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The development of small-sized parabolic trough collectors (PTCs) for processing heat production at medium temperatures (100–250 °C) represents an interesting approach to increase the utilization of solar thermal technologies in industrial applications. Thus, the development of simplified models to analyze and predict their performance under different operative and climatic conditions is crucial for evaluating the application potential of this low-cost technology. In this paper, we present a numerical method that by combining three-dimensional finite element simulations (implemented with COMSOL Multiphysics software version 6.1) with a one-dimensional analysis (based on a MATLAB script) allows for the theoretical determination of the power output of a small-PTC with a nonevacuated tubular receiver operating at a medium temperature. The finite element model considers both the nonuniformity of the concentrated solar flux on the receiver tube (evaluated using Monte Carlo ray-tracing analysis) and the establishment of natural convection in the air gap between the glass envelope and absorber tube. The model calculates, for several values of direct normal irradiance (DNI) and inlet temperatures, the thermal power transferred to the heat transfer fluid (HTF) per unit length. The data are fitted using the multiple linear regression method, obtaining a function that is then used in a one-dimensional multi-nodal model to estimate the temperatures and the heat gains along the receiver tube. The outputs of the model are the outlet temperature and the total thermal power transferred to the HTF. In order to validate the developed methodology for the assessment of the heat transfer characteristics in the small-PTC with a nonevacuated receiver, an experiment at the ENEA Trisaia—Solar Thermal Collector Testing Laboratory was carried out. This work compares the theoretical data with those acquired through experimentation, obtaining a good agreement, with maximum differences of 0.2% and 3.6% for the outlet temperatures and the power outputs, respectively. [ABSTRACT FROM AUTHOR]

The development of small-sized parabolic trough collectors (PTCs) for processing heat production at medium temperatures (100–250 °C) represents an interesting approach to increase the utilization of solar thermal technologies in industrial applications. Thus, the development of simplified models to analyze and predict their performance under different operative and climatic conditions is crucial for evaluating the application potential of this low-cost technology. In this paper, we present a numerical method that by combining three-dimensional finite element simulations (implemented with COMSOL Multiphysics software version 6.1) with a one-dimensional analysis (based on a MATLAB script) allows for the theoretical determination of the power output of a small-PTC with a nonevacuated tubular receiver operating at a medium temperature. The finite element model considers both the nonuniformity of the concentrated solar flux on the receiver tube (evaluated using Monte Carlo ray-tracing analysis) and the establishment of natural convection in the air gap between the glass envelope and absorber tube. The model calculates, for several values of direct normal irradiance (DNI) and inlet temperatures, the thermal power transferred to the heat transfer fluid (HTF) per unit length. The data are fitted using the multiple linear regression method, obtaining a function that is then used in a one-dimensional multi-nodal model to estimate the temperatures and the heat gains along the receiver tube. The outputs of the model are the outlet temperature and the total thermal power transferred to the HTF. In order to validate the developed methodology for the assessment of the heat transfer characteristics in the small-PTC with a nonevacuated receiver, an experiment at the ENEA Trisaia—Solar Thermal Collector Testing Laboratory was carried out. This work compares the theoretical data with those acquired through experimentation, obtaining a good agreement, with maximum differences of 0.2% and 3.6% for the outlet temperatures and the power outputs, respectively.

This research investigates the simulation-based performance of metallic and non-metallic nanoparticles, along with water-based heat transfer fluids, used in parabolic trough concentrator. Its main goal is to analyze the performance enhancement of the concentrator, divided into two phases. The first phase focuses on validating the experimental setup using computational fluid dynamics through ANSYS software. The same validated simulation model is then utilized to assess the performance of solar parabolic trough concentrator with different metallic and non-metallic, plus water-based nanofluids. The study utilizes water alone, along with copper, gold, and silver, and two non-metallic nanoparticles, alumina oxide, and copper oxide, in varying volumetric concentrations from 1% to 3%. The simulation analysis, conducted at a speed of 0.12 m/s, reveals that the highest average temperature increase is observed in the case of alumina + water-based nanofluid at 3% volumetric concentration, with a maximum average heat transfer of 351.89 watts. Additionally, the silver + water-based nanofluid demonstrates the highest average value of the coefficient of convective heat transfer at 88055.5 W/(m2 K). The gold + water-based nanofluid shows a higher average value of the Reynolds Number at 4352.268, while the maximum Nusselt number is observed with alumina oxide + water-based nanofluid, measuring 1.7698.

This research investigates the simulation-based performance of metallic and nonmetallic nanoparticles, along with water-based heat transfer fluids, used in parabolic trough concentrator. Its main goal is to analyze the performance enhancement of the concentrator, divided into two phases. The first phase focuses on validating the experimental setup using computational fluid dynamics through ANSYS software. The same validated simulation model is then utilized to assess the performance of solar parabolic trough concentrator with different metallic and nonmetallic, plus water-based nanofluids. The study utilizes water alone, along with copper, gold, and silver, and two non-metallic nanoparticles, alumina oxide, and copper oxide, in varying volumetric concentrations from 1% to 3%. The simulation analysis, conducted at a speed of 0.12 m/s, reveals that the highest average temperature increase is observed in the case of alumina + water-based nanofluid at 3% volumetric concentration, with a maximum average heat transfer of 351.89 watts. Additionally, the silver + water-based nanofluid demonstrates the highest average value of the coefficient of convective heat transfer at 88055.5 W/(m2 K). The gold + water-based nanofluid shows a higher average value of the Reynolds Number at 4352.268, while the maximum Nusselt number is observed with alumina oxide + water-based nanofluid, measuring 1.7698. [ABSTRACT FROM AUTHOR]

In this work, a validated finite element-based coupled optical, thermal, and electrical model is used to assess the performance of a dual concentrated photovoltaic system thermally regulated using a PCM for the environmental conditions of Lahore, Pakistan. Thermal management of the system is achieved using a selected PCM. That has a melting temperature of 53-56 °C, a thermal conductivity of 19 W/mK, and heat of fusion of 220 kJ/kg. Thermal regulation and power output of the system are analyzed for a clear day of six months of a year. It is found that the maximum temperature of the upper PV cell is ~80 °C while for the bottom PV cell is ~82 °C in July. The percentage power gain obtained after the addition of an upper concentrated PV cell is ~17.9%. The maximum and minimum power of the system is found to be 0.079 kWh/day/m2 and 0.041 kWh/day/m2 in May and November, respectively. [ABSTRACT FROM AUTHOR]

