Dissertations / Theses on the topic 'Concentrated solar power plants'

Concentrating solar power (CSP) plant is a promising technology that exploits direct normal irradiation (DNI) from the sun to be converted into thermal energy in the solar field. One of the advantages of CSP technology is the possibility to store thermal energy in thermal energy storage (TES) for later production of electricity. The integration of thermal storage allows the CSP plant to be a dispatchable system which is defined as having a capability to schedule its operation using an innovative dispatch planning tool. Considering weather forecast and electricity price profile in the market, dispatch planning tool uses an optimization algorithm. It aims to shift the schedule of electricity delivery to the hours with high electricity price. These hours are usually reflected by the high demand periods. The implementation of dispatch optimizer can benefit the CSP plants economically from the received financial revenues. This study proposes an optimization of dispatch planning strategies for the parabolic trough CSP plant under two dispatch approaches: solar driven and storage driven. The performed simulation improves the generation of electricity which reflects to the increase of financial revenue from the electricity sale in both solar and storage driven approaches. Moreover, the optimization also proves to reduce the amount of dumped thermal energy from the solar field.

Doutoramento em Engenharia Mecânica
The PhD project addresses the potential of using concentrating solar power (CSP) plants as a viable alternative energy producing system in Libya. Exergetic, energetic, economic and environmental analyses are carried out for a particular type of CSP plants. The study, although it aims a particular type of CSP plant – 50 MW parabolic trough-CSP plant, it is sufficiently general to be applied to other configurations. The novelty of the study, in addition to modeling and analyzing the selected configuration, lies in the use of a state-of-the-art exergetic analysis combined with the Life Cycle Assessment (LCA). The modeling and simulation of the plant is carried out in chapter three and they are conducted into two parts, namely: power cycle and solar field. The computer model developed for the analysis of the plant is based on algebraic equations describing the power cycle and the solar field. The model was solved using the Engineering Equation Solver (EES) software; and is designed to define the properties at each state point of the plant and then, sequentially, to determine energy, efficiency and irreversibility for each component. The developed model has the potential of using in the preliminary design of CSPs and, in particular, for the configuration of the solar field based on existing commercial plants. Moreover, it has the ability of analyzing the energetic, economic and environmental feasibility of using CSPs in different regions of the world, which is illustrated for the Libyan region in this study. The overall feasibility scenario is completed through an hourly analysis on an annual basis in chapter Four. This analysis allows the comparison of different systems and, eventually, a particular selection, and it includes both the economic and energetic components using the “greenius” software. The analysis also examined the impact of project financing and incentives on the cost of energy. The main technological finding of this analysis is higher performance and lower levelized cost of electricity (LCE) for Libya as compared to Southern Europe (Spain). Therefore, Libya has the potential of becoming attractive for the establishment of CSPs in its territory and, in this way, to facilitate the target of several European initiatives that aim to import electricity generated by renewable sources from North African and Middle East countries. The analysis is presented a brief review of the current cost of energy and the potential of reducing the cost from parabolic trough- CSP plant. Exergetic and environmental life cycle assessment analyses are conducted for the selected plant in chapter Five; the objectives are 1) to assess the environmental impact and cost, in terms of exergy of the life cycle of the plant; 2) to find out the points of weakness in terms of irreversibility of the process; and 3) to verify whether solar power plants can reduce environmental impact and the cost of electricity generation by comparing them with fossil fuel plants, in particular, Natural Gas Combined Cycle (NGCC) plant and oil thermal power plant. The analysis also targets a thermoeconomic analysis using the specific exergy costing (SPECO) method to evaluate the level of the cost caused by exergy destruction. The main technological findings are that the most important contribution impact lies with the solar field, which reports a value of 79%; and the materials with the vi highest impact are: steel (47%), molten salt (25%) and synthetic oil (21%). The “Human Health” damage category presents the highest impact (69%) followed by the “Resource” damage category (24%). In addition, the highest exergy demand is linked to the steel (47%); and there is a considerable exergetic demand related to the molten salt and synthetic oil with values of 25% and 19%, respectively. Finally, in the comparison with fossil fuel power plants (NGCC and Oil), the CSP plant presents the lowest environmental impact, while the worst environmental performance is reported to the oil power plant followed by NGCC plant. The solar field presents the largest value of cost rate, where the boiler is a component with the highest cost rate among the power cycle components. The thermal storage allows the CSP plants to overcome solar irradiation transients, to respond to electricity demand independent of weather conditions, and to extend electricity production beyond the availability of daylight. Numerical analysis of the thermal transient response of a thermocline storage tank is carried out for the charging phase. The system of equations describing the numerical model is solved by using time-implicit and space-backward finite differences and which encoded within the Matlab environment. The analysis presented the following findings: the predictions agree well with the experiments for the time evolution of the thermocline region, particularly for the regions away from the top-inlet. The deviations observed in the near-region of the inlet are most likely due to the high-level of turbulence in this region due to the localized level of mixing resulting; a simple analytical model to take into consideration this increased turbulence level was developed and it leads to some improvement of the predictions; this approach requires practically no additional computational effort and it relates the effective thermal diffusivity to the mean effective velocity of the fluid at each particular height of the system. Altogether the study indicates that the selected parabolic trough-CSP plant has the edge over alternative competing technologies for locations where DNI is high and where land usage is not an issue, such as the shoreline of Libya.
O projeto de Doutoramento aborda o potencial de usar centrais de energia solar concentrada (CSP) como um sistema de produção de energia alternativa disponível na Líbia. Uma análise nas vertentes exergética, energética, económica e ambiental foi realizada para um tipo particular destas centrais – um sistema de 50 MW com receção parabólica, porém ela é suficientemente geral para ser aplicada a outras configurações. A originalidade do estudo, para além da modelação e análise da configuração selecionada encontra-se na utilização do estado da arte em termos da análise exergética combinada com a avaliação do ciclo de vida (LCA). A modelação e simulação da central CSP selecionada são efetuadas no terceiro capítulo tendo em consideração as duas componentes: ciclo de potência e campo de coletores solar. O modelo computacional para a análise do sistema foi desenvolvido com base em equações algébricas que descrevem o sistema, e que são resolvidas usando o software EES. Deste modo, são definidas as propriedades em cada ponto de interesse para os diferentes elementos do sistema, o que assim permite determinar as energias, eficiências e irreversibilidades desses elementos. O modelo desenvolvido tem o potencial de se tornar uma ferramenta de grande utilidade para o projeto preliminar de engenharia de centrais CSP, e também para a avaliação da eventual reconfiguração de centrais elétricas solares comerciais em operação. Além disso, o modelo pode ser utilizado no estudo de viabilidade da operação de centrais CSP, através da análise energética, económica e ambiental, para regiões diferentes da que foi escolhida no presente estudo -Trípoli (Líbia). O cenário total da viabilidade da operação da central CSP é completado através da análise horária com base anual apresentada no quarto capítulo. Esta análise permite a comparação de diferentes sistemas e, eventualmente permite fazer a seleção com base nas componentes económicas e energéticas, que são determinadas dentro do contexto do software greenius. A análise também toma em conta o impacto de financiamento e incentivos dados aos projetos no custo da produção de energia. O principal resultado desta análise é a verificação que o desempenho é mais elevado, com o consequente menor custo nivelado da eletricidade, para a Líbia em comparação com o Sul da Europa (Espanha). Assim a Líbia tem o potencial de se tornar um candidato atrativo para o estabelecimento de centrais CSP com o objetivo, como foi considerado em várias iniciativas europeias, de exportar eletricidade gerada através de fontes de energia renováveis de países do Norte de África e Médio Oriente para a Europa. A análise apresenta uma breve revisão do custo corrente da eletricidade e o potencial para reduzir o custo da energia a partir da tecnologia de receção parabólica de centrais CSP. A avaliação do ciclo de vida com base exergética (ELCA) e a avaliação do ciclo de vida convencional são realizadas para a centrais CSP específicas no quinto capítulo. Os objetivos são 1) avaliar o impacto ambiental e custo, em termos de do ciclo iv de vida exergético do sistema; 2) identificar pontos fracos em termos da irreversibilidade dos processos; e 3) verificar se as centrais CSP podem reduzir o impacto ambiental e o custo de geração de eletricidade em comparação com centrais que consomem combustível fóssil. O capítulo ainda apresenta uma análise termoeconómica com base na metodologia do custo específico da exergia (SPECO), que avalia o custo relacionado com a destruição de exergia. A análise verificou que o impacto mais importante é a contribuição apresentada pelo campo solar (79%), e os materiais com maior impacto são: aço (47%), sal fundido (25%) e óleo sintético (21%). A análise ELCA mostra que a maior demanda de exergia é devida ao aço (47%); a análise existe uma considerável demanda de exergia relacionada com o sal fundido e ainda o óleo sintético. Em comparação com as centrais que consomem combustível fóssil (NGCC e óleo) a central sistema CSP apresenta menor impacto ambiental, enquanto o pior desempenho ambiental é o da central com queima de óleo seguida pela central a gás natural (NGCC). Na central CSP, o campo solar apresenta o custo mais elevado, enquanto o gerador de vapor, entre os componentes do ciclo de potência, apresenta o maior custo. O armazenamento de energia térmica permite que as centrais CSP superem a intermitência de radiação solar para responder à procura de energia elétrica independentemente das condições climáticas, e também possam estender a produção de eletricidade para além da disponibilidade da radiação solar diária. A análise numérica do transiente térmico de um sistema de armazenamento de gradiente térmico é realizada durante a fase de carregamento. O sistema de equações que descreve o modelo numérico é resolvido através da utilização de diferenças finitas implícitas no tempo usando o software Matlab. Os resultados da análise indicam que as previsões estão em boa concordância com os dados experimentais para a evolução no tempo da região de gradiente térmico, em particular para regiões mais afastadas da entrada. Nesta região os desvios observados são provavelmente causados pelo alto nível de turbulência devido à penetração do jato no seio do tanque de armazenamento. O modelo analítico simples para simular a turbulência que foi desenvolvido melhora os resultados. Esta abordagem não requer esforço computacional adicional e determina a difusidade térmica efetiva ao longo do tanque.

The majority of the power generated today is produced using fossil fuels,emitting carbon dioxide and other pollutants every second. Also, fossil fuels will eventually run out. For the increasing worldwide energy demand, the use f reliable and environmentally beneficial natural energy sources is one of the biggest challenges. Alongside wind and water, the solar energy which is clean, CO2-neutral and limitless, is our most valuable resource. Concentrated solar power (CSP) is becoming one of the excellent alternative sources for the power industry. The successful implementation of this technology requires the efficient design of tracking and operation system of the CSP solar plants. A detailed analysis of components needed for the design of cost-effective and optimum tracker for CSP solar systems is required for the power plant modeling, which is the primary subject of this thesis. A comprehensive tracking and operating system of a parabolic trough solar power plant was developed focusing primarily on obtaining optimum and cost effective design through the simplified methodology of this work. This new model was implemented for a 50 kWe parabolic trough solar power plant at University of South Florida, Tampa.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 140-148).
The main drawback to renewable energy systems is the higher cost of production compared to competitors such as fossil fuels. Thus, there is a need to increase the efficiency of renewable energy systems in an effort to make them more cost competitive. In this study, the use of nanosurfaces is evaluated for its benefits in improving the efficiency of a concentrated solar tower power system by increasing the energy retained by the receiver surface, and for reducing the fouling on geothermal heat exchangers. The samples tested for the solar receiver application were Inconel 617, Inconel 617 with a 150 nm layer of platinum, Inconel 617 with a 150 nm layer of platinum and a 550 nm layer of nickel oxide, oxidized nickel, and silicon carbide. The experimental results indicated that the platinum was an ineffective diffusion barrier, nickel oxide displays solar selective properties, and silicon carbide would be the best choice for a surface among the samples tested. This indicates that at the operating temperatures for this receiver at 700 °C, a black body surface is more effective than a practical solar selective surface. The nanosurfaces tested for the antifouling application in geothermal systems were subjected to chemistry conditions similar to that in a Dry Cooling Tower at a geothermal plant in Larderello, Italy. Each sample's performance was measured by determining each samples weight change and surface characterization after exposure in an experimental loop. The best performing coatings, all of which showed negligible weight gain, were the Curran 1000 coating from Curran International, the Curran 1000 coating with nanographene, and the Curralon coating with PTFE. Upon further analysis, the Curran 1000 with nanographene was identified as the most promising coating option.
by Alexander W. Rehn.
S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
Cataloged from PDF version of thesis.
Concentrating solar power (CSP) stands as a promising renewable energy technology with the ability to contribute towards global reduction of carbon emissions. A major obstacle to increased adoption of CSP plants has to do with their high initial investment cost; consequently, there is a powerful desire to find improvements that decrease the initial capital investment for a CSP plant. One such improvement involves connecting modularized parabolic trough segments, each with the same dimensions, decreasing the overall amount of actuators required along with greatly simplifying system control architecture. This thesis is concerned with the extent to which parabolic solar trough modules can be connected together while still being able to operate to desired accuracy under expected load. Accuracy requirements are calculated, along with expected loads resulting in frictional torque on the trough. These expected loads are combined with a model for the effect of connecting multiple trough modules to generate a relationship between number of chained modules and required torsional stiffness. To verify said model, an experimental setup was designed and constructed to simulate loads due to both trough weight and wind loads.
by Kabir Abiose.
S.B.

