Publications Search Results

Now showing 1 - 10 of 83
  • Publication
    Integration enhancements of a solar parabolic trough system in a Chilean juice industry: Methodology and case study
    ( 2021)
    Crespo, A.
    ;
    Muñoz, I.
    ;
    Platzer, W.
    ;
    Ibarra, M.
    A Chilean company dedicated to grape juice production used a 696 m2 parabolic trough collector to pre-heat the feed water of a liquefied petroleum gas boiler in a temperature range of 20-90 °C. During 2017 the solar field generated 241 MWhth of heat, a low value for a concentration collector of such dimensions located in a place with high irradiation. This study presents a methodology to identify enhanced scenarios of solar heat integration into a grape juice industry and among them select the best scenario from an energetic perspective. This methodology started with data gathering of the thermal processes of the industry and the solar field (monitoring campaign and logbook of the industry) to generate the annual thermal demand. In a second step, the maximum theoretical generation potential of the solar field (1,107 MWhth) was obtained with simulations in TRNSYS 18. Then, a Pinch Analysis to the process streams was performed to confirm that a higher solar heat integration potential (520 MWhth) existed. The next step consisted of identifying different scenarios to increase the solar heat integration and analyzing them with simulations in TRNSYS 18 to identify the best-case scenario. The main increase on the solar fraction was achieved for the scenario when the collector working temperature was increased up to 140 °C and when heat was integrated at process level. Furthermore, it was concluded that one of the reasons for low solar fraction was the low thermal demand during months with high solar irradiation.
  • Publication
    Latent thermal energy storage for solar process heat applications at medium-high temperatures - A review
    ( 2019)
    Crespo, A.
    ;
    Barreneche, C.
    ;
    Ibarra, M.
    ;
    Platzer, W.
    Solar thermal energy has the potential to cover the heat demands of industrial processes. However, there may be a time mismatch between energy supplied by the solar field and the process demand. In this case, a thermal energy storage (TES) allows the use of heat at hours without solar irradiation available. Thermal energy storage for solar hot water or heating systems using low temperatures have been optimized since many decades and are in a mature stage. Developments at high temperatures (above 200 °C) for CSP applications have also been deeply studied. However, until this present paper, limited attention has been paid to TES for solar thermal industrial applications at medium-high temperatures (120-400 °C), where there is a potentially huge demand. When talking about TES several aspects have to be discussed: the heat demand that TES is going to be designed to supply, the material where the energy will be stored and the performance of the TES system which includes not only the material but also tanks, piping and connections. In this review, food, brewery and chemical industries were identified as the industries with higher potential in which TES and solar energy could be integrated. Heat integration methodologies have been reviewed to optimize the use of the solar energy in the industrial processes. Regarding the material, latent heat storage or phase change materials (PCM) were selected for this study because they are a very promising type of storage to be integrated in thermal industrial processes, although the state of the art of latent heat thermal energy storage (LHTES) systems is still far from broad commercialization. Until now, no reviews of latent heat storage for industrial applications at medium-high temperatures (120-400 °C) have been published. Therefore, literature related to PCM and latent heat storage (LHS) systems to be used in industrial thermal processes is here reviewed in order to have a general overview of the available technologies for their integration together with solar thermal energy in industrial processes at both experimental and numerical level. More than 100 potential PCMs for heat storage applications in the range of temperatures 120-400 °C have been found. Inorganic eutectic compositions are the group with more potentially available PCM for these applications, with values of heat of fusion between 74 and 535 kJ/kg. Finally, the works related to the performance of the system from the experimental and modelling point of view were presented. The review of experimental TES systems which include PCM in the studied range of temperatures 120-400 °C showed that most of the experimental set-ups were developed for direct steam generation for CSP applications. Regarding numerical modelling, the type of configuration more simulated is the shell and tube configuration.
  • Publication
    Confidence interval computation method for dynamic performance evaluations of solar thermal collectors
    ( 2018)
    Zirkel-Hofer, A.
    ;
    Perry, S.
