The principal objective of this study is to develop, investigate and optimise the Heteroconical Tubular Cavity receiver for a parabolic trough reflector. This study presents a three-stage development process which allowed for the development, investigation and optimisation of the Heteroconical receiver. The first stage of development focused on the investigation into the optical performance of the Heteroconical receiver for different geometric configurations. The effect of cavity geometry on the heat flux distribution on the receiver absorbers as well as on the optical performance of the Heteroconical cavity was investigated. The cavity geometry was varied by varying the cone angle and cavity aperture width of the receiver. This investigation led to identification of optical characteristics of the Heteroconical receiver as well as an optically optimised geometric configuration for the cavity shape of the receiver. The second stage of development focused on the thermal and thermodynamic performance of the Heteroconical receiver for different geometric configurations. This stage of development allowed for the investigation into the effect of cavity shape and concentration ratio on the thermal performance of the Heteroconical receiver. The identification of certain thermal characteristics of the receiver further optimised the shape of the receiver cavity for thermal performance during the second stage of development. The third stage of development and optimisation focused on the absorber tubes of the Heteroconical receiver. This enabled further investigation into the effect of tube diameter on the total performance of the Heteroconical receiver and led to an optimal inner tube diameter for the receiver under given operating conditions. In this work, the thermodynamic performance, conjugate heat transfer and fluid flow of the Heteroconical receiver were analysed by solving the computational governing Equations set out in this work known as the Reynolds-Averaged Navier-Stokes (RANS) Equations as well as the energy Equation by utilising the commercially available CFD code, ANSYS FLUENT®. The optical model of the receiver which modelled the optical performance and produced the nonuniform actual heat flux distribution on the absorbers of the receiver was numerically modelled by solving the rendering Equation using the Monte-Carlo ray tracing method. SolTrace - a raytracing software package developed by the National Renewable Energy Laboratory (NREL), commonly used to analyse CSP systems, was utilised for modelling the optical response and performance of the Heteroconical receiver. These actual non-uniform heat flux distributions were applied in the CFD code by making use of user-defined functions for the thermal model and analysis of the Heteroconical receiver. The numerical model was applied to a simple parabolic trough receiver and reflector and validated against experimental data available in the literature, and good agreement was achieved. It was found that the Heteroconical receiver was able to significantly reduce the amount of reradiation losses as well as improve the uniformity of the heat flux distribution on the absorbers. The receiver was found to produce thermal efficiencies of up to 71% and optical efficiencies of up to 80% for practically sized receivers. The optimal receiver was compared to a widely used parabolic trough receiver, a vacuum tube receiver. It was found that the optimal Heteroconical receiver performed, on average, 4% more efficiently than the vacuum tube receiver across the temperature range of 50-210℃. In summary, it was found that the larger a Heteroconical receiver is the higher its optical efficiency, but the lower its thermal efficiency. Hence, careful consideration needs to be taken when determining cone angle and concentration ratio of the receiver. It was found that absorber tube diameter does not have a significant effect on the performance of the receiver, but its position within the cavity does have a vital role in the performance of the receiver. The Heteroconical receiver was found to successfully reduce energy losses and was found to be a successfully high performance solar thermal tubular cavity receiver.

Parabolic solar trough receivers are used to collect heat via the mean of a heat transfer fluid. This component is one among a myriad of the Concentrated Solar Power (CSP) devices. Parabolic troughs reach high temperatures around 400 ºC. improving the Parabolic Solar Trough's receiver with an IR selective coating will increase the heat transfer absorbed by the heat transfer fluid and reduce the radiative heat loss. Thus, optimizing the receiver will ameliorate the efficiency of the electrical production for a CSP. The parabolic solar receiver existing in industry currently are made of stainless steel with no specific coating for IR solar rays spectrum selection. Therefore, the heat transferred through the absorber is limited to certain light spectrum. Furthermore, numerous receivers proposed are made from materials that contaminates their optical properties when oxidized such as aluminum [1]. The heat transfer and optical analysis of the PTC are essential to optimize and understand its performance under high temperatures and reduce the heat loss. In this paper, our focus is on presenting a super-lattice IR selective coating to minimize the radiative heat loss. Making use of the power of metamaterials to confection optical properties that are inexistent in nature, the coating will serve to maximize the tube's reflectance above 70% in the IR. Not only does the selective coating enhance the optical properties of the receiver, but also it ensures performance stability for high temperatures.