El protagonisme creixent de la tecnologia solar termoelèctrica entre el ventall de les energies renovables es centra en la seva capacitat d’adaptar la seva producció a la demanda energètica exigida. La gestionabilitat d’aquest tipus de centrals s’ha aconseguit amb la integració de sistemes d’emmagatzematge tèrmic en les mateixes. La major part dels sistemes d’emmagatzematge tèrmic, ja sigui els que s’utilitzen a nivell comercial com aquells que es troben en fase de desenvolupament proposen l’ús de sals inorgàniques foses com a medi d’emmagatzematge. Aquestes sals presenten l’inconvenient de la seva alta corrosivitat a altes temperatures. Per un costat, s’han analitzat els fenòmens de corrosió associats a les sals solars utilitzades a la planta pilot TES-PS10 mitjançant la instal·lació de racks de testimonis de corrosió als tancs de sals. A més, al finalitzar l’operació de la instal·lació pilot s’ha dut a terme un estudi post-mortem dels seus. Finalment, amb l’objectiu d’abaratir el cost de l’inventari de sals, s’ha analitzat a nivell de laboratori la corrosivitat de diferents mescles de nitrats de baixa puresa. El segon bloc de la tesi es centra en els sistemes d’emmagatzematge tèrmic en calor latent. Concretament, s’analitza la corrosió associada a la mescla peritèctica 46% LiOH-54% KOH proposta com a material de canvi de fase en un mòdul d’evaporació d’instal·lacions termoelèctriques de generació directa de vapor. D’aquesta forma, s’han dut a terme una sèrie d’assajos a nivell de laboratori amb l’objectiu d’avaluar el comportament envers la corrosió de diferents materials en contacte amb aquests hidròxids.
El creciente protagonismo de la tecnología solar se centra en su capacidad para adaptar su producción a la demanda energética exigida. La gestionabilidad de este tipo de centrales se ha conseguido mediante la integración de sistemas de almacenamiento térmico en sales fundidas. El uso de sales fundidas en sistemas de almacenamiento térmico presenta el hándicap de su corrosividad a alta temperatura. El primer bloque de la Tesis analiza los fenómenos de corrosión asociados a las sales solares en la planta piloto TES-PS10 mediante la instalación de racks de corrosión en los tanques de sales. Además, se ha llevado a cabo un estudio post-mortem de componentes de la instalación. Finalmente, se ha analizado a nivel de laboratorio la corrosividad de distintas mezclas de nitrato de baja pureza. El segundo bloque de la tesis se centra en los sistemas de almacenamiento en calor latente. En concreto, se analiza la corrosión asociada a la mezcla peritéctica 46% LiOH-54% KOH propuesta como material de cambio de fase en el módulo de evaporación en plantas de generación directa de vapor. De este modo, se han llevado a cabo ensayos de corrosión a nivel de laboratorio para evaluar el comportamiento a corrosión de distintos materiales en contacto con los hidróxidos.
The growing of concentrated solar power (CSP) within the different renewable energies is due to its ability to adapt the production to the required energy demand. The dispatchability of this type of plants has been achieved through the integration of molten salts thermal storage systems (TES). Molten salts have a handicap associated to their corrosiveness at high temperature. First block of this Thesis analyzes the corrosion phenomena associated with solar salts used in TES-PS10 pilot plant by installing corrosion racks in the salt tanks. Moreover, a postmortem study of different components was performed after facility shut down. Finally, in order to reduce the cost of the salt inventory in TES systems, the corrosivity of different low purity nitrates mixtures has been analyzed at laboratory scale. The second block of the Thesis focuses on latent heat storage systems. Specifically, it has been analyzed the corrosion associated with the proposed 46% LiOH-54% KOH peritectic mixture as a phase change material in the evaporation module of direct steam generation (DSG) CSP plants. Thus, corrosion tests have been performed at laboratory level to evaluate the corrosion performance of several materials in contact with such hydroxides.

One of the most relevant problems to solve at a planetary scale is the access to an affordable clean source of energy as CO2 equivalent emissions should be reduced significantly. Some authors aim for a zero emissions target for 2050. Renewable energies will play a leading role in this energy transition, and solar energy with storage is a promising technology exploring a renewable and worldwide available resource. Within the present thesis component development like a new thermal storage thermocline tank design or having latent heat storage capability are technological developments that have been pursued and analyzed on a system perspective basis, focusing on reducing the LCOE value of a commercial STE plant using TRNSYS software. Material research with molten salts mixtures and cement based materials has been performed at lab scale. A fully validation should occur through a 13 partners pan-European H2020 project called NEWSOL which has been developed supported on the laboratory data obtained. Moreover, incorporation of local available material, “modern slag” from an old mine of Alentejo region, was also studied. The material could be used as an aggregate incorporated into calcium aluminate cement (CAC) or as filler. This would help to solve a local environmental complex problem related to soil, air and water pollution due to heavy metals and mining activity in Mina de São Domingos, Southeast of Portugal. The integration of these results underlies a broad energy transition model, a proposal is presented in this thesis, with the aim to foster development towards a sustainable usage of resources and promote clean technologies especially in the energy sector. This model can be locally adapted depending on the pattern of existing industries. The goal is to achieve a smooth transition into a clean tech energy society in line with the target of achieving zero emissions for 2050; Optimização Energética de uma Central de Concentração Solar com Armazenamento de Energia Resumo: Um dos problemas mais relevantes a resolver a uma escala planetária é o acesso, com um custo moderado, a fontes limpas de energia considerando que as emissões equivalentes de CO2 derão ser reduzidas drasticamente. Alguns autores ambicionam mesmo um objetivo de zero emissões em 2050. As energias renováveis irão desempenhar um papel preponderante nesta transição energética, sendo que a energia solar com armazenamento é uma tecnologia promissora que aproveita um recurso renovável e disponível em boa parte do Planeta. Na presente tese foi realizado o desenvolvimento de componentes nomeadamente o design que um novo tanque do tipo termocline, ou de novos elementos recorrendo ao calor latente, desenvolvimentos tecnológicos que foram analizados de uma perspectiva de sistema, dando o enfoque na redução do custo nivelado da electricidade (LCOE) para uma planta Termosolar usando o software TRNSYS. Foi também realizada investigação em laboratório ao nível dos materiais com várias misturas de sais fundidos inclusivé em contacto directo com materiais de base cimenticia. Uma validação completa deverá ocorrer no projeto NEWSOL do programa H2020 que reúne um consórcio de 13 parceiros europeus e que foi preparado e submetido tendo por base os resultados laboratoriais obtidos. Adicionalmente, incorporação de material disponível (escória de minério) de uma mina abandonada da região do Alentejo foi outro dos aspectos estudados. Verificou-se que este material poderá ser utilizado como agregado num ligante do tipo cimento de aluminato de cálcio (CAC) ou como “filler”. Este re-aproveitamento resolveria um problema ambiental complexo derivado do elevado conteúdo de metais pesados resultantes da actividade de mineração e que actualamente provocam poluição do solo, água e ar na área da Mina de São Domingos, Sudeste de Portugal. Estes progressos deverão ser integrados num modelo de transição energética mais amplo. Na presente tese, uma proposta concreta é apresentada, com o objectivo de incentivar o desenvolvimento na direção de uma utilização sustentável dos recursos e a promoção de tecnologias limpas nomeadamente no sector da energia. Este modelo poderá ser adaptado localmente dependendo do padrão de indústrias existente. O objectivo é atingir uma transição suave para uma sociedade de energias limpas em linha com o objectivo de atingir zero emissões de CO2 equivalente em 2050.

Thesis (MEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Most rural African villages enjoy high levels of sunlight, but rolling out solar power generation technology to tap into this renewable energy resource at remote rural sites in Africa pose a number of design challenges. To meet these challenges, a project has been initiated to design, build and test/evaluate a knock down 3 kW peak electrical stand-alone self-tracking dual-axis concentrating solar power system. This study focusses on the mechatronic engineering aspects in the design and development of a dynamic mechatronic platform and digital electronic control system for the stand-alone concentrating solar power system. Design specifications require an accurate automatic positioner and control system for a motorized parabolic solar reflector with an optical solar harnessing capacity of 12 kWt at solar noon. It must be suitable for stand-alone rural power generation. This study presents a conceptual design and engineering prototype of a balanced cantilever tilt-and-swing dual-axis slew drive actuation means as mechatronic solar tracking mobility platform for a ∼12 m2 lightweight parabolic solar concentrator. Digital automation of the concentrated solar platform is implemented using an industrial Siemens S7-1200 programmable logic controller (PLC) with digital remote control interfacing, pulse width modulated direct current driving, and electronic open loop/closed loop solar tracking control. The design and prototype incorporates off-the-shelf components to support local manufacturing at reduced cost and generally meets the goal of delivering a dynamic mechatronic platform for a concentrating solar power system that is easy to transport, assemble and install at remote rural sites in Africa. Real-time experiments, conducted in the summer of South Africa, validated and established the accuracy of the engineering prototype positioning system. It shows that the as-designed and -built continuous solar tracking performs to an optical accuracy of better than 1.0◦ on both the azimuth and elevation tracking axes; and which is also in compliance with the pre-defined design specifications. Structural aspects of the prototype parabolic dish are evaluated and optimized by other researchers while the Stirling and power handling units are under development in parallel projects. Ultimately, these joint research projects aim to produce a locally manufactured knock down do-it-yourself concentrated solar power generation kit, suitable for deployment into Africa.
AFRIKAANSE OPSOMMING: Landelike gebiede in Afrika geniet hoë vlakke van sonskyn, maar die ontwerp van betroubare sonkrag tegnologie vir die benutting van hierdie hernubare energie hulpbron by afgeleë gebiede in Afrika bied verskeie uitdagings. Om hierdie uitdagings te oorkom, is ’n projek van stapel gestuur om ’n afbreekbare 3 kW piek elektriese alleenstaande selfaangedrewe dubbel-as son-konsentreeder te ontwerp, bou en te toets. Hierdie studies fokus op die megatroniese ingenieurs-aspekte in die ontwerp en ontwikkeling van ’n dinamiese megatroniese platform en ’n digitale elektroniese beheerstelsel vir die alleenstaande gekonsentreerde sonkrag stelsel. Ontwerp spesifikasies vereis ’n akkurate outomatiese posisionering en beheer stelsel vir ’n motor aangedrewe paraboliese son reflekteerder met ’n optiesekollekteer- kapasiteit van 12 kWt by maksimum sonhoogte, en veral geskik wees vir afgeleë sonkrag opwekking. Hierdie studie lewer ’n konsepsuele ontwerp en ingenieurs-prototipe van ’n gebalanseerde dubbelas swaai-en-kantel swenkrat aandrywingsmeganisme as megatroniese sonvolg platform vir ’n ∼12 m2 liggewig paraboliese son konsentreerder. Digitale outomatisering van die son konsentreerder platform is geimplementeer op ’n industriële Siemens S7-1200 programmeerbare logiese beheerder (PLB) met ’n digitale afstandbeheer koppelvlak, puls-wydte-gemoduleerde gelykstroom aandrywing en elektroniese ooplus en geslote-lus sonvolg beheer. Die ontwerp en prototipe maak gebruik van beskikbare komponente om lae-koste plaaslike vervaardiging te ondersteun en slaag in die algemeen in die doel om ’n dinamiese megatroniese platform vir ’n gekonsentreerde sonkrag stelsel te lewer wat maklik vervoer, gebou en opgerig kan word op afgeleë persele in Afrika. Intydse eksperimente is gedurende die somer uitgevoer om die akkuraatheid van die prototipe posisionering sisteem te evalueer. Dit toon dat die sisteem die son deurlopend volg met ’n akkuraatheid beter as 1.0◦ op beide die azimut en elevasie sonvolg asse, wat voldoen aan die ontwerp spesifikasies. Strukturele aspekte van die prototipe paraboliese skottel word deur ander navorsers geëvalueer en verbeter terwyl die Stirling-eenheid en elektriese sisteme in parallelle projekte ontwikkel word. Die uiteindelike doel met hierdie groepnavorsing is om ’n plaaslik vervaardigde doen-dit-self sonkrag eenheid te ontwikkel wat in Afrika ontplooi kan word.

