The absorption of the sun's radiation and its efficient conversion to useful work by a photovoltaic solar cell is of interest to the community at large. Scientists and engineers are particularly interested in approaches that exceed the Shockley-Queisser limit of photovoltaic solar-energy conversion. The abstract notion of increasing the efficiency of photovoltaic solar cells by constructing a three-transition solar cell via an absorber with intermediate levels is well-established. Until now, proposed approaches to realize the three-transition solar cell do not render the efficiency gains that are theorized; therefore, researchers are experimenting to ascertain where the faults lie. In my opinion, it is unclear if the abstract efficiency gains are obtainable. Furthermore, it is difficult to determine whether three-transition absorbers are even incorporated in the existing three-transition solar cell prototypes. I assert that there are material systems derived from the technologically important compound semiconductors and their ternary alloys that more clearly determine the suitability of employing nanostructured absorbers to realize a three-transition solar cell. The author reports on a nanostructured absorber composed of InAs quantum dots completely enveloped in a GaAsSb matrix that is grown by molecular beam epitaxy. The material system, InAs/GaAs$_{0.88}$Sb$_{0.12}$, is identified as an absorber for a three transition solar cell. This material system will more easily determine the suitability of employing nanostructured absorbers because its quantum-dot heterojunctions have negligible valence-band discontinuities, which abate the difficulty of interpreting optical experimental results. A key tool used to identify the GaAs$_{1-x}$Sb$_{x}$ ($xapprox 0.12$) is a maximum-power iso-efficiency contour plot. This contour plot is only obtainable by first having analyzed the impact of both finite intermediate-band width and spectral selectivity on the optimized detailed-balance conversion efficiencies of the three-transition solar cell. Obtaining the contour plot is facilitated by employing a rapid and precise method to calculate particle flux (Appendix~ ef{ch:Rapid-Precise}). The author largely determines the electronic structure of the InAs/GaAs$_{1-x}$Sb$_{x}$ ($xapprox 0.12$) absorber that is grown by molecular beam epitaxy from optical experimental methods and in particular, from photoluminescent spectroscopy. The interpretation of the experimental photoluminescent spectrum is facilitated by having first studied the theoretical photoluminescent spectra of idealized three-transition absorbers.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho trata do estudo de uma técnica de rastreamento de máxima potência (Maximum Power Point Tracking - MPPT) baseado no método de Otimização por Enxame de Partículas (Particle Swarm Optimization - PSO), o qual é aplicado a um sistema fotovoltaico (Photovoltaic -PV) conectado a uma rede elétrica monofásica. A curva característica corrente-tensão dos painéis/arranjos fotovoltaicos têm um comportamento não-linear, e quando estes são submetidos a condições de sombreamento parcial, pode-se ocorrer o surgimento de pontos distintos de máximos locais e global. A maioria das técnicas de MPPT tradicionais não é capaz de encontrar o ponto de máximo global para a extração da máxima potência fornecida pelo sistema PV. Por conseguinte, a fim de contornar este problema, neste trabalho o método de MPPTPSO proposto é utilizado para buscar a operação do sistema no ponto de máximo global, maximizando a extração de energia dos referidos arranjos PV. Simulações e ensaios experimentais com três topologias diferentes de conversores são apresentados para demonstrar a eficácia da proposta, quando esta é comparada com o método tradicional MPPT-PO conhecido como Perturbação e Observação Observe (P&O). / This paper consists of a study of a maximum power point tracking (MPPT) technique based on the Particle Swarm Optimization (PSO) method, which is applied to a single-phase grid-tied photovoltaic system. Since photovoltaic panels have nonlinear voltage-current characteristic curves, when they are submitted to partial shading conditions, it is possible to appear distinct local and global maximum power points. On the other hand, the most traditional MPPT methods are not able to find the maximum global point for extraction the maximum power provided by the PV array. Therefore, in order to overcome this problem, MPPT-PSO based method is used for obtaining the maximum global point, maximizing the power extraction in the photovoltaic arrangements. Numerical simulations and experimental results with three different topologies of converters are presented to demonstrate the effectiveness of the proposed MPPT-PSO technique, when it is compared with the well-known Perturb and Observe (P&O) MPPT-PO technique.

