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For high-pressure applications, like direct steam generation or hydrothermal liquefaction, homogenizing the radiative flux on the tubular receiver of the parabolic trough concentrators can help avoid thermal stresses and potential material degradation. In the present study Monte Carlo ray tracing is used to analyze different secondary mirrors to enhance the flux uniformity level over the receiver tube of four parabolic troughs with different rim angles. Elliptical, V-shaped, Lambda-shaped (inverted V), and Compound Elliptical Concentrator (CEC) mirrors are considered. The design of these mirrors is optimized for each case using a Differential Evolution Algorithm. Solutions are sought with the maximum possible uniformity while keeping high optical efficiency. Results of the optical modeling show reductions in peak flux over the tube wall by approximately 60% when secondary mirrors are implemented with PTC systems. Furthermore, optical efficiencies of 90% and flux uniformity levels of 86.6% can be achieved by integrating the Elliptical and Lambda-shaped geometries as secondary mirrors. The effect of the secondary mirrors on the PTC efficiency for off-normal incidence was also studied. CECs are very good at increasing off-normal rays' acceptance, followed by V-shaped mirrors, but at the cost of a worsened overall performance. [Display omitted] • Secondary mirrors optimized for parabolic trough concentrated flux homogenization. • Four secondary geometries are studied for different parabolic trough rim angles. • Flux uniformity in parabolic trough receivers is improved by up to 90.6% • Optical efficiencies up to 88 and 91% for elliptical and Λ -shaped mirrors. • Secondary mirrors may improve off-normal ray acceptance. [ABSTRACT FROM AUTHOR]

• Equivalent large-aperture Fresnel lenses were realized using Fresnel lens arrays. • Used a 2 × 2 Fresnel lens array to drive a 1 kW Stirling engine. • Explored the damage threshold of silver mirror at high-magnification sunlight. • Offers guidance on using mirrors for high-magnification sunlight applications. High-concentration solar power systems, such as dish Stirling engine systems, typically necessitate the complex assembly of multiple parabolic mirror segments for the concentrator. An intriguing alternative involves utilizing an array of lightweight, easily manufactured Fresnel lenses to achieve a large effective aperture. In this study, we developed a confocal system that utilizes a large Fresnel lens array, successfully driving a Stirling engine. Experiments demonstrated that while redirecting the high-concentration solar flux flow using mirrors was not feasible, it was possible to alter the direction of the low-concentration solar flux flow. This adjustment facilitated the successful confocal arrangement of a four-beam system, effectively quadrupling the aperture of the concentrator. This approach presents a novel method for realizing large-aperture concentrators through the confocal configuration of a Fresnel lens array. [ABSTRACT FROM AUTHOR]

Cooking is known to be one of the most energy-intensive sectors, with an estimated energy consumption of about 30–40% of global energy consumption, with a significant share in developing and underdeveloped countries. Traditional cooking, mainly based on biomass and fossil fuels, is one of the main sources of particulate matter (PM) emissions in household buildings, which is an important risk factor for lung cancer. Due to the negative impact on the environment and the waste of energy by traditional cooking systems, innovative and environmentally friendly cooking technologies are becoming more and more popular. Solar energy, as a renewable resource, is best suited for integration into cookers. Several researchers have studied solar cooking technologies to improve their performance and support their use worldwide. Among various solar cooking technologies, concentrating solar cookers (CSCs) have recently attracted much attention, especially in large-scale cooking, due to their special characteristics of generating high temperatures and significantly reducing cooking time. This study has focused on CSCs including parabolic through solar cookers (PTSCs), parabolic dish solar cookers (PDSCs), and Fresnel lens solar cookers (FLSCs), and describes their various aspects, including their operating principles, design considerations, thermal operation, and test procedures, while recent progress in the research and evolvement of these cookers are comprehensively discussed, taking into account their economic aspects. The major drawback of CSCs remains their high initial cost, especially when thermal energy storage (TES) is integrated. However, overcoming the limitations and realizing the great advantages of CSCs to replace them with other cooking methods can make their use more successful and improve their possibility to become commercial worldwide. [ABSTRACT FROM AUTHOR]

Solar energy has a high potential to promote sustainability as a renewable energy source when applied to activities like cooking and heating. A review of recent technologies shows solar cookers have a high potential to replace conventional cooking mediums in South Asia. Solar cookers that are outfitted with effective collectors that make use of Mylar tape are a valuable tool for capturing thermal energy. New designs that use features like black chrome absorbers, black pots for cooking and storing food, and changing reflector widths improve efficiency, such as the Linear Fresnel Reflector Solar Concentrating Hot Water system (LFRSCHW). These solar cookers may attain efficiency rates above 41.2% by utilizing technologies such as tilting solar panels and parabolic reflectors with Mylar tape. When scaled up, these cookers should prove to be both cost-effective and environmentally beneficial. Accepting these cutting-edge solar cooking options opens the door to a more environmentally friendly future by addressing energy demands in places like Nepal and South Asia as well as promoting sustainability. [ABSTRACT FROM AUTHOR]

• A beam-down linear Fresnel reflector coupled with a flat plate receiver is studied. • Parabolic secondary reflector for enhancement of the optical efficiency. • Optical, thermal, exergy, and daily performance analysis of the system. • The maximum theoretical optical efficiency was found to be 73.2%. • A total height reduction of 32.5% compared to the conventional system. Beam-down concentrating solar systems are innovative and promising concentrating technologies that consist of two reflections aiming to concentrate the solar irradiation on the ground, where the receiver of such systems is located. The primary mirror field, also located on the ground, focuses the solar irradiation on a secondary mirror that redirects the solar beam in the direction of the receiver. In this paper, a beam-down linear Fresnel reflector coupled with a flat plate receiver is designed and analyzed. The secondary reflector is chosen to be of parabolic shape for achieving higher optical efficiency. The final shape and height from the ground of the parabola are examined and optimized aiming to exploit the maximum possible amount of the incident solar beam irradiation. The maximum theoretical optical efficiency was found to be 73.2 %, which is a promising value. The thermal and exergy analyses were conducted for different operating conditions aiming to develop the collector efficiency curves. Moreover, according to the daily investigation of the system for a typical summer day in Athens, Greece, the maximum thermal efficiency was calculated at 19.9 % and the respective exergy efficiency at 6.11 %. Furthermore, the average heat flux on the absorber surface is equal to 21.4 kW, whereas the average flux concentration is equal to 2.97. It was also evidenced that the optical and thermal efficiencies of the system remain approximately constant for a significant percentage of the day, a fact that makes possible the optimal coupling of the examined unit with the thermal load. [ABSTRACT FROM AUTHOR]

