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[Display omitted] • The 3D-GR/Geo evaporation rate exceeds the theoretical limit value of 2D evaporator. • The evaporation rate of 2 cm-3D-GR/Geo at current of 2A is 5.05 times at 1 sun. • The 3D-GR/Geo has no obvious salt accumulation on the top (72 h, 3.5% NaCl). • The heat loss of 3D-GR/Geo evaporator was analyzed through calculation. Solar-driven evaporation is an ideal technology for freshwater production. However, in the actual production and application process, due to the fluctuation of solar radiant intensity, the limitation of solar lighting time and the generation of dirt, the solar evaporator can only work for a limited time. To realize the all-weather-available efficient application of the evaporator, we mixed slag, metakaolin, graphite, and potassium silicate evenly, added a certain amount of foaming agent, and adjusted its pore size and shape to prepare a low-cost electric compensation evaporator that can be used for all-weather-available efficient evaporation. The geopolymer in the evaporator acts as a support with good hydrophilicity, and graphite exhibits good photothermal performance. At 1 sun, the evaporation rate of the three-dimensional graphite/geopolymer composite (3D-GR/Geo) evaporator reaches up to 3.23 kg/m2/h, and its evaporation efficiency is 186.46%. When the solar-driven evaporation is assisted by an external electric field, the evaporation rate of the 3D-GR/Geo evaporator reaches up to 16.3 kg/m2/h. In addition, after 72 h of alternating tests at 1 sun and an applied current of 2A, no salt accumulates on the top of 3D-GR/Geo, and its quality change curve remains stable, showing excellent stability. This is also consistent with the simulation results, indicating that 3D-GR/Geo can be used effectively over a long period. [ABSTRACT FROM AUTHOR]

• Innovative thermocline TES prototype with internal heat exchangers tested by ENEA. • A vertical internal channel assists the movement of the molten salt in the tank. • A dynamic 2D axis-symmetric CFD model of the prototype has been developed. • The model is validated against the experimental data under justified assumptions. • The model is exploited to assess how the channel diameter affects the performance. Thermocline thermal energy storage is a (potentially) cost-effective alternative to the more widespread two-tank solution, as both the hot and the cold medium are stored in a single tank. An innovative single-medium indirect thermocline technology was recently developed by ENEA and a prototype was experimentally tested at the Casaccia laboratories. The storage tank is equipped with two flat-coil heat exchangers (HXs) located at the bottom and at the top of the tank, for the charge and discharge phases, respectively. The storage medium is a mixture of molten salt (Hitec XL) and the heat transfer fluid is a mineral oil (Delcoterm Solar E15). An internal vertical channel, which assists the motion of the storage medium during the charge and discharge transients, connects the two HXs. In this paper, a detailed, transient 2D axisymmetric Computational Fluid Dynamics (CFD) model of the prototype has been developed. The model simulates the charge and discharge transients, determining the heat losses and the temperature distribution of the molten salt in the tank. The computational domain includes the storage medium, the tank insulated walls and the main components immersed in the molten salt, i.e., the heat exchangers and the vertical channel. The model has been first calibrated by best-fitting the data measured during a test conducted without any thermal load, then validated against another independent set of experimental data. A first comparison against a charge transient showed some discrepancies between the computed and the measured temperatures of the salt, which could be explained by assuming the presence of a bypass at the location of the HXs. This assumption is discussed and justified in the paper. The CFD domain has then been modified to include the bypass, and this allowed to successfully validate the model against experimental data in both charge and discharge phases. The validated model is finally exploited to assess how a variation in the diameter of the internal vertical channel could affect the thermal performance of the storage system in a charge transient. The results indicate that decreasing the channel diameter leads to an increase of the salt temperature at the very top of the tank at the cost of a longer time to fully charge the storage. [ABSTRACT FROM AUTHOR]

• Robust experimental and theoretical modeling frameworks developed for thermal loss estimation. • Host of volumetric absorption based receiver-cover configurations analyzed. • Relative to uncoated glass, ZnO based heat mirrors reduce thermal losses by 27.72%. • Thermal losses are strong functions of the 'side' of the glass that has been coated; i.e. whether 'receiver facing' or 'sky facing'. • Fundamental performance limits of transparent heat mirrors have been determined. The present study investigates efficacy of ZnO based transparent heat mirror covers as thermal loss mitigators in 'direct volumetrically absorbing' solar thermal platforms. Comprehensive experimental and theoretical modeling frameworks have been developed to understand and quantify the heat loss mechanisms. Detailed analysis reveals that performance characteristics are strong functions of the 'side' of the glass that has been coated (i.e. whether 'receiver facing' (RF) or 'sky facing' (SF) sides of the cover has been coated). Results show that employing ZnO based heat mirror as a cover significantly reduces the thermal losses relative to uncoated glass cover (27.72% and 21.44% reduction for RF and SF side coated heat mirrors respectively). Moreover, fundamental performance limits of ideal heat mirrors have also been determined for both RF and SF side coated cover configurations. Relative to the uncoated glass covers, ideal heat mirror covers (viz., RF and SF side coated) promise 47.42% and 36.07% thermal loss reduction respectively (@ 400 °C receiver surface temperature and 1.5 μm cut-off wavelength). Overall, the present work represents a significant step in improving the existing volumetric absorpion based solar thermal systems; particularly aiming at intermediate temperature applications (viz. industrial and domestical heating/cooling). [ABSTRACT FROM AUTHOR]

[Display omitted] • The spectral reshaping intermediate structure on silicon substrate with simple fabrication process. • The hierarchical Si NW absorber exhibits an excellent optical absorption performance from 220 nm to 1100 nm and a lower emittance above 1100 nm. • The Si-W-SiN/SiNO multilayer emitter shows a selective narrowband absorption (i.e., emission) peak in the target wavelength and low thermal radiation loss in long wave range. • The overall efficiency of the whole STPV system is precisely optimized by varying emitter parameters and system parameters. • At achievable light concentration intensity of 1000, the STPV system efficiency can exceed 29% using this integrated silicon-based intermediate structure. Solar thermophotovoltaics (STPV) system is a technique that uses absorber and emitter to remold wide-band solar radiation into narrowband infrared emission and then convert it into electric energy in order to get high energy conversion efficiency. In this study, we fabricated an integrated silicon-based intermediate structure to enable the spectral reshaping. The absorber is a hierarchical Si NW structure, which exhibits excellent absorption performance of over 95 % in the spectral range of 220–1100 nm and a low heat loss in the long-wavelength band. The emitter is planar Si-W-SiN/SiNO structure, exhibiting a selective narrowband absorption (i.e., emission) peak in the target wavelength. When the emission peak of emitter is at 1800 nm, the overall efficiency of the STPV system based on this silicon-based intermediate structure can theoretically exceed 29 % with an achievable solar concentration of 1000 and an emitter-to-absorber area ratio of 4. We also test the prepared spectral reshaping intermediate structures on real systems and discuss further optimizations. [ABSTRACT FROM AUTHOR]

• The influences of rock salt balls with a size diameter of 20 mm at different gap spacing of (3, 4, 5, and 6 cm) are investigated. • The influences of rock salt balls with a size diameter of 20 mm at different gap spacing of (3, 4, 5, and 6 cm) are investigated. • The improvement in the daily pure water product yielded 38.3%, 49.0, 27.65%, and 13.84%, over the CHSS, for different gap distances of 3.0, 4.0, 5.0, and 6.0 cm, respectively. • The daily energy efficiency of hemispheric solar stills utilizing the rock salt balls reached. • 55.92%, 60.10, 51.46%, and 45.98% for different gap distances of 3.0, 4.0, 5.0, and 6.0 cm, respectively, compared to 40.62% achieved by the CHSS. • The utilization of rock salt balls with a gap spacing of 4.0 cm within the hemispheric solar distiller represents the optimum arrangement of rock salt balls. The significant heat losses from the solar distillers are the essential bottlenecks for their deprived performance. Minimization of the heat losses of the solar distillers by utilizing sensible storage materials has been proposed as a promising strategy. In this study, the potential of using rock salt balls as a low-cost sensible storage medium for augmenting the freshwater product of hemispheric solar still (HSS) is investigated. The influences of rock salt balls with a size diameter of 20 mm at different gap spacing of (3, 4, 5, and 6 cm) are investigated and compared to the conventional hemispheric solar still (CHSS) to determine the optimal arrangement of the rock salt balls that maximizes the freshwater production. The experimental results showed the utilization of rock salt balls with a spacing gap of 4.0 cm represents the optimal arrangement that maximizes the energic-economic performance of distillers. The accumulative freshwater reached 6.50, 7.0, 6.0, and 5.35 kg/day.m2 for rock salt balls with gap spacing of 3.0, 4.0, 5.0, and 6.0 cm, respectively, compared to 4.70 kg/day.m2 yielded by the CHSS. The improvement in freshwater for the utilization of rock salt balls reached 38.3 %, 49.0, 27.65 %, and 13.84, respectively. Furthermore, under these conditions, the enhancement in daily energy efficiency for using the rock salt balls is obtained as 55.92 %, 60.10, 51.46 %, and 45.98 %, respectively, compared to CHSS. The proposed hemispheric distillers using the rock salt balls show a 25.23 %, 31.0 %, 19.84 %, and 10.77 %, reduction in the cost per 1.0 L of freshwater than CHSS, respectively. [ABSTRACT FROM AUTHOR]