Orientador: Gilberto de Martino Jannuzzi / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-21T07:52:31Z (GMT). No. of bitstreams: 1 Lima_BrunoWilmerFontes_M.pdf: 4773788 bytes, checksum: 512d3e82e0e392f642f77b5b058267c2 (MD5) Previous issue date: 2012 / Resumo: O consumo de eletricidade no Brasil cresceu 47% na última década e estima-se que aumente outros 55,6% até 2020. A geração da maior parte da eletricidade no país é baseada no modelo de grandes usinas hidrelétricas, distantes dos centros de consumo, assim como a expansão da capacidade de geração para atender o aumento da demanda, mantendo as grandes perdas na transmissão e distribuição da eletricidade. Uma forma de reduzi-las é através do maior uso da geração distribuída, em que a eletricidade é gerada próxima ou no próprio local de consumo, como por exemplo, integrada a edificações. A partir da viabilização deste modelo de geração e dos edifícios eficientes, criou-se o conceito dos chamados Edifícios de Energia Zero (EEZ). EEZs são edifícios com baixas necessidades energéticas e que, ao longo do ano, geram toda a energia que consomem a partir de fontes renováveis de energia. Em 2010, as edificações foram responsáveis por 46,9% do consumo de eletricidade no Brasil e esta participação deve aumentar até o final da década. Dessa forma, um maior emprego da geração distribuída através de fontes renováveis em edificações e também de novos EEZs pode atender parte desta crescente demanda, e consequentemente, adiar ou evitar a construção de novas grandes hidrelétricas e termelétricas movidas a combustíveis fósseis, e reduzindo os impactos socioambientais causados pela sua construção e operação. Esta dissertação propõe uma metodologia para o projeto de sistemas de geração de energia elétrica em EEZs, visando auxiliar engenheiros e arquitetos no dimensionamento destes sistemas, permitindo uma maior adoção deste tipo de edificação. A metodologia consiste de alguns passos simples, que incluem a análise do consumo de energia do edifício e do potencial energético local, o dimensionamento e simulação do sistema de geração, concluindo com a avaliação dos resultados para averiguar se a energia gerada seria suficiente para classificar o edifício como EEZ. Adicionalmente, a metodologia propõe ferramentas para auxiliar na escolha de um sistema de geração, dentre diversas opções de arranjos e tecnologias, como o custo do sistema, da eletricidade produzida por ele e do tempo de retorno de energia. Esta metodologia foi aplicada em um laboratório de ensino, que será construído na Unicamp e tem como meta ter o menor impacto ambiental durante sua construção e operação além de ser um Edifício de Energia Zero. Foi avaliada a viabilidade e contribuição potencial da geração de eletricidade por fontes renováveis de energia no projeto deste laboratório, no caso energia solar fotovoltaica e pequenas turbinas eólicas, como forma de atender a meta EEZ. Também foram avaliados três sistemas fotovoltaicos, cotados com empresas especializadas durante o projeto do laboratório. Adicionalmente, buscando entender melhor a influência da tecnologia e do posicionamento dos sistemas fotovoltaicos na geração de eletricidade, foram realizadas simulações de sistemas com 1kWp, utilizando diferentes tecnologias e orientações. As simulações foram realizadas utilizando o software Homer Energy, de distribuição gratuita / Abstract: Electricity consumption in Brazil increased 47% in the last decade, and it is estimated that it will increase 55.6% until 2020. Most of the electricity generated in the country is based on large hydroelectric dams, located away from the major cities. The planned expansion of the generation park to meet this increase in the demand is also based on this model, leading to great transmission and distribution losses. One way to reduce these losses is through a greater use of distributed generation, where the electricity is generated near or at the point of consumption, e.g., integrated to buildings. With the viabilization of this model of electricity generation and of energy efficient buildings, the concept of Net Zero Energy Buildings (ZEB) was created. A ZEB is a building with low energy needs which, through the course of a year, generated all the energy which it consumes from renewable energy sources. In 2010, the building sector was responsible for 46.9% of all electricity consumption in Brazil, and this share will increase until the end of the decade. That way, a larger use of the distributed generation from renewable sources integrated to buildings and of new ZEB can meet part of this growing demand, and thus postpone or avoid the construction of new large hydroelectric dams and thermoelectric power plants running on fossil fuels, reducing the social and environmental impacts caused by its construction and operation. This dissertation proposes a methodology for the project of electricity generation systems in ZEBs, aiming to help engineers and architects in the dimensioning of these systems, allowing a greater adoption of this kind of building. The methodology consists of a few simple steps, which includes an analysis of the building energy consumption and of the local energy potential, sizing and simulation of the generation