Spectrum-splitting is a multijunction photovoltaic technology that can effectively improve the conversion efficiency and reduce the cost of photovoltaic systems. Microscale PV design integrates a group of microconcentrating photovoltaic (CPV) systems into an array. It retains the benefits of CPV and obtains other benefits such as a compact form, improved heat rejection capacity, and more versatile PV cell interconnect configurations. We describe the design and performance of a two-junction holographic spectrum-splitting micro-CPV system that uses GaAs wide bandgap and silicon narrow bandgap PV cells. The performance of the system is simulated with a nonsequential raytracing model and compared to the performance of the highest efficiency PV cell used in the micro-CPVarray. The results show that the proposed system reaches the conversion efficiency of 31.98% with a quantum concentration ratio of 14.41x on the GaAs cell and 0.75x on the silicon cell when illuminated with the direct AM1.5 spectrum. This system obtains an improvement over the best bandgap PV cell of 20.05%, and has an acceptance angle of +/- 6 deg allowing for tolerant tracking. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

A methodology for the simulation of CPV systems is presented in four distinct sections: input, optics, uncertainty and electrical output. In the input section, existing methods of describing the solar irradiation that is incident at the primary optical element of a CPV system are discussed, the inadequacies of the existing methods are explored and conditions of validity for their use drawn. An improved and spectrally extended model for a variable, spatially resolved solar image is arrived at. The model is used to analyse losses at the primary concentration device stage under varying solar profiles and air masses. A contextual analysis of an example Seattle based CPV system operating with constant solar tracking errors of 0.3-0.4° show a corresponding loss in isolation available to the optical system of 5-20%, respectively. In the optics section, an optical ray trace model is developed specifically for this work. The optical ray trace model is capable of the spectrally resolved ray tracing of all insolation input models discussed above. Plano-convex and Fresnel lenses are designed, investigated and compared using each of the insolation models described in the input section. Common CPV component material samples for the plano-convex and Fresnel lenses are analysed for their spectrally resolved optical properties. The computational expense of high resolution spatial and spectral modelling is addressed by means of a spectrally weighted banding method. The optical properties parameter spectral weighting method can be applied to any arbitrary spectral band. The bands used herein correspond to the active ranges of a typical triple-junction solar cell. Each band shows a different spectral dependency. Banded beam irradiation proportions are shown to change by as much as 10% in absolute terms within the air mass range of 1 to 3. Significant variations in spectrally banded illumination profiles are found with the extended light source insolation model. These banded variations are mostly unaccounted for with the use of approximated insolation models, further compounding the argument for extended light source Sun models in CPV system simulations. In the uncertainty section, the limitations of the manufacturing process are explored. Manufacturing tolerance errors from manufacturer datasheets are presented. These production uncertainties are used in the design of an erroneous plano-convex lens which is then analysed with the optical modelled presented in the optics section and compared to the ideal design specification. A 15% variation in maximum intensity value is found alongside a linear shift in the focal crossover point of approximately 0.2mm, although the optical efficiency of the lens remains the same. Framing manufacture errors are investigated for a square Fresnel lens system resulting in a linear shift of the focal centre of approximately 0.85mm. A process for the calculation of wind loading force on a CPV array is also presented. The process uses real 2 second resolution wind data and highlights the chaotic nature of loading force. A maximum force of 1.4kN was found on an example day for a 3m by 3m by 0.1m cuboid (i.e. CPV array); corresponding to a wind speed of approximately 13m/s, which is well within the typical operating range of a CPV tracking system. In the electrical output section, a spatially resolved solar cell model is identified and used for the investigation of solar cell performance under the inhomogeneous cell illumination profiles produced in the uncertainty section. Significant differences in the maximum power point of the cell IVs are found for the ideal and erroneous system illumination profiles. Approximately, a 15% variation is found in the plano-convex lens example, with a relative difference of 4% attributable to illumination profile distortion, and a 6% variation in the module framing component example. These results further highlight the need for the consideration of production uncertainties in CPV system simulation.

