Thesis (Ph.D.)--City University of Hong Kong, 2009. / "Submitted to Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves [84]-87)

M.Ing. / The focus of the document is the development and use of an algorithm that controls a heliostat, and the high level design of that heliostat. The heliostat is only controlled by the algorithm and had a specified accuracy requirement equal to or better than 0.5 degrees. The algorithm uses the elevation and azimuth angle of sun calculated to an accuracy of 0.0003 degrees as input. The algorithm positions the heliostat to ensure a continuous reflection of sunlight into a predetermined direction for the purpose of indoor illumination. The position of the sunlight reflected into the predetermined direction is marked on a vertical grid-board placed orthogonal to the intended reflection direction. Ideally the sunlight positions marked throughout the day will all be in one location. The reflected sunlight deviated from the intended direction by only 0.28 degrees.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Concentrating solar power as a sustainable energy technology is considered favourable in South Africa due to the high solar resource and the integration possibilities with the current electricity grid. Considering the various concentrating solar power technologies, the central receiver system is thought to be one of the most promising due to its high capacity factor and cost-efficient thermal storage capabilities. These thermal systems are able to reach high temperatures (more than 1000°C have been shown), and to obtain such temperatures, a high solar flux is required. This is achievable by aiming all of the heliostats at the centre of the target. High flux gradients over the receiver surface area and between the outer and inner surfaces of the receiver material can exist. These thermal gradients account for differences in temperatures on the receiver which result in thermal stresses leading to elastic and potentially plastic deformation of the material. To eradicate the thermal stresses, the aim points of the heliostats can be managed such that the flux density distribution over the receiver aperture is decreased and homogenised. The primary objective of this thesis is to develop an aiming strategy specifically for small experimental heliostat fields. To reach this objective, a simulation platform was developed to model any heliostat field and receiver, and an analysis was conducted to compare analytical flux prediction methods to ray tracing. At high incidence angles of between 30° and 60°, the standard deviations of the circular Gaussian flux approximation methods were found to differ between approximately 10 % and 30 % from the ray traced results. A novel method, the Gaussian mixture model, was suggested and deviated less than 4 % from the ray traced results when considering the standard deviation of the flux profile. Two basic aiming strategies were developed using the Tabu search and Genetic algorithm optimisation methods. These two strategies make use of approximate method of flux prediction. Experiments were conducted to investigate static aiming strategies on physical systems and to identify factors that could have an effect on the experimental results. Finally a method of implementing the aiming strategy on a dynamic system was proposed. By implementing both optimisation methods to complement each other, a new aiming strategy was developed that proved to provide better homogenisation of the flux distribution than either of the two methods alone. The accuracy of the final predicted flux distribution was improved by using the Gaussian mixture model as the flux distribution approximation method. / AFRIKAANSE OPSOMMING: Gekonsentreerde sonenergie as ’n hernubare energie bron, word in Suid-Afrika as uitvoerbaar beskou weens die hoë stralingsdigtheid asook die moontlikheid om hierdie tegnologie te koppel aan die huidige energienetwerk. As die verskeie gekonsentreerde sonenergie tegnologieë in ag geneem word, word sentrale ontvangerstelsels beskou as die mees belowende sonenergie konsep as gevolg van die hoë energie kapasiteit en die vermoë om termiese energie te stoor. Hierdie termiese stelsels besit die vermoë om hoë temperature te bereik (meer as 1000°C is al opgemerk), en om hierdie temperature te verkry word ’n hoë termiese vloed benodig. Dit is bereikbaar deur al die heliostate op die middel van die ontvanger te rig. Hoë termiese vloedgradiënte oor die oppervlakte van die opvanger en tussen die buite- en binne laag van die opvanger materiaal kan ontstaan. Termiese vloedgradiënte kan verskille in temperatuur op die ontvanger veroorsaak wat termiese spanning tot gevolg het kan lei tot elastiese en potensieel plastiese vervorming van die materiaal. Omvan die termiese spanning ontslae te raak kan die heliostate deur beheerstelsels na ander dele van die ontvanger