• Assessing the performance of a solar power systems based on 1 kW of capacity can lead to unfavorable decisions. • In terms of effective utilization of land area, photovoltaic solar power systems with horizontal single-axis tracking are the best option for low latitudes. • Nine solar power systems (4 photovoltaic and 5 concentrated solar power) were analyzed computationally considering high-sunshine regions, and were categorized into 3 tiers based on their energy generation intensity (EGI). • Three land-use oriented performance metrics were defined: monthly energy generation intensity (MGI), daily energy generation intensity (DGI), and hourly energy generation intensity (HGI); and were used to interpret the performance of different solar power systems in the summer and in the winter. • Adding solar tracking to photovoltaic power systems at low latitudes near the Tropic of Cancer has a limited improvement that may not justify the expenses and added complications. • There is consistency between the solar simulation tools: Energy3D and PVWatts Calculator, in terms of analyzing PV systems with fixed orientations or two-axis solar tracking. • There is consistency between the solar simulation tools: Energy3D and PVGIS, in terms of optimizing the angular orientation of fixed PV panels, and identifying months of peak performance. • Computer models are very useful in predicting the performance of solar power systems, thereby facilitating improved design and parametric optimization. • Adding absorbers to a linear Fresnel reflector system without adding a proportional number of reflectors (keeping the same ratio of reflectors to absorbers) is not recommended, and can actually cause a performance penalty. Solar radiation can be utilized for electricity generation through two main categories of solar power technologies: (1) photovoltaic (PV), and (2) concentrated solar power (CSP). In this study, three-dimensional computer models of electricity generation from 9 different solar power systems (4 PV and 5 CSP) using the simulation program Energy3D were used to establish a generic ranking of these systems in terms of the expected electric energy output during one year per unit land area. This performance metric is referred to as energy generation intensity (EGI), with 'energy' here referring to electric energy in particular. The analysis is aimed for low-latitude zones near the Tropic of Cancer. Solar power systems composed of long rows of connected PV modules, with single-horizontal-axis solar tracking (variable tilt), or with fixed optimized orientation were found to have the best EGI. On the other hand; heliostats with solar towers, PV units with single-vertical-axis solar tracking, and PV units with two-axis solar tracking were found to have the lowest EGI. Other four CSP systems: parabolic dishes, parabolic troughs, linear Fresnel reflectors (LFR), and compact linear Fresnel reflectors with two absorbers formed an intermediate group. Considering all of the 9 solar systems, the estimated EGI ranged from 113.1 kWh/year.m2 to 227.2 kWh/year.m2. The monthly contributions to EGI were contrasted; and daily and hourly energy generation intensities were examined on December 21 and June 21. Minor validation was performed using the simulation tool PVWatts Calculator for benchmarking, and using the web application PVGIS for PV systems calculation. [ABSTRACT FROM AUTHOR]

Linear Fresnel collectors are good candidates to lower the use of fossil fuels in the built environment and in the industry, due to their compact nature and adaptability. In addition, the technology shows large margins for improvement, in terms of efficiency capital and operational expenditures. The present study presents a new atmospheric double tube absorber, which fully explores non-imaging optics design. An existing LFR system with a second stage concentrator consisting of an evacuated tube with an associated secondary parabolic reflector, is compared with a novel model adopting the same LFR primary field but a new second stage concentrator, which achieves a much wider acceptance angle. It is shown that, beyond a better performance, the novel proposed solution provides simpler maintenance, as in cleaning and parts' replacement, and a reduced cost, as it includes cheaper standard components. The study was conducted in ray-tracing environment with the Tonatiuh++ software, which is able to directly implement non-imaging optics configurations via analytic equations. The present study is centred on the optical performance of the collector. The quantitative comparison demonstrates that the annual yield of the novel model is increased at least by 8.3% while the cost per metre of the receiver is decreased by 45%. [Display omitted] • Non-imaging optics is applied to a double tube atmospheric absorber. • Non-imaging optics is applied Linear Fresnel collector technology. • Large acceptance angle accommodates optical losses due to tracking errors. • Atmospheric absorber reduces capital costs of Linear Fresnel collectors. [ABSTRACT FROM AUTHOR]

Parabolic trough collectors are widely used to generate thermal and/or electrical energy from direct solar irradiation. These collectors use parabolic mirrors to precisely focus sunlight onto so-called absorber tubes. The optimal design and geometric alignment of all necessary components is essential in order to achieve a high degree of efficiency and a high energy yield. However, this optical fine-tuning process can be quite challenging and is in many cases avoided by using absorber tubes with larger diameters, which in turn cause greater thermal losses and a higher material effort. This paper describes a simple, yet reliable and quantifiable way to measure the optical performance of a parabolic trough collector using a commercial multi-junction solar cell (CPV). The presented measurement system allows for convenient adjustment of the parabolic mirror and the effective optimization of the overall collector design. The theoretical background is discussed and the test setup is described in detail. Measurement results are presented, ranging from the determination of the actual optical concentration ratio, the optimal centering and height adjustment of the absorber tube to the measurement of the contribution of the individual mirror segments, revealing that the investigated industrial parabolic trough collector can be improved in terms of optical accuracy. Finally, an optical surveillance of the mirror using a line laser was performed to validate the results. • New way to measure the optical performance of a parabolic trough collector. • Multi-junction solar cell (CPV) are used as a light sensor. • Theoretical background and various measurement setups and results are presented. • Optical concentration ratio of 128 x was measured with a parabolic trough collector. [ABSTRACT FROM AUTHOR]

[Display omitted] • Concentrated-solar powered thermal remediation of petroleum-contaminated soils. • Ignition of petroleum-contaminated soil is achievable with concentrated solar power. • Steel thermal receivers transmit concentrated solar energy to samples effectively. • Total petroleum hydrocarbon (TPH) analysis demonstrates effective treatment. Petroleum-contaminated soil poses an environmental risk and is costly to remediate. Self-sustaining Treatment for Active Remediation (STAR) is an emerging remediation technique that consists of igniting and propagating a smoldering front through a volume of contaminated soil. While effective, the electrical energy demand required to initiate smoldering can be cost-prohibitive in locations without robust electrical infrastructure. To address this, we investigated the viability of a novel concentrated solar power process as a low-carbon alternative to electrically driven heating for STAR. The solar-driven system uses parabolic reflectors to focus solar energy, then directs it through fiber optic bundles to flexibly transmit it to a soil column. This process is demonstrated on ∼ 750 mL samples of petroleum-contaminated soil and detectable hydrocarbons were reduced in each case. Research evaluated several parameters of interest for effective treatment including thermal receiver material and distance between solar output and thermal receiver. Temperature was measured throughout treatment and typically exceeds 400 °C prior to ignition. Steel and quartz thermal receivers show effective temperature distribution, initiating smoldering, reducing detectable hydrocarbons and maintaining durability. The results indicate that concentrated solar power can efficiently ignite smoldering remediation, showing promise as a low-carbon alternative to current methods. [ABSTRACT FROM AUTHOR]

