritivorous hyperbenthic fauna (mysids, isopods and gammarid amphipods). In addition, the volume of drifting macroalgae inshore was a significant predictor (along with physical beach characteristics) for the abundance of decapods and fish. Food web models and network analysis indicated that beaches which accumulate wrack had a greater diversity of trophic links and more functional redundancy, making their food webs more resilient to perturbations. Such perturbations may include stressors induced by climate change, such as increased erosion of sediments during storms, elevated atmospheric and sea surface temperatures and elevated CO2 concentrations. Model simulations of wrack harvesting predicted an immediate decline in primary consumers in direct proportion to the quantity of wrack removed, and a slow decline in shorebirds in response to reduced prey. Primary consumers were predicted to recover to their pre‐harvest biomasses within 1 to 2 years regardless of harvesting intensity, but recovery times for shorebirds were an order of magnitude longer, and increased with harvesting intensity. Harvesting more than 50% wrack predicted a ‘collapse’ in wader populations within 25 years, and recovery times of 45‐60 years were estimated if >70% wrack was removed. The findings of this thesis suggest wrack provides essential food and shelter to coastal fauna, and its large‐scale removal would have significant negative impacts to the ecosystem functioning.

The coastal waters off western Scotland are inhabited by two small under-studied common bottlenose dolphin (Tursiops truncatus) communities: the Inner Hebrides and the Sound of Barra (SoB) community. The region is considered for future developments for the marine renewables industry, which have the potential to negatively impact these communities; however the assessment of impacts and the development of plans to minimise these are currently hampered by a lack of knowledge about the dolphin's distribution and residency patterns, and spatial and temporal mobility. Using a variety of research methods (dedicated cetacean surveys and targeted photo-ID trips, acoustic monitoring and the collection of opportunistic photo-ID and sightings data from the general public) the current study examined local dolphin spatial and temporal mobility patterns by investigation of their spatial distribution and temporal occurrence. Collectively, the results revealed the presence of two socially and geographically separated (at least 2006-2013) resident communities which both demonstrated year-round presence and long-term site-fidelity, but maintained different ranging patterns. Long-term presence of individuals from the Inner Hebrides community dated back to 2001 and dolphins from this community ranged widely in nearshore waters throughout the entire currently known communal range, and practically used the entire range throughout the year. The SoB community, on the other hand, appeared to have a more restricted distribution, and appeared female-dominated. Summer censuses of the SoB community revealed annual estimates of ≤15 dolphins, with four individuals first identified in 1995, and at least eight calves born since 2005. Acoustic presence of dolphins in the SoB varied through the year, and in relation to the tidal and diel cycles. This study demonstrated that the integration of complementary methodological approaches is useful in investigating mobility patterns of low-density populations, and given the indications for social and spatial isolation, these communities should be managed independently.

This thesis considers the effect of disruptive waves and turbulence on a horizontal axis tidal stream turbine (TST), in terms of performance and survivability. The TST reaction to transient fluid flow is modelled analytically using Blade Element Momentum Theory (BEMT). Standard BEMT corrections are evaluated for the TST application and an alternative optimisation method is proposed for the steady state BEMT, improving compatibility with transient and depth dependent inflow, as well as the non-dimensionalisation constant needed to calculate the performance coefficients. Also, an alternative BEMT tip and hub loss implementation has led to a significant improvement of the turbine axial force prediction and in the high induction region. Validation studies are presented for BEMT coupled with regular, nonlinear wave theory and good agreement is found with published experimental data. A novel method to simulate irregular sea states is developed to couple with BEMT and a combined reactive coupling of waves and current is implemented. The TST performance in an irregular sea state is considered against turbine performance with real ADCP data and a good agreement is found. This work evaluates the BEMT implementation for the specific application of modelling TST's and significantly improves the fundamental theory, applicability and quality of results in this case.