    ;
    Kramer, K.
    ;
    Heimsath, A.
    ;
    Scholl, S.
    ;
    Platzer, W.
    For the further development and dissemination of solar thermal technology, a continuous demonstration of its reliability is required. For this purpose, meaningful performance and acceptance testing is indispensable. The reliable determination of optical and thermal collector performance parameters involves a suitable testing and evaluation procedure. It additionally requires a dependable quality assessment of the test results. Sophisticated statistical inference calculations, however, are not commonly available in solar thermal collector testing. If applied at all, mostly standardly implemented (linear) confidence interval computations are used. The present publication proposes an advanced approach of confidence level computation, the so-called bootstrapping technique. It represents a common method in the area of economics and is suited to cope with the complexity of confidence calculations within the context of dynamic performance testing. The basic methodology and specific implementation of the bootstrapping approach are introduced in detail. Since this approach is new in performance evaluation procedures, it is validated with confidence results obtained from an extensive evaluation of a large measurement data basis of a linear Fresnel process heat collector. However, the procedure is equally suited for other collector types as parabolic trough, flat plate, and others. The validation with measurement data reveals the valuable capabilities of the bootstrap procedure. It moreover proves the standard confidence methods to fail, because these provide unrealistically narrow confidence intervals. Comparative results between the different methods are thoroughly discussed. They demonstrate the introduced bootstrapping approach to be a powerful tool, generating considerably more representative and therefore reliable confidence intervals than the customary methods. Consequently, bootstrapping is considered a key feature of an enhanced performance evaluation method, since it may provide improved information concerning parameter distribution, confidence levels, and hence the validity of corresponding test results. Meaningful performance testing represents an essential aspect to further increase the viability and reliability of the solar thermal technology in order to facilitate its easier commissioning and wide acceptance.
  • Publication
    Enhanced dynamic performance evaluation method of line-concentrating solar collectors
    ( 2018)
    Zirkel-Hofer, A.
    ;
    Kramer, K.
    ;
    Heimsath, A.
    ;
    Scholl, S.
    ;
    Platzer, W.
    This publication presents an enhanced dynamic performance testing method for line-concentrating solar thermal collectors. To fully exploit the potential of concentrating solar power and legitimize investments within this sector, a reliable and meaningful performance testing is essential. Dynamic testing is especially beneficial for outdoor testing, particularly on-site, lacking of laboratory facilities and therefore requiring in situ measurements. Those complex test conditions prevail for systems of larger dimensions such as concentrating collectors. The introduced comprehensive performance test method addresses diverse elements of reliable collector certification, such as sophisticated confidence interval computations allowing to properly assess the quality of test results. It moreover includes aspects concerning the selection of suitable measurement instrumentation as well as recommendations regarding an appropriate testing strategy. Both aspects may substantially increase the identification quality of the performance results. Exemplary evaluation results prove the capability, reliability, and high benefit of the introduced dynamic procedure. It allows for a significant reduction of testing time, effort, and consequently costs. Flexible and simultaneously reliable certification procedures are considered crucial for the further establishment of solar thermal technologies and their global acceptance.
  • Publication
    Dynamic Performance Evaluation of Line-Concentrating Steam Collectors
    ( 2018)
    Zirkel-Hofer, A.
    ;
    Kramer, K.
    ;
    Heimsath, A.
    ;
    Scholl, S.
    ;
    Platzer, W.
    This publication presents a newly developed procedure for performance evaluation of direct steam generating collectors. Performance testing and evaluation of solar collectors operating with direct steam are not yet standardized, since accredited testing standard procedures do not foresee testing with compressible heat transfer media. Due to the existence of two-phase flow, the measurement concept as well as the collector simulation model needs to be adjusted. Two approaches of steady-state and dynamic performance evaluation are introduced. The corresponding methodology is applicable to small- and large-scale parabolic trough as well as linear Fresnel collectors. The application of the newly developed simulation model and evaluation procedure to measurement data proves the practicability and reliability of the introduced approach. On the basis of exemplary results, the benefits and remaining drawbacks of the procedure are thoroughly discussed. They particularly demonstrate the adapted testing method to be a valuable tool for fast and simple performance checks of steam generating systems. Meaningful performance testing is considered highly beneficial for a further dissemination and global acceptance of steam collectors and solar process heat in general.