• The heat transfer mathematical model of the collector was analyzed and obtained. • An outdoor experimental platform was built and verified the accuracy of the mathematical model. • The pattern of convection and radiation heat loss with altitude has been simulated and analyzed. • The correction coefficient of total heat loss of collector at different altitudes was obtained. Flat plate solar collectors (FPSC) are a vital component in the medium and low temperature utilization system of solar energy and are widely used at different altitudes throughout China. Changes in altitude can cause changes in outdoor meteorological conditions, which can affect radiation and convection heat transfer processes on the surface of FPSC. Research into the heat loss characteristics of FPSC, when used at different altitudes, is relatively inadequate. To analyze the comprehensive impact of the change in altitude on the heat loss performance of FPSC, a model for the calculation of heat losses of FPSC was developed in this study. The influence of air pressure on air convection and long-wave radiation heat transfer was considered, and the accuracy of the model was verified by experimental test data. The variation of convection heat loss (CHL) and radiation heat loss (RHL) caused by environmental conditions such as atmospheric pressure, air density, solar irradiance and water vapor partial pressure with changes in altitude is investigated using the numerical calculation method. The results show that with increasing altitude, CHL and RHL show opposite trends, with the former gradually decreasing and the latter gradually increasing. The maximum variation of CHL and RHLs as a percentage of total heat loss can exceed 50%. Two opposite processes of heat loss play a combined role in the variation of the total heat loss, resulting in a decreasing and then an increasing trend in the altitude of the total heat loss coefficient, with a maximum variation of 10%. [ABSTRACT FROM AUTHOR]

• A novel photovoltaic thermal internal shading idea was proposed. • MHP-PV/T shading system can be integrated with agricultural buidling. • The findings underlie the feasibility for Chinese greenhouse shading with MHP-PV/T. Due to great heat loss for Chinese greenhouse cooling with vents in winter, Photovoltaic /Thermal (PV/T) was proposed for shading and cooling of Chinese greenhouse in winter and two micro heat pipe PV/T (MHP-PV/T) systems were developed inside and outside a Chinese greenhouse in Lanzhou City. Two systems were compared to discover the electrical, thermal and comprehensive performance when the inclination angle of MHP-PV/T panels was 45° from 20th to 22th of December 2020. The results reveal that daily electrical performance of outside MHP-PV/T (OMHP-PV/T) system is better than inside MHP-PV/T (IMHP-PV/T) system while daily thermal operation of the OMHP-PV/T is significantly lower than the IMHP-PV/T system. The average daily electrical efficiency of OMHP-PV/T system in three days is 8.3%, with the electrical power of 83.94 W, and the mean daily thermal efficiency is 16.07%, with solar thermal power of 96.83 W. It has overall energy power of 317.73 W and overall energy efficiency of 37.91%, the cumulative energy profit is 2.22 kW·h correspondingly. The average daily electrical efficiency of IMHP-PV/T system is about 4.57%, with the electrical power of 32.0 W, and the thermal efficiency of 40.93%, for overall energy power of 375.81 W. Overall energy efficiency is around 53.28%, with a cumulative overall energy gain is 2.63 kW·h relatively. Therefore, the comprehensive performance of IMHP-PV/T is better than OMHP-PV/T. The results of the study establish the feasibility and a new method of using MHP-PV/T to provide shading for China greenhouse cooling and dehumidification in cold winter regions. [ABSTRACT FROM AUTHOR]

• Help in attaining enhances absorption due to multiple reflections as well as concentrating effect within the enclosure. • Reduces the absorption on the side wall temperature and hence, the resultant temperature and the side losses (reduction in both conductive as well radiative heat loss). • A lower heat capacity of the cooking interior due to reduced absorbing surface area which generally do not participate in heat transfer to load but act as surface that loses heat to ambient. • Selection of a TPP that could reflect minimal change- cooker opto-thermal ratio (COR) • Detailed discussion of additionality achieved in terms of performance, economy and carbon saving (environmental aspect) post-retrofit in Indian SBC • Introduced carbon mitigation potential as an objective parameter derived from cooker opto-thermal ratio (COR) Design intervention for improvement in the performance of a solar cooker is required for its mass adoption and popularization. It has remained stagnant for decades for want of a holistic tool which provides metric for prediction of its cumulative optical and thermal(opto-thermal) performance, cooking type/objectives, techno-economic feasibility and climatic impact/carbon mitigation potential. In this work assessment of effectiveness of novel design intervention through retrofitting of internal radiative control in an Indian solar box cooker, one of the most popular family cookers in India, has been investigated using available tools. The solar cooker, with the minimal design intervention, and negligible cost implication shows an improvement of 6.74%, and 6.86% in the values of figures of merit, F 1 and F 2 , respectively, used for the thermal performance evaluation. Here, the standard test procedure for figures of merit mainly accounts for the thermal aspect of the performance as it excludes the use of external booster reflector. Alternatively, the Cooker opto-thermal ratio (COR), a parameter measuring opto-thermal performance, shows a 1.25-fold increase. The retrofitted reflectors enhance localised targeted absorption and reduce thermal losses, resulting in a 25% improvement in COR. The retrofitting process is simple, and easy; and offers superior performance, favourable economics, and potential for carbon mitigation, making it highly attractive. Also, this work demonstrates COR as a tool with higher resolution enabling analysis of the impact of even minimal design intervention. [ABSTRACT FROM AUTHOR]

Building fenestrations are the key components maintaining the connection between building exterior and interior. However, they are also the weakest allowing heat loss, gain and light. To tackle the enhanced building energy demand, active and passive both ways must be included. Benign energy-generating components and passive energy-saving are both concomitantly possible using photovoltaic (PV) window fenestration. In this work, three different generations PV based fenestration integrated photovoltaics (FIPV) have been reviewed to understand how effective FIPVs are for low energy building. Later advanced technologies suitable for FIPV applications are also discussed. [ABSTRACT FROM AUTHOR]

• Investigation of a two-axis tracking Fresnel lens solar collector field. • Solar field peak efficiency of 53.5%, including 11% soiling. • A simulation model was developed in TRNSYS and validated with measurement data. • Annual performance of 373 kWh/m2 at a mean temperature of 70 °C in Denmark. • Due to low heat losses, the collectors are suitable for applications >100 °C. Fresnel lenses are used in a wide range of solar energy applications, primarily due to their reduced material usage, low cost, and high optical efficiency. This study presents an investigation of the world's first full-scale Fresnel lens solar collector field. The collector field consists of 144 two-axis tracking solar collectors manufactured by the Danish company Heliac and supplies heat to the local district heating network in Lendemarke, Denmark. The thermal performance of the solar collector field was determined using the quasi-dynamic test method. It was found that the peak efficiency was 11% lower compared to a brand-new collector and that heat losses from the collectors made up half of the total heat losses of the solar field. The reduction in the peak efficiency was primarily caused by soiling as the collectors were exposed to outdoor conditions for one year without cleaning. Furthermore, the system's annual performance was determined using a simulation model developed in TRNSYS and validated by comparison to measurement data. For 2020, the heat generation was 373 kWh/m2 (relative to aperture area) when operating with an outlet temperature of 90 °C and inlet temperature of 50 °C. Additionally, a sensitivity analysis of the annual heat generation was performed, varying the ground cover ratio, mean collector temperature, and soiling level. The sensitivity analysis showed that the heat generation was relatively insensitive to changes in the mean collector temperature, demonstrating that the collectors are suitable for generating heat above 100 °C, unlike flat-plate collectors. [ABSTRACT FROM AUTHOR]

• A novel configuration of VFPSC is presented. • Three thermal SCs; namely VFPSC, FPSC and ETSC, are investigated and compared. • Developing a computational program for simulating different SCs performance. • Optimisation of number of tubes and cost-effectiveness are discussed. • The proposed VFPSC achieves impressive efficiency for the whole emissivity range. This paper presents a new design of vacuum flat plate solar collector (VFPSC). This inspired design is based on a combination of two conventional systems; the flat plate solar collector (FPSC) and the evacuated tube solar collector (ETSC). The new configuration, which is characterised by a curved evacuated cover and rear Rockwool insulation is compared with FPSC and ETSC. Collectors' performance is predicted through a theoretical approach that includes heat transfer and energy balance equations, where thermo-physical and geometrical properties of each collector are considered. The developed computational program is validated against experimental results carried out on FPSC. The optimal number of tubes is identified to perform a comparative study under the best efficiency point for different values of absorber emissivity including collectors' cost. The new VFPSC proves that the combination of front vacuum insulation and back opaque thermal insulation can result in significant heat loss reduction, and thus performance enhancement for the whole emissivity range. As a result, the proposed VFPSC provides more thermal efficiency than FPSC and ETSC by 7.13% and 28.32%, respectively, for an emissivity of 0.95, while for an emissivity of 0.05, it reaches ratios of 22.77% compared to FPSC and almost the same ETSC efficiency levels, with a much lower cost. Moreover, it shows lower heat loss factor compared to other similar VFPSCs. Overall, VFPSC offers a promising solution that has the required ability for producing hot water with a low cost and may take place as heating device in buildings and industrial sectors. [ABSTRACT FROM AUTHOR]