Uma simulação numérica do ciclo de refrigeração a adsorção é realizada para os pares zeólita-água e carvão ativo AC-35 metanol, justificando a escolha do par bem como do sistema de captação a serem utilizados no protótipo. O protótipo construído compreende um concentrador cilíndrico-parabólico com rastreamento solar, um tubo de calor e uma unidade frigorífica (com zeólita-água). Aspectos tecnológicos como válvulas, soldas e carregamento do par na máquina são analisados. Os resultados dos testes de desempenho são apresentados, discutidos e comparados com a literatura. Uma análise de custos é feita. Paralelamente, construímos termo pilhas pelo método da evaporação. Estas termopilhas foram utilizadas na construção do piranômetro e do pireliômetro. Os instrumentos são caracterizados em termos de sensibilidade, constante de tempo, linearidade, efeitos de temperatura e convecção natural. Os resultados desta caracterização são discutidos e comparados com um modelo fabricado pela Eppley. Finalmente, no apêndice I, testamos o desempenho de um coletor plano utilizando no absorvedor o revestimento seletivo de óxido de alumínio recentemente desenvolvido no IFQSC. As melhores condições para obtenção do revestimento seletivo em placas de grande porte são estudadas. / A numerical simulation of the adsorption refrigeration cycle was made for zeolite/water and activated carbon(AC-35)/ methanol pairs, to select the pair and the solar collector in the prototype. The fabricated prototype consists of a cylindrical paraolic concentrator with solar trackins, a heat pipe and the refrigeration unit (with the zeolite/water pair). The technical aspects of values, welds and out-gassing are analyzed. The results of the performance tests are presented, discussed and compared with the literature. An analysis of costs is made. In parallel thermopiles were constructed using the evaporation method. These thermopiles were used in the construction of the piranometer and the pirheliometer. The instruments were characterized in terms of: sensitivity, stability with time, linearity, effects of temperature and natural convenction. The results of this characterization are discussed and compared with a model made by Eppley. Finally, in Apendix I, we tested the performance of a flat plate collector using a selective coating of aluminium oxide (developed in IFQSC) as absorber. The Best conditions for obtaining the seletive coating on big size plates are discussed.

Este trabalho dimensionou um receptor de cavidade para uso como reator químico de um ciclo de conversão de energia solar para energia química. O vetor energético proposto é o hidrogênio. Isso implica que a energia solar é concentrada em um dispositivo que absorve a radiação térmica e a transforma em energia térmica para ativar uma reação química endotérmica. Essa reação transforma o calor útil em gás hidrogênio, que por sua vez pode ser utilizado posteriormente para geração de outras formas de energia. O primeiro passo foi levantar os pares metal/óxido estudados na literatura, cuja finalidade é ativar um ciclo termoquímico que possibilite produção de hidrogênio. Esses pares foram comparados com base em quatro parâmetros, cuja importância determina o dimensionamento de um receptor de cavidade. São eles: temperatura da reação; estado físico de reagentes e produtos; desgaste do material em ciclos; taxa de reação de hidrólise e outros aspectos. O par escolhido com a melhor avaliação no conjunto dos parâmetros foi o tungstênio e o trióxido de tungstênio (W/WO3). Com base na literatura, foi determinado um reator padrão, cujas características foram analisadas e suas consequências no funcionamento do receptor de cavidade. Com essa análise, determinaram-se os principais parâmetros de projeto, ou seja, a abertura da cavidade, a transmissividade da janela, e as dimensões da cavidade. Com base nos resultados anteriores, estabeleceu-se um modelo de dimensionamento do sistema de conversão de energia solar em energia útil para um processo químico. Ao se analisar um perfil de concentração de energia solar, calculou-se as eficiências de absorção e de perdas do receptor, em função da área de abertura de um campo de coleta de energia solar e da radiação solar disponível. Esse método pode ser empregado em conjunto com metodologias consagradas e dados de previsão de disponibilidade solar para estudos de concentradores de sistemas de produção de hidrogênio a partir de ciclos termoquímicos. / This work aimed to design a cavity receptor for purpose of chemical reactor for cycles of energy conversion of solar energy to chemical energy. The proposed chemical agent is hydrogen gas. Solar energy is concentrated in a device that absorbs thermal radiation, transforming it in thermal energy, used to activate chemical reactions. This reaction transforms the heat in hydrogen gas and the last, in its turn, can be used to generate other forms of energy. The first step oh this work was an assessment of metal/oxides pairs studied in literature, which can be used to activate thermochemical cycles for hydrogen production. These pairs were compared based in four parameters, important to cavity receptor design: reaction temperature, physical state of the reactants and products, material resistance to several cycles; hydrolysis reaction rate and other aspects. The chosen pair, rated as the higher average in all parameters, was the pair tungsten and tungsten trioxide. (W/WO3). Based in the literature, it was determined a standard reactor, which was studied regarding cavity reactor performance. By such analysis, it was possible to determine the main design parameters, therefore, cavity aperture, window transmissivity, and the cavity geometric dimensions. The results allowed to establish a mathematical model in which solar energy can be converted in useful energy for chemical processes, inside a cavity receptor. Given a profile of solar energy concentration, it was calculated absorption and energy lost efficiencies, related to a solar concentration field and radiation available. This method can be used in tandem with available methodologies and data of solar predictions for hydrogen production by concentration systems via thermochemical cycles.