system and comparing the results in order to conclude if it is possible for the building to become a ZEB. Additionally, the methodology proposes tools to help choosing the better option among different systems sizes and technologies, including the cost of the system, of the electricity produced by it and the energy payback time. The methodology will be applied to a university's laboratory, which will be built at Unicamp, which aims to have the lowest environmental impact possible during its construction and operation and to be a Net Zero Energy Building. It was addressed the viability and potential contribution of electricity generation from renewable energy sources, solar photovoltaic and small wind turbines, in the laboratory's project as an strategy to reach the ZEB target. Three photovoltaic systems quoted from specialized companies during the project were also analyzed. Also, in order to address the influence of the technology and positioning of the photovoltaic systems on its performance, several simulations of systems with 1kWp were carried out, in different tilts and orientations, and using different technologies of photovoltaic modules. These simulations were performed using the Homer Energy software, which is free of charge / Mestrado / Planejamento de Sistemas Energeticos / Mestre em Planejamento de Sistemas Energéticos

Orientador: Luiz Carlos Pereira da Silva / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-22T01:49:18Z (GMT). No. of bitstreams: 1 Geraldi_Douglas_M.pdf: 3918130 bytes, checksum: a6b640b4707af6b9173674deab29eece (MD5) Previous issue date: 2013 / Resumo: Existe atualmente um consenso de que as Redes Inteligentes favoreçam a solução de diversos problemas presentes no dia a dia das concessionárias distribuidoras de energia elétrica, tais como a gestão inteligente do carregamento e o gerenciamento automático na recuperação do fornecimento de energia (self-healing). Por outro lado, a implantação de tecnologias de redes inteligentes também pode criar novas dificuldades para as distribuidoras. Especial atenção deve ser dada à facilidade do acesso ao sistema elétrico por parte da microgeração - quer seja solar, eólica, micro turbinas a gás, etc. - possibilitada pela substituição dos medidores atuais por medidores inteligentes e por legislação específica recentemente publicada pela ANEEL. Neste trabalho busca-se apontar e quantificar alguns impactos técnicos relacionados à injeção de potência em um circuito secundário de distribuição. Através do estudo de cenários com crescente nível de penetração de microgeradores fotovoltaicos residenciais (tetos solares) são analisados os impactos na curva de carga do prossumidor, no perfil de tensão da rede, nas perdas elétricas e no desequilíbrio de tensão. As simulações dos cenários supracitados são realizadas através do software livre Gridlab-D, desenvolvido pela Pacific Northwest National Laboratory (PNNL) para estudos de aspectos de redes inteligentes via simulação computacional. Uma das vantagens desse pacote é a integração com base de dados meteorológicos, permitindo, por exemplo, a estimativa da geração fotovoltaica mês a mês para um determinado ano constante na base de dados / Abstract: Nowadays, there is a consensus that the Smart Grid can promote the solution of various problems present in distribution utilities, such as intelligent load management and self-healing. How-ever, the deployment of smart grid technologies can also create new difficulties. Special attention should be given to the open access to the electrical grid from the micro-generation plants, such as solar photovoltaic, wind turbines and gas micro-turbines, which will be possible with the re-placement of the current meters for smart meters and by specific regulation recently published by ANEEL. This work intends to identify and quantify some technical impacts related to power injection from micro-generators in a secondary distribution circuit. Through the study of scenarios with increasing penetration of residential photovoltaic micro-generators (solar roofs) some impacts are analyzed: impacts on the load profile of the prosumer; impacts on the voltage profile of the network; impacts on the electrical losses and voltage imbalance. The simulations of the above scenarios are performed by using Gridlab-D, free software developed by Pacific Northwest National Laboratory (PNNL) to study aspects of smart grids via computer simulation. One ad-vantage of this package is the integration with meteorological database, enabling, for example, the estimation of photovoltaic generation every month for a given year contained in the database / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Semiconductor nanocrystals, or quantum dots, have attracted significant interest for use in solid state lighting, biological imaging, photovoltaics, catalysis, and displays such as televisions or tablets. Quantum dots excel in these applications because of their narrow emission profiles, high absorptivity at high energies, and optoelectronic properties that can be easily tuned using colloidal chemistry. The last point in particular has driven the development of new synthetic methods for producing a range of semiconducting materials on the