• A review of linear Fresnel receiver designs is presented. • Receiver designs are optimized optically with an etendue-conserving CLFR mirrors. • The thermal model settings are validated against experimental work. • Using 2D CFD simulations, the heat losses from each receiver are compared. While several studies of multitube and monotube linear Fresnel receivers exist in the literature, comparative studies on different types of receivers are limited. This paper therefore aims to address this gap within literature by comparing the optical and thermal performance of four different receivers: an adapted compound parabolic concentrator (CPC)-type monotube receiver, an adapted tailored edge ray concentrator (TERC)-type monotube receiver, a trapezoidal multitube receiver and an adapted TERC-type multitube receiver. Existing literature was used to determine the design elements limiting heat loss, which were then incorporated into the receiver design and optical optimisation of the four receivers. Once the geometry was determined through a series of Monte Carlo ray tracing (MCRT) simulations, a validated two-dimensional computational fluid dynamic (CFD) model was used to determine the heat loss of each receiver for the same thermal conditions. Given that these heat loss studies were decoupled from the optical study, they are valid for any type of mirror field. While both adapted TERC-type receivers performed well optically (with daily optical efficiencies of 56.93% and 56.6% for the monotube and multitube receivers, respectively), the adapted TERC-type multitube receiver had the highest thermal loss of all the receivers, increasing the heat loss of the TERC-type monotube receiver by a factor of 2.5. In contrast, the adapted CPC-type monotube receiver had a lower daily optical efficiency of 51.29% when paired with an etendue-conserving compact linear Fresnel mirror field, but had low thermal loss, second only to the lower heat loss of the adapted TERC-type monotube receiver by a factor of 1.26. The standard trapezoidal receiver had a relatively low daily optical efficiency of 53.69% and relatively high heat losses, higher than the adapted CPC- and TERC-type monotube receivers by a factor of 1.5 and 1.9, respectively. The adapted TERC-type monotube receiver was therefore determined to be the best candidate receiver for an etendue-conserving compact linear Fresnel field. [ABSTRACT FROM AUTHOR]

• A novel design of plated volumetric cavity receiver is proposed. • Numerical modelling of molten salt flow inside cells and air flow in the cavity. • Numerical analysis of molten salt flow at different velocities. • Estimated the heat losses from the plated receiver numerically. • Flow circulations observed to be significantly high at very low velocities. The article mainly focuses on the study of thermal performance of liquid volumetric plated cavity receiver which includes the flow characteristics of heat transfer fluid and estimation of heat losses. Due to higher heat capacity, liquids are considered more suitable heat transfer fluid than air. However, it is difficult to use liquid as heat transfer fluid (HTF) in the conventional air volumetric receivers, therefore a plated volumetric receiver is proposed, as it can heat the fluid within the volume of the receiver. The plated receiver consists of a parallel arrangement of rectangular cells suspended in an enclosure. Each cell is enclosed by two large rectangular metallic plates joined together, creating a hollow space between them with inlet and outlet nozzles. The incoming solar radiation is absorbed by outer surface of the cell and transferred to the HTF. Large absorbing surface area and large contact area between the plates and HTF is the key feature for avoiding hot spots on the cell's surfaces. Numerical analysis is carried out for molten salt flow inside the cells and air flow in the cavity. The results show a uniform distribution of flow (with Re = 212) resulting into no hotspots on the receiver surface. Local heat transfer coefficient is estimated to be maximum and minimum in the high and low flux regions, respectively. The thermal efficiency of the receiver is calculated as 90.76 %. The cell thickness and plate size of the receiver is 6 mm and 100 mm × 50 mm, respectively. [ABSTRACT FROM AUTHOR]

• The use of perforated baffles increased the turbulence in the flow and improved air velocities, mass, and heat transfer rate. • The addition of paraffin wax for thermal energy storage allowed the dryer to operate for 3.5 h without sunlight. • The finned tube heat exchanger provided higher efficiency, improved heat transfer, and consistent temperature control compared to the flat plate type dryer. • The airflow velocity increased by 13.75 times and the heat loss was decreased by 11 times. The drying time for 50 Kg of apricots is decreased by 5.28 times at a uniform temperature of 325.8 K in comparison to the first dryer. This study compares two distributive mode active solar dryers: one featuring a flat plate collector with non-uniform drying and the other incorporating an evacuated tube collector (ETC), thermal energy storage (TES), centrifugal blower, perforated baffled trays (PBT), phase change material (PCM), and a drying chamber with enhanced insulation. While the flat plate solar dryer exhibits non uniform non continuous drying, continuous solar dryer exhibits continuous and uniform drying. The evaluation of dryer performance involved mathematical modelling and simulations using ANSYS Fluent software, encompassing the analysis of flow and temperature distribution within the drying chamber. The simulation study also captured the transient behaviour of the PCM during the melting and solidification processes. Results demonstrated that incorporating the perforated baffles significantly enhanced turbulence, improving air velocities, mass transfer, and heat transfer rates. Furthermore, introducing paraffin wax for TES enabled the dryer to operate autonomously for 3.5 h without direct sunlight. The finned tube heat exchanger allowed the continuous solar dryer to achieve higher efficiency, enhanced heat transfer, and consistent temperature control compared to the flat plate dryer. This was evident in the substantial increase in airflow velocity by 13.75 times and a notable reduction in heat loss by a factor of 11. Consequently, the drying time for 50 kg of apricots was significantly reduced by 5.28 times, maintaining a uniform temperature of 325.8 K unlike the flat plate dryer. [ABSTRACT FROM AUTHOR]

• The matt black coated aluminium sheet is covered above the cooking pot, to reduce the top heat losses in box-type solar cooker. • Box-type solar cooker assisted with heat storage material are in need of additional reflector. • Ideal time is utilized to store the heat in portable marble pieces for evening cooking in box-type solar cooker. • Portable heat storage material opted instead of integrating inside a box-type solar cooker. The thermal performance of the current box-type solar cooker is limited, and no provision for evening cooking, which could increase its dependability and attract more consumers. The thermal performance and evening cooking capabilities can be enhanced by employing the waste marble pieces as integrated or portable heat storage material. Also, suggested using a matt black coated aluminium sheet placed additionally below the glass cover to reduce the top heat losses. In this work, two arrangements were proposed: (I) a cooking load with heat storage but no aluminum sheet, and (II) a cooking load with both aluminum sheet and heat storage. The scope of improvement is evaluated using the COMSOL Multiphysics 6.0 software tool and experimental testing conducted in an outdoor environment. The cooking times for arrangements I and II are evaluated experimentally as 154–155 min and 175–176 min respectively, corresponding cooking power are measured as 56.62 W and 48.21 W, respectively and the corresponding thermal efficiencies are 25.79 % and 31.19 %, respectively. The optimal time for heating various weights of marble pieces is investigated using an aluminum sheet cover since the thermal performance and temperature availability till late evening are relatively low. The proposed solar cooker has a payback period of 1.24 years. It is concluded that installing a single solar cooker for two members of a family reduces a total of 148.3 kg of carbon dioxide annually. [ABSTRACT FROM AUTHOR]

This study investigates the wind influence on the operation of an open volumetric cavity receiver (OVR) designed with a tower height of approximately 200 m and a total thermal power of 240 MW t h . The receiver design incorporates an air return system where parts of the air are returned between the OVR modules after the heat exchange, while the remainder is recirculated externally from below the receiver. When operating such a scaled-up OVR, ambient wind becomes a relevant parameter in terms of convective losses and the air return ratio, which must be maintained at a high level to ensure economic viability. In this study, ambient wind and the receiver flow are modelled by CFD simulations with the RANS approach. In addition to the evaluation under windless conditions, the simulations in this study cover lateral wind at 4 and 8 m s wind speed. The simulations show the vulnerability of externally returned air as it is significantly influenced by lateral wind. As a countermeasure, wind-adjusted external return air distributions are investigated, which show the potential to reduce convective heat losses due to incomplete air return. In addition, the application of aerowindows is investigated, which has limited potential due to the size of the receiver aperture. The results highlight the importance of the design of the external air return system and suggest a controllable return air system that can be adapted to the current wind situation. • The influence of wind on the convective heat losses in large scale (≥ 200 m) open volumetric cavity receivers has been investigated with CFD simulations. • Ambient wind should be considered in the design of external return air outlets, as it reduces the rate of recirculated air, when air return systems are used. • Adjustable return air outlet distributions are numerically investigated and show the potential to significantly increase the receiver efficiency in the presence of wind. • The applicability of an air curtain to deflect ambient wind is limited by the size of the receiver and is only feasible for small cavities. [ABSTRACT FROM AUTHOR]