gerig word om sodoende ’n laer en meer egalige termiese vloed oor die oppervlak van die ontvanger te verkry. Die hoofdoel van hierdie tesis is die ontwikkeling van ’n mikstrategie, hoofsaaklik bedoel vir klein eksperimentele heliostaatvelde. Om hierdie hoofdoel te bereik, was ’n simulasieplatform ontwikkel waardeur heliostaatvelde en opvangerstelsels gemodelleer kan word, en ’n analise is gedoen om die verskeidenheid benaderende analitiese metodes te vergelyk met die straalopsporingsmetode. By hoë invalshoeke tussen 30° en 60° is daar gevind dat die benaderende modelle wat die termiese vloed as ’n normale Gaussiese verspreiding beskou, ’n afwyking van die straalopsporingsresultate toon van ongeveer 10 % tot 30 %. ’n Nuwe metode, die Gaussiese mengsel model, was voorgestel en het minder as 4 % van die straalopsporings resultate afgewyk, met die standaard afwyking van die termiese vloed profiel in ag geneem. Twee basiese mikstrategieë is ontwikkel deur gebruik te maak van die Tabu soek en Genetiese algoritme optimeringsmetodes. Hierdie strategieë maak gebruik van die benaderende metodes om termiese vloed te voorspel. Eksperimente is uitgevoer om die implementering van statiese mikstrategieë op ’n fisiese stelsel te beskou en die faktore wat ’n invloed op die eksperimentele resultate sal hê te identifiseer. Ten laaste word ’n metode voorgestel vir die implementering van die mikstrategieë op ’n dinamiese stelsel. Deur beide optimeringsmetodes te implementeer sodat hul mekaar komplimenteer, word ’n nuwe mikstrategie ontwikkel wat beter homogenisering van die termiese vloed verspreiding bewys het as enige van die alleen staande metodes. Die akkuraatheid van die finale voorgestelde termiese vloed verspreiding was verbeter deur gebruik te maak van die Gaussiese mengsel model as die benaderende metode van die termiese vloed verspreiding.

Turning solar collectors, heliostats, is certainly not a new idea but has been explored for at least two decades. Projects on this subject have resulted in more or less realistic constructions, in a commercial point of view. Far too often the technical goals have had higher priority than the economical, which has resulted in a few constructions having the ability to compete with conventional, fix solar collectors. The economical issues have been given high priority in this project, without decreasing the demands on reliability. The system has been given the following mechanical and electronical properties: One-axis movement, fix heat carrying fluid system, microcomputer controlled movement and automatic protection from overheating. According to the development in digital technology with lower prices on advanced semiconductors as a consequence, the conclusion is that the prerequisites of this concept will be even better in the future. The result of this thesis is a heliostat function that increases the energy gain by up to 40%, compared to a field of MaReCo collectors without this function. Though, the cost only increases by 13%.

<p>Turning solar collectors, heliostats, is certainly not a new idea but has been explored for at least two decades. Projects on this subject have resulted in more or less realistic constructions, in a commercial point of view. Far too often the technical goals have had higher priority than the economical, which has resulted in a few constructions having the ability to compete with conventional, fix solar collectors. The economical issues have been given high priority in this project, without decreasing the demands on reliability. The system has been given the following mechanical and electronical properties: One-axis movement, fix heat carrying fluid system, microcomputer controlled movement and automatic protection from overheating. According to the development in digital technology with lower prices on advanced semiconductors as a consequence, the conclusion is that the prerequisites of this concept will be even better in the future. The result of this thesis is a heliostat function that increases the energy gain by up to 40%, compared to a field of MaReCo collectors without this function. Though, the cost only increases by 13%.</p>