Solar Tower Power Plants with thermal energy storage are a promising technology for dispatchable renewable energy in the near future. Storage integration makes possible to shift the electricity production to more profitable peak hours. Usually two tanks are used to store cold and hot fluids, but this means both higher related investment costs and difficulties during the operation of the variable volume tanks. Another solution can be a single tank thermocline storage in a multi-layered configuration. In such tank both latent and sensible fillers are employed to decrease the related cost by up to 30% and maintain high efficiencies.  The Master thesis hereby presented describes the modelling and implementation of a thermocline-like multi-layered single tank storage in a STPP. The research work presents a comprehensive methodology to determine under which market structures such devices can outperform the more conventional two tank storage systems. As a first step the single tank is modelled by means of differential energy conservation equations. Secondly the tank geometrical design parameters and materials are taken accordingly with the applications taken into consideration. Both the steady state and dynamic models have been implemented in an existing techno-economic tool developed in KTH, in the CSP division (DYESOPT). The results show that under current cost estimates and technical limitations the multi-layered solid PCM storage concept is a better solution when peaking operating strategies are desired, as it is the case for the two-tier South African tariff scheme. In this case the IRR of an optimal designed power plant can be decreased by 2.1%. However, if a continuous operation is considered, the technology is not always preferred over the two tank solution, yet is a cheaper alternative with optimized power plants. As a result the obtained LCOE can be decreased by 2.4%.

Renewable energy for energy production, like Solar, is turning out to be very pertinent in today's world [1]. It is very clear that Solar Energy is going to emerge as one of the key sources of energy in future. Moreover, the storage option is going to play an essential role to the future deployment of solar power plants. Concentrated solar power plants with thermal storage, photovoltaic plants integrated with battery energy storage, and hybrid plants are attractive solutions to obtain a stable and dispatchable energy production. Investors or policymakers usually find it challenging to come up with the most feasible solar storage technology because they need to consider techno-economic feasibility, and at the same time, from a market or administrative perspective as well. So, this thesis study will address the key problem which is aimed at investors or policymakers since there is a need to choose the best solar storage technology at a utility level in future based on so many attributes. The thesis project was carried out in two phases which includes forecast modelling & estimations and techno-economic assessment of virtual plants. These two phases helped to address various questions in relation to the problem statement of this study. The entire thesis study broadly covered seven countries spanning across four major regions around the world. The first phase of the thesis, forecast modelling estimations shows how the seven countries will look in future (2020 – 2050) with respect to installed capacity and costs for PV, CSP, and BESS technologies. Some major results from phase 1 include, in low-cost estimates, China will remain to be the market leader in PV & CSP by 2050. In U.S.A and India, the installed costs of PV are projected to decline by 70% by 2050. By 2050, the installed costs of Solar Tower technology are estimated to drop by about 65% in China and Spain. In U.S.A, the prices of BESS technology are likely to fall by around 58 – 60 % by 2050. In the second phase of thesis study, a techno-economic evaluation of virtual plants addressed the aspects which are to be considered for a solar project if it is deployed in future across seven specific countries. Results from this analysis helps investors or policymakers to choose the cheapest solar storage technology at a utility level across seven specific countries in future (2020 – 2050). Key results from this analysis show that, in the U.S.A, by 2050, PV+BESS will be the cheapest storage technology for 4 – 10 storage hours. Addition of another renewable technology will add up more viability to the comparison. In China, Hybrid will be the cheapest storage technology for 4 – 8 hrs by 2050. There is huge potential for deployment of CSP & hybrid plants in future than PV. In South Africa, CSP will be the cheapest storage technology by 2050 for 4 – 10 hours of storage. It is assumed that deployment of BESS projects at utility level starts from 2025 in South Africa. Beyond this, market forces analysis was carried out which offers insights especially for the policymakers of how various drivers and constraints are influencing each solar technology across the specific countries in future. Overall, the entire thesis study provides guidelines/insights to investors or policy makers for choosing the best solar storage technology in future at a utility scale for a particular country.
Förnybar energi för energiproduktion, liksom Solar, visar sig vara mycket relevant i dagens värld [1]. Det är mycket tydligt att solenergi kommer att framstå som en av de viktigaste energikällorna i framtiden. Dessutom kommer lagringsalternativet att spela en väsentlig roll för den framtida distributionen av solkraftverk. Koncentrerade solkraftverk med värmelagring, solcellsanläggningar integrerade med batterilagring och hybridanläggningar är attraktiva lösningar för att få en stabil och skickbar energiproduktion. Investerare eller beslutsfattare brukar tycka att det är utmanande att komma på den mest genomförbara solcellstekniken eftersom de måste överväga teknikekonomisk genomförbarhet, och samtidigt, ur ett marknads- eller administrativt perspektiv också. Så denna avhandlingsstudie kommer att ta itu med nyckelproblemet som riktar sig till investerare eller beslutsfattare eftersom det finns ett behov av att välja den bästa solenergilagringstekniken på en användningsnivå i framtiden baserat på så många attribut. Avhandlingsprojektet genomfördes i två faser som inkluderar prognosmodellering och uppskattningar och teknikekonomisk bedömning av virtuella anläggningar. Dessa två faser hjälpte till att ta itu med olika frågor i samband med problemstudien i denna studie. Hela avhandlingsstudien omfattade i stort sju länder som sträcker sig över fyra stora regioner runt om i världen. Den första fasen i avhandlingen, prognosmodelleringsuppskattningar visar hur de sju länderna kommer att se ut i framtiden (2020 - 2050) med avseende på installerad kapacitet och kostnader för PV-, CSP- och BESS -teknik. Några viktiga resultat från fas 1 inkluderar, i lågkostnadsuppskattningar, att Kina kommer att vara marknadsledande inom PV och CSP år 2050. I USA och Indien beräknas de installerade kostnaderna för PV minska med 70% år 2050. Av 2050 beräknas de installerade kostnaderna för Solar Tower -teknik sjunka med cirka 65% i Kina och Spanien. I USA kommer priserna på BESS -teknik sannolikt att sjunka med cirka 58 - 60 % år 2050. I den andra fasen av avhandlingsstudien behandlade en teknikekonomisk utvärdering av virtuella anläggningar de aspekter som ska övervägas för ett solprojekt om det används i framtiden i sju specifika länder. Resultaten från denna analys hjälper investerare eller beslutsfattare att välja den billigaste solenergilagringstekniken på en användningsnivå i sju specifika länder i framtiden (2020 - 2050). Viktiga resultat från denna analys visar att i USA, år 2050, kommer PV+BESS att vara den billigaste lagringstekniken på 4 - 10 lagringstimmar. Tillägg av en annan förnybar teknik kommer att öka jämförbarheten. I Kina kommer Hybrid att vara den billigaste lagringstekniken i 4-8 timmar fram till 2050. Det finns en enorm potential för distribution av CSP & hybridanläggningar i framtiden än PV. I Sydafrika kommer CSP att vara den billigaste lagringstekniken år 2050 för 4 - 10 timmars lagring. Det antas att distributionen av BESS -projekt på verktygsnivå börjar från 2025 i Sydafrika. Utöver detta genomfördes marknadskravsanalys som ger insikter speciellt för beslutsfattarna om hur olika drivkrafter och begränsningar påverkar varje solteknik i de specifika länderna i framtiden. Sammantaget ger hela avhandlingsstudien riktlinjer/insikter till investerare eller beslutsfattare för att välja den bästa solenergitekniken i framtiden i en nyttoskala för ett visst land.

In response to the extensive energy demands on national and global levels, concentrated solar power (CSP) plants are designed to harness and convert solar energy to electricity. For such green energy application, robust, reliable and durable materials for CSP constructions are required. The corrosion resistance is among many parameters to consider in these thermal-electrical stations such as for pipes and storage tanks in CSP. In this investigation, the corrosion behavior of AISI 304 stainless steel (18 wt. % Cr, 8 wt. % Ni) with the heat transfer fluid, also known as solar salt, has been examined. The ternary eutectic salt mixture with the composition, 53 wt. % KNO3, 40 wt. % NaNO2, and 7 wt. % NaNO3, that melts at 142°C, has a potential use in CSP as a heat transfer fluid. The solar salt was prepared for this corrosion study from reagent grades of high purity nitrites and nitrates. Samples of AISI 304 stainless steel were sectioned from a sheet stock of the alloy and exposed to solar salt at 530°C in air at 1 atmospheric pressure. After test intervals of 250, 500, and 750 hours in total immersion condition, AISI 304 stainless steel samples have developed a scale of corrosion products made up of multiple oxides. X-ray diffraction and scanning electron microscopy with X-ray energy-dispersive spectroscopy were employed to examine the extent of corrosion and identify the corrosion products. Transmission electron microscopy was used to verify the corrosion products identity via electron diffraction patterns. Oxides of iron were found to be the primary corrosion products in the presence of the molten alkali nitrates-nitrite salt mixture because of the dissolution of the protective chromium oxide (Cr2O3) scale formed on AISI 304 stainless steel coupons. The corrosion scale was uniform in thickness and made up of sodium iron oxide (NaFeO2), iron oxide, hematite (Fe2O3), and chromium-iron oxide (Cr,Fe)2O3 solid solution. The latter was found near the AISI 304 stainless steel. This indicates that the scale formed, particularly on the upper layers with presence of sodium iron oxide and iron oxide, hematite, is protective, and forms an effective barrier against penetration of fused solar salt. At the alloy interface with the bulk corrosion scale, the corrosion process induced a compositional modification in the grains located at the interface. There are iron rich and iron depleted grains at the interface if compared to the nominal iron content of the alloy. The mode of attack is identified as uniform at the test temperature of 530°C, showing a parabolic behavior with a parabolic rate constant (Kp) equals to 1.08&"215;10^(-17)(m2/sec). By extrapolation, annual corrosion rate is estimated to reach 0.784 mils per year. Corrosion behavior of AISI 304 stainless steel is discussed in terms of thermodynamics and reaction paths.
M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering

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CAPEs
Notadamente nos últimos anos, a geração de eletricidade a partir de fontes renováveis de energia tem mostrado contínuo aumento que está relacionado, sobretudo, às preocupações com as variações climáticas, à dependência dos combustíveis fósseis e à necessidade de suprir a geração de energia elétrica com recursos que produzam menos impactos ao meio ambiente. A capacidade instalada da energia renovável no mundo, que foi de 800GW em 2004, alcançou 1.712GW em 2014 e a participação na matriz energética global também aumentou, atingindo o percentual de 22,8% em 2014. O Brasil possui uma matriz energética predominantemente renovável. Somente em 2014, aproximadamente 74,6% da eletricidade gerada procedeu das fontes renováveis de energia. O percentual restante (25,4%) proveio dos combustíveis fósseis e das fontes nucleares. Mas, muito embora o País possua uma matriz energética tipicamente renovável, nota-se que o principal sistema de geração é o aproveitamento hidráulico, que é bem vulnerável às variações climáticas globais e pode apresentar, em função disso, redução de sua capacidade instalada em longo prazo. Visando contribuir para a diversificação da matriz energética brasileira, esta pesquisa apresenta dois métodos distintos e macroespaciais para auxiliar a seleção de áreas potenciais para a inserção de usinas solares termoelétricas: o Método baseado no Processo Analítico Hierárquico, que trata o problema da localização sob uma organização hierárquica de critérios, como pressupõe os axiomas do Método AHP; e o Método do Custo de Produção de Eletricidade, que define os locais aptos em função do custo nivelado da eletricidade (LCOE – Levelised Cost of Electricity). Ambas as metodologias foram aplicadas para Pernambuco, localizado na região Nordeste do Brasil, e considerou a implantação de usinas de coletores parabólicos de 80MWe, tipo SEGS, operando somente em modo solar, sem armazenadores térmicos. Com base nas análises realizadas, confirmou-se que Pernambuco apresenta grande potencial para a implantação de usinas solares, principalmente no Sertão Pernambucano, onde foram encontrados os ambientes mais favoráveis à instalação. Na aplicação do Método AHP, por exemplo, o Sertão apresentou alto potencial de instalação em todos os cenários avaliados, inclusive no cenário Ponto de Partida, onde os pesos não foram considerados. No Método do Custo de Produção de Eletricidade, o Sertão também mostrou alto potencial de instalação uma vez que os custos de geração de energia elétrica encontrados foram os menores do estado (da ordem de R$ 337,16/MWh). Este custo é elevado quando comparado com o preço da eletricidade gerada pela fonte hidráulica no país (R$ 182,09/MWh), por exemplo, mas estão em conformidade quanto ao esperado para sua inserção no mercado brasileiro. De modo geral, as abordagens apresentadas se mostraram muito consistentes e revelaram um potencial bastante promissor para o desenvolvimento da tecnologia em Pernambuco. Este potencial deverá ser avaliado detalhadamente e incluir a medição local da radiação solar por pelo menos cinco anos.
Notably in recent years, the generation of electricity using energy from renewable resources has presented continuous increase, which is due to, especially, the concerns about climate changes, the dependency in fossil fuel and the necessity of production of electric energy with resources to decrease the negative impacts in the environmental. The global renewable power generation capacity, which presented 800GW on the beginning of 2004, reaching an estimated 1,712GW at year’s end 2014, and the renewable electricity global production in 2014 presented 22.8%. Brazil has a mainly renewable energy matrix. In 2014, 74.6% of the electricity produced came from renewable sources of energy. The remaining percentage comes from fossil fuels and nuclear sources (25.4%). Although it shows a remarkably renewable character, it is notable that the main source of generation of electricity is the water source, which is susceptible the climate changes, and should present the reduction in your capacity installed in a long term. As a way of contributing to diversify the energy matrix Brazilian, this work presents two different methodologies macro spatial for the selection of the best sites for insertion of solar thermal power plants: the methodologies based on analytic hierarchy process (AHP) where the selection the best site was based on means of the hierarchical organization of criteria according to axioms of the AHP method; and the method based on cost of electricity generation where the best site were selected according to Levelised Cost of Electricity (LCOE). Both studies were made in Pernambuco, located in Northeastern Region of Brazil and considered the implementation of a parabolic trough solar power plant, of 80MWe, operating exclusively in solar mode, without thermal stores. The analyzes performed confirmed that the Pernambuco presents great potential for the installation of solar thermal power plants, especially, in the Sertão Pernambucano where the best sites were located. In the methodologies AHP, for example, this region presented great potential for the installation in all scenarios analyzed, including the Ponto de Partida scenarios where weights are not used. In the method based on cost of electricity, the Sertão presented great potential also. In this region it is possible to find electric energy generation costs by MWh of the order of R$ 337.16. This costs are still high when comparing the cost of generation of the hydraulic source (R$ 182.09/MWh) in Brazil, although, they comply as to expected for its insertion in the Brazilian Market. The methodologies used demonstrated very consistent and identified a promising potential for solar thermal power generation in Pernambuco. This potential should be analyzed in details and include the local measurement of the incident direct normal solar irradiation for at least five years.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 207-215).
This thesis describes a new concentrating solar power central receiver system with integral thermal storage. Hillside mounted heliostats direct sunlight into a volumetric absorption molten salt pool, which also functions as a single tank assisted thermocline storage system. Concentrated light penetrates the molten salt and is absorbed over a depth of several meters; the molten salt free surface tolerates high irradiance levels, yet remains insensitive to the passage of clouds. Thermal losses to the environment are reduced with a refractory-lined domed roof and a small, closeable aperture. The molten salt and cover provide high and low temperature heat sources that can be optimally used to maximize energy production throughout the day, even when the sun is not shining. Hot salt is extracted from the upper region of the tank and sent through a steam generator, then returned to the bottom of the tank. An insulated barrier plate is positioned vertically within the tank to enhance the natural thermocline which forms and maintain hot and cold salt volumes required for operation. As a result, continuous, high temperature heat extraction is possible even as the average temperature of the salt is declining. Experimental results are presented for sodium-potassium nitrate salt volumetric receivers optically heated with a 10.5 kilowatt, 60-sun solar simulator. Designs, construction details and performance models used to estimate efficiency are presented for megawatt-scale molten salt volumetric receivers capable of operating with low cost nitrate or chloride salt eutectics at temperatures approaching 600 'C and 1000 'C, respectively. The integral storage capabilities of the receiver can be sized according to local needs, thereby enabling power generation on demand.
by Daniel Shawn Codd.
Ph.D.

This master’s thesis presents the work performed during a four-month long internship at Azelio AB in Gothenburg. Energy performance models for common energy technologies in microgrid energy systems were developed and validated. The investigated technologies are traditional and bifacial PV modules, wind turbines, Li-ion battery energy storage systems and diesel generators. Subsequently, they were utilised to simulate the energy supply of two remote communities in Queensland, Australia. Azelio’s CSP technology, which combines heliostats, thermal energy storage with phase change materials and Stirling engine, was introduced as well. By means of scenarios and key performance indicators, the possibility of disconnecting such towns from the local electricity distribution network was investigated. Both technical and economic aspects were analysed. This led to the conclusion that 10 MW CSP system would be sufficient to achieve grid independence if extra backup capacity, e.g. diesel generators, or demandside control strategies, are introduced. Sensitivity analysis performed on the possibility of dividing the CSP park into two clusters, the smaller one being subject to a power threshold, was investigated as well. In terms of economic feasibility, off-grid systems resulted more expensive than maintaining the grid connection.
Denna master’s uppsats presenterar alla resultat från examensarbetet hos Azelio AB i Göteborg. Energy performance models för de vanligaste energiteknologerna i microgrid energisystemen designades och validerades. De forskade energiteknologerna var traditionella och bifacial solpaneler, vindkraft, energilagring genom Liion batterier och dieselgeneratorer. Modellerna användes för att simulera energiförsörjning av olika energisystem som representerar två isolerade byar i Queensland, Australia. Azelio’s CSP teknologi, som består av heliostater, värmenergilagring med phase change material och en Stirlingmotor, introducerades också. Genom att designa olika scenarier och key perfomance indicators, möjligheten att koppla av byarna ifrån det lokala kraftnätsystemet utforskades. Båda tekniska och ekonomiska synpunkter värderades. Det beslutades att 10 MW CSP kapacitet kan vara nog mycket för att nå energisjälvständighet om ytterligare backupkapacitet, t.ex. en dieselgenerator, eller demand side control strategies introducerades. Känslighetsanalys utforskade möjligheten att dela CSP systemet i två olika delar, där den med lägre kapacitet kunde avkopplas för att undvika onödig energiförsörjning. Om ekonomiska utförbarhet, off-grid system verkade dyrare än sådana system där byarna var fortfarande kopplat till det lokala kraftnätet.

Il y a un intérêt croissant pour les systèmes d'énergie solaire concentrée (CSP) qui peuvent fonctionner à des températures supérieures à 1000 °C afin d'optimiser leur efficacité. L'un des défis consiste à définir un matériau récepteur qui sera soumis à un chauffage à haute température dans l'air. Contrairement aux revêtements utilisés dans les turbines à gaz, le ou les systèmes revêtement(s)/substrat doivent avoir une conductivité thermique élevée pour assurer un transfert thermique optimal vers le fluide. Les revêtements de nitrure d'aluminium (AlN), déposés par dépôt chimique en phase vapeur à 1100-1200 °C à une vitesse de croissance de 10-50 µm·h-1, sont choisis pour leur conductivité thermique élevée, leur faible coefficient de dilatation thermique, leur stabilité thermique élevée et leur capacité à développer des couches stables d'alumine au-dessus de 1000 °C. Les alliages à base de molybdène sont choisis comme substrat pour leurs excellentes propriétés thermiques et mécaniques. Les alliages à base de fer formant des couches d'alumine sont également choisis comme substrats modèles pour étudier le potentiel de ces revêtements et réduire le nombre de paramètres lors de l'oxydation. Des tests accélérés d'oxydation cyclique et des mesures d'émissivité permettent d'évaluer les revêtements AlN comme matériaux pour les récepteurs CSP haute température. Les systèmes multicouches présentent une faible dégradation après des centaines de cycles thermiques à 800 °C dans l'air et peuvent supporter des températures plus élevées (1100 °C) pendant 100 à 500 h selon l'épaisseur du revêtement. Néanmoins, l'oxydation cyclique rapide dans les fours solaires conduit à des fissures dans les revêtements. Un modèle analytique est développé pour étudier l'évolution des contraintes dans le(s) système(s) revêtement(s)/substrat. Les résultats calculés sont en bon accord avec les données expérimentales. Les mesures des propriétés optiques révèlent une diminution de l'absorptivité après oxydation pour les revêtements AlN, mais une augmentation significative de l'absorptivité lorsque un revêtement de SiC est ajouté comme couche de finition
There is an increasing interest for concentrated solar power (CSP) systems which can work at temperatures higher than 1000 °C to optimize efficiency. One of the challenges is to design the receiver that will be heated at high temperature in air. Compared to coatings in gas turbine engine, the coating(s)/substrate system must have a high thermal conductivity to ensure a good heat transfer to the fluid. Aluminum nitride (AlN) coating, deposited by chemical vapor deposition at 1100-1200 °C at a growth rate of 10-50 µm·h-1, is selected for its high thermal conductivity, low thermal expansion coefficient, high temperature stability and its ability to develop stable alumina scales above 1000 °C. Molybdenum-based alloys are selected as substrate materials for their excellent thermal and mechanical properties. The alumina-forming iron-based alloys are also chosen as model substrates to reduce the influencing parameters in real-life receivers and to study the potential of these coatings. Accelerated cyclic oxidation tests and emissivity measurements allow the evaluation of AlN coatings as materials for high temperature CSP receivers. The multilayered systems exhibit low degradation after hundreds of thermal cycles at 800 °C in air and can support higher temperatures (1100 °C) for 100 to 500 h depending on the coating thickness. Nevertheless, the fast cyclic oxidation in solar furnace leads to cracks through the coatings. An analytical model is developed to study the stress evolution within the coating(s)/substrate system. Calculated results are in good agreement with experimental data. The measurements of the optical properties reveal a decrease of absorptivity after oxidation for AlN coatings, but a significant increase of absorptivity when SiC coating is added as a top layer

Current concentrated solar power plants (CSP) use molten salt at 565°C as a heat transfer and energy storage fluid. Due to thermal energy storage (TES), these solar plants can deliver dispatachable electricity to the grid; however, the levelized cost of electricity (LCOE) for these plants is 12-15 c/kWh, about 2.5 times as high as fossil fuel electricity generation. Molten salt technology limits peak operating temperatures to 565°C and a heat engine efficiency of 40%. Liquid metal (LM), however, can reach >1350°C, and potentially utilize a more efficient (60%) heat engine and realize cost reductions. A 1350 °C LM-CSP plant would require ceramic containment, inert atmosphere containment, additional solar flux concentration, and redesigned internal receiver. It was initially unclear if these changes and additions for LM-CSP were technically feasible and could lower the LCOE compared to LS-CSP. To answer this question, a LM-CSP plant was designed with the same thermal input as a published LS-CSP plant. A graphite internal cavity receiver with secondary concentration heated liquid Sn to 1400°C and transferred heat to a 2-phase Al-Si fluid for 9 hours of thermal energy storage. Input heat to the combined power cycle was 1350°C and had 60% thermal efficiency for a gross output of 168 MW. The cost of this LM-CSP was estimated by applying material cost factors to the designed geometry and scaling construction costs from published LS-CSP estimates. Furthermore, graphite was experimentally tested for reactivity with liquid Sn, successful reaction bonds, and successful mechanical seals. The result is switching to molten metal can reduce CSP costs by 30% and graphite pipes, valves, and seals are possible at least at 400°C.

Solar power tower technology can achieve higher temperatures than the most common commercial technology using parabolic troughs. In order to take advantage of higher temperatures, new power cycles are needed for generating power at higher efficiencies. Supercritical carbon dioxide (S-CO2) power cycle is one of the alternatives that have been proposed for the future concentrated solar power (CSP) plants due to its high efficiency. On the other hand, carbon dioxide can also be a replacement for current heat transfer fluids (HTFs), i.e. oil, molten salt, and steam. The main disadvantages of the current HTFs are maximum operating temperature limit, required freeze protection units, and complex control systems. However, the main challenge about utilizing s-CO2 as the HTF is to design a receiver that can operate at high operating pressure (about 20 MPa) while maintaining excellent thermal performance. The existing tubular and windowed receivers are not suitable for this application; therefore, an innovative design is required to provide appropriate performance as well as mechanical strength. This research investigates the application of s-CO2 in solar power tower plants. First, a computationally efficient method is developed for designing the heliostat field in a solar power tower plant. Then, an innovative numerical approach is introduced to distribute the heat flux uniformly on the receiver surface. Next, different power cycles utilizing s-CO2 as the working fluid are analyzed. It is shown that including an appropriate bottoming cycle can further increase the power cycle efficiency. In the next step, a thermal receiver is designed based on compact heat exchanger (CHE) technology utilizing s-CO2 as the HTF. Finally, a 3MWth cavity receiver is designed using the CHE receivers as individual panels receiving solar flux from the heliostat field. Convective and radiative heat transfer models are employed to calculate bulk fluid and surface temperatures. The receiver efficiency is obtained as 80%, which can be further improved by optimizing the geometry of the cavity.