Parabolrinnen-Kraftwerke sind zurzeit die am häufigsten zum Einsatz kommende und wirtschaftlichste Technologie solarthermisch konzentrierender Systeme (Concentrated Solar Power – CSP) und gehören zu den linienfokussierenden Systemen [1]. In Spanien stellen die solarthermischen Parabolrinnen-Kraftwerke Andasol 1–3 mit einer Kollektorfläche von ca. 150 Millionen m² bereits 150 MW zur Verfügung, mit denen ca. 200.000 Einwohner jährlich mit Strom versorgt werden können [2]–[4]. Das Solarfeld besteht aus ca. 150 m langen, in Reihe angeordneten Kollektoren, die aus einzelnen Parabolrinnen-Kollektormodulen zusammengefasst und im Tagesverlauf der Sonne nachgeführt werden. Die Lagerung erfolgt an den Modulrändern im Schwerpunkt des Kollektormoduls, der mit der Rotationsachse zusammenfällt. Bisher werden die Kollektoren überwiegend als filigranes Stahlfachwerk mit über die Aperturweite parabelförmig, uniaxial gekrümmten und punktuell gestützten Spiegelelementen ausgeführt. Bei der Assemblierung der Stahlfachwerke und der Spiegelelemente ist schon im Bauzustand durchgehend eine hohe Präzision gefordert, um eine maximale Solarstrahlenkonzentration der einfallenden direkten solaren Strahlung auf ein in der Fokallinie befindliches Absorberrohr sicherzustellen [5]. In diesem wird ein Wärmeträgermedium, zumeist Thermoöl, auf eine Prozesstemperatur von ca. 400 °C erhitzt. In einem nachgeschalteten konventionellen Kraftwerksblock wird mittels Dampfturbine Elektrizität erzeugt. Das bisher kommerziell meist genutzte Kollektormodul ist der EuroTrough mit einer Aperturweite von ca. 5,80 m und einer Modullänge von 12 m [6], [7] (Bild 1), welches als Benchmark für die erste Förderphase des Projekts diente. Zur Verbesserung der Wirtschaftlichkeit zielen bisherige Entwicklungen auf eine Vergrößerung der Spiegelfläche zur Steigerung des Wirkungsgrades über einen erhöhten geometrischen Konzentrationsgrad, definiert als das Verhältnis von Reflektor- zu Absorptionsfläche, ab. Module wie der UltimateTrough und der SpaceTube erreichen dies durch die Vergrößerung der Aperturweite auf 7,5 m bzw. 8 m [8], [9]. Ein alternatives Strukturkonzept aus stahlfaserverstärkten Betonfertigteilen der Schweizer Firma Airlight mit einer Aperturweite von 9,7 m besteht aus durch Luftdruck in parabolische Form gebrachten Spiegelfolien als Reflektorsystem und wurde bisher in einem Pilot-Kraftwerk in Ait-Baha, Marokko, umgesetzt [10]. Wesentliche Arbeiten der zweiten Förderphase sind daher – dem Trend zu größerer Apertur folgend – an der visionären Entwicklung von Parabolschalen mit Öffnungsweiten von bis zu 10 m ausgerichtet. [Aus: Einleitung] / Parabolic trough power plants are currently the most frequently used and most economical technology of solar thermal systems (Concentrated Solar Power – CSP) and belong to the linear focus collector types [1]. In Spain, the solar thermal parabolic trough power plants Andasol 1–3 with a collector area of approx. 150 million m² already provide 150 MW, which means that approx. 200,000 inhabitants can be annually supplied with electricity [2]–[4]. The solar field consists of approx. 150 m long collectors arranged in rows, which are combined from individual parabolic trough collector modules and track the sun during the course of the day. The bearings are located at the edges of the module in the centre of gravity of the collector module, which corresponds to the axis of rotation. Up to now, the collectors have mainly been designed as a steel framework with parabolic, uniaxially curved and pointwise supported mirror elements. During the assembly of the steel framework and the mirror elements, high precision is required throughout the manufacturing in order to ensure a maximum solar radiation concentration of the incident direct solar radiation on an absorber tube located in the focal line [5]. A heat transfer medium, usually thermal oil, is heated to a process temperature of approx. 400 °C in the absorber tube. Electricity is generated in a downstream conventional power plant unit by means of a steam turbine. The most commercially used collector module is the EuroTrough with an aperture width of approx. 5.80 m and a module length of 12 m [6], [7] (Fig. 1), which served as a benchmark for the first funding phase of the project. In order to improve economic efficiency, previous developments have aimed to increase the size of the mirror surface in order to increase efficiency by a higher geometric degree of concentration, defined as the ratio of reflector surface to absorption surface. Modules like the UltimateTrough and the SpaceTube achieve this by increasing the aperture width to 7.5 m or 8 m, respectively, [8], [9]. An alternative structural concept consisting of prefabricated steel fibre-reinforced concrete elements from the Swiss company Airlight with an aperture width of 9.7 m consists of parabolic mirror foils as a reflector brought into parabolic shape by air pressure and has already been implemented in a pilot power plant in Ait-Baha, Morocco [10]. Therefore, in line with the trend towards a larger aperture, major work in the second funding phase aims at the visionary development of parabolic shells with aperture widths of up to 10 m. [Off: Introduction]