A heliostat is a motorized mirror used in a Solar Power Tower plant. The technology has been around since the 1970’s, and involves hundreds or thousands of heliostats reflecting the sun’s rays to the top of a high tower, where the incident solar energy is converted to heat energy, which in turn is used to drive steam turbines and produce electricity. Demonstration plants have been built in the U.S.A. and Spain, and a number of new facilities have been added since 2005. To achieve a commercial breakthrough, the technology must be made more efficient so that electricity can be produced at prices comparable with other options such as wind, photovoltaic, nuclear and coal. A critical component in the economics of the Solar Power Tower plant is the cost of the heliostat, which is estimated to account for approximately 50 % of the investment cost of the total plant. This report deals with the heliostat from a multifaceted perspective. Different design approaches are explained. First, mirror geometries, with manufacturing dimensions, for a rotation-symmetric paraboloid-shaped mirror-assembly are obtained for mirrors with different sizes with a Matlab code. Investigating wind loads are among the most important tasks in a heliostat development project, as large wind loads radically complicates the design work. A wind load calculation-method based on previous work by Sandia National Laboratories and finite element method (FEM) is used in this work to design heliostats to withstand expected wind loading. The design of the geometry and the structure to withstand wind loading is illustrated with two azimuth elevation heliostats (25 m 2 and 49 m2). Finally, a number of innovative technical solutions are suggested. These are a new mirror facet mounting technique, sliding bearings, elevation drive, and a very unique azimuth motor module, which uses steel wires as belts with an integrated brake. It is hoped that the results and designs presented in this thesis will be a good foundation for further research in the heliostat structures and heliostat controls at the Robotics lab in IISc and elsewhere. Keywords: Solar Power, Heliostat, Thermal solar power, Solar Power Tower, Central Receiver System / En heliostat är en motordriven spegel som används i tornsolkraftverk, kända som Solar Power Tower, även kallade Central Receiver system. Tekniken har funnits sedan 1970-talet och går ut på att hundratals eller tusentals heliostater speglar solstrålarna till toppen av ett högt torn, där stålningsenergin omvandlas till värmeenergi, som t.ex. kan användas till att driva ångturbiner och producera elektricitet. Demonstrationsanläggningar har byggts i bland annat USA och Spanien, och ett flertal nya installationer har tillkommit sedan år 2005. För att verkligen nå ett kommersiellt genombrott måste tekniken göras billigare så att solelen kan produceras till minst lika bra pris som andra alternativ, så som t.ex. solceller, kärnkraft och kolkraft. En kritisk komponent för tornsolkraftverkens ekonomi är kostnaden för heliostaterna, som beräknas stå för ungefär 50 % av anläggningens totala investeringskostnad. Den här rapporten avhandlar heliostaten ur ett mångfacetterat perspektiv där olika konstruktionsspår förklaras. Vidare behandlar rapporten spegelgeometrier, och en Matlab-kod som genererar tillverkningsmått för en rotationssymmetrisk paraboloidformad spegelyta finns bifogad. Att undersöka vindlaster är bland det viktigaste i ett heliostatutvecklingsprojekt, eftersom dessa är de dimensionerande lasterna för designarbetet. Här används en vindlastberäkningsmetod utgiven av Sandia National Laboratories, som kortfattat går ut på att man multiplicerar det dynamiska vindtrycket med en korrigeringsfaktor som baserats på emiriska studier av heliostatmodeller i vindtunnel. En dimensioneringsprocess för heliostater föreslås och utvecklingsgången för två Azimut-Elevation heliostater i storlek 25 m 2 resp. 49 m2 demonstreras. FEM-mjukvara nyttjas som det främsta verktyget för att dimensionera heliostatkonstruktioner som kan stå emot vindlasterna. Slutligen ges förslag på innovativa tekniska lösningar för spegelmontering, glidlager, montering av elevation-motorerna, och en unik azimut-motormodul, vilken använder stålvajrar som remmar och har en integrerad broms. Med all denna information bör Robotics Lab på IISc ha en god grund att stå på inför vidare forskning inom konstruktion och styrning av heliostater. Nyckelord: Solenergi, Heliostat, Termisk solenergi, Solar Power Tower, Tornsolkraftverk

Submitted by Márcio Maia (marciokjmaia@gmail.com) on 2016-08-08T12:09:17Z No. of bitstreams: 1 arquivototal.pdf: 3228826 bytes, checksum: ddfaa133f9f8a9a5a4d1f5233fb205a5 (MD5) / Made available in DSpace on 2016-08-08T12:09:17Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3228826 bytes, checksum: ddfaa133f9f8a9a5a4d1f5233fb205a5 (MD5) Previous issue date: 2016-04-22 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / With the increase of global perspectives regarding renewable energy and the use of concentrated solar thermal energy, with the goal of increasing the flow of solar radiation incident on the thermal has been shown to be a viable solution for electric power generation. The heliostats devices have the ability to track the Sun and reflect the radiation in a pre-set fixed point, usually known as solar tracking Tower in the middle of the field of heliostats devices. The solar towers have been aim of studies because they have a great potential for electric generation. The higher the desired concentration values of the system, the higher the accuracy requirements