An Experimental Study on Solar Flat Plate Collector Using an Alternative Working Fluid

This paper describes the performance of a solar water heater with an alternative working fluid. A solar flat plate collector of fIxed orientation was fabricated and connected to a heat exchanger, which was kept inside the water storage drum. The developed collector was a low temperature device operating with the temperature range of ambient to 100°C. Acetone was selected as an alternative working fluid and allowed to re-eirculate in a closed loop. A shell and tube type heat exchanger (non-mixing) was designed and fabricated for the heat transfer between acetone and water. The solar intensity increased from 55 mw/cm2 at 8.30 am to 85 mw/cm2 at 1.30 pm and decreased to 64 mw/cm2 at 5.00 pm. The absorber plate temperature, which remained nearly constant for the first two hours, went up to 90°C in the next two hours. It was nearly constant from 11.00 am to 1.30 pm and then dropped down to 72°C in the afternoon. The hot fluid was found to loose heat to the surrounding water at more or less constant rate from 11.30 am to 5.00 pm. The highest temperature of acetone (70°C) was observed during 1.00 pm to 2.00 pm. The temperature of water increased from 30°C to a maximum of 62°C. Overall efficiency of the system was found to be 45% while considering the solar input to the heat gained by the water. Alternative working fluids such as acetone, methanol or ethanol may be considered for substituting water in the flat plate collector in view of the fact that the fluids have low boiling point coupled with high latent heat of evaporation

Design, Manufacturing, Testing, and Mathematical Modeling of Concentrating Solar Systems: a Study Applied to Prototypes of Parabolic Trough Collector and Solar Box Cooker

L'utilizzo di energia solare termica deve essere sostenuto per ridurre il consumo di fonti fossili climalteranti. Nel presente studio si sono progettati e realizzati due sistemi solari a concentrazione: un collettore parabolico assiale (PTC) ed un forno solare a scatola. Il PTC ha un angolo di bordo di 90° ed un rapporto di concentrazione di 19,89. Sul concentratore, realizzato in sandwich composito, sono state applicate pellicole in alluminio ad elevata riflettanza. Il ricevitore è un tubo di acciaio rivestito da una vernice selettiva. Il sistema di inseguimento è governato da un algoritmo solare. I test sperimentali sono stati condotti con acqua ad una temperatura massima di 85 °C. Il PTC è stato caratterizzato ottenendo curve di efficienza termica, modificatore dell'angolo di incidenza e costante di tempo. I risultati mostrano che l'equazione dell'efficienza termica è confrontabile con quella di collettori simili. I dati sperimentali sono stati utilizzati per validare un ambiente di simulazione della resa annuale di PTC. Si è determinata la convenienza nell'adozione di nanofluidi a base di metalli rispetto al fluido di base (acqua). Sono state analizzate 5 temperature del fluido in ingresso e 3 portate in massa. I risultati mostrano che solo le nanoparticelle di Au, TiO2, ZnO e Al2O3 alle più basse concentrazioni presentano ridotti miglioramenti. Il forno solare a scatola ha un rapporto di concentrazione di 11,57, ed è costituito da una camera di cottura, un coperchio superiore vetrato e una doppia fila di specchi riflettenti. Il prototipo consente un allineamento solare manuale sia azimutale che zenitale. La temperatura massima del forno è stata determinata attraverso prove a vuoto. Sono state inoltre svolte prove a carico inserendo nel forno una o due pentole di alluminio, verniciate o meno in nero, riempite con acqua o olio di arachidi. In quest’ultimo caso, si è giunti a temperature superiori a 200 °C e a risultati confrontabili con quelli in letteratura.Use of solar thermal energy has to be sustained to reduce consumption of climate-changing fossil fuels. Thus, in this study two concentrating solar prototypes were designed and manufactured: a parabolic trough collector (PTC) and a solar box cooker. The PTC has a 90° rim angle and a concentration ratio of 19.89. The concentrator is a sandwich composite structure with high-reflectance aluminum foils applied on it. The receiver is a steel pipe painted with a selective coating. The tracking system is based on a solar-position computer program. Experimental tests were carried out with water and temperatures up to 85 °C. Thermal efficiency, incident angle modifier, and time constant curves were found. Results show that the thermal efficiency equation is comparable with that of other PTCs in literature. Experimental data were utilized to validate a simulation environment able to determine the yearly yield of PTCs. The simulation was carried out to evaluate the convenience in adopting metal-based nanofluids respect to the base fluid (water). Five inlet fluid temperatures and three mass flow rates were analyzed. Results show that only Au, TiO2, ZnO, and Al2O3 nanoparticles, at the lowest concentrations, present reduced improvements respect to water. The solar box cooker is a high concentration ratio prototype (11.57). The cooker has a cooking chamber with a glass cover on the top and is composed by two rows of booster mirrors. The prototype allows both an azimuth and a zenith manual orientation. Tests without load were carried out to evaluate the maximum cooker temperature. Tests with load, conduced using aluminum vessels containing a certain amount of water, were accomplished both with non-painted vessels and black-coated ones, and with one or two vessels. Additional tests were carried out with peanut oil. Using this fluid, temperatures higher than the water ones were achieved (> 200 °C) and results exhibited values comparable to those in literature