Orientador: Jorge de Lucas Junior / Coorientador: David Ferreira Lopes / Banca: Mônica Sarolli Silva de Mendonça Costa / Banca: Maura Seiko Tsutsui Esperancini / Resumo: A tecnologia de biodigestão anaeróbia desperta interesse, por apresentar vantagens como a geração de energia elétrica, a redução da poluição dos recursos hídricos, do solo e do ar, com a produção de biogás e biofertilizante; produtos de elevado valor agregado à atividade agropecuária. Objetivou-se avaliar, tecnicamente e economicamente, o efeito da co-digestão de tubérculos de batata doce, com dejetos de bovinos leiteiros confinados, em relação aos potenciais de produção e qualidade do biogás e do biofertilizante, utilizando-se biodigestores de regime semicontínuo. O experimento foi dividido em duas etapas, ensaio de biodigestão anaeróbia e análise de viabilidade econômica. A primeira etapa teve duração de seis meses avaliando-se a inclusão de diferentes quantidades de batata doce (0%, 20%, 30%, 40%, 50%) em relação ao dejeto. Foram abastecidos 20 biodigestores sendo cinco tratamentos com quatro repetições. Para análise dos dados considerou-se um delineamento inteiramente casualizado, utilizando-se o programa Sigmaplot 12.0 com nível de significância de 5%. Na segunda etapa foram definidos os gastos e as receitas geradas com a implantação de biodigestores para cinco cenários estimados, cada qual, com 200 bovinos leiteiros, sendo os dejetos gerados por esses, co-digeridos com diferentes porcentagens de batata doce (0%, 20%, 30%, 40% e 50%). Por meio das técnicas do fluxo de caixa descontado, Valor Presente Líquido, Taxa Interna de Retorno, Payback descontado e Índice de lucrat... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Anaerobic biodigestion technology is of interest because it presents advantages such as the generation of electric energy, the reduction of pollution of water, soil, and air resources, with the production of biogas and biofertilizer; products of high added value to the livestock activity. The objective of this study was to evaluate, technically and economically, the effect of co-digestion of sweet potato root with confined dairy cattle's waste, in relation to the quantity and quality of the biogas and the quality of the biofertilizer, using biodigesters of semicontinuous regime. The experiment was divided into two stages, anaerobic biodigestion test and economic viability analysis. The first stage lasted six months, evaluating the inclusion of different percentage of sweet potatoes (0%, 20%, 30%, 40%, 50%) in relation to the waste. Twenty biodigesters were supplied of five treatments with four repetitions. For data analysis, a completely randomized design was used, using the Sigmaplot 12.0 program with a significance level of 5%. In the second stage, the outgoing and income generated with the implantation of biodigesters for five scenarios were estimated, each one with 200 dairy cattle, and the wastes generated by them, co-digested with different percentages of sweet potatoes (0%, 20 %, 30%, 40% and 50%). The economic data were analyzed.through the techniques of discounted cash flow, Net Present Value, Internal Rate of Return, Discounted Payback and Profitability Index. The addition of sweet potatoes to biodigesters with bovine milk manures increased linearly the production of biogas and methane as the proportions of sweet potatoes increased. The concentrations of methane were between 63% and 65.5%, characterizing the biogas obtained as good quality. The concentrations of nitrogen found in the biofertilizer increased in proportion to the increase of sweet potato, since the concentrations ... / Mestre

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2016. / Landfill gases, principally methane, CH4 are produced from the decomposition of the municipal solid wastes deposited on landfill sites. These gases can be captured and converted into usable energy or electricity which will assist in addressing energy needs of South Africa. Its capture also reduces the problems associated with greenhouse gases. The aim of this study is to estimate gases that can be produced from the Bellville landfill site in Cape Town. The landfill gas capacity was estimated using Intergovernmental Panel on Climate Change (IPCC) model. The IPCC model showed that 48 447m3/year of landfill gas capacity was determined only in 2013. The LFGTE process plant is designed in a manner of purifying landfill gas, which at the end methane gets up being the only gas combusted. As a matter of fact 14 544kg/year of gases which consists mainly methane gets combusted. The average energy that can be produced based on the generated landfill gas capacity (methane gas) is 1,004MWh/year. This translates to R1. 