No description available.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Thesis. 1979. M.Arch.A.S.--Massachusetts Institute of Technology. Dept. of Architecture. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH. / Includes bibliographical references. / by Stephen Hale. / M.Arch.A.S.

As the cost of solar energy continues to drop, the major hurdle limiting the widespread use of intermittent renewable solar energy is the lack of efficient and cost-effective energy storage. Electrochemical technologies, such as electrolyzers, photoelectrochemical cells, and fuel cells, have the potential to compensate for solar energy intermittency on a large scale, by converting excess solar energy into storable solar fuels, such as hydrogen (H2), which can be converted back to electrical energy at a later time. However, improvements in the efficiency and lifetime of these technologies, in particular the electrocatalysts, are necessary for their commercialization. During operation, efficiency losses result from energetic penalties (overpotentials) associated with several processes occurring at or near the electrocatalyst/electrolyte (ohmic resistance, kinetic barriers, and mass transport limitations). These losses can be further exacerbated due to electrocatalyst durability issues such as dissolution, agglomeration, detachment, and poisoning. A major challenge in electrocatalysis field is developing methods to mitigate these losses without adversely affecting the electrocatalytic stability, selectivity, and/or activity. One promising solution is an oxide-encapsulated electrocatalyst architecture, which has been shown to improve electrocatalyst durability and provide mechanisms for controlling reaction pathways. Previous studies on oxide-encapsulated electrocatalysts, in which metal catalysts are fully or partially covered by ultrathin layers of permeable oxide films, have mostly focused on supported nanoparticles because of their high electrochemically active surface area per catalyst loading. However, these nanoparticle-based architectures tend to have poorly defined and/or non-uniform structures which make it difficult to understand and elucidate structure-property-relationships. This dissertation investigates well-defined oxide-coated electrocatalysts, which serve as model platforms for gaining a fundamental understanding of kinetic and transport phenomena that underlie their operation. This dissertation presents three studies which highlight the versatile functionalities of oxide-encapsulated electrocatalysts to improve the electrocatalyst stability, selectivity, and activity in different electrochemical systems. This dissertation demonstrates the ability of room temperature synthesized silicon oxide (SiOx)-encapsulated Pt electrocatalysts to: i) stabilize nanoparticles and improve electron transfer, ii) mitigate catalyst poisoning and control reaction pathways through selective transport, and iii) alter reaction energetics associated with catalysis at the buried interface. First, this dissertation establishes the ability of room temperature synthesized SiOx coatings to stabilize nanoparticle electrocatalysts by mitigating electrocatalyst migration, coalescence, and detachment on metal-insulator-semiconductor (MIS) photoelectrodes for solar-driven water splitting. Metallic Pt nanoparticles are inherently unstable on the insulating support due to poor physical adhesion and electronic coupling between Pt and SiO2. To overcome this issue, a room temperature UV ozone synthesis process was used to deposit 2-10 nm thick SiOx overlayers on top of electrodeposited Pt nanoparticles to stabilize Pt on the electrode surface. The photoelectrodes containing oxide-encapsulated electrocatalysts exhibit superior durability and electron transfer (ohmic) properties compared to the photoelectrode that lacked the SiOx encapsulation. While this study demonstrates that the oxide-encapsulated electrocatalyst architecture improves the stability of electrocatalytic nanoparticles deposited on insulating materials, it does not elucidate how reactants and products transport through the SiOx barrier to reach the Pt surface. In order to gain a better understanding of kinetic and transport phenomena that govern performance of oxide-encapsulated electrocatalysts, the following studies investigate model electrodes consisting of continuous SiOx overlayers of uniform thickness deposited onto smooth Pt thin films. This planar electrode geometry allows for simple and unambiguous characterization of structure-property relationships. The next study systematically evaluates the influence of SiOx thickness on the HER performance to understand species transport through SiOx. Through detailed characterization and electroanalytical tests, it is shown that proton and H2 transport occur primarily through the SiOx coating such that the HER occurs at the buried Pt|SiOx interface. Importantly, the SiOx nanomembranes were found to exhibit high selectivity for proton and H2 transport compared to Cu2+, a model HER poison. Leveraging this property, it is shown that SiOx–encapsulation can enable poison-resistant operation of Pt HER electrocatalysts. This oxide-encapsulated architecture offers a promising approach to enhancing electrocatalyst stability while incorporating advanced catalytic functionalities such as poison resistance or tunable reaction selectivity. The final study demonstrates ability of SiOx overlayers to alter reaction energetics associated with catalysis at the buried interface. Carbon monoxide (CO), methanol, and ethanol oxidation reactions are studied for their relevance in direct alcohol fuel cell applications. Oxide-supported catalysts have been shown to enhance alcohol oxidation by promoting CO oxidation at metal/oxide interfacial regions through the so-called bifunctional mechanism, in which hydroxyls on the oxide facilitate the removal of adsorbed CO−intermediates from active sites. A key advantage of the oxide-encapsulated electrocatalyst design compared to oxide–supported nanoparticles is that the former maximizes the density of metal/oxide interfacial sites. This study shows that the SiOx overlayer provides proximal hydroxyls, in the form of silanol groups, which can enhance CO and alcohol oxidation through unique interactions at the buried Pt|SiOx interface. Overall, this dissertation highlights the potential of using oxide-encapsulated electrocatalysts for stable, selective, and efficient electrochemical production and use of solar fuels.