• Half acceptance angle and Collector tilt angle of CPC should be optimized to gain maximum annual energy. • Optimization Program result in a half acceptance angle of 25° and collector tilt angle of 35°. • Three different panel included PV, CPC-PV and CPC-PVT constructed and tested. • Use of a CPC with and without cooling, led to a 10 % and 20 % increase in the output power, respectively. • Cooling system should be employed to obtain acceptable output power when reflectors is used. To enhance the production and efficiency of photovoltaic systems, research has been conducted on various techniques including the use of compound parabolic reflectors (CPCs). A mathematical model is developed using the governing solar radiation and CPC geometry equations to optimize the geometrical parameters required for the experimental setup. The optimal values for the half acceptance angle and tilt angle were found to be 25° and 35°, respectively. Based on these optimal parameters, a laboratory setup was fabricated and evaluated. To compare the performance of our CPC-based system, three different panels constructed: a simple PV panel without a concentrator, a PV panel with a concentrator but without cooling (CPC-PV), and a PV panel with a concentrator and water cooling (CPC-PVT). Results showed that the use of a CPC with a concentration ratio of 1.7 in both modes, with and without cooling, led to a 10 % and 20 % increase in the output power, respectively, compared to the simple PV panel. In summary, this study demonstrates the effectiveness of using a CPC in enhancing the production and efficiency of photovoltaic systems. The mathematical model developed in this research can be utilized for optimizing the geometrical parameters required for the design of CPC-based systems. The experimental results obtained from this study indicate that the use of a CPC with water cooling can significantly improve the energy output of the photovoltaic system. These findings can aid in the design of cost-effective and efficient photovoltaic systems. [ABSTRACT FROM AUTHOR]

• Development of sCO2 solar flow loop. • On-sun testing of supercritical CO 2 receiver. • Evaluation of thermal and hydraulic performance. • Analysis of failure mechanisms. The thermal characterization of a micro-pin solar thermal receiver (MSTR) for supercritical carbon dioxide (sCO 2) gaseous working fluid is presented. In a companion paper of this two-part study [1] , the design and fabrication methodologies employed in the development of the MSTR were presented. As described in Fronk et al. [1] , the MSTR is formed by a microlamination process with brazed headers to form multiple unit cell flow paths with fluid inlet/outlet ports. In this part of the study, on-sun tests to estimate the thermo-fluidic performance of the MSTRs using a parabolic dish concentrator are described for a 15 cm × 15 cm design with 6 unit cells. The MSTR is installed in a closed-loop sCO 2 test facility coupled to a seven-meter diameter parabolic dish. On-sun tests were performed at a receiver inlet pressure of up to 15.5 MPa and a receiver inlet temperature ranging between 31 to 398 °C. Receiver thermal efficiencies were calculated using an indirect estimation of the absorbed flux, by summing the convective and radiative losses and absorbed energy to the fluid. Thermal efficiency greater than 0.98 were obtained for estimated incident heat flux of 34–40 W/cm2 at average surface temperatures ranging from 113 to 332 °C and peak surface temperatures of up to 550 °C. A sensitivity analysis, performed on the convective and radiative losses, indicates the lower limit of efficiency to be within 1.5 % of the estimated value. After a few hours of testing, the receiver failed due to an internal flow blockage that led to overheating. Optical and microstructure analysis is performed on the 15 cm × 15 cm and a failed 8 cm × 8 cm MSTR from prior work to identify possible reasons for failure. [ABSTRACT FROM AUTHOR]

[Display omitted] • The paper introduces a new passive collector design for the purpose of light collection for daylighting. • Maintain uniform lighting levels for the most part of the day under clear sky sun. • The average illuminance of around 400 lx was observed on the floor of the experimental room for the most part of the day. • The performance of proposed designed collectors leads under the low-altitude sun when compared to conventional designs. A tubular skylight (TS) is an effective system for transporting natural sunlight into the building interiors. However, the passive nature of the system may not account for the changing orientation of the sun and the conventional daylight collector designs like transparent dome are less effective under low altitude sun. This paper focuses on the performance evaluation of specifically designed TS having rectilinear parabolic-profile reflectors integrated with plane surface reflectors and wedge-shaped prism for daylight collection. The designed configuration redirects the low altitude incident rays efficiently into a vertical mirror light pipe having a rectangular cross-section and aims at giving desired levels of lighting throughout the sunny day. Numerical analysis of the same was carried out for various sky conditions. Experimental results for the proposed TS design show improved lighting levels during the low-altitude sun and reduced but consistent lighting during the mid-day. Average illuminance of ~ 400 lx was observed on the floor of the experiment room for the most part of the day. Along with capturing beam sunlight a significant amount of diffuse daylight capturing ability under clear sky conditions is observed using the proposed TS. The average illuminance value obtained on the work plane during winter solstice through the most optimized configured TS was more than twice the lighting value achieved by a conventional daylight-collecting transparent dome and almost twice the lighting value achieved by a TS with a prismatic dome collector. Under overcast sky conditions, the performance of the proposed configuration of TS is at par. [ABSTRACT FROM AUTHOR]

• A homogeniser inspired by the crustacean's eye using for the CPV system. • Such homogeniser can evolve a uniform version of light distribution. • The best structure displays a uniformity ~85% and an optical efficiency ~90%. • Toward relaxing a secondary mirror in the existing CPV system using a parabolic mirror. We devise an implicitly new design for boosting the light uniformity in the concentrated photovoltaics (CPV) system, whereby addressing the overheating issue of the PV cell and enhancing the electrical cell efficiency. Rather than using a well-known system of the Cassegrain concentrator design, consisting of double mirrors + a homogeniser, in this study, we mimic a structure of crustacean's eyes for a design of homogeniser, consisting of an array of a mirror channel. Such proposed design allows making use of only a primary parabolic mirror + a homogeniser to concentrate and redistribute the sunlight, representing a large departure from virtually all of the previous studies. Specifically, such homogeniser can furcate the light beam into the small channels/trenches, redirect the light ray at the reflective plate and probably mix them to evolve a uniform version of light distribution. In general, the homogeniser can affect the uniformity and optical efficiency, which are good probes to assess the light performance, in a number of ways. We found that light performance depends sizably on the structural parameters such as the size and the number of channels of the homogeniser. The best structure displays a calculated uniformity of ~85% of the flux distribution on solar cell and a calculated optical efficiency of ~90% of the entire CPV system. We also assess the light performance against some scenarios of error in installation and operation processes such as tolerance and misalignment and compare well with the current design. The compelling of this proposed design is highly efficient light performance, compactness and inexpensive, which likely address virtually existing bottlenecks in the CPV system. [ABSTRACT FROM AUTHOR]

• A new design of solar cooker with tracking-type bottom parabolic reflector (TBPR) proposed. • Cooker performance rating done based on two different Thermal Performance Parameters (TPPs) and objective parameters (OPs). • Thermal Performance of the cooker evaluated using intermediate temperature test load. • Effectiveness and role of TBPR evaluated realistically using Effective Concentration Ratio (ECR). • Economic analysis of cooker done using two indicators, LOCH and LCCM. To fulfil the sustainable development goals (SDGs) of the United Nations, the solar cooker is one of the key devices. The objective of this work is to propose a new design of solar cooker equipped with internal reflectors and a tracking-type bottom parabolic reflector (TBPR) which may help in attainment of SDGs. The performance of cooker is determined using Cooker Opto-Thermal Ratio (COR) as a Thermal Performance Parameter (TPP) and glycerine as test load. Also, the effectiveness of the booster reflector is estimated using the Effective Concentration Ratio (ECR). First Figure of Merit (F 1) and overall cooker efficiency (η) are used to comment on performance of the proposed cooker. The real cooking tests are conducted for family of four people which describes usefulness of the proposed solar cooker. Experimental results depict the mean values of COR for the cooker with and without TBPR as 0.165 and 0.123, respectively. Also, the value of F 1 is found to be 0.119 while the value of the ECR for the cooker is 1.34. The overall cooker efficiencies for cooker with and without TBPR are estimated to be 10.7% and 12.5%, respectively. The results show that cooker with TBPR is able attain the intermediate temperatures ~ 140–150 °C. An economic analysis is done using two indicators, Levelized Cost of Heat (LCOH) and Cooking a Meal (LCCM) and there is a reduction of ~ 44% and 18% in the LCOH and LCCM respectively, for the cooker with TBPR compared to the cooker without TBPR. [ABSTRACT FROM AUTHOR]