This paper proposes and analyzes a novel solar-assisted air conditioning system integrating a parabolic trough concentrator coupled to a vapor compression refrigeration cycle operating on environmentally friendly refrigerants. This system, designed to allow relatively high temperatures to be reached thanks to the concentrator, makes it possible to valorize solar energy by expanding the compressed and superheated working fluid in a power sub-cycle. The research aims to evaluate system performances and the energy savings achievable following an energy analysis under different operating conditions. Simulation of the developed system model using EES software showed that the best-performing fluid is R123, followed by R1233zd(E), out of the fifteen candidate fluids. In the absence of solar irradiation, the system operates according to the conventional compression refrigeration cycle, while in the presence of solar irradiation of up to 1000 W/m2, the system operates in a combined cycle with solar backup. In the latter case, this results in energy savings of about 25.3% and 43.8% when the system operates with condensation temperatures of 40 °C and 35 °C, respectively. An optimal mass fraction model of fluid deviating in the solar sub-cycle was also analyzed. The effect of evaporation temperature on generated energy savings has also been analyzed.

The solar trough concentrator is used to increase the solar radiation intensity on absorbers for water heating, desalination, or power generation purposes. In this study, optical performances of four solar trough concentrators, viz. the parabolic trough concentrator (PTC), the compound parabolic concentrator (CPC), the surface uniform concentrator (SUC), and the trapezoid trough concentrator (TTC), are simulated using the Monte Carlo Ray Tracing method. Mathematical models for the solar trough concentrators are first established. The solar radiation distributions on their receivers are then simulated. The solar water heating performances using the solar trough concentrators are finally compared. The results show that, as a high-concentration ratio concentrator, the PTC can achieve the highest heat flux, but suffers from the worst uniformity on the absorber, which is only 0.32%. The CPC can generate the highest heat flux among the rest three low-concentration ratio solar trough concentrators. Compared with the PTC and the CPC, the TTC has better uniformity, but its light-receiving ratio is only 70%. The SUC is beneficial for its highest uniformity of 87.38%. Thermal analysis results show that the water temperatures inside the solar trough concentrators are directly proportional to their wall temperature, with the highest temperature rise in the PTC and the smallest temperature rise in the TTC. The solar trough concentrators' thermal deformations are positively correlated to their wall temperatures. The radial deformation of the SUC is much larger than those of other solar trough concentrators. The smallest equivalent stress is found in the SUC, which is beneficial to the long-term operation of the solar water heating system. [ABSTRACT FROM AUTHOR]

In this paper, a reflux solar methanol steam reforming reactor (SMSRR) system is proposed for efficient solar thermal hydrogen produced. A two-dimensional (2D) axisymmetric model is used to compare the comprehensive performance of three different SMSRRs: no reflux tube (SMSRR0), flow from the inside of the reflux tube to the outside (SMSRR1) and flow from the outside of the reflux tube to the inside (SMSRR2). The results showed that the reflux SMSRR uses the heat of the fluid at the outlet to further provide the reaction heat, which greatly reduces the outlet temperature, thereby improving the overall performance of the SMORE. By optimizing the diameter of the reflux tube and the operating conditions, the energy conversion rate can be increased by 19.5%, and the temperature distribution coefficients can be increased by 1.89% while the methanol conversion is increased by 6.43%, and the hydrogen yield is increased by 5.96%. • A new solar receiver-reactor of reflux structure is proposed. • A three-dimensional comprehensive model was established for solar receiver-reactors with secondary reflection.. • The optimized reflux reactor greatly reduces ΔT io , thereby improving the energy conversion efficiency. • The reflux structure in the optimized systems enables the reactor to obtain better uniformity of the temperature field. [ABSTRACT FROM AUTHOR]

Due to population growth and industrial development consumption of non-renewable energy sources, and consequently pollution, has increased. In order to reduce energy utilisation and preserve the environment, developed and developing countries are increasingly trying to find solutions based on renewable energy sources. Cost-effective wastewater treatment methods using solar energy would significantly ensure effective water source utilisation, thereby contributing towards sustainable development goals. In this paper, special emphasis is given to the use of solar energy as the driving force of the process, as well as the use of highly active magnetic TiO2-based catalysts. Therefore, in this study, we investigated the possibility of photocatalytic degradation of aqueous magenta graphic dye using titanium dioxide as a catalyst and DSD model in order to achieve the best process optimisation. TiO2 was successfully coated with magnetic nanoparticles by one step process and characterized using different techniques (BET, SEM/EDS, FTIR, XRD). Based on DSD statistical method optimal reaction conditions were pH = 6.5; dye concentration 100 mg/L; TiO2–Fe3O4 0.6 g/L, at which the highest degree of magenta dye decolourisation was achieved (85%). Application of solar energy coupled with magnetic TiO2 catalyst which could be recovered and reused makes this approach a promising alternative in green wastewater treatment. [ABSTRACT FROM AUTHOR]

• A novel flat reflector was incorporated into a PTC to improve overall performance. • An optimal diameter of the AT was also studied to meet the 580 °C outlet temperature and maximum temperature below 600 °C. • AT's optimal diameter was 70 mm for this design reaching a 75% optical efficiency and 60.8% thermal efficiency at DNI = 1000 W/m2. • The optical efficiency could be increased by 4–12% and improved the uniformity by 2%–22% through adding a novel FR. Using a larger-aperture parabolic trough concentrator can reduce cost and improve cycle efficiency. At present, the maximum output temperature of the typical parabolic trough concentrator systems is lower than the set 580 °C. Here a novel flat reflector was incorporated into the absorber tube to improve the intercept factor and optical efficiency and hence the overall performance. At the same time, the optimal diameter of the collector tube was also researched to meet the outlet temperature exceeding the set 580 °C and the absorber tube's maximum temperature below 600 °C. A large-aperture parabolic trough concentrator (8 m aperture wide with 80° half rim-angle) is used as a case to demonstrate the effect of a flat reflector and advantages of the optimal absorber tube. Results obtained through simulations show that, in the large-aperture parabolic trough concentrator system with the flat reflector, the optimal diameter of the absorber tube was 70 mm for this design reaching 75% optical efficiency and 60.8% thermal efficiency at DNI = 1000 W/m2 and 53% daily average thermal efficiency for DNI = 400–1000 W/m2. Through adding a flat reflector, the optical efficiency and the uniformity were increased by 4–12% and 2–22% respectively, but the benefit gradually decreases with increasing the absorber tube diameter. To meet the requirement of outlet temperature more than 580 °C and absorber tube's maximum temperature below 600 °C and reduce the thermal strain, a scheme of adjusting flow rate was incorporated. [ABSTRACT FROM AUTHOR]