No description available.

The thesis addresses the research question of how and why ‘prosuming' solar electricity evolves over time among social housing tenants with prepayment electricity meters. Prosuming is defined here as deliberately and simultaneously producing and consuming electricity. Using a Social Practice Theory framework, but also drawing on Time Geography, the thesis analyses prosuming as a ‘project'. This sees practitioners actively mobilising elements (meanings, skills and materials), as well as orchestrating everyday practices (i.e. laundering) and projects (i.e. 'Feeding-the-Meter') to the fulfilment of the 'Prosuming Project'. The overarching research question is ‘How and why does prosuming evolve for social housing tenants?' It is broken down into four subsidiary questions that firstly explore the period before solar panels, and then the three stages of the conceptual framework – adopting, establishing and committing to the Prosuming Project. The first question addresses how householders use electricity prior to the installation of solar panels and the role of two dominant, institutional projects: 'Feeding-the-Meter' and 'Maintaining-Family-Routines'. The second examines the features of households adopting the Prosuming Project and the need to mobilise a set of elements from within a disadvantaged community. The third question explores how the establishing phase is marked by a complex relationship between prosuming as a secondary, voluntary project, and dominant, institutional projects. This is further complicated by the role of synchronicity, finances and the changing seasons. The final subsidiary question addresses how a new vocabulary of elements emerged as practitioners committed to the Prosuming Project. It also explores how a transformative process took place both for practitioner and the project itself. In particular it highlights the potential in the future for an Energy Shifting, Storing, Saving & Sharing Project that could support disadvantaged communities, if they are able to mobilise the elements they need to perform it. This case study adopts an in-depth qualitative methodology, using serial interviews with seven households over ten months. The interviewees live in an area that in 2010 was ranked as within the ten percent most deprived in England, according to English Indices of Deprivation (DCLG). The research explores their lived experiences of the Prosuming Project. The thesis focuses on UK social housing tenants, who appear not to have been researched before for a prosuming-focused, social practice study. This enables the research to contribute to topical debates about future sustainability ‘winners and losers'. It also offers methodological insights into undertaking a social practice case study that explored lived experiences within a disadvantaged community. The research provides insights into how prosuming solar power is embedded in everyday life: how it can be supported or challenged by dominant projects, and how householders may develop new skills, understandings, and ways of using materials as their performances evolve.