• Multi-objective optimization of a small-sized PV-T water collector is performed for the first time. • Taguchi based orthogonal experiments are performed to obtain suitable design space of parameters. • ANOVA analysis is done to obtain the significant parameters to control the collector performance. • NSGA based optimization is performed to obtain Pareto optimal fronts. • TOPSIS is used to obtain most optimal solution for maximum thermal and electrical efficiency. Small-sized solar photovoltaic thermal (PV-T) collector can achieve better overall performance due to less aperture plane heat losses and the possibility of concentrating more radiant flux per unit aperture area compared to their large counterpart designs. Despite its potential, studies on its performance optimization have not yet been explored. This study aims to perform a multi-objective optimization of the performance of a small-sized PV-T water collector with channel type absorber design by using a two-step procedure i.e., implementation of Non dominated sorting genetic algorithm (NSGA-II) followed by a decision making method i.e., a technique for order preference by similarity to ideal solution (TOPSIS). Based on the Taguchi orthogonal array design for three control parameters i.e., mass flow rate, inlet temperature, and inclination angle, an experimental campaign is undertaken. The design space created on the basis of Taguchi design of experiment is used to conduct a total 16 number of experiments. An analysis of variance is carried out to obtain the significant design and operating parameters controlling the collector performance, which are used to fit the objective function equations for both thermal and electrical efficiency. A multi objective optimization strategy is then developed by a variant of NSGA-II to simultaneously optimize its average thermal and electrical efficiencies. From the obtained Pareto fronts, the most optimal solution is obtained by using TOPSIS method. The highest thermal and electrical efficiency of 82.55% and 10.45% is obtained under an optimal mass flow rate of 0.02 kg/s, inlet temperature 32 °C and inclination angle 38.88°. The influence of solar radiation on its optimized performance demonstrates a little less higher thermal efficiency of 81.05% and electrical efficiency of 11.43% obtained at a radiation of 700 W/m2. On experimental verification of the optimized performance, the highest thermal and electrical efficiency is obtained within an agreement of ± 3.51% and ± 6.9%, respectively. The present optimized efficiency values are higher compared to that of a typical experimental day with un-optimized input conditions and also higher than some of the recent published papers. [ABSTRACT FROM AUTHOR]

• A silica aerogel-based photovoltaic/thermal (PV/T) collector is proposed. • The aerogel-based PV/T collector significantly suppress radiation heat loss. • The thermal performance of the aerogel-based PV/T collector is enhanced by 46%. • The performance of aerogel-based PV/T is equivalent to that of spectrally selective PV/T with a thermal emissivity of 0.1. • The exergy efficiency of the aerogel-based PV/T collector is increased by16.2%. Photovoltaic/thermal (PV/T) collector can convert incident sunlight into electrical and heat energy simultaneously. However, compared with the solar thermal collector, the radiative heat loss of the PV/T absorber is larger since the spectrally selective PV/T absorber is difficult to design and fabricate after introducing PV cells, which leads to lower thermal efficiency. Thus, an approach that can reduce the radiative heat loss of the PV/T collector without the requirement for spectrally selective PV/T absorber is emergently needed. Here, a novel aerogel-based PV/T collector is proposed to suppress radiative heat loss and improve efficiency by introducing the silica aerogel that is highly transparent to sunlight and opaque to infrared light, as well as ultra-low effective thermal conductive into the PV/T collector. A numerical model is established to evaluate the performance of the aerogel-based PV/T collector, and the results present that the heat loss of the PV/T collector at the operating temperature of 70°C can be dramatically reduced by approximately 75% after using the silica aerogel and the thermal efficiency can also be increased by 46%. Moreover, a parametric study is conducted to investigate the influence of solar radiation, ambient temperature, and emissivity of the PV/T absorber on the performance of the aerogel-based PV/T collector. This study is devoted to exploring a new method to suppress the radiative heat loss of the PV/T collector and enhance its solar harvesting performance correspondingly, which gives a reference for the design of high-performance PV/T utilization. [ABSTRACT FROM AUTHOR]

• The effectiveness of a variety of suction configuration is quantified. • The effectiveness of an air curtain configuration at a yaw angle of 45° is assessed. • A novel approach of combination of suction and blown air curtain is assessed. • Reduction of up to a maximum 43% is achieved for a tilted cavity at forced convection regime. We explore the potential for adaptive air barriers to mitigate convective heat losses from cavity receivers, especially at large tilt angles, using both suction and blowing nozzles. A heated scaled-down cylindrical cavity receiver was fitted with nozzles on four sides of the aperture, at 30° to the aperture plane. The tilted cavity receiver was mounted in a large wind tunnel to allow systematic variation of wind speed and direction. The effectiveness of different nozzle arrangements was calculated from the measured convective heat losses for a series of different mitigation strategies. The results reveal that a suction nozzle mounted at the bottom of the aperture is more effective than a blowing nozzle mounted at the top of aperture for tilt angles of θ = 45°, and under different wind speeds. The effectiveness ranged from 0 at a low suction flow rate to ~80% at a high suction flow rate. With the use of three suction nozzles, at the bottom and both sides of aperture, the effectiveness decreased markedly for both tilt angles and all wind speeds. For more challenging conditions of a 45° tilt angle and 45° yaw angle, the most effective approach is the use of suction through nozzles aligned diametrically opposite to the wind, while other nozzle combinations were ineffective in mitigating losses. Finally, the results highlight the need to apply an adaptive aerodynamic strategy that can respond to measured changes in the environmental conditions to achieve the highest thermal efficiency. [ABSTRACT FROM AUTHOR]

• The baffle structure effect on the microscopic characteristics of flow and heat transfer was numerically analyzed. • Depressing the vortex played a key role in improving thermal performance of the SSAHs. • The optimal structure of baffles with right angle and rectangular holes at turnings was proposed. In order to further improve the thermal performance of spiral solar air heaters (SSAHs), three-dimensional mathematical models of four proposed types of spiral solar air heaters, including right angle spiral solar air heaters (RA-SSAHs), arc spiral solar air heaters (ARC-SSAHs), arc spiral solar air heaters with rectangular holes (ARC-RH-SSAHs) and rectangular holes spiral solar air heaters (RH-SSAHs), were developed by CFD to analyze the effect of baffles structure on the microscopic characteristics of flow and heat transfer. The profiles of velocity proved that the channel with both right angle turnings and rectangular holes contributed to decreasing the pressure loss by depressing the intensity and scale of the separated vortex and corner vortex. RH-SSAHs, which exhibited the highest collection efficiency among the four types of SSAHs, proved that the optimizing structure of baffles in channels contributed to reducing the heat loss rate by transparent cover plate more significantly than reducing the absorbed heat rate of air by increasing the transverse velocity and decelerating the air flowing along the channels due to bypass air through the holes. [ABSTRACT FROM AUTHOR]

• Annual thermal performance of PTES in Dronninglund, Denmark monitored and analyzed. • Trnsys model of the PTES developed and validated against measurement in 2015. • The annual charged and discharged energy were predicted with a deviation < ±4%. • Ratio of heat loss from the cover, the sides and the bottom respectively 60%, 38%, 2%. • Influence of soil types and diffuser positions on annual performance investigated. Water pit heat storage is an effective long-term heat storage. Experimental and theoretical investigations of a 60,000 m3 water pit heat storage in Dronninglund, Denmark was carried out with an aim to study its long-term thermal performance. Experimentally, detailed measurements were analyzed to monitor thermal behavior of the store, including flow rates, temperatures of the inlet and outlet flow, thermal stratification in the store and temperatures of the surrounding soil at four different depths. Theoretically, a simulation model of the water pit heat storage was developed based on the Type 343 model (ICEPIT) in TRNSYS. The calculated temperatures were compared to the measurements. The developed model was used to investigate the influence of soil properties and inlet arrangement on the thermal performance of the store. The result show that the simulation model predicts well the thermal behavior of the store. Over the whole year, the calculated average temperature of the store differed within ±4.7 K from the measured values. The measurements show that the annual charged and discharged heat are 12,787 MWh and 11,957 MWh respectively. The deviation of the charged and discharged energy between the simulation and the experiment did not exceed ±4%. The annual storage efficiency reached 90% in the second year of operation. The calculated ground temperatures were consistent with the measured ones at different depths. Measured heat loss of the store is 1392 MWh. As elucidated by the model, the heat loss from the cover contributed to 60% of the annual heat loss, while the heat loss from the sidewall and the bottom contributed 38% and 2% respectively. The influence of soil types on thermal performance of the store is significant. For a PTES surrounded by dry soil, the storage efficiency can reach 90%, while for a PTES surrounded by wet sandy gravel, the storage efficiency decreases by 7%. Change of the height of the middle inlet/outlet diffuser could slightly improve the storage efficiency by 1%. The restrains of the model were analyzed and the focus areas of further investigations were pointed out. The findings of the paper give good reference for researchers, designers and consultants in planning of a solar heating plant with a large water pit heat storage. [ABSTRACT FROM AUTHOR]

• A Fresnel lens is used to focus sunlight into the desalination system. • Solar concentrating and bubbling technologies are combined into desalination system. • The accumulated yield can reach 5.61L/d/m2 under actual weather conditions. • System performance ratio is 0.69 under actual weather and 0.71 with electrical heater. A bubbling humidification-dehumidification (HDH) desalination system directly heated by concentrated sunlight is presented in this work. Sending directly the concentrated sunlight into bubbling humidification chamber can save the circulation pipeline and solar receivers, and reduce the heat loss of the pipeline which simplifies the device's structure and adds its operation reliability. The HDH system consists of a Fresnel lens solar concentrator, a bubbling humidification chamber and a bubbling dehumidification chamber. The operating principle and the structural design of the bubbling chambers are explained. A cylindrical Fresnel lens is used to focus sunlight into the humidification chamber to directly heat the seawater. With air coming out from the perforated wall of the immerged pipe, bubbles will generate underwater to obtain sufficient heat and moisture transfer. Experimental tests under different conditions were carried out to verify the design and study the performance characteristics. The results that the maximum freshwater productivity is about 1.24L/h/m2 when the maximum solar irradiance is 980 W/m2. The accumulated yield can reach 5.61L/d/m2 with an average thermal efficiency about 69% for sunny weather conditions in October in Beijing. Besides, the average thermal efficiency is about 71% under steady-state condition. Compared to some published works, the proposed bubbling HDH desalination system has relatively higher freshwater productivity owing to its effective heat and moisture transfer enhancement by direct solar heating and bubbling. The economic analysis showed that the price of the produced water for the system is about 0.027$/L. [ABSTRACT FROM AUTHOR]