nanoscale. Academically, interest in the synthesis of quantum dots has also extended to the mechanism of their formation and its implications for the growth of nanoscale crystals more generally. This thesis addresses facets of both points above, first by developing several novel syntheses for indium and gallium phosphide nanocrystals, and second by leveraging the synthetic control it allows to study the mechanisms of homogeneous crystal growth. Chapter 1 provides a brief overview of the colloidal syntheses, optoelectronic properties, and formation mechanisms of quantum dots. Emphasis is placed on the development of new chemical syntheses for nanoscale materials and how the size, size distribution, and morphology can be carefully controlled by thoughtful reaction design. The progression of quantum dot synthesis is presented and specific innovations to the precursor and surfactant design are highlighted. Next, a brief discussion about nanocrystal surface chemistry and its impact on the photophysical properties of the inorganic core is described along with its proposed influence on the kinetics of nanocrystal growth. Finally, classical theories of homogeneous crystal growth are presented and used to explain the origin of the exceptionally narrow size distributions accessible in a wide range of materials. Chapter 2 introduces two novel synthetic pathways to InP nanocrystals. The first describes a small library of substituted aminophosphines that can control the precursor conversion reactivity by over an order of magnitude. Leveraging the collection of aminophosphines, it is demonstrated that at sufficiently high temperatures, the rate of precursor conversion can be used to vary the final nanocrystal size—disputing previous findings for InP nanocrystals. We show that the reactivity of the phosphine is governed by a pre-equilibrium between the precursor and an intermediate (P(NHR)3) that goes on to form InP. Variations to the initial aminophosphine substitution pattern change the position of the pre-equilibrium, thereby allowing the rate of [InP]i deposition to be controlled. The second synthetic method leverages metal phosphonate salts as a surfactant to synthesize large samples of InP. We find that the nanocrystals grow via a ripening mechanism and display excellent crystallinity as determined by powder X-ray diffraction and pair distribution function analysis. Finally, we demonstrate that the final nanocrystals are bound by both phosphonates and phosphines through the use of 31P nuclear magnetic resonance spectroscopy. Chapter 3 expands on the syntheses of InP in the previous chapter by developing methods to form GaP, InxGa1-xP, and InP-based core-shell structures. At the onset, two distinct syntheses of GaP are introduced, one similar to the metal phosphonate route used to form InP, and one that used a mixture of amines to stabilize GaP colloidally. The phosphonate method results in small GaP with somewhat indistinct scattering patterns, while the amine method results in large GaP whose morphology can be varied depending on the solvent selected. Leveraging the newly developed InP and GaP syntheses we demonstrate that InxGa1-xP alloys could be directly synthesized from mixtures of In3+ and Ga3+ salts. We also show that InxGa1-xP can be accessed indirectly via cation exchange of Zn3P2 or Cd3P2, however attempts at synthesizing alloys via cation exchange with phosphonate bound GaP were found to be largely unsuccessful. Finally, the chapter contains initial attempts at synthesizing GaP/InP core-shells with the intention of producing GaP/InP/GaP spherical quantum well architectures. Preliminary data show that InP can be deposited using several different methods, though it remains unclear whether the optical properties will be suitable for integration in solid state lighting applications. Chapter 4 examines the crystal growth processes that precede the formation of monodisperse ensembles of InP, PbS, and PbSe nanocrystals. Surprisingly, we find that nucleation persists for a substantial portion of the total reaction time—a stark departure from the canonical “burst” of nucleation proposed originally by Victor LaMer. We go on to measure the nucleation period for a variety of different reaction conditions and find that the fraction of reaction time nucleation extends over is sensitive to both the material and reaction temperature. This is consistent with a mechanism where faster kinetics of monomer attachment reduce the duration of crystal nucleation—a conclusion that can be surmised by nucleation mass balance models that show a clear material and temperature dependence on the rate of nanocrystal growth. We also interrogate the claim that solute molecules accumulate prior to the formation of mature nanostructures. In situ X-ray experiments clearly corroborate the appearance of solute-like species at early reaction times that build up prior to the appearance of crystals with extended structure. Finally, we propose a novel size-focusing mechanism predicated on a size dependent growth rate. Using population mass balance modeling we show that the measurements of size and size distribution are qualitatively consistent with a growth rate inversely proportional to nanocrystal size.