Summary: Nitrate salt with low melting point as heat transfer and storage fluid simplifies the heat transfer, storage, and exchange processes, and organic Rankine cycle as heat and power conversion system can realize the distributed energy supply. This study experimentally investigated the solar organic Rankine cycle with parabolic trough concentrator using nitrate salt as heat transfer and storage fluid, and the main problems and phenomena during the operation process have been described and analyzed in detail. Experimental results showed that the temperature difference of collector tube changes with direct normal irradiation and lags behind the changes of direct normal irradiation. Molten salt heat storage system can effectively restrain the temperature fluctuation at the collector tube outlet. The abrupt temperature drop at the evaporator inlet was caused by the heat imbalance between R123 and nitrate salt and inappropriate design of the evaporator. The effects of expander inlet pressure and expansion ratio on the ORC electrical power output were obtained at different superheating degrees of the expander inlet. The researches on each component are instructive to the technology of the parabolic trough concentrated solar power generation system with molten salt as heat transfer and storage fluid and provide some guides for the subsequent research. Furthermore, the energy and exergy analyses on overall system were developed, and results indicated the system average efficiency can reach 1.5%. Novelty statement: Experimental study on parabolic trough concentrated solar ORC system with nitrate salt as heat transfer and storage medium were firstly analyzed.Single screw expander was firstly applied in a real solar thermal power generation system and showed a stable performance.Dynamic changes on the temperatures of PTC, molten salt tanks, and ORC were shown, and energy and exergy analyses on overall system were carried on. [ABSTRACT FROM AUTHOR]

This study presents the design and performance evaluation of a novel concentration photovoltaic/thermal (PV/thermal) system based on parabolic trough concentrator and indium tin oxide-ethylene glycol (ITOEG) nanofluid spectral filter. The overall design principle of the PV/thermal system is introduced, and the ITOEG nanofluid spectral filter is prepared and experimentally tested. For the full spectrum, the average transmittance and absorbance of the nanofluid spectral filter are 69.1% and 30.9%. The optical behaviour evaluation results reveal a double-peak radiation flux density distribution on the nanofluid channel bottom surface as well as on the solar cell module surface. When the north-south sun-tracking error increases to 0.2°, the optical efficiency of the PV/thermal system decreases to 93.7%. That means the system has a relatively good adaptability to the sun-tracking error. The thermodynamic analysis results reveal that the theoretical photoelectric conversion and solar thermal efficiencies of the PV/thermal system are 29.1% and 17.2%. The thermal efficiency of the PV/thermal system can be increased by increasing the nanofluid inlet flow velocity or by decreasing the nanofluid inlet temperature properly.

Parabolic trough solar thermal technology is the most cost-effective approach for concentrated solar energy applications. The concentrator thickness significantly affects the performance of the parabolic trough collector. To examine the effect of mirror refraction in the concentrator, the focal plane concentration for different concentrator thicknesses was studied using theoretical calculations, simulations, and experimental verification. A longitudinal offset of the focal plane is proposed to optimize the focal plane concentration. The deviation of the reflected sunlight depending on the concentrator thickness was found to strongly affect the concentration in the focal plane. When the concentrator thickness was increased by a factor of 5, the focal plane was 5 times as wide, the maximum energy flux density in the focal plane decreased by a factor of 5, and the optical efficiency decreased by 0.24%. The longitudinal offset of the absorber plane position was introduced to avoid local overheating of the absorber and low collector temperature by maintaining the focal plane width and maximum energy flux density in the focal plane within appropriate ranges. The experimental results showed that with optimization, the maximum energy flux density, uniformity, and optical efficiency increased by 5.75%, 3.35%, and 2.43%, respectively. [ABSTRACT FROM AUTHOR]

Increasing the aperture of the parabolic trough concentrator (PTC) can effectively reduce costs and help promote. This paper proposed a circle and semicircle absorber tubes (AT) with a flat reflector (FR) in it for the large-aperture PTC system and the size of the AT was determined for the PTC with 8 m aperture width and 80° half rim-angle. The result shown the PTC system using a semi-circular AT with a diameter of 100 mm has the highest average thermal efficiency of 71.6% with DNI 400–1000 W/m2 at about 500 °Cand has best uniformity of 38.8%. However, its deformation is highest and 1.7 and 1.6 times other two ATs. Therefore, how to reduce the deflection has become a research direction in the future. Currently, the circular AT with a diameter of 80 mm is the most practical with an average thermal efficiency of 69.1% and a minimum deflection. [ABSTRACT FROM AUTHOR]

Abstract In the present investigation, a solar parabolic trough concentrator (PTC) with a linear cavity was examined by using a developed numerical model. More specifically, a V‐shape cavity receiver was studied in this work as a new and alternative design. The use of a cavity in a PTC is a very promising idea because it leads to high efficiency and to low investment cost. Up today, the emphasis in the use of cavities is given in dish concentrators and so there is a need for investigation of cavities also in linear concentrators. Different dimensional and operational parameters of the PTC with a V‐shape cavity were considered. More specifically, the position, aperture area, and the tube diameter of the V‐shape cavity, solar irradiance, inlet temperature level, and mass flow rate were evaluated based on sensitivity analysis. The results revealed that the highest optical performance was attained when the cavity was placed at the PTC focal line. Moreover, it is found that there is an optimum cavity aperture area to determine the greatest thermal efficiency. For the optical errors of 5, 10, 15, 20, and 35 mrad, the optimum cavity aperture wide was calculated at 5, 5, 6, 7, and 8 cm, respectively, with the tracking error to be 0°. The highest thermal performance has found when the collector operates with low inlet temperature, high flow rate, high solar irradiation level, and small cavity tube diameter.