tracking and reflection of the heliostats, and the quality of reflective surfaces will be. This study aims to design and construction of the heliostat of two degrees of freedom for power generation in solar Tower systems using control methods for tracing and reflection on LabView platform. Applying tracking algorithms based on the solar behavior equations and mechanical design, allowing a two degrees’ freedom dynamic, it was gain results with 0.201 degrees in precision in the tracking of radiation reflection. / Com o aumento das perspectivas mundiais a respeito das energias renováveis e a utilização da energia solar térmica concentrada, com o objetivo de aumentar o fluxo de radiação solar incidente em sistemas térmicos tem se mostrado uma solução viável para geração de energia elétrica. Os dispositivos heliostatos tem a capacidade de rastrear o sol e refletir a radiação em um ponto fixo pré – estabelecido, normalmente conhecido como torre solar localizando se ao meio de um campo de dispositivos heliostatos. As torres solares tem sido alvo de estudos por possuir um grande potencial para geração de energia elétrica. Quanto maior os valores de concentração pretendido do sistema, maiores serão os requisitos de precisão de rastreamento e reflexão do heliostato e da qualidade das superfícies refletoras. Este trabalho tem como objetivo de projeto e construção de um heliostato de dois graus de liberdade para geração de energia em sistemas de torres solares utilizando métodos de controle para rastreamento e reflexão ótima em plataforma LabView. Aplicando algoritmos de rastreamento baseado nas equações de comportamento solar e projeto mecânico permitindo uma dinâmica de dois graus de liberdade foi obtido resultados de 0,201 graus de precisão no rastreamento de reflexão da radiação.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The ability of concentrating solar power (CSP) to efficiently store large amounts of energy sets it apart from other renewable energy technologies. However, cost reduction and improved efficiency is required for it to become more economically viable. Significant cost reduction opportunities exist, especially for central receiver system (CRS) technology where the heliostat field makes up 40 to 50 per cent of the total capital expenditure. CRS plants use heliostats to reflect sunlight onto a central receiver. Heliostats with high tracking accuracy are required to realize high solar concentration ratios. This enables high working temperatures for efficient energy conversion. Tracking errors occur mainly due to heliostat manufacturing-, installation- and alignment tolerances, but high tolerance requirements generally increase cost. A way is therefore needed to improve tracking accuracy without increasing tolerance requirements. The primary objective of this project is to develop a heliostat field control system within the context of a 5MWe CRS pilot plant. The control system has to govern the tracking movement of all heliostats in the field and minimize errors over time. A geometric model was developed to characterize four deterministic sources of heliostat tracking errors. A prototype system comprising 18 heliostats was constructed to function as a scaled down subsection of the pilot plant heliostat field and to validate the chosen control method and system architecture. Periodic measurements of individual heliostats’ tracking offsets were obtained using a camera and optical calibration target combined with image processing techniques. Mathematical optimization was used to estimate model coefficients to best fit the measured error offsets. Real-time tracking error corrections were performed by each heliostat’s local controller unit to compensate for a combination of error sources. Experimental tracking measurements were performed using the prototype system. Daily open-loop RMS tracking errors below one milliradian were obtained, thereby satisfying the project’s primary objective. The thesis concludes that high tracking accuracy can be achieved using the control method proposed here. This could potentially lead to a reduction in heliostat cost, thereby lowering the levelised cost of electricity for CRS plants. / AFRIKAANSE OPSOMMING: Gekonsentreerde sonkrag se vermoë om groot hoeveelhede energie effektief te stoor onderskei dit van ander hernubare energie tegnologieë. Kostebesparing en hoër effektiwiteit word egter vereis om dit ekonomies meer lewensvatbaar te maak. Beduidende kostebesparingsgeleenthede bestaan wel, spesifiek vir tegnologieë vir sentraal-ontvangerstelsels (central receiver system (CRS)) waar die heliostaatveld 40 tot 50 persent van die totale kapitaalbestedings uitmaak. CRS aanlegte gebruik heliostate om sonlig op ’n sentrale ontvanger te reflekteer. Heliostate met ’n hoë volgingsakkuraatheid word vereis om hoë sonkragkonsentrasieverhoudings te laat realiseer. Dit maak hoë