The rapid growth of population and climate change has subjected our civil infrastructures to high load demands and fast aging or degradation over time. Temperature plays a key role in the performance of the aging infrastructure in form of thermal stress and cracking, temperature-induced material aging and degradation, temperature-dependent deformation, and softening. Thus, the importance of predicting the consequent behavior of the infrastructures under environmental conditions becomes imperative. This research characterizes three infrastructure surface materials, namely asphalt pavement, solar panels, and phase change materials (PCM), models the efficacy of modifiers and novel methods to improve their performance and uses these materials in the design and testing of thermal management systems for different applications. The connection between these materials is the thermal management in pavement overlays, which can be extended to other infrastructure surfaces. Asphalt pavement modified with recycled crumb rubber (CR) is a sustainable way to reuse the millions of tires that used to end in landfills. However, the ultraviolet (UV) rays from the sun have been shown to adversely affect the asphalt’s performance in the long run. The severe photo-oxidation can cause changes in the volatile components of the asphalt and result in hardening, aging, and thermal cracks in it. The effect of UV rays on the rubber-modified asphalt may be even more complex due to the presence of crumb rubber particles and their chemical/physical incompatibility and changes in the glass transition. In order to examine these effects, a PG 64-22 is modified with two percentages of 16.6 wt.% and 20.0 wt.% crumb rubber. Results show the specific heat capacities increase with UV aging with 16.6% having the highest value. The addition of the rubber particles does not change the chemical composition of the binder as confirmed by the elemental analysis. However, after UV exposure, peaks associated with carbonyl and sulfoxide are observed, proving that the rubber-modified binder is subject to photo-oxidation as well. The 16.6. wt.% shows the best performance against aging with the lowest sulfoxide index and the highest aliphatic index. Another advantage of adding crumb rubber particles is the formation of a matrix due to the crosslinking of the rubber particles with the binder after being heated, as approved by microscopic images. The carbon nanotubes (CNT) are used to modify the asphalt binder to improve its rheological characteristics while also enhancing the thermal conductivity of the mixture to facilitate the transfer of heat to the surface. In this study, two samples of 3% and 6% multi walled carbon nanotubes (MWCNTs) are prepared using a foaming technology. Foaming the asphalt via water lowers its viscosity and temperature resulting in the saving of the base material and consumed energy while increasing the coating of the aggregates. The results show the CNTs can improve the thermal conductivity of the foamed binder by almost 2X while not negatively affect its rheology. For the other end of the thermal management system, a new hydronic system is introduced for the building integrated photovoltaics and thermal (BIPVT) silicon module that acts for the dual objectives of collecting heat to be used for the thermal management of the pavement and controlling the surface temperature of the solar module itself for the optimal efficiency under different operating conditions. The BIPVT panel with different flow rates of 100 to 600 ml/min were tested for the effectiveness of the cooling design. The results from experiments and simulations show that at 200 ml/min, an optimal balance for the performance of the panel is achieved to not only reduce the temperature of the panel from 88°C to 65°C, but also generate a partially heated water outlet of 37°C (compared with the 23°C inlet) that can be used for the hot water system of the building, or as the inlet feed to the hydronic cooling/heating pavement system. In addition, the BIPVT design proves to restore the