05million per year at Eskom’s current tariff of R2.86 /kWh) including sales from CO2 which is a by-product from the designed process plant. A LFGTE process plant has been developed from the gathered information on landfill gas capacity and the amount of energy that can be generated from the gas. In order, to start-up this project the total fixed capital costs of this project required amounted up to R2.5 million. On the other hand, the project made a profit amounted to R3.9million, the Net profit summed up to R1. 3million and the payback time of Landfill Gas ToEnergy (LFGTE) project is 4years.The break-even of the project is on second year of the plant’s operation. The maximum profit that this project can generate is around R1. 1million. The life span of the plant is nine years. Aspen plus indicated that about 87% of pure methane was separated from CO2 and H2S for combustion at theabsorption gas outletstream. I would suggest this project to be done because it is profitable when by-products such as CO2 sales add to the project’s revenues.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / Power fluctuations in a microgrid are caused by disturbances due to the connection and disconnection of Distributed Generators (DG’s), as well as the irregular input of the sun and wind renewable energy. Renewable penetration such as the sun, wind and tidal energy causes intermittency which directly affects the input and resultant output power of a microgrid. Control systems have to be implemented on three different levels to ensure the stability and reliability of the power supplied to the load. This can be achieved by implementing the following: 1) Primary control with mechanical valves and actuators to translate feedback signals through droop control. 2) Secondary control with power electronics to facilitate maximum power point tracking, phase lock loops and switch mode inverters to manipulate the electrical signals to a desired set points including PID control. 3) Tertiary control with software program management to monitor the power flow as well as to evaluate congregated logic and implement decision making. Energy storage systems like super capacitors can compensate for power imbalance by providing excess stored energy to the microgrid for short periods of time. The added advantage of capacitor banks is that it can facilitate power factor correction where inductive loads like rotating motors form large part of the total load. Battery banks can compensate for energy shortage for longer periods of time. The duration of the compensation can be determined by the size, topology and the type of batteries used. The objectives of this study is to improve the unstable power output responses of a renewable energy microgrid by designing and analysing control strategies intended at power wavering compensation which also includes energy storage. Sub control systems is created and simulated in Matlab/Simulink for analytical comparative observations. Results of the simulated model are discussed and recommendations are given for future works.

Orientador: Carlos Alberto Canesin / Banca: Guilherme Azevedo e Melo / Banca: Moacyr Aureliano Gomes de Brito / Resumo: Com a motivação existente pela necessidade de crescimento das novas fontes de energia alternativas, bem como pelos avanços das tecnologias para os sistemas de conversão de energia, o presente estudo propõe a utilização do conversor integrado três estados Buck-Boost monofásico para o aproveitamento da energia proveniente dos sistemas solares fotovoltaicos. Os sistemas de painéis fotovoltaicos fornecem tensões contínuas, contudo, a grande maioria de aparelhos ou cargas de uso domiciliar necessita de tensões alternadas, com valores eficazes nominais de 127 V ou 220 V, no Brasil. Isso leva à necessidade do estudo de estruturas conversoras CC-CA, conhecidas como inversores. Considerando que as tensões alternadas fornecidas pelos inversores encontram-se dependentes do valor máximo da tensão de entrada, é indispensável a inclusão de um estágio elevador no sistema geral, antes de fornecer energia para as cargas, resultando, assim, em uma redução no rendimento, devido à quantidade de componentes, ao aumento de peso e ao volume. Nesta dissertação, o inversor estudado realiza, em uma única estrutura, a função do estágio elevador ou redutor, garantindo níveis reduzidos de distorção harmônica na corrente injetada e tensão de saída no modo ilhado, com um bom rendimento, fornecendo energia para cargas conectadas em modo de operação ilhado ou conectado à rede. Neste conversor, o sistema de chaveamento de três estados proporciona uma