• New in-house 3D model for raytracing analyses of Linear Fresnel Collectors. • Study of the optical and energy efficiency of a real Fresnel plant. • Plant geometry optimization considering gap between mirrors and receiver height. • Maximization of the radiant energy arriving at the receiver aperture area. • Optimum value of the receiver height is not unique all over the year. Despite their few installations, Linear Fresnel Collectors (LFC) represent a very promising technology for efficient solar energy exploitation at medium to high temperatures thanks to their lowest land area per electric energy ratio. Their first appearance was in the '60, thanks to Professor Giovanni Francia realizations at the University of Genova, Italy. This research aims to determine the performance of a LFC and perform parametric studies through 3D ray-tracing simulations. The in-house developed code accounts for all geometrical parameters of the mirrors and receiver assembly, including mirror dimensions, curvature and distance, primary mirror optical errors, receiver aperture area and elevation, secondary mirror compound parabolic shape. The present study includes a detailed investigation on shading, blocking and end effect issues while introducing 6 different different optical and energy efficiency definitions. A parametric analysis is applied to the distance between mirrors and the receiver height. After the code validation against Tonatiuh, the calculations are performed to analyse in details the performance of a real LFC plant in Morocco. The peak optical efficiency of the test case plant has been estimated up to 87% but it is demonstrated the selection of the efficiency definition is crucial for performing successful geometry optimizations. [ABSTRACT FROM AUTHOR]

• A real-size CPVT collector has been built and experimentally tested. • Optical experimental and theoretical evaluation of a CPVT is presented. • Thermal and electrical efficiency diagrams of a CPVT are presented. • Electrical longitudinal and transversal IAM is presented. This paper presents an experimental investigation of a photovoltaic-thermal solar collector (commonly known as PVT) that generates both electricity and heat from the same gross area. PVT solar collectors, in theory, achieve higher combined electrical and heat yields. Additionally, PVT enables a thermal coupling between PV cells and a heat transfer cooling medium. Electrical and thermal outdoor testing measurements have been performed on a low concentration PVT solar collector based on a parabolic reflector geometry with a wedge PVT receiver. Several outdoor experiments have been carried out and presented, such as daily instantaneous electrical and thermal performance efficiency diagrams, as well as optical efficiency charts. Moreover, an electrical Incidence Angle Modifier (for both transversal and longitudinal directions) assessment has been performed and presented. Furthermore, an overall heat loss coefficient of 4.1 W/m2.°C has been attained. A measured thermal optical and electrical efficiency of 59% and 8% have been achieved, respectively. Additionally, the placement of the wedge receiver shown to be very sensitive to high incidence angles, as the electrical transversal Incidence Angle Modifier factor decreases significantly after reaching its electrical peak efficiency at 10°. [ABSTRACT FROM AUTHOR]

• Roughened modified cavity receivers with conical protrusions are developed for solar dish. • Smooth receiver performance compared with that of roughened receivers. • Mathematical analysis simulating one of the experimental test situations is also presented. The performances of parabolic dish collector systems depend on the losses encountered during converting solar energy into thermal energy. It encompasses optical losses from the reflector and heat losses through the solar receiver. The geometry and surface properties of the receiver were seen considerably influencing the system performance. Thermally conductive copper fins (conical shaped, tip/cone angle 30°) have been fixed inside the cavity surface for three different pitch values e.g. 12.5 mm, 22 mm and 44 mm. During brazing operation, a selective Copper Oxide (CuO) surface was formed inside of the cavity, on account of heating. The system collection efficiency values obtained using finned cavities were compared with that of smooth (conventional) one. Performance improvement of about 23.56% and 31.35% (on average) over a smooth cavity was noticed after providing conical protrusions on the radiative surface of the modified cavity receiver, with medium and higher heat boundary conditions. The percentage contributions of heat losses by conduction, convection, and radiation modes, from the examined cavities, were obtained as 1.4–3.2%, 70–75%, and 22–28% of the total losses, respectively, in case of medium irradiation concentration. The energy concentration was seen influencing these contributions of heat losses from the receivers. Mathematical analysis is also presented for comparing one of the experimental test situations outcomes. [ABSTRACT FROM AUTHOR]

• First simultaneous emission of three solar laser beams from a single pump cavity. • 18.3 W solar laser power was measured with 5.1% slope efficiency. • 0.036 W laser beam brightness figure of merit for each beam. • Capable of adjusting individually the laser output power of each beam. • Capable of adjusting individually the beam quality of each beam. We report here, to the best of our knowledge, the first simultaneous emission of three continuous-wave solar laser beams by end-side-pumping three 3.0 mm diameter, 25 mm length Nd:YAG single-crystal rods within a single conical pump cavity. An aspheric fused silica lens was used to couple the concentrated solar radiation from the focal zone of a parabolic mirror with 1.0 m2 effective collection area into the laser rods within the pump cavity. 18.3 W multimode solar laser power was measured, resulting in 5.1% laser slope efficiency. 0.036 W laser beam brightness figure of merit was also achieved for each beam, being 9 times more than that of the most efficient solar laser with 32.5 W/m2 collection efficiency. Since the three laser rods were associated with their own 1064 nm output mirrors, it was possible to adjust individually both solar laser output power levels and beam qualities of the three laser beams by adopting different resonant cavity lengths, enabling potential solar laser applications. [ABSTRACT FROM AUTHOR]

• The manuscript is focused on efficiency analysis of parabolic dish collector systems, working in a range of low/medium temperatures, which is of great importance in industrial practice. • A comparison of several receivers (flat-plane and cavity) has been performed, based on a detailed modeling of the radiant power losses due to reradiation, convection and conduction losses. • In practice, the flat-plate receiver should be used with some care, since its temperature is very high in the zones of high concentration. An open cavity solves this problem with the biggest reduction of temperature, but has a relatively modest increasing of thermal efficiency. It is found that the cavity receiver with a cover is the most efficient with an increasing up to a 20% with respect to the flat-plate receiver, with a very significative reduction of the cavity temperature. Application of parabolic dish collector systems working in a range of low/medium temperatures is of great importance in industrial practice. In this work, a thermal efficiency analysis will be performed for different receivers such as a flat-plate receiver and a cavity receiver (with and without a glass cover). Most of the previous receivers analyses found in the literature have been performed for applications with high temperatures. Moreover, a detailed analysis including losses such as reradiation, natural and forced convection, and conduction, have been performed, developing new correlations for natural and forced convention. The obtained results are discussed in detail, obtaining a significant increasing of efficiency of the cavity receivers against the flat-plat receiver with much less working temperatures: up to 20 % for the covered cavity receiver in comparison with the flat-plate receiver, with a temperature reduction at the receiver of more than 450 ° C. [ABSTRACT FROM AUTHOR]