power of the solar module by 24.6% at a 200 ml/min flow rate, as confirmed from the I-V curves. Finally, the feasibility study of converting the waste animal fat to a phase change material (PCM) is explored. In PCMs, the high latent heat characteristics are used to store or release energy during the phase change. The use of PCMs can significantly lower the temperature variation of buildings and the consequent energy use. While most common PCMs are paraffin-based and too expensive for large scale applications, a bio-based and more economic alternative could be the key to its vast use in infrastructure systems. However, more research is needed to achieve an animal fat PCM with high latent heat values. In this study, characterizing the raw fat shows a ~20% saturated content. After hydrolysis, the saturated portion has been increased to 65%, but the improvement in the latent is not significant. However, after separation of the fatty acids by use of crystallization, the resulting fully saturated fatty acids (palmitic and stearic acids) show a 3.5X increase in the value of the latent heat, increasing it from ~55 J/g for free fatty acids to ~195 J/g for saturated fatty acids. The promising results of the high latent heat values make the current bio-based PCM a good alternative that needs to be further explored in the future to be used for applications in buildings and BIPVT panels. Overall, the results of this PhD study provide a comprehensive understanding of materials and systems for thermal management of asphalt pavements and enable the design and development of durable self-heated pavements, which can be immediately extended to other infrastructure applications such as wall panels, net-zero buildings, and solar panels.

M.Tech (Department of Electronic Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / Due to the fickle nature of weather upon which renewable energy sources mostly depend, a shift towards a sustainable renewable energy system should be accompanied with a good intermediate energy storage system, such as a battery bank, set up to store the excess supply from renewable sources during their peak periods. The stored energy can later be utilised to supply a regulated and steady power supply for use during the off-peak periods of these renewable energy sources. Battery banks, however, are often faced with the challenge of charge imbalance due to the disparities that occur in the operating characteristics of the batteries that constitute a bank. When a battery bank with charge imbalance is repeatedly used in applications without an effective battery management system (BMS) through active charge equalisation, there could be an early degradation, loss of efficiency and reduction of service life of the entire batteries in the bank. In this research, a universal battery management system (BMS) in stand-alone photovoltaic application was proposed and designed. The BMS consists majorly of a switched capacitor (SC) active charge equaliser, designed with a unique configuration of high capacitance and relatively low switching frequency, which can be applicable to common battery types used in stand-alone photovoltaic application. The circuit was mathematically optimised to minimise losses attributed to impulsive charging and tested with lead acid, silver calcium, lead calcium and lithium ion batteries being commonly used in stand-alone photovoltaic application. The SC design was verified by comparing its simulation results to the digital oscilloscope results, and with both results showing similar values and graphs, the design configuration was validated. The design introduced a simple control strategy and less complicated circuit configuration process, which can allow an easy setup for local usage. The benefit of its multiple usage with different stand-alone photovoltaic battery types saves the cost of purchasing a different charger and balancer for different battery types. More so, the design is solar energy dependent. This could provide an additional benefit for usage in areas where energy dependence is off-grid.