The solar trough concentrator is used to increase the solar radiation intensity on absorbers for water heating, desalination, or power generation purposes. In this study, optical performances of four solar trough concentrators, viz. the parabolic trough concentrator (PTC), the compound parabolic concentrator (CPC), the surface uniform concentrator (SUC), and the trapezoid trough concentrator (TTC), are simulated using the Monte Carlo Ray Tracing method. Mathematical models for the solar trough concentrators are first established. The solar radiation distributions on their receivers are then simulated. The solar water heating performances using the solar trough concentrators are finally compared. The results show that, as a high-concentration ratio concentrator, the PTC can achieve the highest heat flux, but suffers from the worst uniformity on the absorber, which is only 0.32%. The CPC can generate the highest heat flux among the rest three low-concentration ratio solar trough concentrators. Compared with the PTC and the CPC, the TTC has better uniformity, but its light-receiving ratio is only 70%. The SUC is beneficial for its highest uniformity of 87.38%. Thermal analysis results show that the water temperatures inside the solar trough concentrators are directly proportional to their wall temperature, with the highest temperature rise in the PTC and the smallest temperature rise in the TTC. The solar trough concentrators’ thermal deformations are positively correlated to their wall temperatures. The radial deformation of the SUC is much larger than those of other solar trough concentrators. The smallest equivalent stress is found in the SUC, which is beneficial to the long-term operation of the solar water heating system.

This study investigates the performance enhancement of parabolic trough concentrators (PTCs) with transparent insulation material shell (TIMS) of different diameters and thicknesses integrated into evacuated and non-evacuated heat collection elements (HCEs). The results show that non-evacuated TIMS-HCEs have higher energy and exergy efficiencies by up to 62.4 and 63.2%, compared to conventional evacuated HCEs, and by up to 109.2 and 110.9%, compared to conventional non-evacuated HCEs. At high flow rates and low fluid temperatures, the energetic performance of a conventional evacuated HCE is only 6.3% higher than that of the modified non-evacuated one. The modified design also enhances the circumferential temperature uniformity and shows a marginal drop in efficiency when the vacuum is lost. By simulating the PTC performance during four typical days, and without vacuum, the proposed design increased the daily useful heat gain by up to 1.36 and 5.64 kWh, compared to conventional evacuated and non-evacuated HCEs, respectively. Hence, it is proposed as a low-tech alternative to HCE evacuation and as a method of boosting the performance of PTCs operating at low flow rates and high temperatures. [Display omitted] • Receiver of parabolic trough collector is enhanced using transparent insulation. • An MCRT-FVM model is developed for evaluating conventional and modified designs. • Without vacuum, the modified design outperforms a conventional evacuated one. • Energy and exergy efficiencies are enhanced by up to 62.4 and 63.2%, respectively. • The modified design shows better temperature uniformity with no consumed power. [ABSTRACT FROM AUTHOR]

Three parabolic trough collectors, with its two axes sun manual tracking system were designed, constructed, and operated in order to generate hot water and moderate temperature steam. An experimental investigation for testing the performance of a PTC is presented. The tests have been carried out in NAJAF climatic conditions (32.02 N, 44.33 E) during selective days of August. The thermal performance of PTC evaluated according to the Standard ASHRAE 93-1986 (RA 91) and the efficiency curve for the PTC was estimated. In the performance analysis of the PTC array, the effects of collector inlet temperature, ambient conditions, two cases for glass receiver and the variation in mass flow rate of the working fluid were investigated. A peak efficiencies close to (50% and 18.8%) were obtained for solar collectors with evacuated and non-evacuated glass receiver respectively at higher flow rate. The collector efficiency equation that is obtained in the present work agrees with other researches.

In the present investigation, a solar parabolic trough concentrator (PTC) with a linear cavity was examined by using a developed numerical model. More specifically, a V‐shape cavity receiver was studied in this work as a new and alternative design. The use of a cavity in a PTC is a very promising idea because it leads to high efficiency and to low investment cost. Up today, the emphasis in the use of cavities is given in dish concentrators and so there is a need for investigation of cavities also in linear concentrators. Different dimensional and operational parameters of the PTC with a V‐shape cavity were considered. More specifically, the position, aperture area, and the tube diameter of the V‐shape cavity, solar irradiance, inlet temperature level, and mass flow rate were evaluated based on sensitivity analysis. The results revealed that the highest optical performance was attained when the cavity was placed at the PTC focal line. Moreover, it is found that there is an optimum cavity aperture area to determine the greatest thermal efficiency. For the optical errors of 5, 10, 15, 20, and 35 mrad, the optimum cavity aperture wide was calculated at 5, 5, 6, 7, and 8 cm, respectively, with the tracking error to be 0°. The highest thermal performance has found when the collector operates with low inlet temperature, high flow rate, high solar irradiation level, and small cavity tube diameter. [ABSTRACT FROM AUTHOR]

In this study, the efficiency of a large aperture 2-stage parabolic trough concentrator (PTC) is improved using an innovative design method for the secondary reflector (SR). The design method is based on an adaptive approach in which the SR is step-wise optimized to maximally reflect back to the absorber tube (AT) the part of solar radiation reflected by the primary reflector (PR) but not captured by the AT. The adaptive design method results in a SR design which consists of several parabolas with different focal lengths, each having a focus which lies in the focus of the PR. This ensures that the originally unabsorbed solar radiation will now hit the surface of AT. The optical efficiency of the PTC could be increased by 5.2% and thermal efficiency by 4.9%, respectively, compared to a case without optimized SR. In addition, the uniformity of the solar radiation flux on the AT's outer wall could be doubled, its temperature was more even. The new adaptive design approach of the SR could help to better optimize PTC systems. • New design approach for secondary mirror in parabolic trough concentrator. • Adaptive method to design secondary mirror. • Step-wise optimization to maximally reflect radiation to absorber. • Optical and thermal efficiency of concentrator increased by 5.2% and 4.9%. [ABSTRACT FROM AUTHOR]