• Direct photograph of concentrated flux of parabolic trough concentrator. • Flux image-based diagnosis of solar tracking error and slope error. • Diagnosis based on flux shape without intensity calibration. In practical applications, there are many optical errors in the parabolic trough concentrators (PTC), such as mirror slope errors and tracking errors. Image detection is a no contact technique that has a potential to diagnose the optical errors at large plants in use. In this study, a CCD (Charge Coupled Device) camera was used to directly observe the absorber, and the images of the flux peaks were successful obtained. The CCD image showed two bright peaks on the outer wall of the tubular absorber. By comparing the CCD image with the simulation results, the concave deformation of the parabolic mirror was diagnosed, and the slope error of the parabolic mirror was figured out. The images also revealed that sun tracking errors can cause a synchronous shift in the flux. The flux image method does not influence the normal operation of PTC and is an on-line method, which facilitates the field application. [ABSTRACT FROM AUTHOR]

• First analytical modeling of a single ring-array concentrator (RAC) unit. • First ZEMAX® numerical optimization of the 3D RAC solar furnace. • First ANSYS® analysis of the 3D RAC furnace temperature at its focal spot. • Enhanced maximum temperature of the 3D RAC furnace at large collection area. • Largely enhancements in average and minimum temperatures of the 3D RAC furnace. A single ring-array concentrator solar furnace unit was firstly modeled analytically, and then optimized numerically by ZEMAX® and ANSYS® software, reaching a temperature of 3778 K, nearly equivalent to that of a medium size solar furnace with 3.14 m2 collection area. A novel three-dimensional ring array concentrator solar furnace was subsequently proposed and analyzed. It consisted of five single ring array concentrators, forming a compact box-shaped solar furnace with an opening at the rear side for an easy access to a common focal spot in the center. Based on the edge-ray principle of non-imaging optics, 30,960 solar concentration ratio was analytically calculated for this solar furnace, leading to significantly enhanced thermal and optical efficiencies. The temperature performance of the three-dimensional ring-array concentrator furnace as a function of receiver size and collector area was analyzed numerically and compared to that of the medium size solar furnace. For a 5.68 mm diameter spherical receiver and large collection area varying from 3.14 m2 to 100 m2, 1.1 times gradual enhancement in the maximum attainable temperature was calculated for the ring array concentrator furnace. More importantly, its average and minimum temperatures were significantly improved by 870 K and 1140 K, respectively, as compared to that of the medium size solar furnace. In addition, the three-dimensional ring-array concentrator also presented a significant tracking error compensation capacity in relation to that with the medium size solar furnace. [ABSTRACT FROM AUTHOR]

• A polygeneration plant has been investigated for a site using Concentrated Solar Power Plants based on Parabolic Dish. • Adopting Working Fluid high temperatures, these plants can be used for polygeneration of electricity, cooling, heating and fresh water. Heat storage or hybridization can run the plant 24 h per day. Polygeneration of electric power, cooling and fresh water from seawater and brackish water by using solar energy is discussed in this paper. The best plant component arrangement has been selected for a 400–600 square meter Solar Dish surface. The engine is made of turbomachinery derived from the Internal Combustion Engine Turbocharger Technology for reliability and economy reasons. The Micro Gas Turbine has been selected taking the ©GICE complex arrangement concept into account. Such an arrangement is capable of concurrent production of power and of a cold stream by the expansion in the Power Turbine. Such a cold stream is used for ©CryoDesalination of seawater and cooling. An example has been presented, it demonstrates the potential of large solar dish technology used to feed solar energy in an integrated system made of a ©GICE engine, ©CryoDesalination group and a collector of the cold streams for cooling purposes. Two options have been explored and compared. [ABSTRACT FROM AUTHOR]

Highlights • A solid concentrator photothermal/day lighting system was developed for greenhouse. • The maximum instantaneous thermal efficiency and power were 32.2% and 353 W/m2·s. • The area of the module was 0.09 m2, matching the size of the greenhouse roof panel. • The semi-transparency of the module allows co-production of crops and energy. Abstract Currently, the excess light above a light saturation point cannot be harnessed for plant growth in conventional greenhouse covers. In this study, we developed a solid compound parabolic concentrator (CPC) cover for use in greenhouses to convert excess light into heat. Optical simulation software was used to track the sunlight at different incident angles over time. We also conducted experiments to determine the transmittance and heating power of the solid CPC coating under real weather conditions. The maximum instantaneous thermal efficiency and thermal energy of a single solid CPC cover plate were 32.2% and 353 W/m2, respectively. The simulation results were in good agreement with the experimental output power and the trend of the actual transmittance of the covering material. The transmittance of the covering material was low when the midday sun was intense, and the transmittance was relatively high in the morning and afternoon. The variation of red and blue light in the greenhouse with the spectrum was analyzed at the same time. Studies have shown that this new greenhouse covering material can better adjust the brightness, make the illumination in the greenhouse more uniform, and thus improve the thermal environment in the greenhouse. The heat pipes converted excess light into heat, thereby achieving comprehensive utilization of solar light and heat. [ABSTRACT FROM AUTHOR]

Highlights • Miniature dielectric crossed compound parabolic concentrator (dCCPC) as skylights. • The performance of dCCPC skylight panel is compared for fourteen chosen cities. • The polynomial transmittance model of dCCPC is implemented in Grasshopper. • The energy savings in thermal load and lighting of building are investigated. Abstract The potential of miniature dielectric crossed compound parabolic concentrator (dCCPC) panel as skylights for daylighting control has drawn a considerable research attention in the recent years, owing to its feature of variable transmittance according to the sun position, but the viability of using it as skylights in buildings has not been explored yet comprehensively. This paper aims to study the feasibility of utilizing miniature dCCPC panel as skylight in different locations under various climates in terms of energy saving potential besides its daylighting control function. The transmittance of dCCPC panel varies at every moment according to the sky condition and sun position. Due to this specific property, this study novelly implemented a polynomial formula of the dCCPC transmittance in the Grasshopper platform, from which EnergyPlus weather data can be called to calculate the hourly transmittance data of dCCPC skylight panel throughout the whole year. An hourly schedule of transmittance is generated according to the hourly sky condition determined by the daylight simulation through Radiance and Daysim, and is then input to EnergyPlus simulation to predict the energy consumption of a building with dCCPC skylight. Fourteen locations around the world are therefore compared to find the most appropriate place for using miniature dCCPC panel as skylights. The energy saving in cooling, heating and lighting with use of dCCPC skylight panel are investigated and compared with low-E and normal double glazing. The results show that the dCCPC skylight panel can reduce cooling load by mitigating solar heat gain effectively although its performance is affected by several criteria such as sky conditions and local climates. It is generally more suitable for the locations with longer hot seasons, e.g., Log Angeles, Miami, Bangkok and Manila, in which dCCPC could provide up to 13% reduction in annual energy consumption of building. For the locations having temperate and continental climates like Beijing, Rome, Istanbul and Hong Kong, a small annual energy saving from 1% to 5% could be obtained by using dCCPC skylight panel. [ABSTRACT FROM AUTHOR]