Phase change materials (PCM) for solar energy usages and storage: An overview

© 2019 by the authors. Solar energy is a renewable energy source that can be utilized for different applications in today's world. The effective use of solar energy requires a storage medium that can facilitate the storage of excess energy, and then supply this stored energy when it is needed. An effective method of storing thermal energy from solar is through the use of phase change materials (PCMs). PCMs are isothermal in nature, and thus offer higher density energy storage and the ability to operate in a variable range of temperature conditions. This article provides a comprehensive review of the application of PCMs for solar energy use and storage such as for solar power generation, water heating systems, solar cookers, and solar dryers. This paper will benefit the researcher in conducting further research on solar power generation, water heating system, solar cookers, and solar dryers using PCMs for commercial development

Industrial and Agricultural Applications of Solar Heat

Mankind’s earliest use of solar energy was probably the drying of food crops to aid their preservation. Open sun drying of fruit, vegetables, fish and meats often improved or enhanced particular flavors and textures such that solely because of those attributes many dried products remain in culinary use today, as examples, dried seaweed, sun-dried tomatoes, raisins and dried pistachio nuts. Open sun drying is displaced increasingly by glazed solar dryers that (i) enable equilibrium moisture content to be reached sooner and (ii) avoid losses of the crop to insects and rodents. A further agricultural application, the greenhouse extended the use of solar energy from post-harvest to crop-production. Today greenhouses are ubiquitous with a huge variety of designs providing a wide range of modified climates for plant growth. Solar energy also finds use in agriculture in solar water pumping for irrigation and in the desalination of brackish water. Solar cooking has taken the use of solar energy in the food production chain directly to the end-user. Broader industrial uses of solar energy have also tended to be linked to food and beverage production because the temperatures required can be satisfied readily in many climates by a well-designed solar thermal system. Non-agricultural technologies such as solar furnaces have considerable potential but have had limited practical use to-date. This chapter discusses the attributes, contexts and applications of the full range of industrial and agricultural applications of solar heat

Insulated Solar Electric Cooker with Phase Change Thermal Storage Medium

This final design review document outlines the senior design project carried out by a team of four mechanical engineering students at the California Polytechnic State University – San Luis Obispo under the sponsorship of Dr. Peter Schwartz of the Cal Poly Physics department. The aim of this project was to improve upon the design of previously developed Insulated Solar Electric Cookers (ISECs) by adding a thermal storage system to allow for quicker cook times and the ability to cook food at non-peak solar hours. The team’s goal was to develop a working prototype utilizing a phase change medium as the thermal storage system by the end of the 1-year project that would be tested against other contemporary, inexpensive cooking systems. The team was able to successfully design, manufacture, and test two functioning prototypes. The final design utilized diodes connected to a solar panel as the heating element due to their extremely low cost as well as their thermal properties. The phase change material selected for thermal storage was a sugar alcohol known as erythritol. The final prototype could boil 1 liter of water in under 20 minutes with a device efficiency of 35% and continued to store energy for over 4 hours. As a result, the ISEC with thermal storage exceeded or met all but one of the design requirements as it was unable to completely melt the erythritol in the allotted time. A discussion of these successes and possible solutions to this shortcoming are also discussed within this report. This document presents the summation of the team’s work on the project from the project scope to the finished results and the process used to achieve these results. This document has been presented to Dr. Schwartz for review and approval