• S-CO 2 properties are strongly temperature-dependent in the operating conditions of PTC. • S-CO 2 properties vary considerably while passing through the receiver tube. • The net heat flux from one half of the heat collecting element is always negative. • The thermal efficiency of PTC varies slightly during a typical summer day. • Change of available solar incidence dramatically alters the outlet temperature of PTC. Recently, supercritical carbon dioxide, S-CO 2 , has been suggested for utilization as the working fluid in solar thermal power plants. Replacing current working fluids with S-CO 2 , however, is not a straightforward task. This work numerically investigates the heat transfer and flow filed in a parabolic trough solar collector which carries S-CO 2. A full-scale three-dimensional model of the parabolic trough is developed and analyzed using the Star CCM + software. The variation of carbon dioxide's thermophysical properties inside the receiver tube is considered. The computational model is validated against a set of experimental data published by Sandia National Laboratories with no more than a 2.81% error margin. The numerical experiment is carried out at five different times during a typical summer day in Albuquerque, NM. Numerical results confirm that in all cases, heat loss from the upper half of the receiver tube is more than the absorbed solar incidence on that side. At noon, when the absorbed heat flux on the lower surface of the receiver tube reaches its maximum at 29810 W/m2, the net heat loss flux from the upper half of the receiver tube reaches 2622 W/m2. Consequently, the heat transfer from the upper half of the receiver tube unfavorably impacts the thermal efficiency of the parabolic trough. Additionally, while from 8 AM to 12 PM thermal efficiency drops less than 2.4%, the S-CO 2 temperature increment grows over 182%. A reverse trend occurs from noon to 4 PM, mainly due to the change in the available solar incidence. [ABSTRACT FROM AUTHOR]

• Floating PV panels experience cooling by deployment on water-bodies. • Open system designs leads to an increase in the heat loss coefficient of floating PV panels. • Similar trends of the cooling effect in two climates have been observed. • Simulations show an increase in annual energy yield of FPV systems, up to 6%, due to the cooling effect. An enormous area could potentially be unlocked, when more photovoltaic (PV) systems would be deployed on water bodies. Especially in densely populated areas this opens a pathway for PV to contribute to the energy transition in a large scale. Another potential benefit of floating PV (FPV) systems is that they can outperform conventional PV systems in terms of energy yield due to the cooling effect from the water. However, there is very little field data available to quantify the cooling effect and compare it across different climatic condition. The research presented here has thoroughly studied this effect and translated it into an estimated specific yield comparison between conventional and floating PV systems. The study is based on field tests that are located in two different climate zones: a temperate maritime climate (the Netherlands) and a tropical climate (Singapore). Irradiance weighted average temperatures of FPV systems have been compared with a land-based system in Netherlands and a rooftop system in Singapore as references. The best performing FPV systems showed 3.2 °C (Netherlands) and 14.5 °C (Singapore) lower weighted temperatures compared to their benchmarks. Open system designs, where the PV panels of the floating system are widely exposed to the water surface, lead to an increase in the heat loss coefficient of floating PV panels (a measure for the cooling effect) of up to 22 W/m2K compared to reference PV systems. Annual specific yields of the PV systems were estimated by the measured irradiance-weighted temperature difference and by a PVsyst model with inputs of the heat loss coefficients. Based on these calculations, we observe that the gain in energy yield from the cooling effect of FPV systems compared to the reference PV systems is up to 3% in the Netherlands and up to 6% in Singapore. [ABSTRACT FROM AUTHOR]

• Heat Transfer anaylsis for Scheffler dish collector was conducted to identify areas from where heat losses are occurring. • Efficiency of cooking pots was analysed to estimate overall performance of the system. • Recommendations for operations and maintenance are provided based on thermal analysis. The escalation of energy demand in both developed and developing countries has prompted people to search and utilize clean and sustainable energy resources. Omshanti Retreat Centre (ORC) situated in Gurugram, Haryana, India utilizes solar energy to meet most of its energy demand. It has installed Scheffler dish type solar thermal cooking system having a capacity to cook 6000 meals per day in the year 2001 and is being utilized to cook food three times a day for approximately 200 days per year. The present research was conducted to study the performance of the solar thermal cooking system both experimentally and analytically; identify areas from where heat losses are occurring in the system and suggest steps that should be taken for improvement of overall system performance. Experiments were performed for seven consecutive days at ORC during summer. The system consists of twenty eight collectors arranged in such a way that a pair of Scheffler reflectors of 10 m2 aperture area concentrates solar radiation on one absorber. Thermal efficiency of 70–80% was obtained for the collectors experimentally for an average direct normal irradiance of 800 W/m2. The overall system efficiency was estimated to be 25% which suggests significant losses in the overall process. The research identified the areas which act as sources for heat losses from the system. [ABSTRACT FROM AUTHOR]

• Floating PV panels experience cooling by deployment on water-bodies. • Open system designs leads to an increase in the heat loss coefficient of floating PV panels. • Similar trends of the cooling effect in two climates have been observed. • Simulations show an increase in annual energy yield of FPV systems, up to 6%, due to the cooling effect. An enormous area could potentially be unlocked, when more photovoltaic (PV) systems would be deployed on water bodies. Especially in densely populated areas this opens a pathway for PV to contribute to the energy transition in a large scale. Another potential benefit of floating PV (FPV) systems is that they can outperform conventional PV systems in terms of energy yield due to the cooling effect from the water. However, there is very little field data available to quantify the cooling effect and compare it across different climatic conditions. The research presented here has thoroughly studied this effect and translated it into an estimated specific yield comparison between conventional and floating PV systems. The study is based on field tests that are located in two different climate zones: a temperate maritime climate (the Netherlands) and a tropical climate (Singapore). Irradiance weighted average temperatures of FPV systems have been compared with a land-based system in Netherlands and a rooftop system in Singapore as references. The best performing FPV systems showed 3.2 °C (Netherlands) and 14.5 °C (Singapore) lower weighted temperatures compared to their benchmarks. Open system designs, where the PV panels of the floating system are widely exposed to the water surface, lead to an increase in the heat loss coefficient of floating PV panels (a measure for the cooling effect) of up to 22 W/m2K compared to reference PV systems. Annual specific yields of the PV systems were estimated by the measured irradiance-weighted temperature difference and by a PVsyst model with inputs of the heat loss coefficients. Based on these calculations, we observe that the gain in energy yield from the cooling effect of FPV systems compared to the reference PV systems is up to 3% in the Netherlands and up to 6% in Singapore. [ABSTRACT FROM AUTHOR]

• Heat transfer characteristics of closed and circulated air cavities are obtained. • Design of insulation inside the cavity is proposed for a TW in Western China. • Indoor thermal environment of a CTW room is analyzed. Integrating the design of insulation, heat storage, and solar heating can help to improve indoor thermal environment during winter in Western China. However, insulation at night is often overlooked for Trombe walls (TWs). The present study considers a panel curtain installed in the cavity to enhance the preservation of heat of TWs at night. The effects of the structural parameters related to insulation inside the cavity on the TWs were analyzed in Western China and a design approach for insulation inside the cavity was proposed. In addition, the indoor air temperature of a TW with a built-in panel curtain (CTW) room was analyzed. The results indicate that the heat efficiency in the nighttime can be significantly improved by setting a panel curtain in the air cavity. Low emissivity film should be attached to the closed cavity side. The emissivity of the panel curtain's exterior surface plays an important role in the closed cavity and the effect is more significant with low emissivity. The optimum thickness depends on the climate, i.e., 0.02–0.06 m for a large solar radiant heat loss ratio (SHLR), 0.02–0.05 m for a medium SHLR, and 0.02–0.04 m for a low SHLR. The thickness of the circulated cavity should be larger than 0.07 m, and the effect varies within a small range when the thickness exceeds 0.1 m. A panel curtain can significantly improve the indoor air temperature in a CTW room. [ABSTRACT FROM AUTHOR]

• Introducing a new baffled water photovoltaic/thermal (PV/T) system. • Utilizing integrated collector storage (ICS) system as thermal unit in new PV/T system. • Studying transient dynamics of baffled PV/T system under field conditions during a day. • Evaluating energy efficiency of baffled PV/T system under field conditions. • Assessing exergy efficiency of baffled PV/T system under field conditions. This study analyzes a new baffled photovoltaic/thermal (PV/T) collector consisting of a baffled integrated collector storage (ICS) system integrated with a polycrystalline silicon PV panel. ICS systems have a significant advantage: combining absorbing and storage components causes a simple, affordable structure; furthermore, to improve the convection mechanism, several baffles are installed in the ICS. The energy and exergy analyses were carried out experimentally to discuss the efficiency of the PV/T collector comprehensively. The reserved water stratifies in the tank during daytime, and its temperature obtains the maximum values of 47.2 °C and 38.1 °C at the top and bottom of the tank. Interestingly, the mean water temperature is lower than the ambient temperature in the morning due to radiative sky cooling at night. The thermal, electrical, and overall energy efficiencies of the PV/T system are high in the early morning, nearly 21.67%, 15.22%, and 65.09%; then, these energy efficiencies reduce due to increasing ambient heat losses and PV temperature. Thermal exergy efficiency reaches nearly 0.15%, while electrical exergy efficiency varies between 21% and 22% during daily hours. Therefore, the simple structure with high overall efficiency, nearly 65%, causes the new baffled PV/T collector to be an affordable, robust PV/T system. [ABSTRACT FROM AUTHOR]