• Innovation in the field of solar renewable energy applications. • Propose an ecological cooking method. • Heating mode at high temperature (>200°) using a fluid and solar energy. In this article, we describe the structure, the functioning, and the tests of parabolic trough solar thermal cooker (PSTC). This oven is designed to meet the needs of rural residents, including Urban, which requires stable cooking temperatures above 200 °C. The cooking by this cooker is based on the concentration of the sun's rays on a glass vacuum tube and heating of the oil circulate in a big tube, located inside the glass tube. Through two small tubes, associated with large tube, the heated oil, rise and heats the pot of cooking pot containing the food to be cooked (capacity of 5 kg). This cooker is designed in Germany and extensively tested in Morocco for use by the inhabitants who use wood from forests. During a sunny day, having a maximum solar radiation around 720 W/m2 and temperature ambient around 26 °C, maximum temperatures recorded of the small tube, the large tube and the center of the pot are respectively: 370 °C, 270 °C and 260 °C. The cooking process with food at high (fries,..), we show that the cooking oil temperature rises to 200 °C, after 1 h of heating, the cooking is done at a temperature of 120 °C for 20 min. These temperatures are practically stable following variations and decreases in the intensity of irradiance during the day. The comparison of these results with those of the literature shows an improvement of 30–50 % on the maximum value of the temperature with a heat storage that could reach 60 min of autonomy. All the results obtained show the good functioning of the PSTC and the feasibility of cooking food at high temperature (>200 °C). [ABSTRACT FROM AUTHOR]

Summary: Solar thermal electricity generating technology is an alternative solution to energy crises and environmental problems, which has caused wide concern in recent decades. In this paper, a molten salt parabolic trough‐based concentrated organic Rankine cycle system is proposed and investigated. A quadribasic nitrate salt with low melting temperature is employed as a heat transfer and storage medium. A stable heat transfer and economic model is established with Matlab. The radial and axial temperature distributions in the collector tube are obtained, and the impact of condensation and evaporation temperatures on the heat transfer area is analyzed. Results show that the temperature along the axial direction linearly increases, and the temperature at the collector tube exit decreases with the increase of molten salt mass flow rate. The maximum temperature difference along the radial direction of the collector tube happens in the annular gap. Heat transfer and thermodymanic analysis indicates that condensation temperature has a more evident effect on heat transfer area than that of evaporation temperature. An increase in condensation temperature leads to a decrease in the evaporator area, the condenser area increases, and the total area decreases. Economic analysis indicates the collector cost plays a predominant role in total capital costs, and decreasing molten salt mass flow rate can considerably reduce collector cost. Levelized energy cost sensitivity analysis indicated that operation time per year has a more evident effect than that of the four factors. Heat transfer and economic analysis on the system helps in the selection of operation parameters. [ABSTRACT FROM AUTHOR]

A calculation and optimization algorithm is proposed for operating modes of composite parabolic trough mirror-concentrating sysetms (MCSs) with allowance for the geometric and optical parameters of the concentrator heat receiver in a wide range of operating conditions, as well as temperature conditions of the system as a whole. The thermal and exergy efficiency (i.e., the reversible thermal Carnot cycle) are estimated, the values of which for the developed linear composite parabolic trough concentrators are 0.4438 and 0.0932, respectively. [ABSTRACT FROM AUTHOR]

The paper presents the novel design of double glazing helical coil solar cavity receiver for solar thermal applications. Performance model has been developed for the experimental setup based on energy balance equations. The results obtained were compared with horizontal tube receiver for the same experimental setup. The result shows that the 87.96% improvement in the convective heat transfer coefficient for the double glazing helical coil solar cavity receiver. Maximum conversion efficiency achieved is 21% more than that would be obtained for horizontal tube receiver. This paper also investigates how the quality of vacuum degraded with the temperature of the glass cover. [ABSTRACT FROM AUTHOR]

• Pyrolysis of date palm waste to biochar using PTC was simulated. • PTC pyrolysis is more cost-effective than conventional electric-based pyrolysis. • PBT and ROI of PTC pyrolysis are 4 years 132 days and 22.9%, respectively. • CO 2 emissions from PTC pyrolysis are 38% of that of conventional pyrolysis. • PBT is more sensitive to changes in biochar selling price than cost of acquiring date palm waste. A system of concentrated solar energy for pyrolysis of date palm waste to biochar is designed and simulated using SuperPro Designer v8.5. Both economic and environmental sustainability implications are evaluated by bench-marking with the conventional process (electric heating-based pyrolysis). Economic analysis shows that this process is more economically viable than the conventional process, with payback time (PBT) of 4 years and 132 days, internal rate of return (IRR) of 14.8%, return on investment (ROI) of 22.9% and gross margin of 35.5%. Environmental impact assessment shows that CO 2 emissions from concentrated solar energy-based pyrolysis accounts for only 38% of that of the conventional pyrolysis, indicating that concentrated solar energy pyrolysis is more environmentally friendly. Sensitivity analysis shows that PBT is more sensitive to changes in biochar selling price than changes in the cost of acquiring date palm waste. This process presents sustainable opportunities for biochar production while reducing life cycle emissions and costs. [ABSTRACT FROM AUTHOR]

Sustainable power generation, energy security, and global warming are the big challenges to the world today. These issues may be addressed through the increased usage of renewable energy resources and concentrated solar energy can play a vital role in this regard. The performance of a parabolic-trough collector's receiver is here investigated analytically and experimentally using water based and therminol-VP1based CuO, ZnO, Al2O3, TiO2, Cu, Al, and SiC nanofluids. The receiver size has been optimized by a simulation program written in MATLAB. Thus, numerical results have been validated by experimental outcomes under same conditions using the same nanofluids. Increased volumetric concentrations of nanoparticle is found to enhance heat transfer, with heat transfer coefficient the maximum in W-Cu and VP1-SiC, the minimum in W-TiO2 and VP1-ZnO at 0.8 kg/s flow rate. Changing the mass flow rate also affects heat transfer coefficient. It has been observed that heat transfer coefficient reaches its maximum of 23.30% with SiC-water and 23.51% with VP1-SiC when mass-flow rate is increased in laminar flow. Heat transfer enhancement drops during transitions of flow from laminar to turbulent. The maximum heat transfer enhancements of 9.49% and 10.14% were achieved with Cu-water and VP1-SiC nanofluids during turbulent flow. The heat transfer enhancements of nanofluids seem to remain constant when compared with base fluids during either laminar flow or turbulent flow. [ABSTRACT FROM AUTHOR]