Performance comparison of two solar cooking storage pots combined with wonderbag slow cookers for off-sunshine cooking

Two similar storage cooking pots are experimentally evaluated and compared during solar cooking and storage off-sunshine cooking periods. One storage pot has sunflower oil as the sensible heat storage material, while the other has erythritol as the phase change material (PCM). To test their thermal performance during off-sunshine periods, the two pots are placed in insulated wonderbag slow cookers. Water and sunflower oil are used as the cooking fluids in the experimental tests. The sunflower oil cooking pot shows better performance during the solar cooking periods since it shows shorter cooking times (1.8–5.6 h) compared to the erythritol PCM pot (3.8–6.6 h). The sunflower oil pot also attains higher maximum storage temperatures (124–145 °C) compared to the erythritol PCM pot (118–140 °C). Storage efficiencies for the sunflower oil pot (3.0–7.1%) are also greater than those of the PCM pot (2.5–3.7%). During the storage cooking periods, the erythritol based phase change material cooking pot shows better performance as evidenced by the lower temperature drops (0.1–9.7 °C) from the maximum cooking temperatures compared to 8.3 to 34 °C for the sunflower oil pot. The heat utilisation efficiencies for the erythritol pot (4.8–14.3%) are also greater compared to the sunflower oil pot (3.7–6%)

Experimental Analysis of Nucleation Triggering in a Thermal Energy Storage Based on Xylitol Used in a Portable Solar Box Cooker

Sugar alcohols have interesting thermodynamic properties that make them good options as heat storage materials (HSMs) to be used in solar cookers. Among sugar alcohols, xylitol is affected by severe supercooling that can significantly alter its usefulness in thermal energy storage (TES) systems. To overcome the supercooling issue, in this work the thermal behavior of a xylitol-based TES installed in a portable solar box cooker was investigated experimentally. The solar cooker has a 4.08 concentration ratio and the TES is a double-pot system filled with 2.5 kg of commercial-grade xylitol. The TES includes a manual mixing device that can be used to trigger the nucleation of xylitol. The effectiveness of the TES system with and without triggering was assessed through several outdoor tests, divided into heating and cooling phases, using silicone oil as absorbing media. It was found that the average load cooling time, in the temperature range of the test fluid from 110 to 80 °C, increased by about 346% when the solar cooker was equipped with the xylitol-triggered TES. The mixing device can therefore be considered an effective solution for regarding xylitol as an actual and performing phase change material