Highlights • We propose a time-dependent model for the efficiency of an NDAPSC. • Dimensional analysis reveals four controlling dimensionless numbers. • We obtain a time-dependent analytic expression of system temperature. • We redefine the standard instantaneous solar collector efficiency measure. Abstract In this paper we propose a time-dependent, three-dimensional model for the efficiency of a nanofluid-based direct-absorption parabolic trough solar collector under a turbulent flow regime. The model consists of a system of equations: a partial differential equation for conservation of energy, and a time-dependent radiative transport equation describing the propagation of solar radiation through the nanofluid. Writing the model in dimensionless form reveals four controlling dimensionless numbers: one describing the relative importance of conduction and advection and three describing the heat loss to the surroundings. Realistic parameter values are applied to reduce the model further and these indicate that two of the dimensionless groups have a much smaller impact on the performance of the solar collector. We use the resulting solution for the temperature to calculate an analytic expression for the collector's efficiency. This expression permits optimisation of design parameters such as particle loading, incoming radiative intensity, receiver dimensions, the inlet temperature, and solar concentration ratio. [ABSTRACT FROM AUTHOR]

Here we propose a forced air circulation system to reduce the convective heat loss across the aperture of a dish concentrator. The function of the proposed system was validated with computational fluid dynamics (CFD) simulations. Compared to a concentrator without such a system, the modified solar dish cavity receiver could clearly reduce the convective heat loss and its fluctuation in the receiver. In the best case studied, the convective heat losses could be suppressed by up to 58%. In addition, two types of air circulation modes (clockwise and anticlockwise) were compared, showing that the anticlockwise mode yields better performance. [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]

Parabolic dish technology, for concentrating solar power (CSP) applications, has been continuously modified and improved since the pioneering work in the 1970s. Best practice dishes now have features such as lightweight structure, balanced design, high-quality, low-cost mirror panels, and can be deployed rapidly with little in-field labour. This review focuses on the evolution of dish design, by examining features such as mode of tracking, structure and mirror design, for a wide selection of CSP dish examples. The review includes a brief summary of power generation options – both on-dish and central plant – as well as a discussion about options for storage and hybridisation. [ABSTRACT FROM AUTHOR]

To achieve higher operating temperatures, power output and system efficiencies in parabolic dish cavity receivers, larger dish sizes and structures are used to increase the concentration ratio. This increases capital investment and installation costs, which in turn places a much stronger emphasis on accurately predicting the performance of the system and the heat loss from it. Numerous studies have investigated the natural convection heat losses from cavity receivers, and some have examined a cavity exposed to wind. However, the effect of the dish on the wind flow and subsequently the heat loss from the receiver has not been widely considered. In this work, computational fluid dynamics was used to model the flow of air around a parabolic dish concentrator operating at varying angles of operation. The flow fields were validated using wind tunnel testing and published data regarding the aerodynamic characteristics of parabolic dishes. The results showed that the orientation of the dish has a significant effect on the flow structure near the receiver. Subsequently, using the validated method, the convective heat loss from the receiver of a large parabolic dish system was determined for a range of operating conditions. The results support the assertion that the flow characteristics near the cavity receiver aperture depend strongly on the orientation of the dish structure. This resulted in the calculated heat loss being up to 40% lower than previous studies where the presence of the dish was included. As such, the wind flow around the dish needs to be accounted for when analyzing the performance of parabolic dish systems to avoid an overly conservative and hence more expensive design. [ABSTRACT FROM AUTHOR]

A new approach to calculate the angular acceptance function of cylindrical parabolic collectors has been developed. The procedure is rapid, simple and enables obtaining the acceptance function with or without absorber deviations. In a simple way, it registers the view angle of an eye slipping along the reflector surface. In case there are deviations, as a result of loss of symmetry, the function splits into four branches: two for the right and left hand side of the reflector section and two for the left and right hand side of the light cone reaching the aperture. As a result of deviations some branches are affected by windows where sun light escapes, reducing the optical efficiency of the collector. Deviations are computed as: (a) distance (d) between parabola focus and deviated absorber center and (b) rotation angle of the absorber (ω). Examples of perfect and non-perfect collectors are given and a variety of situations simulated: distance (d) varying between 0 and 1.0∗Rabs and rotation angle (ω) between (−90°) and (+90°). A procedure to generate angular acceptance functions monotonically decreasing with the view angle is described and discussed. Results are exposed as sensitivity curves where the main parameters of the angular acceptance function are registered. The method described enables to map a large variety of optical configuration errors, which can be used for quality tests, design procedures and collectors development. Non-parabolic geometries can also be treated with a similar procedure, showing that the method developed is a general and versatile approach. [ABSTRACT FROM AUTHOR]

This paper presents a novel concept of using a phase change material (PCM) to store thermal energy directly within a heat pipe evacuated tube collector equipped with a compound parabolic concentrator (CPC). The excellent insulating properties of evacuated tubes and the use of latent heat are significant advantages of a PCM integrated evacuated tube collector/storage (ETC/S) over traditional solar water heaters. However, during the charge cycle of the ETC/S, direct solar radiation only reaches the exposed area of the evacuated tubes, which results in uneven heating of the PCM due to a lower energy input in the shaded area. This can be prevented by using a CPC to concentrate the solar radiation on the shaded area of the evacuated tubes, thereby raising the temperature of the PCM and quantity of stored heat. Therefore, a polished, thin aluminum sheet was used as low cost CPC with a concentration ratio of 1.2x. Technical grade paraffin with an onset melting temperature of 51.24 °C was used as the PCM. The results from this study showed that the application of the CPC caused the temperature of paraffin on the shaded side of the evacuated tubes to increase more rapidly, especially during and after melting of the paraffin. Furthermore, the use of a CPC in a PCM integrated ETC/S improved the average gross charging efficiency from 31% to 36% and the maximum charging efficiency from 40% to 49%. [ABSTRACT FROM AUTHOR]

In this paper, the opto–geometric performance of fixed-focus solar concentrators (FFSCs), namely, the high temperature concentrator (HTC), the Scheffler concentrator and the Scheffler-type solar concentrator (STSC), is analysed. The goal of this study is to determine the behaviours of FFSCs as a function of their dimensions and to compare the results to the results of parabolic dish (PD) solar concentrators. An algorithm based on opto–geometric models of these concentrators was developed, and numerical calculations were performed for each type in a range of thermal power of 1–50 kW. The numerical results indicate that FFSCs require a reflector with a diameter 45% larger than the diameter of a PD concentrator and increase the diameter of the solar image at the receiver by 350% compared with a PD concentrator. The increase in the diameter of the solar image by the fixed receiver in the FFSC produces a lower concentration. For thermal demands of less than 10 kW, FFSCs do not have significantly large dimensions. The proposed algorithm can be employed to evaluate the potential use of FFSCs and an FFSC instead of a PD concentrator because of the operational advantages of the fixed receivers of the different types. [ABSTRACT FROM AUTHOR]