• Heat transfer model of greenhouse cover under all operating conditions proposed. • The model can calculate the heat loss on the surface of greenhouse cover. • First study the long wave radiation relationship between crops and greenhouse cover. • First study on the influence of latent heat on the heat loss of the covering layer. • Considering the impact of greenhouse building layout on heat loss. The solar greenhouses in China are composed of gables on the east and west sides, north walls, and north and south roofs. The south roof is the main heat dissipation surface of the greenhouse. To quantitatively and comprehensively analyse the heat transfer characteristics and heat loss pathways of the south roof of a solar greenhouse, based on the actual usage of the greenhouse, the heat transfer of the south roof is classified into two working conditions: heat transfer of the transparent covering material (TCM) and heat transfer of the composite thermal insulation coating (CTIC). A theoretical heat transfer model of the covering layer of the solar greenhouse under all working conditions is constructed by applying the heat transfer theory. The model was tested using field test data from two areas different regions in China: Beijing and Lhasa. The results show good agreement between the simulated and measured values, the relative errors between simulated and measured values were 18.54% and 8.17%, respectively, with root mean square errors of 1.69 and 1.92. The model can comprehensively and accurately reflect the comprehensive heat transfer coefficient and heat loss changes of the south roof of the solar greenhouse. It can be used to analyze the proportion of heat loss caused by radiation, convection, and water vapor condensation. The analysis shows that condensation heat loss cannot be ignored during the winter night period. Measures such as covering the roof with plastic film and controlled irrigation can help reduce condensation heat loss. [ABSTRACT FROM AUTHOR]

• A concept of modified shape coefficient of building was proposed. • The shape coefficient of building was modified based on solar radiation factors. • The modified shape coefficient of building was experimentally proved. • The shape coefficient of building was reduced by 32.4% in this present case. • The restriction on shape coefficient of building could be liberalized moderately. The shape coefficient of building (SCB) is a measure of correlating a building's shape and its energy consumption. However, strictly adhering to restrictions the SCB may not be conducive to reducing energy consumption, as it disregards the potential benefits of solar radiation. To address this, a novel concept and method for determining the modified shape coefficient of building (MSCB) have been introduced in considerations of heat loss and solar heat gain. Field measurements were conducted in western Sichuan to establish a comprehensive understanding of the factors influencing indoor thermal environments, involving collecting indoor air temperature data for model buildings under natural and heating conditions, including solar radiation, building orientations, and U-values. Results demonstrated that maintaining an identical SCB did not consistently ensure similar indoor thermal environments. The indoor thermal environments were significantly influenced by building orientations, U-values, and solar radiation, highlighting the limitations of relying solely on SCB. A simulation method validated through experiments was utilized to predict the dynamic heating load of an actual building. The influence of building orientations on the MSCB across different time scales and actual climatic conditions was investigated. Results illustrated a potential reduction of the SCB by up to 32.4% in the specific case. This reduction correlated with trends observed in the monthly correction factors and heat consumption, suggesting that moderate relaxation of SCB restrictions could be viable even in scenarios with high heating demands. This research contributes valuable insights into the realm of energy-efficient building design. [ABSTRACT FROM AUTHOR]

• The model is developed with consideration of flow rate variations. • Matrix derivation is applied to obtain an analytical solution. • The model could present the temperature variations of each component. • The dynamic model is validated by the on-site test in the cold region. The dynamic thermal model of the collector could serve as a useful tool for the thermal prediction. Normally, collectors' thermal prediction models are developed based on the dynamic thermal process, and then the thermal output or the mean temperature of the fluid would be obtained from the mathematical derivation. The critical parameters in the equations are fitted from the test data. In which, the heat loss coefficient F ′ U L has a close relationship with the flow rate, and thus the fitting formula could only be used for a given flow rate. In this paper, a dynamic heat transfer model of the normal flat plate solar collector is introduced, with consideration of the mass flow rate variations. Matrix is employed for solving the heat transfer equations. The analytical solution of the model indicates that the temperatures at time τ are determined by the initial value and the accumulated effect of the ambient environment. The model is validated by the on-site experiment carried out in Zhangjiakou, Hebei Province, in the north part of China. The main trend of the simulation and measurement was in accordance continually in the initialization, operation, and halt phase for around 24 h. While, the thermal mass of the duct connected to the collector is not included in the model, leading to the accuracy reduction of the model prediction. The modification with consideration of the pipeline's thermal mass will be conducted in future work. [ABSTRACT FROM AUTHOR]

• Heat loss from a cavity dish solar receiver is accurately determined using CFD. • Radiation losses are simulated using the Discrete Ordinates method. • The solar heat source is determined using ray tracing on a complex geometry. • The numerical simulation is validated using a full-scale heating experiment. • Convection loss is simulated for various wind speeds and dish orientations. The process of obtaining an accurate estimate of the heat losses of a tubular cavity receiver absorbing concentrated solar energy from a parabolic dish at various inclination angles and wind speeds is described. Computational fluid dynamics (CFD) was used to simulate the conjugate heat transfer of the absorbed solar radiation to the heat transfer fluid while considering thermal radiation as well as forced and natural convective heat losses. Validation is performed against an experimental heating test at full-scale using heated air and measured wind conditions. On-sun conditions were modelled using the ray-tracing software, SolTrace, adapted for complex geometry receivers using ANSYS mesher and user coding. A 200 million ray result was found to be ray and mesh independent for a meshed receiver surface containing 30 000 elements. The SolTrace heat flux distribution was implemented as a volumetric source in ANSYS Fluent employing user-defined functions. The losses due to thermal radiation out of the cavity, and due to natural convection (using the buoyancy-driven mechanism afforded by gravity and the ideal gas formulation) and forced convection (due to the atmospheric wind) are presented. For the dish considered, 40–50% of the absorbed solar power was transferred to the heat transfer fluid for dish orientations from −45° to 45°, and wind speeds between 0.5 m/s and 4 m/s. This variation was mainly due to a variation in convective heat losses, with thermal radiative heat losses remaining constant at about 30%. The Nusselt numbers from the CFD simulations are compared against correlations from literature. [ABSTRACT FROM AUTHOR]

• Thermo-enviro-economic modeling of novel passive multi chamber vertical diffusion still. • East-west manually tracked unit is superior than sole south oriented unit. • Yield, exergy efficiency and performance ratio of about 11.13 kg/m2-d, 23.15% and 2.0. • Mitigation of 67.9 tons of CO 2 emission in 20 Yr life time. • Low distillate production cost of about 0.90 INR/L. Multiple-effect solar distillation units are more promising in fulfilling the potable water demands of population in rural and remote areas. Among multiple-effect distillation units, diffusion type is more compact, portable and high productive. In the present study, a novel type of passive multi-chamber vertical solar diffusion still is proposed and the impact of various system and climatic parameters on its performance and economics has been evaluated and presented. Triple chamber vertical diffusion still is found economical and it has a performance ratio and exergy efficiency of around two and 23.15%, respectively. Exposing the aperture of distillation unit to wind flow revealed a negative impact on its yield but the reverse is observed when the last condensing unit is exposed to the wind. Lower distillation and exergy efficiency is observed for 1st diffusion chamber compared to other chambers due to increased heat loss from absorber plate. Evaporative heat transfer ratio of diffusion chambers increased from 0.81 to 0.97 with increase in solar radiation intensity from 100 to 1000 W/m2. The optimized unit is simulated under the climatic conditions of various locations of Tamil Nadu state of India under sole south orientation and east-west manually tracked mode. Annual average yield of 11.13 kg/m2d is obtained with an exergy efficiency of 13.85% for east-west manually tracked unit. Distillate production cost and financial payback time of the unit are estimated to be 900.00 INR/kL and 0.63 Year, respectively. The proposed unit also has a capability to mitigate 67.93 tons (average) of CO 2 emission during its 20 Year lifetime. Better yield, low distillate production cost and huge environmental benefits justify the capability of proposed triple chamber passive vertical solar diffusion still for sustainable desalination in under privileged/developing countries. [ABSTRACT FROM AUTHOR]

• A first of its kind 1 MW concentrating solar power plant in a desert environment. • Experimental demo of the solar salt tech in parabolic trough collectors up to 550 °C. • Testing operation procedures and methods in a stand-alone plant with molten salts. • Analysis of heat losses, overall solar field performances and management issues. • Interplay between a gas-fired back-up heater and the concentrating solar field. The use of molten salt as Heat Transfer Fluid (HTF) in linear concentrators to reach temperatures >500 °C has received increasing interest in the CSP sector. So far, some experiences have been carried out on small test loops, while results obtained on larger (pre-commercial) plants have not been thoroughly published in the open literature, yet. This paper reports results obtained and lessons learned during the experimental operation of a CSP plant using Molten Salts (MS) as HTF in linear Parabolic Trough (PT) collectors. This demonstration has been carried out in the framework of the EU project MATS and refers to a stand-alone and fully-integrated 1 MWe CSP plant built in a typical desert environment in Egypt. With about 10,000 m2 mirrors' surface, the MS-PT solar field of MATS plant is the first of its kind and size. The solar field was in operation for more than 2500 h with solar salt circulation under different conditions, including start-up, draining, night circulation and solar tracking tests. The technical issues dealing with the management of a MS-PT solar field (and, in general, in linear concentrators) are discussed. Results demonstrated the reliability of the MS-PT technology for future exploitation on commercial scale plants. [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]