Thermal energy storage solutions for building applications

El canvi climàtic constitueix un dels reptes més importants per a les generacions actuals i futures. El Grup Intergovernamental d'Experts sobre el Canvi Climàtic (IPCC) estima que les activitats humanes han estat responsables aproximadament de 1.0 ºC d'escalfament global per sobre dels nivells preindustrials, portant grans impactes negatius. En aquest context, l'IPCC ha fixat l'objectiu de limitar l'escalfament global a 1.5 ºC per al 2050; per sobre d'aquest valor, els danys serien irreversibles. Les emissions de gasos amb efecte d'hivernacle (GHG) són els principals impulsors del canvi climàtic. El període 2010-2019 va donar els seus valors més alts de la història. Durant aquest període, el sector dels edificis va aportar el 21% de les emissions mundials de GHG. Aquestes dades van impulsar aquesta tesi, emmarcada en l’estudi dels sistemes que componen les emissions de GHG en edificis, així com el desenvolupament de les tecnologies que permetin mitigar-les. La primera secció analitza, mitjançant tècniques d’anàlisi bibliomètrica, els principals sistemes que componen la demanda energètica dels edificis. Per això, es van estudiar els serveis dels edificis i el seu impacte sobre el canvi climàtic. A més, es van estudiar els electrodomèstics i les seues tendències en eficiència energètica, correlacionades amb les polítiques implementades a nivell global. Així mateix, es van estudiar els co-beneficis de l'emmagatzematge d'energia tèrmica (TES) extrapolats des del camp de les energies renovables, identificant el TES com a transcendental en la transició energètica. La segona secció de la tesi es va embrancar en l’anàlisi experimental i mitjançant simulacions de tres sistemes d’emmagatzematge tèrmic. El primer sistema es va enfocar a disminuir les pèrdues tèrmiques d’un dipòsit d’emmagatzematge per a calefacció mitjançant l’ús d’aïllament al buit. Es va demostrar que aquest aïllament pot disminuir fins a 10 vegades les pèrdues tèrmiques respecte al convencional. El segon estudi va realitzar una avaluació comparativa entre dos dissenys de materials de canvi de fase (PCM) macro-encapsulats en un TES. Es va concloure que el disseny a utilitzar dependrà de l'aplicació i d’un compromís entre més densitat energètica o més entrega de calor. El tercer estudi va identificar els principals reptes en la utilització del concret per emmagatzemar energia a alta temperatura, alhora que es va proposar i analitzar un nou disseny per superar aquests reptes. Els resultats d’aquesta tesi han demostrat que l’emmagatzematge d’energia tèrmica té un gran potencial en la transició energètica de manera general i dels edificis de manera particular.El cambio climático constituye uno de los retos más importantes para las actuales y futuras generaciones. El Panel Intergubernamental sobre Cambio Climático (IPCC) estima que las actividades humanas han sido responsables aproximadamente de 1,0 ºC de calentamiento global por encima de los niveles preindustriales, trayendo consigo grandes impactos negativos. En este contexto, el IPCC ha fijado el objetivo de limitar el calentamiento global en 1.5 ºC para el 2050; por encima de este valor los daños serían irreversibles. Las emisiones de gases de efecto invernadero (GHG) son los principales impulsores del cambio climático. El período 2010-2019 arrojó sus valores más altos de la historia. Durante este período, el sector de los edificios aportó el 21% de las emisiones mundiales de GHG. Tales datos impulsaron esta tesis, enmarcada en el estudio de los sistemas que componen las emisiones de GHG en edificios, así como el desarrollo de las tecnologías que permitan mitigarlas. La primera sección analiza, mediante técnicas de análisis bibliométricos, los principales sistemas que componen la demanda energética de los edificios. Para esto, se estudiaron los servicios de los edificios y su impacto sobre el cambio climático. Así como, los electrodomésticos y sus tendencias en eficiencia energética, correlacionadas con las políticas implementadas a nivel global. Al igual que, los co-beneficios del almacenamiento de energía térmica (TES) extrapolados desde el campo de las energías renovables, identificando al TES como trascendental en la transición energética. La segunda sección de la tesis se centró en el análisis experimental y mediante simulaciones de tres sistemas de almacenamiento térmico. El primer sistema se enfocó en disminuir las pérdidas térmicas de un depósito de almacenamiento para calefacción mediante el uso de aislamiento al vacío. Se demostró que este aislamiento puede disminuir hasta en 10 veces las pérdidas térmicas con respecto al convencional. El segundo estudio realizó una evaluación comparativa entre dos diseños de materiales de cambio de fase (PCM) macro-encapsulados en un TES. Se concluyó que el diseño a utilizar dependerá de la aplicación y de un compromiso entre mayor densidad energética o mayor entrega de calor. El tercer estudio identificó los principales retos en la utilización del hormigón para almacenar energía a alta temperatura, a la vez que se propuso y analizó un nuevo diseño para superar dichos retos. Los resultados de esta tesis han demostrado que el almacenamiento de energía térmica tiene un gran potencial en la transición energética de manera general y de los edificios de manera particular.Climate change is one of the most important challenges for current and future generations. The Intergovernmental Panel on Climate Change (IPCC) estimates that human activities are responsible for approximately 1.0 °C of global warming above pre-industrial levels, resulting in major negative impacts. In this context, the IPCC has set a target of limiting global warming to 1.5 °C by 2050, above which the damage will become irreversible. Greenhouse gas (GHG) emissions are the main drivers of climate change. The period 2010-2019 showed their highest values in history. During this period, the buildings sector accounted for 21% of global GHG emissions. Such data motivated this thesis, framed in the study of the systems that comprise GHG emissions in buildings, as well as the development of technologies to mitigate them. The first section analyses, using bibliometric analysis techniques, the main systems that drive the energy demand of buildings. Therefore, building services and their impact on climate change were studied. In addition, household appliances and their trends in energy efficiency, correlated with the policies implemented at global level, were also studied. Likewise, the co-benefits of thermal energy storage (TES) extrapolated from the field of renewable energies were also studied, identifying TES as transcendental in the energy transition. The second section of the thesis focused on the experimental and simulation analysis of three thermal energy storage systems. The first system focused on decreasing the thermal losses of a heating storage tank by using vacuum insulation. It was found that vacuum insulation can reduce thermal losses by up to 10 times compared to conventional insulation. The second study performed a benchmark evaluation between two designs of phase change material (PCM) macro-encapsulation in a TES. It was concluded that the design to be used will be determined by the application and a trade-off between higher energy density or higher heat transfer. The third study identified the main challenges in using concrete to store energy at high temperature, and a new design was proposed and analysed to overcome these challenges. The results of this thesis have demonstrated that thermal energy storage represents a great potential in the energy transition in general and in buildings in particular