melhora das características dinâmicas. A adição do terceiro estado simplifica o controle por modo tensão, na medida em que elimina o zero presente no semiplano direito da função de transferência do conversor Buck-Boost convencional. Para o desenvolvimento das estratégias de controle, adotou-se o modelo matemático por valores médios instantâneos, em espaço de estados. Adicionalmente, foi realizada uma revisão e avaliação de alguns dos algoritmos de MPPT (Maximum Power Point... / Abstract: The current motivation of growing need for new alternative energy sources, as well as by improvements in technologies for energy conversion systems, this study proposes the use of the single-phase tri-states Buck-Boost integrated converter for the use of energy from solar photovoltaic systems. Photovoltaic systems provide DC voltages and, on the other hand, the large majority of machines or domestic use loads require alternating voltage with RMS values of 127 V or 220 V in Brazil. This points out to the need to study of DC-AC converter structures, known as inverters. Due to the limitation that the alternating voltage supplied by the inverters are dependent on the maximum value of the input voltage, the inclusion of an elevator stage in the general system is necessary, before providing power to the load, thus resulting in a reduction in the performance by the number of components, increased weight and volume. In this dissertation, the studied inverter performs, in a single structure, the functions of the elevator stage or reducer stage, also performs the continues in alternating voltage conversion function, ensuring reduced levels of harmonic distortion in the current injected to the main grid and the output voltage in islanding mode, with an increase performance in the output voltage, and that should provide power to loads connected in both modes islanding or grid connected. In the presented converter, the switching system of three states has improved the behavior of dynamic characteristics due to the addition of the third estate, simplifying the control by eliminating the zero present in the right half-plane of the transfer function of Buck-Boost inverter, controlled in voltage mode. For the development of control strategies is adopted the mathematical model for instantaneous average values. The modeling of the structure is made by the mean values method in the state spaces. Additionally, is carried out a review and assessment of some ... / Mestre

A crescente demanda energética mundial é um dos principais problemas a ser enfrentado pela sociedade, uma vez que, a produção de energia elétrica na atualidade tem sua base em combustíveis fósseis, os quais possuem reservas não perenes e seus efeitos maléficos ao meio ambiente tem causado um impacto muito grande na natureza. Estes fatores têm incentivado a busca por alternativas para produção de energia elétrica a partir de fontes renováveis, principalmente em unidades de Geração Distribuída. A energia solar fotovoltaica se destaca neste contexto principalmente por sua flexibilidade quanto à potência e o ponto de conexão dos geradores, indo ao encontro do conceito de Geração Distribuída. Visando a expansão do emprego de geradores fotovoltaicos a redução do custo da energia gerada é fundamental, para tanto se deve conceber conversores eletrônicos capazes de adequar a energia CC produzida pelos geradores para que esta seja diretamente injetada na rede elétrica CA. No caso de geradores com um único módulo fotovoltaico, tem-se a oportunidade de extrair a máxima potência gerada pelo mesmo evitando-se problemas de sombreamento e dissimilaridades entre módulos, todavia o emprego de conversores eletrônicos com alto ganho de tensão com a maior eficiência possível é imprescindível. Nesta dissertação é proposta uma nova metodologia de integração de conversores estáticos, permitindo que novos conversores estáticos não isolados com alto ganho de tensão sejam derivados. Esta metodologia baseia-se no emprego de indutores acoplados que são compartilhados pelos conversores integrados e cujas seções e terminais são associados de modo que a topologia resultante possua um ganho de tensão que corresponde a soma dos ganhos individuais de cada conversor. Como exemplo e estudo de caso é analisada a integração dos conversores boost e flyback. São apresentados os modos de operação e as principais características dos conversores boost-flyback derivados neste trabalho, bem como uma metodologia de projeto para os circuitos e resultados experimentais. Os protótipos avaliados em laboratório mostram que os conversores boost-flyback derivados operando com ganho estático de dez vezes podem obter eficiência