werkstemperature moontlik vir effektiewe energie-omsetting. Volgingsfoute kom hoofsaaklik voor a.g.v. die heliostaat se vervaardigings-, installasie- en instellingstoleransies, maar hoë toleransie-vereistes verhoog gewoonlik die koste. Daar is dus ’n manier nodig om volgingsakkuraatheid te verbeter sonder om die toleransie-vereistes te verhoog. Die primêre doel van hierdie projek is om ’n heliostaat aanleg kontrole-stelsel te ontwikkel binne die konteks van ’n 5 MWe CRS toetsaanleg. Die kontrole-stelsel moet die volgingsbeweging van al die heliostate in die aanleg bestuur en ook met verloop van tyd volgingsfoute verminder. ’n Geometriese model is ontwikkel om die vier bepalende bronne van heliostaat volgingsfoute te karakteriseer. ’n Prototipe stelsel met 18 heliostate is gebou om as ’n funksionele skaalmodel van die toetsaanleg heliostaatveld te dien en om die gekose kontrole-metode en stelselargitektuur geldig te verklaar. Periodieke metings van die individuele heliostate se volgingsafwykings is verkry deur ’n kamera en optiese kalibrasie teiken te kombineer met beeldprosesseringstegnieke. Wiskundige optimering is gebruik om die model se koëffisiënte te skat om die beste passing te bepaal vir die gemete foutafwykings. Intydse volgingsfoutregstellings is deur elke heliostaat se plaaslike beheereenheid gedoen om te vergoed vir ’n kombinasie van foutbronne. Eksperimentele volgingsmetings is uitgevoer met die prototipestelsel. Daaglikse ooplus RMS volgingsfoute onder een milliradiaan is verkry, en sodoende is die projek se primêre doel behaal. Die tesis maak die gevolgtrekking dat hoë volgingsakkuraatheid behaal kan word deur die gebruik van die beheer-metode soos hier voorgestel. Dit kan potensieel bydra tot kostebesparing in die heliostaatveld van CRS aanlegte om sodoende die geykte koste van elektrisiteit te verminder.

Notions générales relatives au rayonnement solaire et au rayonnement thermique. Collecteur plan: performances, utilisation, coût. concentrateurs: étude des différents types. l'analyse morphologique et son application à l'étude de systèmes. application à l'optimisation d'un champ d'heliostats.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: There are two methods generally used for heliostat field layout optimization: the field growth method and the pattern method. A third, less commonly used method also exists: the free variable method. Each of these three methods offers its own set of advantages and disadvantages. The purpose of this study is to explore the subject of heliostat field layout optimization and to examine the free variable method. In order to achieve this objective, optimization was conducted using the free variable method. To perform optimization, a technical model of the heliostat field was constructed using approximating functions from literature and geometric analysis. Results of this study indicated that the free variable method is possible using a gradient-based optimization algorithm. The free variable method was applied to redesign the field of a commercial plant, PS10, located in Spain. The original plant was improved by 1.2% in annual intercepted energy. The study has demonstrated some of the characteristics, advantages and pitfalls of the free variable method and has proved useful in contributing to the understanding of heliostat field layout optimization. The free variable method requires more research and development before it may be used commercially. / AFRIKAANSE OPSOMMING: Daar word oor die algemeen twee metodes gebruik om 'n heliostaatveld se uitleg te optimeer: die terreinvermeerderingsmetode (field growth) en die patroonmetode (pattern). 'n Derde, minder algemeen gebruikte metode bestaan ook: die vrye veranderlike metode (free variable). Elkeen van hierdie drie metodes bied sy eie voordele en nadele. Die doel van hierdie studie is om die onderwerp van heliostaat veld uitleg optimalisering te verken en die vrye veranderlike metode te ondersoek. Ten einde te hierdie oogmerk te bereik, is die optimalisering uitgevoer met gebruik van die vrye veranderlike metode. Om optimalisering uit te voer, is 'n tegniese model van die heliostaat veld gebou met behulp van benader funksies van letterkunde en geometriese analise. Resultate van hierdie studie het aangedui dat die vrye veranderlike metode moontlik is deur gebruik te maak van 'n gradientbebaseerde optimeeringslagoritme. Die vrye veranderlike metode is ook aangewend om die terrien van 'n kommersiele aanleg, PS10 in Spanje, te herontwerp. Die oorspronklike aanleg is in jaarlikse onderskep energie verbeter met 1.2%. Die studie het sommige van die eienskappe, voordele en slaggate van die vrye veranderlike metode getoon en het nuttige bewys om by te dra tot die begrip van heliostaat veld uitleg optimalisering. Die vrye veranderlike metode vereis meer navorsing en ontwikkeling voordat dit kommersieel gebruik kan word.