Ethiopia has been facing problems regarding power generation, distribution, balancingbetween demand and supply and access to modern energy service. About 92.4% of energysupply is from biomass (mostly in traditional) 5.7% oil which is not friendly with theenvironment and about 1.6% of energy supply is from renewable energy resource,hydropower plants.Being dependent on hydropower plant causes the country to face many challenges indistribution and balancing demand and supply. This thesis provides another way ofconsidering and implementing renewable energy resource (solar energy resource) throughtechnologies like grid-connected roof mounted solar PV system and CSP plant with the helpof PVGIS, PVWatt and SAM software.This thesis aims to come up with an idea that will work out for current engineering, socialand political issue that is seen in the country. Considering new way in planting PV system onthe roof is strongly recommended and increasing the alternative sites for power generationalong with the appropriate technology is recommended as another way. The possibility andpower generating efficiency is checked through each application.Based on the demonstration in all software’s used, it is clearly visible that the country couldhave been satisfied the needed demand and become the hub of east Africa as mentioned inthe policy and strategy. However, this dependency causes the country to insufficiently supplythe need. Apart from the possibilities and estimation, ideas that might help the country tocome over these challenges are provided in recommendation section.

The main objective of this research is to enhance the performance of a solar powered Micro Gas Turbine (MGT) by exploring suitable methods to be applied to the turbomachinery components to increase their efficiency and improve the predictability of their performance over the operating range of the MGT. A novel idea of reducing turbine rotor friction losses through adding riblets to the rotor hub was explored thoroughly. Computational Fluid Dynamics (CFD) has been used to study the effects of those features at design point conditions of the MGT. Riblets with different height and spacing have been examined to determine the riblet geometry where the maximum drag reduction is achieved. To improve the predictability of performance of the turbomachinery components of the MGT over the operating envelope, a prediction methodology was developed during this research which used a combination of CFD and empirical correlations to account for losses that are not included in the CFD model. It was found that riblets reduce the cross-stream motion of the low momentum fluid flow near the hub surface of the rotor passage, and separate the streamwise vortex from interaction with the hub surface. The maximum drag reduction was found to occur with riblets of a relative height of 2.5% with respect to the rotor inlet blade height. The performance prediction method was successfully applied to a radial turbine and centrifugal compressor designed for a 6 kWe solar powered MGT. A purpose-built test rig was built and the actual performance map for the turbine was achieved while running it using warm compressed air from an external air supply. The comparison between the actual and the predicted data revealed a good match between both results, which indicates the validity of the demonstrated performance prediction method.

Direct absorption solar collectors offer possible improvement in efficiency over traditional surface absorbing collectors, because they have fewer heat transfer steps and has the ability to utilise higher radiation fluxes. Carbon black based nanofluids, in a base fluid of salt water, were synthesised by a two-step method where the carbon black nanoparticles were treated with a surfactant, TWEEN-20, in a 1:2 mass ratio and sonicated for 60 minutes to break up agglomerates. The synthesised nanofluids showed stability for over 31 days. The different carbon black concentration nanofluids' solar irradiation absorption properties were compared with each other and with the base fluid of salt water in a concentrating, as well as non-concentration scenario. It was found that the carbon black nanofluids showed excellent absorption properties over the entire solar radiation spectrum. A 1 m2 concentrating unit using a two-axis tracking system, with two mirrors and a 1 m diameter circular Fresnel lens, was used to concentrate solar radiation on a direct absorption solar collector flow cell with a 10 cm2 collection area. An optimum concentration of 0.001 volume % carbon black was found to show a 42 % increase in heating rate, compared to that of salt water. The collector was, however, hampered by high energy losses and the maximum collector efficiency achieved was only 46 %, 23 % higher than that of salt water. The overall system efficiency was only 22 %. This low efficiency can be attributed to the high optical concentration losses (50 % - 70 %) present in the concentrating unit.
Dissertation (MEng)--University of Pretoria, 2016.
Chemical Engineering
MEng
Unrestricted

This thesis analyses novel technology for renewable electricity generation: the solar thermal chimney (STC) power plant and the suspended chimney (SC) as a plant component. The STC consists of a solar collector, a tall chimney located at the centre of the collector, and turbines and generators at the base of the chimney. Air heated in the collector rises up the chimney under buoyancy and generates power in the turbines. STCs have the potential to generate large amounts of power, but research is required to improve their economic viability. A state-of-the-art STC model was developed, focussing on accurate simulation of collector thermodynamics, and providing data on flow characteristics and plant performance. It was used to explore power generation for matched component dimensions, where for given chimney heights, a range of chimney and collector radii were investigated. Matched dimensions are driven by the collector thermal components approaching thermal equilibrium. This analysis was complemented with a simple cost model to identify the most cost-effective STC configurations. The collector canopy is an exceptionally large structure. Many of the designs proposed in the literature are either complex to manufacture or limit performance. This thesis presents and analyses a series of novel canopy profiles which are easier to manufacture and can be incorporated with little loss in performance. STC chimneys are exceptionally tall slender structures and supporting their self-weight is difficult. This thesis proposes to re-design the chimney as a fabric structure, held aloft with lighter-than-air gas. The performance of initial, small scale suspended chimney prototypes under lateral loading was investigated experimentally to assess the response to wind loads. A novel method of stiffening is proposed and design of larger prototypes developed. The economic viability of a commercial-scale suspended chimney was investigated, yielding cost reductions compared to conventional chimney designs.

Concentrated solar power (CSP) is a fast-growing technology for electricity production. With mirrors (heliostats) irradiation of the sun is concentrated onto a receiver run through by a heat transfer fluid (HTF). The fluid by that reaches high temperatures and is used to drive a steam turbine for electricity production. A CSP power plant is most often coupled with an energy storage unit, where the HTF is stored before it is dispatched and used to generate electricity. Electricity is most often sold at an open market with a fluctuating spot-prices. It is therefore of high importance to generate and sell the electricity at the highest paid hours, increasingly important also since the governmental support mechanisms aimed to support renewable energy production is faded out since the technology is starting to be seen as mature enough to compete by itself on the market. A solar power plant thus has an operational protocol determining when energy is dispatched, and electricity is sold. These protocols are often pre-defined which means an optimal production is not achieved since irradiation and electricity selling price vary. In this master thesis, an optimization algorithm for electricity sales is designed (in MATLAB). The optimization algorithm is designed by for a given timeframe solve an optimization problem where the objective is maximized revenue from electricity sales from the solar power plant. The function takes into consideration hourly varying electricity spot price, hourly varying solar field efficiency, energy flows in the solar power plant, start-up costs (from on to off) plus conditions for the logic governing the operational modes. Two regular pre-defined protocols were designed to be able to compare performance in a solar power plant with the optimized dispatch protocol. These three operational protocols were evaluated in three different markets; one with fluctuating spot price, one regulated market of three fixed price levels and one in spot market but with zero-prices during sunny hours. It was found that the optimized dispatch protocol gave both bigger electricity production and revenue in all markets, but with biggest differences in the spot markets. To evaluate in what type of powerplant the optimizer performs best, a parametric analysis was made where size of storage and power block, the time-horizon of optimizer and the cost of start-up were varied. For size of storage and power block it was found that revenue increased with increased size, but only up to the level where the optimizer can dispatch at optimal hours. After that there is no increase in revenue. Increased time horizon gives increased revenue since it then has more information. With a 24-hour time horizon, morning price-peaks will be missed for example. To change start-up costs makes the power plant less flexible and with fewer cycles, without affect income much.
Koncentrerad solkraft (CSP) är en snabbt växande teknologi för elektricitets-produktion. Med speglar (heliostater) koncentreras solstrålar på en mottagare som genomflödas av en värmetransporteringsvätska. Denna uppnår därmed höga temperaturer vilket används för att driva en ångturbin för att generera el. Ett CSP kraftverk är oftast kopplat till en energilagringstank, där värmelagringsvätskan lagras innan den används för att generera el. El säljs i de flesta fall på en öppen elmarknad, där spotpriset fluktuerar. Det är därför av stor vikt att generera elen och sälja den vid de timmar med högst elpris, vilket också är av ökande betydelse då supportmekanismerna för att finansiellt stödja förnybar energiproduktion används i allt mindre grad för denna teknologi då den börjar anses mogen att konkurrera utan. Ett solkraftverk har således ett driftsprotokoll som bestämmer när el ska genereras. Dessa protokoll är oftast förutbestämda, vilket innebär att en optimal produktion inte fås då exempelvis elspotpriset och solinstrålningen varierar. I detta examensarbete har en optimeringsalgoritm för elförsäljning designats (i MATLAB). Optimeringsscriptet är designat genom att för en given tidsperiod lösa ett optimeringsproblem där objektivet är maximerad vinst från såld elektricitet från solkraftverket. Funktionen tar hänsyn till timvist varierande elpris, timvist varierande solfältseffektivitet, energiflöden i solkraftverket, kostnader för uppstart (on till off) samt villkor för att logiskt styra de olika driftlägena. För att jämföra prestanda hos ett solkraftverk med det optimerade driftsprotokollet skapades även två traditionella förutbestämda driftprotokoll. Dessa tre driftsstrategier utvärderades i tre olika marknader, en med ett varierande el-spotpris, en i en reglerad elmarknad med tre prisnivåer och en i en marknad med spotpris men noll-pris under de soliga timmarna. Det fanns att det optimerade driftsprotokollet gav både större elproduktion och högre vinst i alla marknader, men störst skillnad fanns i de öppna spotprismarknaderna. För att undersöka i vilket slags kraftverk som protokollet levererar mest förbättring i gjordes en parametrisk analys där storlek på lagringstank och generator varierades, samt optimerarens tidshorisont och kostnad för uppstart. För lagringstank och generator fanns att vinst ökar med ökande storlek upp tills den storlek optimeraren har möjlighet att fördela produktion på dyrast timmar. Ökande storlek efter det ger inte ökad vinst. Ökande tidshorisont ger ökande vinst eftersom optimeraren då har mer information. Att ändra uppstartkostnaden gör att solkraftverket uppträder mindre flexibelt och har färre cykler, dock utan så stor påverkan på inkomst.

In recent years there has been an increasing interest in power generation using small-scale concentrated solar power units. Currently, photovoltaics are the main commercialised technology thanks to their low capital cost. However, their relatively low efficiency and power density has motivated research on the application of thermal engines. Dish-Stirling systems achieve reasonable efficiencies, but are relatively expensive and unreliable because of their technical complexity. The reliability of micro gas turbines and their potentially lower costs has motivated the current research, which is part of the EU funded OMSoP project, to study the thermo-economic performance of a micro gas turbine (MGT) engine coupled with dish concentrators in order to achieve suitable efficiency at low cost. To achieve this goal a system design, which takes into account the state of the art technology, is required to achieve an acceptable efficiency with minimised capital cost to promote dish-MGT systems in the market. An important issue to be addressed is to consider the effect of system design parameters on dish-MGT performance under the considerable variations of the solar irradiance. A computational model for pure solar dish-MGT systems has been developed, which combines the cycle analysis of the MGT with component models to perform design point performance simulation, generate component performance maps and perform off-design performance simulation. The method has been proven to be quick and effective, particularly in terms of using minimal data and providing the component performance maps for off-design simulation. Different strategies which can be applied to pure solar dish-MGT systems are examined and novel concepts have been proposed to increase the generated electricity. The computational model has been coupled with an up to date economic model which was specifically developed through the OMSoP project for dish-MGT systems. The integrated model is coupled to an optimisation platform to find system designs which lead to optimal thermo-economic performance for a 5kWe system. Then the optimisation has been extended over the rated power of 5-30kWe to find the power rating which results in the minimum cost of generated electricity by the dish-MGT systems. The proposed concepts for the control and operation of the dish-MGT systems are shown to be advantageous for increasing electricity production and dealing with the variations of power demand. The results demonstrate the potential of pure solar dish-MGT systems to achieve economically competitive electricity when the economy of scale of these systems is taken into account.