Freshwater scarcity is a dire problem for exposed human societies and natural ecosystems—a problem expected to grow worse with anticipated climate change. Reverse osmosis (RO) desalination is currently the most energy-efficient and ubiquitous desalination process used for freshwater production in water-scarce regions. The synergy of high solar radiation and significantly reduced costs in photovoltaics (PV) creates the opportunity for PV to become a dominant and sustainable solution for powering the energy-intensive process of desalination and reducing greenhouse gas emissions.While photovoltaic-powered reverse osmosis (PVRO) is a promising technological solution, several significant challenges must be further addressed to sustain high RO performance. First, the inherently intermittent nature of solar energy generation can adversely affect the freshwater conversion process and thereby decrease water recovery and quality. Furthermore, global desalination capacity is dominated by large-scale plants, whereas PVRO systems are currently limited to small-scale systems. Thus, to truly integrate renewable energy with desalination systems in an impactful way, there is a need to explore pathways for modifying the RO process to enable flexible operation on a large-scale, in response to power variability. Furthermore, the techno-economic feasibility of flexible, renewable-powered RO processes and the potential benefits that could be provided to variable renewable energy (VRE) plants and the electric grid warrants investigation. Brine minimization is another major challenge for sustainable desalination. Brine management is especially an issue for inland desalination plants. Novel approaches that are less costly and less energy intensive are needed to facilitate minimal and zero liquid discharge. To enable high-salinity desalination, several variations of osmotically assisted RO, which each surpass the pressure limitation of conventional RO, have been proposed in the literature but require further assessment. The promise of these enhanced RO approaches entails a reduction in energy consumption when compared with thermal desalination methods. The primary deliverables and novel contributions of this thesis include the development of (i) design, simulation, and cost optimization models for variable-powered, variable-salinity RO systems, (ii) module-scale, cost-optimization models for enhanced RO technologies that reduce transmembrane osmotic pressure to enable high-salinity desalination and brine minimization, (iii) examining the effects of cyclic reverse osmosis on inorganic scaling mitigation, and (iv) quantifying the availability of unconventional, alternative water sources to alleviate local water scarcity in the contiguous US. First, the techno-economic feasibility of PV-powered RO desalination plants in the Gulf region was assessed using Hybrid Optimization Model for Electric Renewables (HOMER) and Desalination Economic Evaluation Program (DEEP) to model both the power system and desalination system, respectively. Subsequently, an hourly simulation model for desalination was developed to replace the use of DEEP in the workflow. Grid-connected and off-grid cases with combinations of PV, batteries, and diesel generators were evaluated primarily by the levelized cost of electricity (LCOE) and levelized cost of water (LCOW). The shortcoming of conventional and PV-powered RO is that variable power compromises cumulative water production, which in turn increases water costs. Thus, we proposed the concept of active-salinity-control reverse osmosis (ASCRO) which enables control of the transmembrane osmotic pressure and water production in response to variable power. The ASCRO system dynamically controls energy consumption by operating across a range of feed salinity, allowing it to shift over a wide range of pump feed flows and pressures. To accomplish this, ASCRO utilizes feedwater from both low- and high-salinity sources. Enabling a dynamic power consumption profile can enhance demand-response capabilities, compensating for stressors on the grid. Moreover, ASCRO can improve the integration of renewable energy (RE) by responding to power fluctuations without compromising permeate production. This system can include on-site RE and energy storage to power the ASCRO plant and provide services to the grid. We considered the following grid-connected scenarios: 1) ASCRO, 2) ASCRO and battery storage, 3) ASCRO and photovoltaics (PV), and 4) ASCRO, battery storage, and PV. The LCOW was minimized by providing load-shifting and regulation capacity services in the California Independent System Operator (CAISO) market. We quantified that the ASCRO plant can ramp from minimum to maximum load within 84 seconds, which is adequate for participation in fast-timescale markets. The LCOW for these scenarios ranged from 49 – 59 cents/m³. We also present sensitivity analyses showing the effects of capital cost, CAISO market prices, and PV size on LCOW. To investigate alternative pathways to minimal and zero liquid discharge, low-salt rejection reverse osmosis (LSRRO), cascading osmotically mediated reverse osmosis (COMRO), and osmotically assisted reverse osmosis (OARO) were comparatively assessed via module-scale, cost optimization models to gain an accurate perspective of the performance differences between each of these configurations. We quantified the optimal LCOW of each technology for the case of desalinating feedwater at 70 g/L at 75% recovery, which would result in a brine concentration near 250 g/L, a level that allows further treatment with crystallizers. For baseline scenarios, LCOW results for OARO, COMRO, and LSRRO were 5.14, 7.90, and 6.63 $/m³ of product water, respectively, while the corresponding specific energy consumption (SEC) values were 10.31, 12.77, and 28.90 kWh/m³. A sensitivity analysis is also presented. Additionally, we sought to examine the possibility of whether adaptive RO operation could provide the added benefit of fouling mitigation. Using the Pitzer model, nucleation theory, and dissolution kinetics to guide a set of bench-scale fouling experiments, CaSO₄-NaCl solution, supersaturated with respect to gypsum, was fed through a membrane test cell to determine nucleation induction times, rates of flux decline, and scale reversal. Lastly, a geospatial analysis was conducted to estimate volumes of water deficits and potential alternative water sources for the contiguous US. Namely, wastewater effluent, brackish groundwater, agricultural drainage water, and produced water were considered in this analysis as alternatives for alleviating water scarcity. We formulated a conservative estimate of groundwater availability based on environmental flow limits. Additionally, agricultural drainage volumes were estimated based on USGS water use data. Overall, the results showed that water deficits amounted to an equivalent daily capacity of 149 million m³/day—nearly 50% more than the desalination capacity of the world in 2020. Furthermore, the total availability of alternative water sources was estimated to be between 192 – 240 million m³/day, but most of this volume was not in the same location as deficits. Thus, 58 – 65% of national water deficits would have to be alleviated via long-range transport. Additionally, the potential for integrating desalination and water reuse by interconnecting existing RO plants with wastewater treatments plants was also assessed.