In this thesis report for Dalarna University in Borlange and Absolicon company the study of a possibility to add an array of concentrating solar collectors to a Torsång district heating system was done. The whole idea of this work was to make a simulation of this kind of system, trying to get 15-20% of solar fraction, and make an economical evaluation. At the same time, another goal was to make two comparisons: between concentrating and flat-plate collector in the same system, and between two tools for collector analysis – Polysun and Absolicon tool, based on TRNSYS, which was designed to estimate the output of the collector for a certain temperature, without any load. During the study, the analysis of the simulating tools was made and the combination of those two tools was used. Using long iteration cycles, involving changing the field layout, number of collectors and distance between collector rows in flat-plate collector case, both types of collectors were analyzed. The method of the analysis was to get an equal output of the field and see the differences, which appear while using different collector types.

Das Erkenntnistransferprojekt baut auf die im SPP-Projekt „Leichte Verformungsoptimierte Schalentragwerke aus mikrobewehrtem UHPC am Beispiel von Parabolrinnen solarthermischer Kraftwerke“ (s. S. 536 ff .) erzielten Ergebnisse der ersten Förderperiode auf. Der Fokus liegt auf der Entwicklung von linienartig verstärkten, vollwandigen Parabolschalen mit zur bestehenden Kraftwerkstechnik passenden EuroTrough-Rinnenabmessungen. Es sollten die bisherigen Erkenntnisse zusammen mit professionellen Anwendungspartnern vorwettbewerblich ausgebaut werden, so dass sie Grundlage für eine Serienfertigung bilden können. Dementsprechend setzten sich die Kooperationspartner aus dem Deutschen Zentrum für Luft- und Raumfahrt DLR (Systemführer für linienfokussierende Solarkraftwerke), der Fa. Solarlite CSP (Hersteller von Solaranlagen in Parabolrinnentechnik), der INNOGRATION GmbH (Hersteller von Stahlbetonfertigteilen) und der Fa. Dyckerhoff Zement (Hersteller von Ausgangsstoffen für Hochleistungsbetone) zusammen.

This thesis presents and demonstrates procedures to model and optimize the collector field of a parabolic trough solar thermal power plant. The collector field of such a plant is universally organized into parallel loops of solar collectors. Heat transfer fluid returning from the energy conversion plant is heated to a moderately high temperature in the field. Typically fluid enters a collector loop around 270 °C and leaves at 380 °C. The fluid is then returned to the plant to generate steam. In the first part of this thesis, the collector field and the energy conversion system of a typical parabolic trough solar thermal power plant are modeled. The model is compared with actual performance data and is enhanced and verified as necessary. Originally, the collectors in the plants under consideration were provided with evacuated tube receivers of the highest feasible efficiency without much regard for cost effectiveness. In practice, these receivers have failed at an unexpected rate and need replacement. It is unlikely that a very expensive evacuated tube receiver is now the most cost effective for every location in a collector loop. In particular, a receiver optimized for 270 °C operation may not be optimal at 380 °C. For example, a relatively inexpensive receiver with a flat black absorber and no vacuum may be more cost effective in the lower temperature segments of a loop. In the second part of this thesis, a procedure for the optimum deployment of collectors is developed and demonstrated. The results of this research should be directly applicable to the refurbishment and upgrading of several of the largest solar energy plants in the world.