• A hybrid power generation with solar ORC and AST systems was considered. • A solar PTC parabolic was as the heat source of the ORC system. • Smooth and corrugated tubes were considered as the PTC receiver. • Different CFCs were investigated as the ORC working fluid. • An AST was structurally and operationally optimized for power generation. In this research, an energy harvesting system was developed for power generation using a combination of an Archimedes Screw Turbine (AST) and a solar Organic Rankine Cycle (ORC) system. An AST was numerically used and optimized for producing mechanical power as an energy harvesting technique. Different structural parameters including the screw inclination angle, number of flights and the screw length were considered. A parabolic trough concentrator was numerically modeled as a heat source of the ORC system. Two different types of absorber were considered using a smooth and corrugated tube. Different ORC working fluids were investigated in the solar ORC system including R134a, R245ca, R245fa, R152a, R113, R11, and R114b. The results of numerical modeling were validated with experimental results and good agreement was found. The results revealed that R113 at the saturated condition at turbine inlet gave the highest ORC net power, ORC efficiency, and total efficiency compared to the other investigated working fluids. The solar PTC system with the corrugated tube showed the higher ORC net power, and overall efficiency compared to the smooth tube as the PTC receiver. The highest efficiency resulted in the screw length of 1.5 m was 58.24% with inclination angle of 25° and flight number of 1. Finally, the optimized characteristics of power generation system including a solar ORC system and a screw turbine (hybrid system) were presented to harvest energy. Application of the presented hybrid system is an acceptable way for increasing and optimizing the ORC power generation. [ABSTRACT FROM AUTHOR]

Highlights • The parabolic reactor showed good performance and high efficiency of the process. • Solar assisted Fenton process-energy saving treatment. • Photolysis of hydrogen peroxide has an important role in the process of decolorization. • Large specific surface area of AlFeB exhibited higher catalytic activity than CuOFeB. • Decolorization reaction rate is higher using Al, Fe-bentonite catalyst. Abstract In this work, the decolorization efficiency of Reactive Red 120 (RR120) synthetic solution using ferrioxalate (CuOFeB) and Al, Fe-bentonite (AlFeB) catalysts in the solar-assisted Fenton process was evaluated, as well as impact of H 2 O 2 photolysis on the process efficiency.The photo-Fenton oxidation of dye has been investigated using a concentrating solar parabolic reactor with constant solar radiation of 550 W/m2 and 950 W/m2 for spring and summer periods, respectively. Experimental data has proved that photolysis of hydrogen peroxide has an important role in the process of decolorization, achieving a decolorization efficiency over 80.78% at pH 7. Under the optimal reaction conditions, both catalysts showed a good stability in the processes with dye removal over 90%. The mineralization efficiency depends on the intensity of the solar radiation, wherein ∼50% was achieved under the higher solar intensity. Comparing reaction rate it is important to note that the larger specific surface area of AlFeB (155.83 m2/g) makes him a superior catalyst and thus solar-assisted Fenton process with this catalyst fast and efficient. Based on the decolorization rate constants, the examined processes can be placed in the following order: AlFeB (950 W/m2) > AlFeB (550 W/m2) > CuOFeB (950 W/m2) > CuOFeB (550 W/m2). These findings are confirmed on real effluent, whereby a greater degree of decolorization (91.89%) and mineralization (43%) has been achieved with AlFeB catalyst compared to CuOFeB (30.09% and 15%) during the process. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Numerical modeling of the flow dynamics and heat exchange in the tube receiver of a solar parabolic trough module (PTM) has been performed. The study is based on a dimensionless mathematical model that describes turbulent conduction of heat and momentum. An analysis has been carried out and a turbulence model has been selected. The proposed model describes the features of heat exchange near the wall most accurately. A numerical algorithm and Fortran program have been developed on the basis of the mathematical model. The major geometric, dynamic, and energy parameters of the PTM receiving system have been determined. The results can be useful in designing solar energy systems with parabolic trough concentrators (PTC) of different power and purpose. [ABSTRACT FROM AUTHOR]

• A novel idea by dividing a solar source into two components in the open angle is proposed for design of PTC; • PTC equipped with a flat mirror as the secondary reflector (PTC-FM) is designed as a trial of the idea; • A mathematical procedure to characterize the geometry of PTC-FM is developed and examined; • Effects of geometric and design parameters on the concentration ratio (C g) of PTC-FM are investigated; • Comparisons of C g between PTC-FM and similar conventional PTC are performed; • Empirical expressions for a quick estimation of geometric parameters of optimized PTC-FM are presented; Parabolic trough concentrators with a tubular receiver (PTCs) are widely used for the production of solar thermal power. However, the geometric concentration ratio (CR) of PTCs falls short of thermodynamic concentration limit (C 0) by a factor larger than π, and restricted by the angle subtended by solar sources (Δ s = 2θ a). To increase CR, a novel idea by dividing a solar source into two components in the open angle is proposed for the design of PTC equipped with a secondary reflector (SR), and PTC with a flat mirror (FM) is designed as a trial of the idea. For such design idea, rays incident at rims of primary parabolic reflector (PR) from one component (S1) are required to directly redirect onto on the absorber tube (AT) and those from another component (S2) are required to arrive on the AT after reflections from PR first then from FM. To investigate effects of the angular division factor (k) of solar sources (Δ s2 = kΔ s) and rim angle (ϕ e) of PR on the effective CR (C g), a mathematical procedure to characterize the geometry is suggested and examined by ray-tracing technique. The analysis shows that the geometry of PTC-FM is dependent on k , ϕ e and θ a , and a set of optimal k and ϕ e for maximizing C g can be obtained when θ a is given. Calculation results show that the optimal k for maximizing C g is 0.5 regardless of θ a , but the optimal ϕ e of PTC-FM for maximizing C g , is sensitive to θ a. As compared to conventional PTCs, the C g of optimized PTC-FM is increased more than 80%, larger than 56.5% of C 0 , for k = 0.5 and θ a < 1.0°. Empirical expressions for a quick estimation of optimal ϕ e are also proposed based on numerical calculations. Results by ray-tracing analysis indicate that the optimal ϕ e for maximizing CR and average solar concentration ratio are almost identical when the reflectivity of PR and FM is higher than 0.8. In principle, the novel idea is applicable for the design of other solar concentrators, therefore a further increase of C g of PTCs is possible by using other imaging and non-imaging optics as the SR. [ABSTRACT FROM AUTHOR]