superior a 90% quando aplicados em um painel fotovoltaico de 200W. / World increasing demand for energy is one of the most challenging problems to be faced by societies in the near future. And it is getting worst because the fossil fuels retain the majority of the world energy share. Besides the risk of outage caused by the depletion of fossil fuel sources, their side effects on the environment have causing a huge impact on the environment. These issues have motivating the search for renewable sources of energy, mainly in distributed generation units. In the renewable resources scenario, the photovoltaic energy has a major role due to its advantages, such as its power flexibility and easy on site placement of generators, which is very favorable for Distributed Generators Systems. Aiming to ensure the worldwide applications of PV systems, it is required to lower the PV energy cost per watt, which can be achieved with more efficient power processing systems that are used to convert the DC power produced by the PV modules in AC power to be injected to the grid. In systems with a power converter per PV module the best performance of the module is achieved in terms of energy efficiency, avoiding shadowing and aging dissimilarity problems that may plague PV generators with a large amount of PV modules. However, to achieve such benefits, power converters with high efficiency and large conversion range are required. In this dissertation it is proposed a novel methodology to synthesize integrated non-isolated DC/DC power converters with wide conversion range. This methodology is based on the use of coupled inductors to integrate the input sections of two power converters, meanwhile their output sections are associated in either, series, parallel or cascade configuration, yielding in a conversion ratio that is the sum of the individual integrated converters. As a case study, the integrated boost-flyback topologies are analyzed. Their modes of operation, chief characteristics as well as design rules are discussed. The analyses are validated by means of experimental results obtained from three laboratory prototypes. The prototypes operate with conversion ratio greater than ten times and the efficiency achiever is higher than 90% when designed for a 200W PV module.

A crescente demanda energética mundial é um dos principais problemas a ser enfrentado pela sociedade, uma vez que, a produção de energia elétrica na atualidade tem sua base em combustíveis fósseis, os quais possuem reservas não perenes e seus efeitos maléficos ao meio ambiente tem causado um impacto muito grande na natureza. Estes fatores têm incentivado a busca por alternativas para produção de energia elétrica a partir de fontes renováveis, principalmente em unidades de Geração Distribuída. A energia solar fotovoltaica se destaca neste contexto principalmente por sua flexibilidade quanto à potência e o ponto de conexão dos geradores, indo ao encontro do conceito de Geração Distribuída. Visando a expansão do emprego de geradores fotovoltaicos a redução do custo da energia gerada é fundamental, para tanto se deve conceber conversores eletrônicos capazes de adequar a energia CC produzida pelos geradores para que esta seja diretamente injetada na rede elétrica CA. No caso de geradores com um único módulo fotovoltaico, tem-se a oportunidade de extrair a máxima potência gerada pelo mesmo evitando-se problemas de sombreamento e dissimilaridades entre módulos, todavia o emprego de conversores eletrônicos com alto ganho de tensão com a maior eficiência possível é imprescindível. Nesta dissertação é proposta uma nova metodologia de integração de conversores estáticos, permitindo que novos conversores estáticos não isolados com alto ganho de tensão sejam derivados. Esta metodologia baseia-se no emprego de indutores acoplados que são compartilhados pelos conversores integrados e cujas seções e terminais são associados de modo que a topologia resultante possua um ganho de tensão que corresponde a soma dos ganhos individuais de cada conversor. Como exemplo e estudo de caso é analisada a integração dos conversores boost e flyback. São apresentados os modos de operação e as principais características dos conversores boost-flyback derivados neste trabalho, bem como uma metodologia de projeto para os circuitos e resultados experimentais. Os protótipos avaliados em laboratório mostram que os conversores boost-flyback derivados operando com ganho estático de dez vezes podem obter eficiência superior a 90% quando aplicados em um painel fotovoltaico de 200W. / World increasing demand for energy is one of the most challenging problems to be faced by societies in the near