Absolicon Solar Collector AB in Härnösand, Sweden, develops concentrating solar collectors with a parabolic trough. In the solar collector trough, there is thermal loss due to convection. A convection suppressor was made and used as a method to reduce thermal loss due to convection in the trough. The objective of the project was to evaluate the convection suppressor for solar collectors with a parabolic trough and its impact on the performance (thermal loss characteristics) in two different orientations of the trough, horizontal and inclined. The performance of the solar collector was first measured without the convection suppressor; these results were compared to two previous quasi-dynamical tests of the solar collector performance made by two different institutes, Research Institute of Sweden and SPF Institut für Solartechnik (Switzerland). The comparison was made to validate the test results from the tests without the convection suppressor, which matched. Secondly, when the convection suppressor was made and tested in the two different orientations, the results of the performance with and without the convection suppressor was evaluated as well as the convection suppressor itself. The results showed a significant improvement of the solar collector performance in the aspect of reduced thermal loss when the convection suppressor was used, hence higher efficiency. / Absolicon Solar Collector AB I Härnösand, Sverige, utvecklar koncentrerande solfångare med ett paraboliskt tråg. I solfångarens tråg uppstår termiska förluster som en följd av konvektion. En konvektionsreducerare tillverkades och användes som metod för att minska de termiska förlusterna i tråget. Målet med projektet var att testa och utvärdera konvektionsreduceraren för koncentrerande solfångare med ett paraboliskt tråg samt dess inverkan på verkningsgraden i två olika positioner för tråget, horisontell och lutande. För att kunna mäta konvektionsreducerarens inverkan på solfångaren mättes först solfångarens prestanda utan konvektionsreduceraren i de två olika positionerna, detta resultat användes som referens efter validering. Valideringen gjordes genom att resultatet jämfördes sedan med två andra prestandamätningar (quasi-dynamical test) av solfångaren gjorda av två olika institut, Research Institute of Sweden och SPF Institut für Solartechnik (Schweiz). Därefter, när konvektionsreduceraren var tillverkat och testad i de olika positionerna på samma sätt som mätningarna utan konvektionsreducerare, jämfördes resultaten med och utan konvektionsreducerareet samt att en utvärdering gjordes av dess inverkan. Resultatet visade en signifikant förbättring av solfångarens prestanda i form av minskade termiska förluster när konvektionsreduceraren användes och därav ökad verkningsgrad.

In Sweden, the residential and industrial energy demand is provided by a significant part of district heating. In a decarbonization plan to reduce the CO2 emissions, the integration of a large-scale solar system in the district heating can be a suitable option. The most used types of collectors are flat plate collectors (FPC), for which efficiency drops at high temperature levels. Parabolic through collectors (PTC) have seen increased interest in later years, due to their higher efficiency at higher temperature levels, which could improve system performance both energetically and economically. A hybrid concept using a combination of FPC and PTC for a solar thermal system has previously been studied for a solar district heating system in Denmark, with the aim to maximize the solar production by operating the solar collectors in the temperature ranges where they excel. The first aim of this thesis was to adapt the hybrid solar system in a district heating system for a Swedish case study and to evaluate if the hybrid optimization studied has similar positive effects in the overall thermal production of the system in Sweden, as it did in Denmark. The second aim of this thesis was to investigate the use of photovoltaic thermal collectors (PVT) instead of FPC for parts of the solar thermal system. With PVT, a single solar collector module allows for simultaneous production of heat and electricity and integration of photovoltaic thermal collectors in the solar assisted district heating could improve the overall performance of the system, both in terms of energy production and economical gain.The study was performed using the simulation tool TRNSYS based on a model developed in a danish case study. It was performed a parametric analysis on the percentage of share of the different types of solar collectors in the total area. The results given from the simulations have been used to carry out an economic evaluation based on the levelized cost of substituted energy, the annual operation and maintenance costs, and the marginal operational cost difference between a conventional district heating system supplied by a boiler only and a solar assisted district heating system. Based on the results found, it has been proved that a greater proportion of parabolic trough collectors in the solar field contribute to a greater production of thermal energy but also to higher expenses in the economy of the project. The best configuration which balanced these two factors was composed by 70 % of flat plate collectors and 30 % of parabolic trough collectors, based on the total area. The integration of photovoltaic thermal has been demonstrated to be not cost-effective for the studied location compared to the optimized ratio of FPC to PTC, mainly due to the high and uncertain price of the new technology. The use of photovoltaic thermal system is not yet widely developed in projects and there are only a few existing projects in operation today. In the future, the development of photovoltaic thermal in solar assisted district heating projects might have a higher realizable economic potential due to the industry learning curve, but more studies will need to be performed on this.