This paper investigates the coupling of parabolic dish concentrator with air micro gas turbine engine (net power output equal to 32.9 kW el ). With the aim of increasing the conversion efficiency of the incoming solar radiation, a high temperature system (up to 1100 °C) has been considered: this solution implies the adoption of a ceramic expander coupled with a high temperature indirectly-irradiated solar receiver. A flexible Matlab® suite has been developed for the plant sizing and for the part-load simulation; in addition, the model is able to handle general solar field configurations through the computation of reciprocal shading effect. The obtained yearly sun-to-electric efficiency (26.48%) reveals the energetic advantage over other CSP technologies that can mitigate the technological issues and consequently higher investment cost, related to high operating temperatures. The potential of a hybrid version of the dish is also discussed. [ABSTRACT FROM AUTHOR]

This contribution presents a new field Solar Spectrum Reflectometer for solar-weighted specular reflectance characterization of planar, spherical or parabolic mirrors. This reflectometer is designed to provide fast and reliable field measurements and to be valid for any type of mirror currently installed in concentrated solar power systems, including parabolic trough, Stirling dish and central receiver power plants. The optical design of the Solar Spectrum Reflectometer, which includes 6 LEDs in the VIS–NIR band, is described, and its tolerance to variations in the geometrical parameters of the mirrors discussed and evaluated. The contribution of diffuse reflection and its impact on the measured reflectance is also calculated for different concentrated solar power systems. [ABSTRACT FROM AUTHOR]

A compact high concentrating photovoltaic module based on cassegrain optics is presented; consisting of a primary parabolic reflector, secondary inverse parabolic reflector and a third stage homogeniser. The effect of parabolic curvatures, reflector separation distance and the homogeniser’s height and width on the acceptance angle has been investigated for optimisation. Simulated optical efficiencies of 84.82–81.89% over a range of ±1° tracking error and 55.49% at a tracking error of ±1.5° were obtained. The final singular module measures 169 mm in height and 230 mm in width (not including structural components such as cover glass). The primary reflector dish has a focal length of 200 mm and is a focal with the secondary inverse reflector which has a focal length of 70 mm. The transparent homogenising optic has a height of 70 mm, an entry aperture of 30 × 30 mm and an output aperture of 10 × 10 mm to match the solar cell. This study includes an analysis of the optical efficiency, acceptance angle, irradiance distribution and component errors for this type of concentrator. In particular material stability and the surface error of the homogeniser proved to be detrimental in theoretical and experimental testing – reducing the optical efficiency to ∼40%. This study proves the importance of material choice and simulating optical surface quality, not simply assuming ideal conditions. In the experimental testing, the acceptance angle followed simulation results as did the optical efficiency of the primary and secondary reflectors. The optical efficiency of the system against increasing solar misalignment angles is given for the theoretical and experimental work carried out. [ABSTRACT FROM AUTHOR]

PVT collectors aim for the co-generation of pv electricity and heat. The following concept intents to raise the thermal efficiency by concentrating sunlight with CPC reflectors, in order to access a higher number of solar thermal applications. The work presented here, focuses on the influence of the CPC reflectors on the pv efficiency. Parabolic concentrators in general, and CPC reflectors in particular, cause a non-uniform illumination of the pv cells, which decreases the pv efficiency. Ray tracing calculations of one particular CPC geometry result in a characteristic, angular dependent solar flux distribution in the cell plane. The effect of this flux distribution was measured on a real scale experimental collector on a outdoor solar test stand. The incidence angle modifier (IAM) of the pv efficiency was measured for three different concentrations, as well as for an improved CPC geometry, aiming to homogenize the flux distribution in the cell plane. The experiments showed, that the pv efficiency drops from 15% at STC to between 9% and 11%, depending on the solar concentration factor, which influences the efficiency negatively. The predicted efficiency boost of the improved CPC geometry could not be validated experimentally, as the additional optical losses of the more complex setup were high compared to its improvement effect. In order to understand these results, a theoretical model was built, combining ray tracing, electrical and thermal modeling of the CPC PVT collector. This model enabled to calculate the temperature distribution, as well as the pv efficiency simultaneously, by dividing the pvt absorber into finite elements. [ABSTRACT FROM AUTHOR]

A simple high-brightness TEM 00 mode solar laser design with a grooved Nd:YAG rod pumped through a heliostat–parabolic mirror system is proposed here. A fused silica semi-cylindrical lens was combined with a 2V-shaped pumping cavity to provide efficient side-pumping along the grooved 1.0 at.% Nd:YAG rod. Optimum pumping and laser beam parameters were found through ZEMAX and LASCAD numerical analysis. The proposed scheme offered a circularly symmetric and uniform absorption profile. Maximum TEM 00 mode solar laser power of 25.5 W was numerically achieved with a 3.5 mm diameter grooved rod, corresponding to 8.5 W/m 2 collection efficiency. 17.1 W laser beam brightness figure of merit was attained, being 4.3 times more than the previous record with TEM 00 mode Nd:YAG solar laser, and 10,000 times higher than last year’s result with a large grooved Nd:YAG rod. To validate the proposed pumping scheme, a solar laser prototype was built and firstly tested with a small-scale heliostat–parabolic mirror system of Universidade NOVA de Lisboa, producing 4.0 W continuous-wave TEM 00 mode solar laser power at 3.6 W/m 2 collection efficiency and 3.0 W laser beam figure of merit. [ABSTRACT FROM AUTHOR]

In this article, a 3-D numerical modeling is carried out to determine combined convection and surface radiation heat losses from a modified cavity receiver of parabolic dish collector used as mono-tube boiler for sub-cooled, saturated and superheated steam generation conditions. The forced convection heat loss from the modified cavity receiver is estimated using Nusselt number correlation developed for the modified cavity receiver. The effect of receiver inclination ( β ) , operating temperature ( T w ) , emissivity of the cavity cover ( ∊ ) , thickness of insulation ( t ins ) on the combined heat losses from the modified cavity receiver is investigated. The boundary conditions for wall temperature and insulation thicknesses are chosen to match the three steam generation conditions. It is found that the natural convection heat losses are higher at β = 0 ° (receiver facing sideward) and lower at β = 90 ° (receiver facing down) whereas the forced convection heat loss is higher at β = 90 ° and lower at β = 0 ° . The variation of radiation heat losses is marginal for all values of β and vary with T w . The effect of various parameters such as receiver inclination, wind direction ( φ ) , wind speed and diameter ratios on forced convection heat loss from the receiver has also been studied. The forced convection heat loss at lower wind speeds (<2.5 m/s) is lower than the natural convection heat losses. The maximum heat losses occur at side-on wind direction ( φ = 0 ) followed by head-on wind directions ( φ = 30–90°) and back-on wind directions ( φ = - 90 ° to - 30 ° ) . The heat losses vary with diameter ratios for different configurations of the receiver. The forced convection heat loss is 1.2–9 times higher than natural convection heat loss for diameter ratio (ratio of cavity diameter to aperture diameter, d / D ) = 0.4 at 5 m/s and receiver inclinations varying from 0° to 90 ° . Nusselt number correlations have been proposed based on the numerical analysis to estimate the combined convective and radiative heat loss. The present study attempts to estimate natural convection, forced convection and surface radiation heat losses from the modified cavity receiver under various conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Solar trough plants present a highly nonlinear dynamics and multiple disturbance sources. [•] The antiresonance modes may be excited if fast responses are required. [•] An observer-based MPC strategy is developed. [•] Real tests at the ACUREX field show a good performance. [•] Fast responses are obtained without exciting the antiresonance modes. [Copyright &y& Elsevier]