  • Publication
    Potential for solar thermal energy in the heap bioleaching of chalcopyrite in Chilean copper mining
    ( 2017)
    Murray, C.
    ;
    Platzer, W.
    ;
    Petersen, J.
    Bioleaching of chalcopyrite is only possible in the presence of thermophilic micro-organisms. While suitable conditions can be generated within a heap naturally through the exothermic reaction, the effectiveness of the process can be improved with an additional heat source. Chilean copper mines are primarily located in the Atacama Desert, which has the highest solar irradiation levels on the planet. Solar thermal energy can be incorporated into the heap bioleaching process to raise the temperature in the heap and increase the copper extraction rates. A heap bioleaching system, including ponds and a solar thermal collector field, has been simulated over one year using HeapSim and TRNSYS. The maximum copper extraction achievable for the system without a solar thermal field is 67% with a 7 kg/h m2 solution flow rate. A maximum extraction of 85% over one year could be achieved with a collector field to heap area ratio of 1:1 and a 10 kg/h m2 solution flow rate. An economic analysis compares the capital cost of the solar thermal system to the revenue from additional copper extraction. The net present value and internal rate of return were positive for collector areas in the range of 10,000-150,000 m2 for a heap area of 200,000 m2. The peak NPV occurs at 50,000 m2 at which point an extractionof 76% is achieved over one year of leaching.
  • Publication
    The role of PGE2 in alveolar epithelial and lung microvascular endothelial crosstalk
    ( 2017)
    Bärnthaler, T.
    ;
    Maric, J.
    ;
    Platzer, W.
    ;
    Konya, V.
    ;
    Theiler, A.
    ;
    Hasenöhrl, C.
    ;
    Gottschalk, B.
    ;
    Trautmann, S.
    ;
    Schreiber, Y.
    ;
    Graier, W.F.
    ;
    Schicho, R.
    ;
    Marsche, G.
    ;
    Olschewski, A.
    ;
    Thomas, D.
    ;
    Schuligoi, R.
    ;
    Heinemann, A.
    Disruption of the blood-air barrier, which is formed by lung microvascular endothelial and alveolar epithelial cells, is a hallmark of acute lung injury. It was shown that alveolar epithelial cells release an unidentified soluble factor that enhances the barrier function of lung microvascular endothelial cells. In this study we reveal that primarily prostaglandin (PG) E-2 accounts for this endothelial barrier-promoting activity. Conditioned media from alveolar epithelial cells (primary ATI-like cells) collected from BALB/c mice and A549 cells increased the electrical resistance of pulmonary human microvascular endothelial cells, respectively. This effect was reversed by pretreating alveolar epithelial cells with a cyclooxygenase-2 inhibitor or by blockade of EP4 receptors on endothelial cells, and in A549 cells also by blocking the sphingosine-1-phosphate1 receptor. Cyclooxygenase-2 was constitutively expressed in A549 cells and in primary ATI-like cells, and was upregulated by lipopolysaccharide treatment. This was accompanied by enhanced PGE(2) secretion into conditioned media. Therefore, we conclude that epithelium-derived PGE(2) is a key regulator of endothelial barrier integrity via EP4 receptors under physiologic and inflammatory conditions. Given that pharmacologic treatment options are still unavailable for diseases with compromised air-blood barrier, like acute lung injury, our data thus support the therapeutic potential of selective EP4 receptor agonists.
  • Publication
    Long-term soiling analysis for three photovoltaic technologies in Santiago region
    ( 2017)
    Besson, P.
    ;
    Munoz, C.
    ;
    Ramirez-Sagner, G.
    ;
    Salgado, M.
    ;
    Escobar, R.
    ;
    Platzer, W.