• High-resolution simulations are conducted to investigate convective heat exchange. • Discussion of louvers' geometric and thermal attributions on Nu is performed. • A model is presented to describe the flow between the façade and louvers. • Correlations is established to predict the averaged Nu of the façade with louvers. Exterior louver blinds are increasingly utilized to protect the building envelope from solar radiation. However, with the existing correlations from studies on a smooth flat/a surface of the bluff body, the convective heat exchange at louver blinds and the façade behind them will be underestimated and overestimated respectively. In this work, Computational Fluid Dynamic (CFD) simulations have been conducted to analyze the forced convective heat transfer at the windward façade with louver blinds, which are validated with wind-tunnel experiments. The 3D steady Reynolds-averaged Navier-Stokes (RANS) function with Low-Reynolds Number Modelling (LRNM) treatment has been employed for precision improvement. The theoretical simulations are performed for 5 louver angle φ (from 0° to 60°), 3 installing distance W (from 0.025 H to 0.08 H), 5 slat width B (from 0.02 H to 0.10 H), 8 temperature difference between the façade and blinds θ (from 1 to 7) and 5 reference wind velocity U H (from 2.56 m·s−1 to 4.27 m·s−1). It was found that the convective heat loss at the louver shows a positive correlation with the growth of φ , W and the reduction of B. Meanwhile, the convective heat loss on the façade behind is positive to B , W and negative to φ and θ. Finally, with some conversions of expressions, a group of correlations are established which can predict the surface-averaged Nu of the façade and louver blinds, of which relative errors are less than 13% compared that of simulation data. [ABSTRACT FROM AUTHOR]

• The MOSAIC H2020 project proposes an innovative solar bowl system. • The design of the receiver for the MOSAIC prototype is presented. • The choice of the helical configuration among other alternatives is discussed. • The detailed design is based on ad-hoc optical and thermal-fluid-dynamics models. • The rate of the (wall) temperature change is determined in transient operations. This paper presents the design methodology of the receiver developed within the MOSAIC H2020 project, which proposes and is now commissioning an innovative solar bowl system, also known as SRTA (Spherical Reflector Tracking Absorber), aiming at reducing the Levelized Cost Of Electricity (LCOE) with respect to the most popular Concentrated Solar Power (CSP) technologies. The solar bowl technology consists of a fixed (non-tracking) spherical mirror that concentrates the solar radiation on a receiver, which moves tracking the sun. Past investigations of this technology were limited so far, although it can potentially reduce both capital and operational costs because of the adoption of a non-tracking mirror, which imposes special attention and care in the design of the receiver. The design methodology for the MOSAIC receiver presented in the paper consists of three main steps. First, a preliminary study is performed, which results in the choice of the helical receiver configuration among other alternatives. Second, the "macroscopic" features of the chosen configuration, which define the external size of the receiver, are determined, based on an ad-hoc developed optical model, adopting the Monte-Carlo ray-tracing technique implemented in the Tonatiuh software to compute the heat flux distribution over the receiver surface. Third, and last, the "microscopic" design parameters, i.e. the absorber tubes diameter and the number of parallel threads in the helix, are optimized by means of an ad-hoc developed quasi-3D thermal-fluid-dynamic model. This model solves the 1D mass, momentum and energy balance of the coolant and the lumped heat conduction problem in the solid wall, calculating the heat losses and, consequently, the thermal performance of the receiver. Finally, an example of application of the model to the analysis of transient operation is presented: the resulting rate of change of the tube wall temperature in the case of a fast start-up determines the minimum transient duration required to avoid excessive thermal stresses on the receiver. [ABSTRACT FROM AUTHOR]

• A non-reciprocal MIR window with pyramidal micro-structures is designed. • The non-reciprocal window allows to radiate heat to outer space while suppressing the incoming heat flux. • A temperature reduction limit of 110 °C is possible under a low-transparency sky. • A temperature reduction of 10 °C can be preserved under an unfavourable weather and surroundings condition. • Use of the non-reciprocal window promises a 45% energy savings for cooling during China's summer, around 180 TWh. Passive radiative cooling has a potential impact on global energy consumption, while it is vulnerable to weather and surroundings, hindering its practical applications. Here, we present a facile pyramidal micro-structure that can be formed on a mid-infrared (MIR) window for achieving non-reciprocal propagation whereby the incoming heat flux from low-transparency atmosphere and/or surrounding high-rise buildings is suppressed without limiting the outgoing radiation from radiative coolers. In an ideal case without solar absorption, convective, and conductive heat losses, a temperature reduction limit of 110 °C is simulated even under a low-transparency sky. For an unfavorable weather and surrounding obstruction condition, the radiative cooler integrated with the non-reciprocal MIR window can still reach a 10 °C temperature reduction, while a standalone radiative cooler fails the sub-ambient cooling. The effects of non-reciprocal MIR windows on China's average temperatures in summer are estimated, roughly corresponding to a 45% energy savings for cooling, around 180 TWh. This universal strategy would remove the bottlenecks of putting passive radiative cooling into practice worldwide even if local weather and surrounding terrain conditions are undesirable. [ABSTRACT FROM AUTHOR]

• Two-part study proposing an alternative approach to realising BIPV/T facades. • Part 1 reviews theory & potential, Part 2 describes prototype realisation & testing. • Integrated Collector-Storage Solar Water Heater element reduces overheating. • Planar Liquid-Vapour Thermal Diode element reduces overnight heat losses. • Model results show that approach meets conventional performance benchmarks. Building Integrated Photovoltaic Thermal (BIPV/T) systems are promising solutions for serving local electricity and heat demands in Net Zero Energy Buildings (NZEB). Despite BIPV/T offering clear energetic and space saving advantages compared to separate BIPV and solar thermal, overheating occurs when no thermal demand exists, resulting in reduced yields, stagnation damage, and excessive fluid pressures. Whilst continuous fluid flows mitigate overheating, corresponding parasitic demands and space requirements are significant (pumps, large storage tanks or heat rejection equipment). This two-part study examines an alternative approach to BIPV/T, addressing overheating by combining BIPV and Integrated Collector-Storage Solar Water Heater (ICSSWH) concepts. Solar heating capabilities of ICSSWH collectors are well established and their overnight heat loss characteristics provide passive overheating control. BIPV-ICSSWH approaches have yet to be investigated extensively. This paper (Part 1 of 2) reviews state-of-the-art and performance benchmarks in BIPV/T and ICSSWH; proposes new performance metrics enabling fairer comparisons; and develops a heat transfer model for BIPV-ICSSWH façade elements employing Planar Liquid-Vapour Thermal Diodes (PLVTD) to regulate absorber temperatures and heat losses. Multi-day solar thermal collection, photovoltaic generation, and overnight heat retention behaviours are simulated in different climates. The modelling results (experimentally validated in Part 2 of 2) suggests BIPV-PLVTD-ICSSWHs with single transparent covers and ς ≈ 90% PLVTD diodicity achieve η T , c o l ≈ 60% solar thermal efficiency at N ≈ 0.035m2K·W−1, PV/T performance ratio PR T3 ≈ 75%, and heat loss coefficient U r,sys A sys /u ≈ 20 W·m−3K−1. The novel BIPV-PLVTD-ICSSWH approach can reduce maximum stagnation by 20 °C compared to conventional BIPV/T and therefore support NZEB realisation during global efforts to tackle the climate crisis. [ABSTRACT FROM AUTHOR]

• Two-part study proposing an alternative approach to realising BIPV/T facades. • Part 1 reviews theory & potential, Part 2 describes prototype realisation & testing. • Integrated Collector-Storage Solar Water Heater (ICSSWH) element reduces overheating. • Planar Liquid-Vapour Thermal Diode (PLVTD) element reduces overnight heat losses. • Experimental results offer BIPV-PLVTD-ICSSWH benchmarks & validate theoretical model. Building Integrated Photovoltaic Thermal (BIPV/T) systems which generate electricity and heat simultaneously are promising solutions for Net Zero Energy Buildings (NZEB). Despite BIPV/T offering clear energetic and space saving advantages compared to separate PV and solar thermal, overheating problems occur when no thermal demand exists, resulting in reduced yields, stagnation damage, and excessive fluid flow pressures. This two-part study examines an alternative approach combining BIPV, Planar Liquid-Vapour Thermal Diodes (PLVTD) and Integrated Collector-Storage Solar Water Heaters (ICSSWH) to achieve BIPV/T functionality and retain heat overnight to minimises parasitic demands and reduce overheating. The introductory paper (Part 1 of 2) established novelty and rationale for BIPV-PLVTD-ICSSWH concepts, reviewed state-of-the-art and performance benchmarks, and used theoretical modelling to predict behaviour from key design and operational parameters. This paper (Part 2 of 2) describes prototype realisation and multi-day solar simulator laboratory thermal and photovoltaic testing for covered and uncovered variants exposed to different irradiance levels. Measured solar thermal efficiencies with and without transparent covers were η T,col = 60% and 58% respectively under zero heat loss conditions whilst overnight heat loss coefficients were U r,sys A sys /u = 23.0 and 25.4 W·m–3 K−1 respectively, showing good agreement with theoretical predictions. Photovoltaic performance reduced with increasing absorber temperature as expected, although maximum power point efficiencies (η E,mpp = 11.4% at T 1 ≈ 25 °C and 5.6% at T 1 ≈ 89 °C, without cover) were lower than expected owing to partial delamination and PV cell damage. The work demonstrates practical operation of a vertical BIPV-PLVTD-ICSSWH, identifies key areas for design development, and highlights benefits of application in NZEB facades. [ABSTRACT FROM AUTHOR]