Thesis. (M. Tech. (Dept. Electronic Engineering, Faculty of Engineering and Technology))--Vaal University of Technology, 2011. / There are a number of ways to produce hydrogen using solar energy as the primary source. Water electrolysis, which uses solar electrical energy, is the rapidly available process. Hydrogen can be produced by using solar electric energy from photovoltaic (PV) modules for the electrolysis of water without emitting carbon dioxide or requiring fossil fuels. Solar hydrogen energy systems are considered one of the cleanest hydrogen production technologies, where the hydrogen is obtained from sunlight by directly connecting the photovoltaic modules to the hydrogen generator. This dissertation presents a designed solar photovoltaic electrolyser hydrogen production and storage system for various applications such as in the power generation and telecommunications industries. Various experiments were performed on the designed system to ensure its reliability and conformity with theoretical findings. The purity of the generated hydrogen was determined. The relationship between the amount of solar irradiance reaching the surface of the PV panel, the PV panel surface temperature, the PV panel tilt angle and the maximum power point voltage and current of the PV panel array were also considered. The effect of dust on the panel voltage and current outputs was also determined. Finally, the factors to consider when designing a solar photovoltaic electrolyser hydrogen system (based on this study) were enumerated.

M. Tech. (Engineering, Electrical, Department Electronic Engineering, Faculty of Engineering and Technology), Vaal University of Technology / In order to facilitate sustainable development, it is necessary to further improve and increase the energy efficiency and use of renewable energy and its related technologies. The main limiting factors to the extensive use of photovoltaic (PV) modules include the high initial investment cost and the relatively low conversion efficiency. However, other factors, such as an increase in ambient temperature, exert a considerable negative influence on PV modules, with cell efficiencies decreasing as the cell’s operating temperature increases. Higher PV module surface temperatures mean lower output voltages and subsequent lower output power. Therefore, this dissertation focuses on optimizing the available output power from a PV module by investigating and controlling the effect that the PV module’s surface temperature exerts on the amount of electrical energy produced. A pilot study was conducted by using a PV module set to three different tilt angles with an orientation angle and temperature sensors placed at different points. This was done to determine temperature distribution on the PV module surfaces as well as identify which tilt angle produces the highest PV module surface temperature. The main study was designed to investigate the electrical performance of a PV module with different cooling systems (water and forced air) as against a referenced measurement (no cooling). The cooling systems will be switched on and off at specific time intervals with the help of an electronic timer circuit incorporating a PIC microcontroller. The pilot study was conducted for a 50 week period where the results indicated a direct correlation between temperature rise and voltage decrease. The PV module’s temperature is highest at a tilt angle of 16° during the day and lowest at night time. It further reveals that the PV module’s front and back surface temperature can be distinctly different, with the highest recorded values occurring at the back of the PV module. The main study was conducted for a period of 15 weeks with results indicating that the water cooling system resulted in an average higher output power of 49.6% when compared to the reference system (no cooling system). Recommendations are made that sufficient space should be included between the module frames and mounting structure to reduce high operating temperatures owing to poor air circulation.