Centrala solmottagarsystem (CRS) är på frammarsch på grund av deras höga koncentrationsfaktor och höga potential att minska kostnaderna genom att öka kapacitetsfaktorn av solkraftanläggningar med lagring. I CRS kraftanläggningar är solljuset fokuserat på mottagaren genom arrangemanget av tusentals speglar för att omvandla solstrålning till värme för att driva värmecykler. Solmottagare används för att överföra värmeflux från solen till arbetsmediet. Generellt arbetar solmottagare i driftpunkter med hög temperatur och därför genereras strålningsförluster. Vidare har solmottagaren en betydande påverkan på den totala kostnaden för kraftverket. Således har konstruktion och modellering av mottagaren en signifikant påverkan på kraftanläggningseffektivitet och kostnad. Målet med detta examensarbete är att utveckla en designmetodik för att beräkna geometrin hos solmottagaren och dess verkningsgrad. Denna designmetodik riktar sig främst till stora kraftverk i området 100 MWe, men även skalbarheten av designmetoden har studerats. Den utvecklade konstruktionsmetoden implementerades i in-house designverktyg devISEcrs som även integrerar andra moduler som modellerar solspegelfält, lagring och kraftblocket för att beräkna den totala kraftverksverkningsgraden. Designmodeller för de andra komponenterna är delvis redan implementerade, men de är modifierade och/eller utvidgade för att integrera den nya CRS mottagarmodellen. Slutligen har hela mottagarmodellen validerats genom att jämföra resultaten med testdata från litteraturen.
Central Receiver Systems (CRS) are gaining momentum because of their high concentration and high potential to reduce costs by means of increasing the capacity factor of the plant with storage. In CRS plants, sunlight is focused onto the receiver by the arrangement of thousands of mirrors to convert the solar radiation into heat to drive thermal cycles. Solar receivers are used to transfer the heat flux received from the solar field to the working fluid. Generally, solar receivers work in a high-temperature environment and are therefore subjected to different heat losses. Also, the receiver has a notable impact on the total cost of the power plant. Thus, the design and modelling of the receiver has a significant influence on efficiency and the cost of the plant. The goal of the master thesis is to develop a design methodology to calculate the geometry of the receiver and its efficiency. The design methodology is mainly aimed at large-scale power plants in the range of 100 MWe, but also the scalability of the design method has been studied. The developed receiver design method is implemented in the in-house design tool devISEcrs and also it is integrated with other modules like solar field, storage and power block to calculate the overall efficiency of the power plant. The design models for other components are partly already implemented, but they are modified and/or extended according to the requirements of CRS plants. Finally, the entire receiver design model is validated by comparing the results of test cases with the data from the literature.

Thesis (MScIng)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: This study investigates energy generation by large-scale solar tower power plants. The performance characteristics of a so-called reference plant with a 4000 m diameter glass collector roof and a 1500 m high, 160 m diameter tower are determined for a site located in South Africa. The relevant draught and conservation equations are derived, discretized and implemented in a numerical model which solves the equations using speci ed meteorological input data and determines the power delivered by the plant. The power output of a solar tower power plant over a twenty-four hour period is presented. Corresponding temperature distributions in the ground under the collector are shown. Variations in seasonal generation are evaluated and the total annual electrical output is determined. The dependency of the power output on collector diameter and tower height is illustrated, while showing that greater power production can be facilitated by optimizing the roof shape and height. The minor in uence of the tower shadow falling across the collector is evaluated, while the e ect of prevailing winds on the power generated is found to be signi cant.
AFRIKAANSE OPSOMMING: Hierdie studie ondersoek elektrisiteitsopwekking deur grootskaalse sontoringkragstasies. Die uitsetkarakteristieke van 'n sogenaamde verwysings-kragstasie met 'n 4000 m deursnee glas kollektor en 'n 1500 m hoë, 160 m deursnee toring word ondersoek vir 'n spesi eke ligging in Suid-Afrika. Die toepaslike trek- en behoudsvergelykings word afgelei, gediskretiseer en geimplementeer in 'n numeriese rekenaarmodel. Die rekenaarmodel los die betrokke vergelykings op deur gebruik te maak van gespesi seerde meteorologiese invoerdata en bepaal dan die uitset gelewer deur die kragstasie. Die uitset van 'n sontoring-kragstasie oor 'n periode van vier-en-twintig uur word getoon. Ooreenstemmende temperatuurverdelings in die grond onder die kollektor word geïllustreer. Die variasie in seisoenale elektrisiteitsopwekking word ondersoek en die totale jaarlikse elektriese uitset bepaal. Die invloed wat die kragstasie dimensies (kollektor deursnee en toring hoogte) op die uitset het, word bestudeer en resultate getoon. Daar is ook bevind dat verhoogde uitset meegebring kan word deur die vorm en hoogte van die kollektordak te optimeer. Die geringe e ek van die toringskadu op die kollektor word bespreek, terwyl bevind is dat heersende winde 'n beduidende e ek op die kragstasie uitset het.

The provision of a sustainable energy supply is one of the most importantissues facing humanity at the current time, and solar thermal power hasestablished itself as one of the more viable sources of renewable energy. Thedispatchable nature of this technology makes it ideally suited to forming thebackbone of a future low-carbon electricity system.However, the cost of electricity from contemporary solar thermal power plantsremains high, despite several decades of development, and a step-change intechnology is needed to drive down costs. Solar gas-turbine power plants are apromising new alternative, allowing increased conversion efficiencies and asignificant reduction in water consumption. Hybrid operation is a furtherattractive feature of solar gas-turbine technology, facilitating control andensuring the power plant is available to meet demand whenever it occurs.Construction of the first generation of commercial hybrid solar gas-turbinepower plants is complicated by the lack of an established, standardised, powerplant configuration, which presents the designer with a large number ofchoices. To assist decision making, thermoeconomic studies have beenperformed on a variety of different power plant configurations, includingsimple- and combined-cycles as well as the addition of thermal energy storage.Multi-objective optimisation has been used to identify Pareto-optimal designsand highlight trade-offs between costs and emissions.Analysis of the simple-cycle hybrid solar gas-turbines revealed that, whileelectricity costs were kept low, the achievable reduction in carbon dioxideemissions is relatively small. Furthermore, an inherent trade-off between thedesign of high efficiency and high solar share hybrid power plants wasidentified. Even with the use of new optimised designs, the degree of solarintegration into the gas-turbine did not exceed 63% on an annual basis.In order to overcome the limitations of the simple-cycle power plants, twoimprovements were suggested: the integration of thermal energy storage, andthe use of combined-cycle configurations. Thermal energy storage allowed thedegree of solar operation to be extended, significantly decreasing carbondioxide emissions, and the addition of a bottoming-cycle reduced the electricitycosts. A combination of these two improvements provided the bestperformance, allowing a reduction in carbon dioxide emissions of up to 34%and a reduction in electricity costs of up to 22% compared to a combination ofconventional power generation technologies.
Hållbar energiförsörjning är för närvarande en av de viktigaste frågorna förmänskligheten. Koncentrerad solenergi är nu etablerad som en tillförlitlig källaav förnybar energi. Den reglerbara karaktären hos tekniken gör den specielltintressant för uppbyggnaden av ett framtida koldioxidsnålt elsystem.Kostnaden för elektricitet från nuvarande termiska solkraftverk är hög trottsflera decennier av utveckling. Ett genombrått på tekniknivå krävs för att drivaned kostnaderna. Sol-gasturbiner är ett av de mest lovande alternativen, somger en ökad verkningsgrad samtidigt som vattenkonsumtionen reducerasdrastiskt. Sol-gasturbintekniken gör det möjligt att blandköra solenergi ochandra bränslen för att möta efterfrågan vid alla tidpunkter, en attraktiv aspekt iförhållande till alternativa lösningar.Uppbyggnaden av första generationens kommersiella hybrida solgasturbinkraftverkförsvåras dock av bristen på etablerade och standardiseradekraftverkskonfigurationer. Dessa ger planeraren ett stort antal valmöjlighetersom underlag för beslutsfattande. Termoekonomiska studier har genomförtsför ett flertal olika kraftverkskonfigurationer, däribland kraftverk med enkelcykel, kombikraftverk samt möjligheten att utnyttja termisk energilagring.Pareto-optimala konfigurationer har identifierats med hjälp av multiobjektsoptimeringför att belysa balansen mellan kostnader och utsläpp.Analysen av det enkla hybrida sol-gasturbinkraftverket visade attelektricitetskostnaden hållits på en låg nivå, men att den möjliga minskningen avkoldioxidutsläpp är relativt liten. Dessutom identifierades en inre balans mellanatt bibehålla en hög verkningsgrad hos konfigurationen och en hög andelsolenergi i produktionen. Andelen av solenergi i gasturbinen överskred aldrig63% på årlig bas, även med optimerade kraftverkskonfigurationer.Två förbättringar föreslås för att övervinna begränsningarna hos kraftverk medenkel cykel: integration av termisk energilagring samt nyttjande avkombikraftverkskonfigurationer. Termisk energilagring tillåter en ökad andelsolenergi i driften och reducerar koldioxidutsläppen drastiskt, medan denytterligare cykeln hos kombikraftverket reducerar elektricitetskostnaden.Kombinationen av dessa förbättringar ger den bästa prestandan, med enreduktion av koldioxidutsläppen på upp till 34% och reducerade elektricitetskostnaderpå upp till 22% i jämförelse med andra kombinationer avkonventionella kraftverkskonfigurationer.

QC 20130503

Parts of the auxiliary power systems at Fortum's hydro power stations are usingdirect current, which is fed from the generators at the plant and converted byrectifiers. As photovoltaic solar cells produce direct current there are severalhypothetical advantages to use solar power for the auxiliary power supply, e.g.enabling more of the power from the generator to be sold to the grid. It eliminatesthe need of an inverter, conversion losses are avoided and less load is put on therectifiers. However the exclusion of an inverter also prevents the solar cells to have adirect connection to the grid, which in turn makes them ineligible for the Swedishgovernmental solar power investment support program. The lesser load on therectifiers will not affect their lifetime according to manufacturers and thus achieves noeconomic gain. Avoiding conversion losses will increase the gain from the producedelectricity by enabling even more power to be sold to the grid. The economic gainfrom avoiding conversion losses is however too small to gain any feasibility in a smallsolar power installation at a hydro power plant, as the small size will make itexpensive in terms of investment per Wp.

The performance of parabolic trough based solar power plants over the last 25 years has proven that this technology is an excellent alternative for the commercial power industry. Compared to conventional power plants, parabolic trough solar power plants produce significantly lower levels of carbon dioxide, although additional research is required to bring the cost of concentrator solar plants to a competitive level. The cost reduction is focused on three areas: thermodynamic efficiency improvements by research and development, scaling up of the unit size, and mass production of the equipment. The optimum design, performance simulation and cost analysis of the parabolic trough solar plants are essential for the successful implementation of this technology. A detailed solar power plant simulation and analysis of its components is needed for the design of parabolic trough solar systems which is the subject of this research. Preliminary analysis was carried out by complex models of the solar field components. These components were then integrated into the system whose performance is simulated to emulate real operating conditions. Sensitivity analysis was conducted to get the optimum conditions and minimum levelized cost of electricity (LCOE). A simplified methodology was then developed based on correlations obtained from the detailed component simulations. A comprehensive numerical simulation of a parabolic trough solar power plant was developed, focusing primarily on obtaining a preliminary optimum design through the simplified methodology developed in this research. The proposed methodology is used to obtain optimum parameters and conditions such as: solar field size, operating conditions, parasitic losses, initial investment and LCOE. The methodology is also used to evaluate different scenarios and conditions of operation. The new methodology was implemented for a 50 MWe parabolic trough solar power plant for two cities: Tampa and Daggett. The results obtained for the proposed methodology were compared to another physical model (System Advisor Model, SAM) and a good agreement was achieved, thus showing that this methodology is suitable for any location.