future. And it is getting worst because the fossil fuels retain the majority of the world energy share. Besides the risk of outage caused by the depletion of fossil fuel sources, their side effects on the environment have causing a huge impact on the environment. These issues have motivating the search for renewable sources of energy, mainly in distributed generation units. In the renewable resources scenario, the photovoltaic energy has a major role due to its advantages, such as its power flexibility and easy on site placement of generators, which is very favorable for Distributed Generators Systems. Aiming to ensure the worldwide applications of PV systems, it is required to lower the PV energy cost per watt, which can be achieved with more efficient power processing systems that are used to convert the DC power produced by the PV modules in AC power to be injected to the grid. In systems with a power converter per PV module the best performance of the module is achieved in terms of energy efficiency, avoiding shadowing and aging dissimilarity problems that may plague PV generators with a large amount of PV modules. However, to achieve such benefits, power converters with high efficiency and large conversion range are required. In this dissertation it is proposed a novel methodology to synthesize integrated non-isolated DC/DC power converters with wide conversion range. This methodology is based on the use of coupled inductors to integrate the input sections of two power converters, meanwhile their output sections are associated in either, series, parallel or cascade configuration, yielding in a conversion ratio that is the sum of the individual integrated converters. As a case study, the integrated boost-flyback topologies are analyzed. Their modes of operation, chief characteristics as well as design rules are discussed. The analyses are validated by means of experimental results obtained from three laboratory prototypes. The prototypes operate with conversion ratio greater than ten times and the efficiency achiever is higher than 90% when designed for a 200W PV module.

The nominal power of single Wind Energy Conversion Systems has been steadily growing, reaching power ratings close to 10 MW. In the power conversion stage, medium-voltage power converters are replacing the conventional low-voltage back-to-back topology. Modular Multilevel Converters have appeared as a promising solution for Multi-MW WECSs due to their characteristics such as modularity, reliability and the capability to reach high nominal voltages. Thereby, this thesis discusses the application of the Modular Multilevel Matrix Converter to drive Multi-MW Wind Energy Conversion Systems (WECSs). The modelling and control systems required for this application are extensively analysed and discussed in this document. The proposed control strategies enable decoupled operation of the converter, providing maximum power point tracking capability at the generator-side, grid-code compliance and Low Voltage Ride Through Control at the grid-side and good steady-state and dynamic performance for balancing the capacitor voltages of the converter. The effectiveness of the proposed control strategies is validated through simulations and experimental results. Simulation results are obtained with a 10MW, 6.6 kV Modular Multilevel Matrix Converter based WECS model developed in PLECS software. Additionally, a 5 kVA downscale prototype has been designed and constructed during this Ph.D. The downscale prototype is composed of 27 H-Bridges power cells. The system is controlled using a Digital Signal Processor connected to three Field Programmable Gate Array which are equipped with 50 analogue-digital channels and 108 gate drive signals. Two programmable AMETEK power supplies emulate the electrical grid and the generator. The wind turbine dynamics is programmed in the generator-side power supply to emulate a generator operating in variable speed/voltage mode. The output port of the Modular Multilevel Matrix Converter is connected to another power source which can generate programmable grid sag-swell conditions. Simulation and experimental results for variable-speed operation, grid-code compliance, and capacitor voltage regulation have confirmed the successful operation of the Modular Multilevel Matrix Converter based WECSs. In all the experiments, the proposed control systems ensure proper capacitor voltage balancing, keeping the flying capacitor voltages bounded and with low ripple. Additionally, the performance of the generator-side and grid-side control system have been validated for Maximum Power Point Tracking and Low-Voltage Ride Through, respectively.