Today, application of cavity receivers in solar concentrator systems is suggested as an interesting and novelty research subject for increasing thermal performance. In this research, a parabolic trough concentrator (PTC) with a rectangular cavity receiver was energetically investigated. The cavity receiver was studied with smooth and corrugated tubes. Different solar heat transfer fluids were considered, including water, air, and thermal oil. The effect of different operational parameters, as well as structural parameters, was investigated. The results showed that the linear rectangular cavity receiver with corrugated tube showed higher amounts of the absorbed heat and energy performance compared to the smooth tube as the cavity tube. Thermal performance of the rectangular cavity was improved using the application of water as the solar heat transfer fluid, which was followed by thermal oil and, finally, air, as the solar heat transfer fluid. Finally, it could be recommended that the rectangular cavity receiver with smooth tube using air as the solar heat transfer fluid is more appropriate for coupling this system with a Bryton cycle, whereas the rectangular cavity receiver with the corrugated tube using water or oil as the solar heat transfer fluid is recommended for achieving higher outlet temperature of the heat transfer fluid.

In this paper, the design process steps of a conventional solar parabolic trough with large rim angle are presented. The various parameters which intervene to obtain the suitable parabolic trough form of the concentrator are applied. Through an experimental characterization, the real focal distance and the focal zone size of the designed concentrator have been determined and compared with those calculated theoretically. Then, its concentration ratio is evaluated and the focused solar flux at the focal zone along the absorber tube is calculated using Soltrace code. It should be noted that the wind speed effect was not taken into account in the experimental tests which are conducted under a solar irradiation of 970 W/m 2 and a receiver inclination angle of 36° which corresponds to the experimentation site latitude. [ABSTRACT FROM AUTHOR]

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A detailed computational method Ray Tracing 3Dimensions-4Rays (RT3D-4R) of parabolic trough collector (PTC) system based on the ray tracing techniques is presented and developed to determine the heat flux distribution along the PTC system receiver tube. In the present study, the local concentration ratio (LCR) and the heat flux density distribution on the absorber tube surface were investigated to validate the proposed method. Also, the effects of the geometric concentration ratio and the rim angle on the heat flux density distribution and on the total intercepted solar energy on the receiver tube were analyzed and investigated. Moreover, the total intercepted solar energy on the receiver tube and the daily solar gain made by a one-axis tracked and dual tracked PTC system were investigated, for different geometric concentration ratio and rim angle, using the case study of the Monastir city, Tunisia. [ABSTRACT FROM AUTHOR]

• A new CPVT model is provided using a photovoltaic module and pulsating heat pipe in its collector. • Different HTFs including Glycerine, Ethylene Glycol, and Calcium Chloride water mixture experimentally tested. • Enhancing heat pipe performance, a variety of working fluids were tested. • The provided cooling system recycles 47.3% of the thermal energy, resulting in a 48.8% efficiency increase. In this paper, the experimental investigation of the performance of a concentrated hybrid photovoltaic thermal solar system is sought. Accordingly, there is a parabolic trough concentrator receiver that consists of three components: a triangular duct, photovoltaic cells covering the duct, and a three-turn PHP. The PHP cools down the photovoltaic cells efficiently and regenerates waste heat. The duct is filled with a heat transfer fluid surrounding the PHP's evaporator. The condensation section of the PHP is located outside the solar concentrator. Using a one-axis polar mechanism, the concentrator tracks the sun from east to west. The system experiment setup was fabricated and tested outdoors in Tehran's climate. Different heat transfer fluids, including Glycerine, Ethylene Glycol, and Calcium Chloride water mixture, were tested. Given the enhancement of PHP performance, a variety of working fluids were tested, including graphene oxide nanofluid/water, acetone, and pure water. The experiments showed that graphene oxide nanofluid/water mixture provided the highest thermal performance. With the use of graphene oxide nanofluid/water (as a working fluid) and glycerine (as heat transfer fluid), experiment results showed a decrease of 7.84 °C in PV temperature and a consequent increase of 21.85% in electrical efficiency in best condition. Furthermore, the provided cooling system recycles a maximum of is 190.4 kJ of thermal energy equivalent 52.5% thermal efficiency, increasing overall efficiency by 74.35%. Lastly, the IRR of 65.41%, PBT of 1.04 years, and LCOE of 1.84 $/kWh demonstrate appropriate financial profitability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbon dioxide-based receivers are analyzed for parabolic trough collectors. • An analytical model is proposed to evaluate and optimize the shielded receiver. • Shielded receivers boost the efficiency of conventional receivers by up to 10.6%. • A maximum energy efficiency of 77.2% is achieved using an 80 mm absorber tube. • A maximum exergy efficiency of 45.9% is achieved using a 50 mm absorber tube. An urgent need to enable the operation of parabolic trough concentrators at higher temperatures for higher efficiency of the coupled power cycles is manifested in the state-of-art literature. Supercritical carbon dioxide is a promising fluid for the next generation of these concentrators. However, the inflated radiative thermal losses at elevated temperatures are the main challenge, and the relatively large absorber diameters are questionable for supercritical pressures. This study proposes a novel 1-D analytical model, coupled with Monte Carlo ray tracing, for evaluating internally shielded receivers based on the absorber tube's diameter and eccentricity, the heat shield's opening angle, as well as the operating conditions. The results suggest that increasing the tube diameter reduces the performance dependency on tube eccentricity, but also reduces the optical performance. Shielding the receiver is favorable for opening angles up to 160°. The impact of operating pressure is marginal, compared to flow rate and temperature. A shielded receiver with an opening angle of 160°, eccentricity of −10 mm, and tube diameter of 50 mm maximizes the exergy efficiency up to 45.9%, whereas a receiver with corresponding values of 80°, −15 mm, and 80 mm, respectively, maximizes the energy efficiency up to 77.2%. Shielded receivers also boost the efficiency by up to 10.6%, compared to conventional 70 mm receivers. These performance enhancements are expected to elevate the efficiency of the integrated systems with minimal economic and environmental impacts due to the simplicity of the proposed solution. [ABSTRACT FROM AUTHOR]