Thesis (PhD)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Concentrating solar power plants are a promising means of generating electricity. However, they are dependent on the sun as a source of energy, and require thermal storage to supply power on demand. At present thermal storage – usually molten salt – although functional, is expensive, and a cheaper solution is desired. It is proposed that sensible heat storage in a packed bed of rock, with air as heat transfer medium, is suitable at temperatures of 500 – 600 °C. To determine if this concept is technically feasible and economically competitive with existing storage, rock properties, packed bed pressure drop and thermal characteristics must be understood. This work addresses these topics. No previously published data is available on thermal cycling resistance of South African rock, and there is limited data from other countries in the proposed temperature range for long-term thermal cycling, so samples were thermally cycled. There is rock which is suitable for thermal storage applications at temperatures of 500 – 600 °C. New maps of South Africa showing where potentially suitable rock is available were produced. Dolerite, found extensively in the Karoo, is particularly suitable. Friction factors were measured for beds of different particles to determine the importance of roughness, shape, and packing arrangement. Five sets of rock were also tested, giving a combined dataset broader than published in any previous study. Limitations of existing correlations are shown. The friction factor is highly dependent on particle shape and, in the case of asymmetric particles, packing method. The friction factor varied by up to 70 % for crushed rock depending on the direction in which it was poured into the test section, probably caused by the orientation of the asymmetric rock relative to the air flow direction. This has not been reported before for rock beds. New isothermal correlations using the volume equivalent particle diameter are given: they are within 15 % of the measurements. This work will allow a techno-economic evaluation of crushed rock beds using more accurate predictions of pumping power than could previously be made. Thermal tests below 80 °C show that bed heat transfer is insensitive to particle shape or type. A heat transfer correlation for air in terms of the volume equivalent diameter was formulated and combined with the E-NTU method. The predicted bed outlet temperatures are within 5 °C of the measurements for tests at 530 °C, showing that the influence of thermal conduction and radiation can be reasonably negligible for a single charge/discharge cycle at mass fluxes around 0.2 kg/m2s. A novel method for finding the optimum particle size and bed length is given: The Biot number is fixed, and the net income (income less bed cost) from a steam cycle supplied by heat from the bed is calculated. A simplified calculation using the method shows that the optimum particle size is approximately 20 mm for bed lengths of 6 – 7 m. Depending on the containment design and cost, the capital cost could be an order of magnitude lower than a nitrate salt system.
AFRIKAANSE OPSOMMING: Gekonsentreerde son-energie kragstasies is n belowende manier om elektrisiteit op te wek, maar hulle is afhanklik van die son as n bron van energie. Om drywing op aanvraag te voorsien moet hulle energie stoor. Tans is termiese stoor – gewoonlik gesmelte sout – hoewel funksioneel, duur, en n goedkoper oplossing word gesoek. Daar word voorgestel dat stoor van voelbare warmte-energie in n gepakte rotsbed met lug as warmteoordrag medium geskik is by temperature van 500 – 600 °C. Om te bepaal of dié konsep tegnies gangbaar en ekonomies mededingend met bestaande stoorstelsels is, moet rotseienskappe, gepakte bed drukval en hitteoordrag verstaan word. Hierdie werk spreek hierdie aspekte aan. Geen voorheen gepubliseerde data is beskikbaar oor die termiese siklus weerstand van Suid-Afrikaanse rots nie, en daar is beperkte data van ander lande in die voorgestelde temperatuurbereik, dus is monsters onderwerp aan termiese siklusse. Daar bestaan rots wat geskik is vir termiese stoor toepassings by temperature van 500 – 600 °C. Nuwe kaarte van Suid-Afrika is opgestel om te wys waar potensieel geskikte rots beskikbaar is. Doleriet, wat wyd in die Karoo voor kom, blyk om veral geskik te wees. Wrywingsfaktore is gemeet vir beddens van verskillende partikels om die belangrikheid van grofheid, vorm en pak-rangskikking te bepaal. Vyf rotsstelle is ook getoets, wat n saamgestelde datastel gee wyer as in enige gepubliseerde studie. Beperkings van bestaande korrelasies word aangetoon. Die wrywingsfaktor is hoogs sensitief vir partikelvorm en, in die geval van asimmetriese partikels, pakkings metode. Die wrywingsfaktor het met tot 70 % gevarieer vir gebreekte rots, afhanklik van die rigting waarin dit in die toetsseksie neergelê is. Dit is waarskynlik veroorsaak deur die oriëntasie van die asimmetriese rots relatief tot die lugvloei rigting, en is nie voorheen vir rotsbeddens gerapporteer nie. Nuwe isotermiese korrelasies wat gebruik maak van die volume-ekwivalente partikel deursnee word gegee: hulle voorspel binne 15 % van die gemete waardes. Hierdie werk sal n tegno-ekonomiese studie van rotsbeddens toelaat wat meer akkurate voorspellings van pompdrywing gebruik as voorheen moontlik was. Termiese toetse onder 80 °C wys dat die warmteoordrag nie baie sensitief is vir partikelvorm en -tipe nie. n Warmte-oordragskorrelasie vir lug in terme van die volume-ekwivalente deursnee is ontwikkel en met die E-NTU-metode gekombineer. Die voorspelde lug uitlaat temperatuur is binne 5 °C van die meting vir toetse by 530 °C. Dit wys dat termiese geleiding en straling redelikerwys buite rekening gelaat kan word vir n enkele laai/ontlaai siklus by massa vloeitempos van omtrent 0.2 kg/m2s. n Oorspronklike metode vir die bepaling van die optimum partikelgrootte en bedlengte word gegee: Die Biot-getal is vas, en die netto inkomste (die inkomste minus die bed omkoste) van n stoomsiklus voorsien met warmte van die bed word bereken. n Vereenvoudigde berekening wat die metode gebruik wys dat die optimum grootte en lengte ongeveer 20 mm en 6-7 m is. Afhangende van die behoueringsontwerp en koste, kan die kapitale koste n orde kleiner wees as dié van n gesmelte nitraatsout stelsel

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 43-44).
Carbon Dioxide emissions from power production are believed to have significant contributions to the greenhouse effect and global warming. Alternative energy resources, such as solar radiation, may help abate emissions but suffer from high costs of power production and temporal variations. On the other hand, Carbon Capture and Sequestration allows the continued use of fossil fuels without the CO2 emissions but it comes at an energetic penalty. The Advanced Zero Emissions Plant (AZEP) minimizes this energy loss by making use of Ion Transport Membrane (ITM)-based oxy-combustion to reduce the cost of carbon dioxide separation. This work seeks to assess if there are any thermodynamic gains from hybridizing solar-thermal energy with AZEP. The particular focus is hybridizing of the bottoming cycle with supplemental solar heating. A simple model of parabolic solar trough was used to hybridize a model of the AZEP cycle in ASPEN Plus*. Two cycle configurations are studied: the first uses solar parabolic troughs to indirectly vaporize high pressure steam through Therminol and the second uses parabolic troughs to directly preheat the high pressure water stream prior to vaporization. Simulations of the solar vaporizer hybrid by varying the total area of collectors (holding fuel input constant) show an increase of net electric output from 439MW for the non-hybridized AZEP to 533MW with an input solar share of 38.8%. The incremental solar efficiency is found to be around 16% for solar shares of input ranging from 5% to 38.8%. Moreover, simulations of variable solar insolation for collector area of 550,000 m2 , show that incremental solar efficiency increased with solar insolation reaching a plateau around 17%. Simulations of the direct solar preheater, show a net electric output of 501.3 MW for a solar share of 35%, (an incremental solar efficiency of 13.73%). The power generation and hence incremental efficiency is lower than in hybridization with steam vaporization with the same input solar share. Synergy analysis for the steam vaporization hybrid indicates no thermodynamic gains from hybridization.
by Ragheb Mohamad Fawaz El Khaja.
S.B.

This thesis examined solar thermal collectors for use in alternative hybrid solar-biomass power plant applications in Gujarat, India. Following a preliminary review, the cost-effective selection and design of the solar thermal field were identified as critical factors underlying the success of hybrid plants. Consequently, the existing solar thermal technologies were reviewed and ranked for use in India by means of a multi-criteria decision-making method, the Analytical Hierarchy Process (AHP). Informed by the outcome of the AHP, the thesis went on to pursue the Linear Fresnel Reflector (LFR), the design of which was optimised with the help of ray-tracing. To further enhance collector performance, LFR concepts incorporating novel mirror spacing and drive mechanisms were evaluated. Subsequently, a new variant, termed the Elevation Linear Fresnel Reflector (ELFR) was designed, constructed and tested at Aston University, UK, therefore allowing theoretical models for the performance of a solar thermal field to be verified. Based on the resulting characteristics of the LFR, and data gathered for the other hybrid system components, models of hybrid LFR- and ELFR-biomass power plants were developed and analysed in TRNSYS®. The techno-economic and environmental consequences of varying the size of the solar field in relation to the total plant capacity were modelled for a series of case studies to evaluate different applications: tri-generation (electricity, ice and heat), electricity-only generation, and process heat. The case studies also encompassed varying site locations, capacities, operational conditions and financial situations. In the case of a hybrid tri-generation plant in Gujarat, it was recommended to use an LFR solar thermal field of 14,000 m2 aperture with a 3 tonne biomass boiler, generating 815 MWh per annum of electricity for nearby villages and 12,450 tonnes of ice per annum for local fisheries and food industries. However, at the expense of a 0.3 ¢/kWh increase in levelised energy costs, the ELFR increased saving of biomass (100 t/a) and land (9 ha/a). For solar thermal applications in areas with high land cost, the ELFR reduced levelised energy costs. It was determined that off-grid hybrid plants for tri-generation were the most feasible application in India. Whereas biomass-only plants were found to be more economically viable, it was concluded that hybrid systems will soon become cost competitive and can considerably improve current energy security and biomass supply chain issues in India.

Mechanical Engineering
Ph.D.
Thermal energy storage systems as an integral part of concentrated solar power plants improve the performance of the system by mitigating the mismatch between the energy supply and the energy demand. Using a phase change material (PCM) to store energy increases the energy density, hence, reduces the size and cost of the system. However, the performance is limited by the low thermal conductivity of the PCM, which decreases the heat transfer rate between the heat source and PCM, which therefore prolongs the melting, or solidification process, and results in overheating the interface wall. To address this issue, heat pipes are embedded in the PCM to enhance the heat transfer from the receiver to the PCM, and from the PCM to the heat sink during charging and discharging processes, respectively. In the current study, the thermal-fluid phenomenon inside a heat pipe was investigated. The heat pipe network is specifically configured to be implemented in a thermal energy storage unit for a concentrated solar power system. The configuration allows for simultaneous power generation and energy storage for later use. The network is composed of a main heat pipe and an array of secondary heat pipes. The primary heat pipe has a disk-shaped evaporator and a disk-shaped condenser, which are connected via an adiabatic section. The secondary heat pipes are attached to the condenser of the primary heat pipe and they are surrounded by PCM. The other side of the condenser is connected to a heat engine and serves as its heat acceptor. The applied thermal energy to the disk-shaped evaporator changes the phase of working fluid in the wick structure from liquid to vapor. The vapor pressure drives it through the adiabatic section to the condenser where the vapor condenses and releases its heat to a heat engine. It should be noted that the condensed working fluid is returned to the evaporator by the capillary forces of the wick. The extra heat is then delivered to the phase change material through the secondary heat pipes. During the discharging process, secondary heat pipes serve as evaporators and transfer the stored energy to the heat engine. Due to the different geometry of the heat pipe network, a new numerical procedure was developed. The model is axisymmetric and accounts for the compressible vapor flow in the vapor chamber as well as heat conduction in the wall and wick regions. Because of the large expansion ratio from the adiabatic section to the primary condenser, the vapor flow leaving the adiabatic pipe section of the primary heat pipe to the disk-shaped condenser behaves similarly to a confined jet impingement. Therefore, the condensation is not uniform over the main condenser. The feature that makes the numerical procedure distinguished from other available techniques is its ability to simulate non-uniform condensation of the working fluid in the condenser section. The vapor jet impingement on the condenser surface along with condensation is modeled by attaching a porous layer adjacent to the condenser wall. This porous layer acts as a wall, lets the vapor flow to impinge on it, and spread out radially while it allows mass transfer through it. The heat rejection via the vapor condensation is estimated from the mass flux by energy balance at the vapor-liquid interface. This method of simulating heat pipe is proposed and developed in the current work for the first time. Laboratory cylindrical and complex heat pipes and an experimental test rig were designed and fabricated. The measured data from cylindrical heat pipe were used to evaluate the accuracy of the numerical results. The effects of the operating conditions of the heat pipe, heat input, and portion of heat transferred to the phase change material, main condenser geometry, primary heat pipe adiabatic radius and its location as well as secondary heat pipe configurations have been investigated on heat pipe performance. The results showed that in the case with a tubular adiabatic section in the center, the complex interaction of convective and viscous forces in the main condenser chamber, caused several recirculation zones to form in this region, which made the performance of the heat pipe convoluted. The recirculation zone shapes and locations affected by the geometrical features and the heat input, play an important role in the condenser temperature distributions. The temperature distributions of the primary condenser and secondary heat pipe highly depend on the secondary heat pipe configurations and main condenser spacing, especially for the cases with higher heat inputs and higher percentages of heat transfer to the PCM via secondary heat pipes. It was found that changing the entrance shape of the primary condenser and the secondary heat pipes as well as the location and quantity of the secondary heat pipes does not diminish the recirculation zone effects. It was also concluded that changing the location of the adiabatic section reduces the jetting effect of the vapor flow and curtails the recirculation zones, leading to higher average temperature in the main condenser and secondary heat pipes. The experimental results of the conventional heat pipe are presented, however the data for the heat pipe network is not included in this dissertation. The results obtained from the experimental analyses revealed that for the transient operation, as the heat input to the system increases and the conditions at the condenser remains constant, the heat pipe operating temperature increases until it reaches another steady state condition. In addition, the effects of the working fluid and the inclination angle were studied on the performance of a heat pipe. The results showed that in gravity-assisted orientations, the inclination angle has negligible effect on the performance of the heat pipe. However, for gravity-opposed orientations, as the inclination angle increases, the temperature difference between the evaporator and condensation increases which results in higher thermal resistance. It was also found that if the heat pipe is under-filled with the working fluid, the capillary limit of the heat pipe decreases dramatically. However, overfilling of the heat pipe with working fluid degrades the heat pipe performance due to interfering with the evaporation-condensation mechanism.
Temple University--Theses