Highlights: [•] We simulate the heat loss of compound parabolic concentrator (CPC) collectors. [•] We compare computational fluid dynamics (CFD) to particle image velocimetry (PIV). [•] The velocity field and the temperatures agree well between simulation and experiment. [•] The individual heat transfer mechanisms can be quantified and separated by CFD. [Copyright &y& Elsevier]

Highlights: [•] The paper presents infinitesimal etendue and SMS optics for fixed receiver troughs. [•] The paper presents a calculation of the center of mass for each optic. [•] The paper compares the new optics with a conventional parabolic trough (PT). [•] The comparison is made for the same size receiver and the same acceptance angle. [•] Infinitesimal etendue and SMS optics have higher CAP values than the PT optic. [Copyright &y& Elsevier]

Highlights: [•] Optical simulations and optimization of parabolic solar dish concentrator with flat receiver are presented. [•] Analytic functions to calculate the intercept factor and optical efficiency of the system. [•] Gaussian effective source. [•] Solar to net heat efficiency optimization for a year. [Copyright &y& Elsevier]

Abstract: High-voltage silicon Vertical Multi-Junction (VMJ) cells can accept high concentration with peak efficiency potentially reaching close to 30%. Dense-array modules with high-voltage cells should allow a parallel connection with voltage matching rather than series connection with current matching, leading to lower mismatch losses under non-uniform illumination. The performance of a dense array with VMJ cells connected in parallel under non-uniform illumination is investigated, in comparison to a module with conventional cells connected in series. The incident flux distribution corresponds to that of a parabolic dish with and without a homogenizer. The number of junctions in each VMJ cell is a free parameter for optimization. The results show a clear advantage of the VMJ module over the conventional module under non-uniform illumination, allowing reduction or even elimination of homogenizing secondary optics, and easing the tracking accuracy requirements. [Copyright &y& Elsevier]

Abstract: The design and optimization of novel type of receiver for a paraboloidal concentrator with 90° rim angle is carried out by means of detailed ray tracing simulations. Cylindrical, conical, and spherical geometries are compared and their dimensions optimized. The chosen design is based on a conical cavity, which differs from similar receivers developed for concentrators with smaller rim angles. In particular, the receiver is able to catch concentrated solar energy both on its outer side and on the inner walls. Water flows inside the receiver along the conical geometry, in a double layer configuration. The receiver was built and implemented in a 90° rim angle paraboloidal concentrator. Thermal efficiency of the system is evaluated for different flow rates and inlet temperatures, both in stationary and in transient regimes, and results for fluid temperatures are compared with the results predicted by a thermal model. The time constant is evaluated. [Copyright &y& Elsevier]

Abstract: The Australian National University (ANU) has worked for many years on paraboloidal dish solar concentrators and demonstrated a 400m2 system in 1994. The commercialization of this technology has involved a re-design of the Big Dish concept for mass production. The new design is a 500m2 concentrator with 13.4m focal length and altitude–azimuth tracking. It uses 380 identical spherical 1.17m×1.17m mirror panels, which incorporate the Glass-on-Metal Laminate mirrors. Construction of a first prototype on the ANU campus began in the first quarter of 2008. The first on sun test was carried out on 29 June 2009. [Copyright &y& Elsevier]

Abstract: Scheffler fixed focus concentrators are successfully used for medium temperature applications in different parts of the world. These concentrators are taken as lateral sections of paraboloids and provide fixed focus away from the path of incident beam radiations throughout the year. The paper presents a complete description about the design principle and construction details of an 8m2 surface area Scheffler concentrator. The first part of the paper presents the mathematical calculations to design the reflector parabola curve and reflector elliptical frame with respect to equinox (solar declination=0) by selecting a specific lateral part of a paraboloid. Crossbar equations and their ellipses, arc lengths and their radii are also calculated to form the required lateral section of the paraboloid. Thereafter, the seasonal parabola equations are calculated for two extreme positions of summer and winter in the northern hemisphere (standing reflectors). The slopes of the parabola equations for equinox (solar declination=0), summer (solar declination=+23.5) and winter (solar declination=−23.5) for the Scheffler reflector (8m2 surface area) are calculated to be 0.17, 0.28, and 0.13 respectively. The y-intercepts of the parabola equations for equinox, summer and winter are calculated as 0, 0.54, and −0.53 respectively. By comparing with the equinox parabola curve, the summer parabola is found to be smaller in size and uses the top part of the parabola curve while the winter parabola is bigger in size and uses the lower part of the parabola curve to give the fixed focus. For this purpose, the reflector assembly is composed of flexible crossbars and a frame to induce the required change of the parabola curves with the changing solar declination. The paper also presents the calculation procedure of seasonal parabola equations for standing reflectors in the southern hemisphere as well as for laying reflectors in the northern and southern hemispheres. Highly reflective aluminium sheets are used on the crossbar profiles to complete the concentrator. The reflector is installed at the required site by setting its axis of rotation at an angle equal to the latitude of the site. For daily tracking, these concentrators rotate along an axis parallel to the polar axis of the earth at an angular velocity of one revolution per day with the help of simpler and cheaper self-tracking devices. For seasonal tracking, the reflector rotates at half the solar declination angle with the help of a telescopic clamp mechanism. The design procedure is simple, flexible and does not need any special computational setup, thus offering the prospect of potential application in domestic as well as industrial configurations. [Copyright &y& Elsevier]

The experience of the 25 years operation of two concentrators of solar energy (CSE) of 2.8 and 5.0 m diameter manufactured by gluing plane facets of thin glass onto metal radio antennae convincingly demonstrates their technical and economic efficiency. Besides (or in addition to) simplicity of manufacturing and the possibility to achieve temperatures up to 2000 K and more, there is one more undoubted advantage of such concentrators: it is possible to get a focal spot with rather uniform distribution of the irradiance. The problem of determining the plane facets’ optimum configuration and the structure of their arrangement on the CSE surface which guarantees forming a focal spot of the given dimension is solved by this work. Perfect geometric configuration of the facets and paraboloid is assumed. The working zone of the facets reflecting the incident solar radiation at the circular focal spot is approximately an ellipse. Trapezoid is an optimum configuration for the facets taking up a minimum area and ensuring the maximum use of CSE surface. A system of equations is obtained for calculation of a CSE structure with annular packing of the facets. The results of calculations for the 1.8 m and 15 m diameter concentrators are presented. [Copyright &y& Elsevier]