A prototype practical solar-thermoelectric cogenerator composed of (1) a primary component of a pile of solar-selective absorber (SSA) slab, thermoelectric (TE) modules, and a depressed water flow tube (multichannel cooling heat sink, MCS), and (2) a parabolic trough concentrator with aperture area of 2 m Ã- 2 m and eastâ€'west focal axis was constructed. Its cogeneration performance under the best climatic and solar insolation conditions in Guangzhou, China was tested. For simplicity, the evacuated glass tube to cover the primary component was eliminated from the system. Six BiTe TE modules were arranged in series, directly bonded to the rear surface of the solar absorber slab. The hot-side temperature of the TE module reached up to 152°C. The experimentally obtained instantaneous results for the solar to electrical conversion efficiency, heat exchange coefficient of the MCS, and overall system efficiency under the best environmental and solar insolation conditions were about 1.14%, 56.1%, and 49.5%, respectively. To justify these values, an equivalent thermal network diagram based on a single-temperature-node heat transfer model representing the respective system components was used to analyze the thermal transfer and losses of the system. Finally, electrical power of 18 W was generated, with 2 L/min of hot water at 37°C being produced and stored in the insulated container. [ABSTRACT FROM AUTHOR]

• A new type of CPC and PTC based CPV/T-STEG hybrid system is proposed. • A steady-state 1-D optical-thermal-electrical coupled model has been elaborated. • The developed mathematical model is validated using a 3-D numerical simulation. • The impact of critical parameters on the system's performance is discussed. • Improvements in electrical and thermal output over existing CPV/T-TEG systems. This article discusses the electrical and thermal performance of a hybrid concentrator photovoltaic thermal and solar thermoelectric generator (CPV/T-STEG) system using a compound parabolic concentrator (CPC) and a parabolic trough concentrator (PTC). For the first time, the idea of merging imaging and non-imaging concentrators for a CPV and TEG hybrid system is examined, providing an option to retrofit or remodel existing PTC-based CSP systems. The thermal resistance concept is applied to establish a steady-state mathematical model of the proposed hybrid CPV/T-STEG system. A Newton-Raphson iterative approach is employed to solve the mathematical model and compute the temperature in every layer of the hybrid system. After validation, the mathematical model is employed to evaluate the overall performance of the hybrid system. The modelling results revealed that the electrical and thermal output of the developed hybrid system were higher by 2 and 1.6 times, respectively, when compared with the prior parabolic trough-based hybrid CPV/T-STEG system described in the literature. The effects of ambient temperature, wind speed, flow rate, number of TEGs, and solar concentration ratio on the electrical and thermal performance were investigated. The optimal number of TEGs required for maximum electrical performance under different solar concentration ratios is also obtained. Finally, the hybrid system's exergy efficiency is investigated for various solar concentration ratios. The simulation results revealed that the increase in the Reynolds number from 100 to 2000 improves the net electrical and thermal efficiency by 10.21% and 5.7%, respectively. At a fixed solar concentration ratio (C CPC = 4 s u n s and W PTC = 2 W CPC), the electrical efficiency of TEG drops by 81.4%, but the thermal efficiency increases by 16.81%, provided that the number of TEGs is increased from 1 to 17. The highest exergy of the hybrid system is 8.36% when C CPC = 2 s u n s and W PTC = 2 W CPC. Due to the poor efficiency of commercial TEGs, the overall exergy efficiency of the hybrid system decreases with an increasing solar concentration ratio. In the proposed hybrid system, a fluid channel separates both the PV and TEG modules; hence the electrical conversion efficiencies of both modules are not closely related. [ABSTRACT FROM AUTHOR]

Solar thermoelectric co-generators (STECGs) are an attractive means of supplying electric power and heat simultaneously and economically. Here we examine the effects of environmental factors on the conversion efficiencies of a new type of STECG comprising parabolic trough concentrators and thermoelectric modules (TEMs). Each TEM array was bonded with a solar selective absorber plate and directly positioned on the focal axis of the parabolic concentrator. Glass tubular collectors were not used to encase the TEMs. Although this makes the overall system simpler, the environmental effects become significant. Simulations show that the performance of such a system strongly depends on ambient conditions such as solar insolation, atmospheric temperature and wind velocity. As each of these factors increases, the thermal losses of the STECG system also increase, resulting in reduced solar conversion efficiency, despite the increased radiation absorption. However, the impact of these factors is relatively complicated. Although the electrical efficiency of the system increases with increasing solar insolation, it decreases with increasing ambient temperature and wind velocity. These results serve as a useful guide to the selection and installation of STECGs, particularly in Guangzhou or similar climate region. [ABSTRACT FROM AUTHOR]

Five parabolic trough concentrating solar collectors were designed, constructed, evaluated, and operated in order to generate hot water and low-enthalpy steam. Three of them were designed with a rim angle of 90° and the other two have a rim angle of 45°. All of them were designed with a solar collector area close to 2.6 m2 and a concentration ratio close to 14. The purpose of the size of both designs is to provide modular solar collectors that can be operated in a serial or parallel arrangement depending on the thermodynamic availability that is required. All elements of both designs are made of aluminium with the aim of having a light but robust structure that has good resistance to outdoor conditions. In the construction of both collectors there is no need for sophisticated machinery or skilled labour and during the assembly only hand tools are required. The design of both collectors considers unshielded receivers and without glass cover in order to reduce manufacturing and transportation costs. A low temperature test for both designs was conducted according to the Standard ASHRAE 93-1986 (RA 91). Thermal and optical analyses were carried out for each collector, and the efficiency curve for each concentrator one was estimated. A peak efficiency of 35% was obtained for solar collectors with a rim angle of 45° and a peak efficiency of 67% was estimated for collectors with a rim angle of 90°. On the other hand, a serial arrangement using the five collectors was assembled and evaluated in order to obtain low-enthalpy steam generation. In preliminary results it was possible to obtain a temperature close to 110 °C with low steam quality. The overall efficiency of the arrangement system was evaluated to be between 25 and 45%. The cost of both designs is close to 170 US$/m2. [ABSTRACT FROM AUTHOR]