Proposal of a non-linear curve for reporting the performance of solar cookers

Performance parameters of solar cookers have conventionally been determined by assuming a linear trend between the cooker power and the difference between load temperature and ambient air temperature. This approach may not be convenient for some solar cooker designs. In the present work, the suitability of a non-linear regression derived from fitting the measured load temperature to a second order exponential polynomial was investigated and compared with the linear regression. Both regressions were compared with the corresponding experimental curves of a panel cooker and a box cooker. In the case of the panel cooker, the linear trend of the experimental plot was confirmed over a large period of the conducted test. Minor deviations from the experimental data were observed only at the beginning and at the end of the test. On the contrary, in the box solar cooker, significant deviations between the linear regression plot and the experimental points were observed, while smaller deviations were obtained using the non-linear regression. Thus, the proposed method can be seen as a promising approach that should be considered when updating the existing procedures for testing and reporting the performance of solar cookers.info:eu-repo/semantics/publishedVersio

Thermal storage of nitrate salts as Phase Change Materials (PCMs)

This study presents the energy storage potential of nitrate salts for specific applications in energy systems that use renewable resources. For this, the thermal, chemical, and morphological characterization of 11 samples of nitrate salts as phase change materials (PCM) was conducted. Specifically, sodium nitrate (NaNO3), sodium nitrite (NaNO2), and potassium nitrate (KNO3) were considered as base materials; and various binary and ternary mixtures were evaluated. For the evaluation of the materials, differential Fourier transform infrared spectroscopy (FTIR), scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) to identify the temperature and enthalpy of phase change, thermal stability, microstructure, and the identification of functional groups were applied. Among the relevant results, sodium nitrite presented the highest phase change enthalpy of 220.7 J/g, and the mixture of 50% NaNO3 and 50% NaNO2 presented an enthalpy of 185.6 J/g with a phase change start and end temperature of 228.4 and 238.6 °C, respectively. This result indicates that sodium nitrite mixtures allow the thermal storage capacity of PCMs to increase. In conclusion, these materials are suitable for medium and high-temperature thermal energy storage systems due to their thermal and chemical stability, and high thermal storage capacity