The irruption of renewable energy sources with power electronics interfaces is transforming power systems. To minimize the possible adverse effects that these generating systems may have on the power grid, transmission system operators define different strategies, such as increasing the active power reserves for frequency control and power balancing purposes, and require all connected systems to comply with various rules and regulations. In an effort to better integrate these renewable sources in power systems, some power converter controllers have been proposed that aim at reproducing certain features of conventional synchronous machines. This work deals with the analysis of the impact that large power-electronics-based power plants, in the range of hundreds of megawatts, have on the stability of power systems. First, the main characteristics of these advanced controllers, sometimes referred to as virtual synchronous machines, are reviewed, and their constituting blocks are systematically classified. This classification allows performing a detailed comparison of different aspects regarding their implementation and dynamics. The proposals usually found in the literature are compared in terms of their need for ancillary synchronization systems, their ability to energize a grid, or their effectiveness to limit the current injected during a fault and keep the converters connected to the grid. Additionally, time-domain simulations comparing the response of power converters employing these controllers are carried out and analyzed. Afterwards, since the study of power system stability requires adequate models of the elements interacting with the system, the modeling of an actual 100 MW photovoltaic power plant, consisting of 100 power converters, is addressed. Thus, a detailed model of the power plant is developed, considering a single-phase equivalent for transient stability studies in balanced systems. This model includes the internal network buses, cables, and transformers, and the power converters with their control systems and primary resources. Moreover, the model is implemented in a flexible way that allows considering power converters employing conventional controllers or synchronous power controllers, and the photovoltaic resource can be replaced by a storage system. Furthermore, a method to derive an equivalent model of power plants employing these advanced controllers is developed, and three equivalent models of the power plant, with different degrees of detail, are implemented employing this method. These models allow reducing the complexity of the original model and its associated computational burden, while reproducing its dynamics with accuracy, making them more suitable for the analysis of power systems with a large number of generating units, loads, passive elements, and controllers. Finally, the stability of power systems integrating this type of generating stations is analyzed. A first analysis is carried out in a 12-bus test system, considering a simpler model of the plant where the photovoltaic characteristics are modeled only through an active power limitation, and comparing the impact of these plants as the solar penetration grows, up to a 50% level. This is followed by the analysis of the power system of northern Chile, considering the actual location of the power plant previously modeled, and including the full detail of the photovoltaic resource. Lastly, the impact of hybrid power plants consisting of a synchronous generator and a photovoltaic system, with different configurations with the possibility of curtailing the solar production or employing a storage system, is assessed. These analyses comprise the study of the eigenvalues of the system and its response to different types of events through time-domain simulation, and prove the ability of the studied controllers to increase the damping of the system , to reduce the oscillations suffered by other generators, and to limit maximum frequency deviations.
La irrupción de fuentes de energía renovables como la energía solar fotovoltaica está transformando los sistemas eléctricos. Para minimizar los posibles efectos adversos sobre la red eléctrica de los sistemas de generación conectados mediante convertidores de electrónica de potencia, los operadores de los sistemas eléctricos definen diferentes estrategias y exigen que todos los sistemas conectados a la red cumplan diferentes normas. Con el objetivo de permitir una mejor integración de estas fuentes renovables, se han propuesto varios controladores de convertidores de potencia que intentan reproducir algunas características de las máquinas síncronas convencionales. Esta tesis trata sobre el análisis del impacto que las centrales eléctricas de grandes dimensiones basadas en electrónica de potencia tienen en la estabilidad de los sistemas eléctricos. En primer lugar, se clasifican estos controladores avanzados, lo que permite realizar una comparación detallada de varios aspectos relacionados con su implementación y su dinámica. Las propuestas más comunes se comparan en cuanto a su necesidad de sistemas de sincronización auxiliares, su habilidad para energizar una red, o su efectividad a la hora de limitar la corriente inyectada durante una falta y mantener los convertidores conectados a la red. Además, se realizan y analizan simulaciones de la respuesta de convertidores de potencia que utilizan estos controladores. A continuación, se presenta el modelado de una planta fotovoltaica real de 100 MW formada por 100 convertidores de potencia, considerando su equivalente monofásico para estudios de estabilidad transitoria en sistemas equilibrados. Este modelo incluye los terminales, cables y transformadores de la red interna, así como los convertidores de potencia con sus sistemas de control y recursos primarios. Además, el modelo está diseñado de manera flexible, permitiendo considerar controladores convencionales o controladores de potencia síncronos, y el recurso fotovoltaico se puede sustituir por un sistema de almacenamiento. Adicionalmente, se desarrolla un método para calcular un modelo equivalente de las centrales eléctricas que utilizan esta clase de controladores avanzados y se obtienen tres modelos equivalentes de la planta, con distintos niveles de detalle. Estos modelos permiten reducir la complejidad del modelo original y su carga computacional asociada, al mismo tiempo que reproducen su dinámica con precisión, haciéndolos más adecuados para el análisis de sistemas eléctricos con un gran número de unidades de generación, cargas, elementos pasivos y controladores. Finalmente, se analiza la estabilidad de sistemas eléctricos que integran este tipo de plantas generadoras. Se lleva a cabo un primer análisis en un sistema de pruebas de doce barras, considerando un modelo más sencillo de la planta donde las características fotovoltaicas se modelan únicamente mediante una limitación de la potencia activa, y se compara el impacto de estas plantas en distintos escenarios con una penetración solar creciente, llegando a un nivel del 50% de la generación total. Después, se analiza el Sistema Interconectado del Norte Grande de Chile, teniendo en cuenta la situación real de la planta modelada previamente e incluyendo el recurso fotovoltaico en detalle. Por último, se evalúa el impacto que pueden tener las plantas híbridas formadas por un generador síncrono y un sistema fotovoltaico, con diferentes configuraciones con la posibilidad de reservar parte de la producción solar o utilizar un sistema de almacenamiento. Estos análisis comprenden el estudio tanto de los valores propios del sistema como de su respuesta a diferentes tipos de eventos mediante simulaciones en el dominio del tiempo, y demuestran la capacidad de los controladores estudiados para incrementar el amortiguamiento del sistema, reducir las oscilaciones a las que se ven sometidos otros generadores y limitar las máximas desviaciones de frecuencia.

The current energy scenario in the developing nations with abundant sun resource (e.g. southern Mediterranean countries of Europe, Middle-East & North Africa) relies mainly on fossil fuels to supply the increasing energy demand. Although this long adopted pattern ensures electricity availability on demand at all times through the least cost proven technology, it is highly unsustainable due to its drastic impacts on depletion of resources, environmental emissions and electricity prices. Solar thermal Hybrid power plants among all other renewable energy technologies have the potential of replacing the central utility model of conventional power plants, the understood integration of solar thermal technologies into existing conventional power plants shows the opportunity of combining low cost reliable power and Carbon emission reduction. A literature review on the current concentrating solar power (CSP) technologies and their suitability for integration into conventional power cycles was concluded, the best option was found be in the so called Integrated solar combined cycle systems (ISCCS); the plant is built and operated like a normal combined cycle, with a solar circuit consisting of central tower receiver and heliostat field adding heat to the bottoming Rankine cycle. A complete model of the cycle was developed in TRNSYS simulation software and Matlab environment, yearly satellite solar insolation data was used to study the effect of integrating solar power to the cycle throw-out the year. A multi objective thermo economic optimization analysis was conducted in order to identify a set of optimum design options. The optimization has shown that the efficiency of the combined cycle can be increased resulting in a Levelized electricity cost in the range of 10 -14 USDcts /Kwhe. The limit of annual solar share realized was found to be around 7 % The results of the study indicate that ISCCS offers advantages of higher efficiency, low cost reliable power and on the same time sends a green message by reducing the environmental impacts in our existing power plant systems.

The percentage of renewable energy within the global electric power generation portfolio is expected to increase rapidly over the next few decades due to increasing concerns about climate change, fossil fuel costs, and energy security. Solar thermal energy, also known as concentrating solar power (CSP), is emerging as an important solution to new demands for clean, renewable electricity generation. Dish-Stirling (DS) technology, a form of CSP, is a relatively new player in the renewable energy market, although research in the technology has been ongoing now for nearly thirty years. The first large plant utilizing DS technology, rated at 1.5 MW, came online in January 2010 in Peoria, AZ, and plants rated for several hundred MW are in the planning stages. Increasing capacity of this technology within the utility grid requires extensive dynamic simulation studies to ensure that the power system maintains its safety and reliability in spite of the technological challenges that DS technology presents, particularly related to the intermittency of the energy source and its use of a non-conventional asynchronous generator. The research presented in this thesis attempts to fill in the gaps between the well established research on Stirling engines in the world of thermodynamics and the use of DS systems in electric power system applications, a topic which has received scant attention in publications since the emergence of this technology. DS technology uses a paraboloidal shaped dish of mirrors to concentrate sunlight to a single point. The high temperatures achieved at the focal point of the mirrors is used as a heat source for the Stirling engine, which is a closed-cycle, external heat engine. Invented by the Scottish clergyman Robert Stirling in 1816, the Stirling engine is capable of high efficiency and releases no emissions, making it highly compatible with concentrated solar energy. The Stirling engine turns a squirrel-cage induction generator, where electricity is delivered through underground cables from thousands of independent, autonomous 10-25 kW rated DS units in a large solar farm. A dynamic model of the DS system is presented in this thesis, including models of the Stirling engine working gas and mechanical dynamics. Custom FORTRAN code is written to model the Stirling engine dynamics within PSCAD/EMTDC. The Stirling engine and various other components of the DS system are incorporated into an electrical network, including first a single-machine, infinite bus network, and then a larger 12-bus network including conventional generators, loads, and transmission lines. An analysis of the DS control systems is presented, and simulation results are provided to demonstrate the system's steady state and dynamic behavior within these electric power networks. Potential grid interconnection requirements are discussed, including issues with power factor correction and low voltage ride-through, and simulation results are provided to illustrate the dish-Stirling system's capability for meeting such requirements.

Computational fluid dynamics was used to simulate solar chimney power plants and investigate modeling techniques and expected energy output from the system. The solar chimney consists of three primary parts: a collector made of a transparent material such as glass, a tower made of concrete located at the center of the collector, and a turbine that is typically placed at the bottom of the tower. The collector absorbs solar radiation and heats the air below, whereby air flows inward towards the tower. As air exits at the top of the tower, more air is drawn below the collector repeating the process. The turbine converts pressure within the flow into power. The study investigated three validation cases to numerically model the system properly. Modeling the turbine as a pressure drop allows for the turbine power output to be calculated while not physically modeling the turbine. The numerical model was used to investigate air properties, such as velocity, temperature, and pressure. The results supported the claim that increasing the energy into the system increased both the velocities and temperatures. Also, increasing the turbine pressure drop decreases the velocities and increases the temperatures within the system. In addition to the numerical model, analytical models representing the vertical velocity without the turbine and the maximum power output from a specific chimney were used to investigate the effects on the flow when varying the geometry. Increasing the height of the tower increased the vertical velocity and power output, and increasing the diameter increased the power output. Dimensionless variables were used in a regression analysis to develop a predictive equation for power output. The predictive equation was tested with new simulations and was shown to be in very good agreement.
Master of Science

>Magister Scientiae - MSc
Phase change material (PCM) through latent heat of molten salt, is a convincing way for thermal energy storage in CSP applications due to its high volume density. Molten salt, with (60% NaNO3 and 40% KNO3) has been used extensively for energy storage however; the low thermal conductivity and specific heat have limited its large implementation in solar applications. For that, molten salt with the additive of silver nanowires (AgNWs) was synthesized and characterized. This research project aims to investigate the thermophysical properties enhancement of nanosalt (Mixture of molten salt and silver nanowires). The results obtained showed that by simply adjusting the temperature, Silver nanowires with high aspect ratio have been synthesized through the enhanced PVP polyol process method. SEM results revealed a network of silver nanowires and TEM results confirmed the presence of silver nanowires with an average diameter of 129 nm and 16 μm in length.

An experimental investigation is presented on a novel High Temperature Falling Particle Receiver for Concentrated Solar Power (CSP) to quantify the extent of erosion of the receiver structural materials by the flowing particulate matter. The current receiver design uses a series of metal wire mesh screens to slow down the particulate flow through the receiver in order to increase their residence time thereby achieving the desired temperature rise within the receiver without the need for particulate recirculation. The solid particulates are gravity fed through the receiver where they absorb the incident thermal energy before flowing to a high temperature storage bin upstream of a heat exchanger where the heat stored in the particulate material is transferred to the working fluid for the power cycle. To assess the effective life of the receiver, this experimental investigation is undertaken. This thesis includes the development of an apparatus to test wire meshes under high temperature and particle abrasion conditions, and the presentation and analysis of these results.