The change in climate as a consequence of anthropogenic activities is a subject ofmajor concerns. In order to reduce the amount of greenhouse gas emissions inthe atmosphere, the utilization of renewable, fossil-free power generationapplications becomes inevitable. Geothermal and solar energy play a major rolein covering the increased demand for renewable energy sources of today’s andfuture’s society. A special focus hereby lies on the Concentrating Solar Powertechnologies and different geothermal concepts. The costs for producingelectricity through Concentrating Solar Power and therefore Parabolic Trough Collectorsas well as geothermal conversion technologies are still comparatively high. Inorder to minimize these expenses and maximize the cycle’s efficiency, thepossible synergies of a hybridization of these two technologies becomeapparent. This thesis therefore investigates the thermodynamic and economicbenefits and drawbacks of this combination from a global perspective. For that,a Parabolic Trough Collector system is combined with the geothermal conversionconcepts of Direct Steam, Single and Double Flash, Organic Rankine as well asKalina Cycles. The solar integrations under investigation are Superheat,Preheat and Superheat & Reheat of the geothermal fluid. The thermodynamicanalysis focuses on the thermal and utilization efficiencies, as well as therequired Parabolic Trough Collector area. The results indicate that in the caseof the Superheat and Superheat & Reheat setup, the thermal efficiency canbe improved for all geothermal concepts in comparison to their correspondinggeothermal stand-alone case. The Preheat cases, with the major contributionfrom solar energy, are not able to improve the cycle’s thermal efficiencyrelative to the reference setup. From an exergy perspective the findings varysignificantly depending on the applied boundary conditions. Still, almost allcases were able to improve the cycle’s performance compared to the referencecase. For the economic evaluation, the capital investment costs and thelevelized costs of electricity are studied. The capital costs increasesignificantly when adding solar energy to the geothermal cycle. The levelizedelectricity costs could not be lowered for any hybridization case compared tothe reference only-geothermal configurations. The prices vary between20.04 €/MWh and 373.42 €/MWh. When conducting a sensitivity analysison the solar system price and the annual mean irradiance, the Kalina Superheatand Superheat & Reheat, as well as the Organic Rankine Preheathybridizations become cost competitive relative to the reference cases.Concluding, it is important to remark, that even if the hybridization of the ParabolicTrough and the different geothermal concepts makes sense from a thermodynamicperspective, the decisive levelized costs of electricity could not be improved.It is, however, possible that these costs can be further reduced under speciallocal conditions, making the addition of Parabolic Trough solar heat tospecific geothermal concepts favorable.

Reducing carbon emissions in our societies requires a massive shift towards renewables. In Sweden, biomass is the dominant source for the district heat production, but growing demand for biomass in other sectors may cause pressure on it. In this context, this thesis explores the possibility to supply heat with solar parabolic thermal collectors to a district heating system in Kosta, a locality in Lessebo municipality, Kronoberg county. The simulations and calculations are based on the locally available hourly data of weather conditions, supply and return temperatures of district heat and heat demand profiles. The energy production as well as the profitability of the installation is evaluated through the calculation of carbon abatement costs, considering that heat supplied from solar collectors spares biomass which can be made available for decarbonating the power sector. Results have shown that a solar installation that cover most of the heat demand during the months of summer, thus 10% of the annual heat demand, can be profitable. This study also investigates different scenarios with increased costs for the biomass resource to simulate the growing pressure around this resource and concludes that with growing costs of the biomass resource, solar application will become more attractive, allowing to make larger solar district heating plants profitable.