    The effect of soiling on PV systems impacts negatively the energy production. This phenomenon is highly dependant on the environmental context and conditions of operation. Indeed dirt, dust, and other air contaminants are site-specific and their accumulation on PV modules depends on the installation configuration. This study, conducted in Santiago de Chile over a period of two and half years, focuses on analyzing power production and soiling losses of three photovoltaic technologies, monocrystalline, polycrystalline, and thin-film Si. We present the method used for analyzing time series of production data, and demonstrate the seasonality of soiling rates in Santiago city. Indeed, soiling rate values for winter season, where contamination is high, are three times higher than values for summer season, where contamination is low. A yearly trend of soiling is determined and used to study the link between economical parameters and cleaning pattern applied. The results allow us to define an optimal cleaning period depending on the period of the year.
  • Publication
    State of the art of performance evaluation methods for concentrating solar collectors
    ( 2016)
    Hofer, A.
    ;
    Valenzuela, L.
    ;
    Janotte, N.
    ;
    Burgaleta, J.I.
    ;
    Arraiza, J.
    ;
    Montecchi, M.
    ;
    Sallaberry, F.
    ;
    Osório, T.
    ;
    Carvalho, M.J.
    ;
    Alberti, F.
    ;
    Kramer, K.
    ;
    Heimsath, A.
    ;
    Platzer, W.
    ;
    Scholl, S.
    For the development and establishment of concentrating solar thermal collectors a reliable and comparable performance testing and evaluation is of great importance. To ensure a consistent performance testing in the area of low- temperature collectors a widely accepted and commonly used international testing standard (ISO 9806:2013) is already available. In contrast to this, the standard ISO 9806:2013 has not completely penetrated the testing sector of concentrating collectors yet. On that account a detailed literature review has been performed on published testing procedures and evaluation methodologies as well as existing testing standards. The review summarizes characteristics of the different steady-state, quasi-dynamic and fully dynamic testing methods and presents current advancements, assets and drawbacks as well as limitations of the evaluation procedures. Little research is published in the area of (quasi-) dynamic testing of large solar collectors and fields. As a complementary a survey has been conducted focusing on currently implemented evaluation procedures in this particular field. Among the ten participants of the survey were project partners of relevant industry and research institutions within the European project STAGE-STE (Work package 11 - Linear focusing STE technologies). The survey addressed general aspects of the systems under test, as well as required process conditions and detailed characteristics of the evaluation procedures. In congruence with the literature review, the survey shows a similar tendency: the quasi-dynamic testing method according ISO 9806:2013 presents the most common and advanced evaluation procedure mainly used in the context of tracking concentrating collectors for the performance assessment of parabolic trough collectors operating with thermal oil or pressurized water. These common solar systems can be evaluated with minor adaptions to the testing standard. Evaluation procedures focused on in-situ measurements in solar fields or collectors are scarce and complex as well as an evaluation of linear Fresnel collectors or other systems operating with non-common heat transfer media like molten salt and direct steam. As those are still presenting niche products and testing wise challenging systems under real test conditions a more sophisticated evaluation procedure such as the dynamic testing method is expected to be better suited.
  • Publication
    Solar thermal systems - towards a systematic characterization of building integration
    ( 2016)
    Aelenei, L.
    ;
    Smyth, M.
    ;
    Platzer, W.
    ;
    Norton, B.
    ;
    Kennedy, D.
    ;
    Kalogirou, S.
    ;
    Maurer, C.
    Characterization is defined as the act of describing distinctive characteristics or essential features. In most solar thermal collecting systems the energy performance characterization is commonly used as the most important criteria by which the system (or component) is represented. Building Integrated Solar Thermal Systems (BISTS) however are typically classified across a range of operating parameters, system features and mounting configurations, and other criteria are similarly important to be considered. Therefore BISTS characterization should also account for the architectural and building physics integration based on structural, functional and aesthetical features. A comprehensive characterization of BISTS is necessary to give designers, installers and end users confidence that the final solution selected is appropriate to the comprehensive building requirements.