• Annual dynamic simulations of solar water heating system with and without phase change materials were conducted. • A thorough parametric study was carried out in different climate zones. • Optimization of phase change temperature and design parameters usage amount was performed. • The highest power saving rate using phase change material is 31% in Lhasa. • The highest heat loss saving rate using phase change material is 9.9% in Guangzhou. Recently there have been many reports on the application of phase change materials (PCM) in solar water heating system (SWHS). However, there are some doubts and different views in this field, since the sensitivity of the system to the PCM design parameters and external conditions. In this study, a typical SWHS with a PCM storage tank is proposed to overcome the existing problems. The mathematical model is established and validated against experimental data. Annual simulations have been done under a typical user load and different PCM design parameters (phase change temperature, PCM usage amount) among six cities which have different meteorological conditions. The results indicate that the application of PCM in SWHS can reduce the power consumption of electric auxiliary heater (EAH) and the heat loss, but the benefits vary widely by regions and PCM design parameters. The highest power saving rate is up to 31% in Lhasa which has extremely abundant solar energy, while for the heat loss saving rate the highest value is 9.9% in Guangzhou which is located in the hot summer and warm winter zone. Besides, a parametric study has been conducted to explore the power saving potentials with different PCM design parameters in different regions, as well as to discuss the optimal phase change temperature and the PCM usage amount. This study aims to provide theoretical references and suggestions for the design of the PCM storage tank in SWHS. [ABSTRACT FROM AUTHOR]

• A model for evaluating both shading and power generation effects of PV roof was proposed. • The comprehensive energy saving effects of shading and power generation was investigated. • The application of PV roofs in 13 respective cities of China was studied and analyzed. The photovoltaic (PV) roofs have two main energy-saving effects, which are shading and power supply. Considering the shading and power generation gain jointly, a roof is changed from the building energy end to the building energy supply end, thus changing its energy use system greatly. Therefore, this paper carries out research on the comprehensive energy-saving effect integrating the shading and the power supply gain. Three types of PV rooftops, namely, horizontally-mounted overhead PV rooftop, tilted overhead PV rooftop, and attached PV rooftop are studied to explore their impacts on the heat gain and heat loss of the roof and building's heating and cooling load. In order to estimate the overall energy-saving in different climatic regions in China, an overall energy-saving evaluation method that considers the power generation and shading benefit effects of the PV rooftop is proposed. Based on the climate and solar radiation zones in China, 13 respective cities are selected to be included in the research. The results show that, by considering only the shading effect of PV panels, the tilted PV is more suitable in summer, reducing the heat input, whereas the horizontally-mounted PV is more effective in winter to prevent more heat loss. Regarding the overall energy-saving that considers both the shading and power generation effects of PV panels, building with horizontally-mounted PV rooftop has the highest efficiency in the summer season, while the building with tilted PV rooftop has the highest efficiency in the winter season. The model and analysis of the overall energy-saving presented in this work can provide a guide for the application of rooftop solar PV panels in different climate zones in China. [ABSTRACT FROM AUTHOR]

• Thermal modeling of PVT-CPC integrated active conical solar still has been presented. • Experimental validation of passive solar still with conical condensing cover has been carried out. • Energy and exergy analysis of PVT-CPC and PVT-FPC active conical solar stills. In this work, an analytical expressions of various temperatures namely, water and condensing cover temperatures, yield and electrical power output of PVT-CPC active solar distillation system have been derived. These expressions depend on basic energy balance equations of the proposed system. Effect of inclination of condensing cover (θ), packing factor (β c) and mass flow rate (m ̇ f) on hourly yield have been studied in brief in terms of overall thermal energy and exergy. The present thermal model for passive conical solar still has also been validated with the experimental results of Gad et al. (2015) for a given design parameters. Special cases of the proposed system have also been carried out. It has been found that the yield increases with an increase in inclination of conical shape of condensing cover for a given mass flow rate due to an increase in heat losses from condensing cover to the ambient air. Further, the yield also increases with the decrease in packing factor for a given mass flow rate as per our expectation. [ABSTRACT FROM AUTHOR]

• A new type of high-performance aerogel foamed concrete was prepared. • The delay time of aerogel foamed concrete is twice of polystyrene or concrete. • The heat loss of aerogel foamed concrete was ~1/3 of concrete. A new type of high-performance aerogel foamed concrete was prepared by using aerogel powder as filling material and chopped glass fiber as reinforcement. By using the aerogel foamed concrete and the other materials (viz. ordinary concrete and EPS) as the insulation, an insulted box was carried out on the thermal performance under a constant outside temperature of 35℃ and initial inside temperature of 25℃. The results indicate that when inside temperature increased to 90% of the stable 35℃, the required time for the aerogel foamed concrete was prolonged to 9 h compared to 5 and 4.5 h for EPS and ordinary concrete. Meanwhile, a 3R2C heat transfer model was established for the insulated box, whose calculated results agreed well with the experimental. By using the model, the predicted time lag of the aerogel foamed concrete insulation box is twice as long as that of the EPS or ordinary concrete box. The heat loss in 48 h of the aerogel foamed insulating concrete box was 59.79 J, approximately 1/3 of that from the ordinary concrete box. The results indicate that the aerogel foamed concrete has better thermal insulating performance from solar radiation or extremely hot weather for applications in low and zero energy buildings. [ABSTRACT FROM AUTHOR]

• An experimental study on particle to air heat exchanger (PAHX) is presented. • Excessive heat loss was found between the lower part of the PAHX and the concrete platform. • Results show that the particle velocity has a big effect on heat transfer coefficient. • Current tubes shape is enhancing the particulate sliding at the tubes sides. The paper presents an experimental study of the heat characteristics of the bulk flow of red sand over diamond-shaped tubes in a particle-to-air heat exchanger (PAHX). The objective of this work is to demonstrate the suitability of solid particles as a working medium in applications such as concentrating solar power (CSP). The tests are conducted at the experimental central receiver facility at King Saud University in Riyadh, Saudi Arabia. The PAHX is a custom-made heat exchanger in which the particle flow rate can be controlled by a slide gate at the bottom. A custom-made (100 kW e) microturbine is used to heat the particles inside the PAHX as they are circulated inside a tower by a lifting system. Experiments are conducted to investigate the effect of the particle flow rate (particle velocity) on the heat transfer coefficient on the sand side. The results show that the particle velocity strongly affects h sand. Increasing the sand velocity by less than 20% can cause an increase of more than 100% in h sand. The maximum h sand value of 84 W/m2·°C is obtained at the maximum particle velocity of 0.71 mm/s. However, this value is expected to increase when slightly smaller particles with more uniform shapes are used. [ABSTRACT FROM AUTHOR]

• PCM and insulation component are used to improve thermal performance of Trombe wall. • Effects of design parameters of insulation component are studied using the validated model. • Design approach of heat preservation at night of a TW-PCM is proposed. • Thermal comfort is analyzed based on operative temperature and radiant temperature asymmetry. A classical Trombe wall cannot satisfy the thermal comfort for the whole day due to the limited heat storage capacity and large heat loss at night. In present work, phase change materials and an external insulation component are used to improve thermal performance of a Trombe wall. The design approach of heat preservation at night is first obtained. An unsteady heat transfer model of a Trombe wall with phase change materials under heat preservation condition in the nighttime is established by MATLAB. The reliability of the mathematical model is validated by an experiment in Yuzhong (Gansu, China). With this model, the effects of the design parameters of the external insulation component on the thermal performance are analyzed. Finally, the indoor thermal comfort of a passive solar room is analyzed based on the experimental data. The results indicate that, it has a significant impact of the thermal conduction resistance of the insulation component and the thermal resistance of the closed air cavity. For closed air cavity, the internal surface emissivity of the insulation component plays an important role. The optimized additional thermal resistance for the external insulation component is 2 m2⋅°C⋅W−1, and the corresponding maximum thermal resistance of the closed air cavity is determined as about 0.5 m2⋅°C⋅W−1. Compared with no heat preservation at night, the operative temperature improves significantly, and the radiant temperature asymmetries of two massive walls are similar. The investigation can provide a design approach of heat preservation at night for a Trombe wall. [ABSTRACT FROM AUTHOR]

• Experimental study of heat dynamic of ASCs in field conditions. • Assessment of two different glazing strategies: with glazing and without glazing. • Evaluate heat dynamic of unglazed and glazed ASC when solar irradiation is negligible. • Energy analysis of ASCs with glazing and no glazing. Exposure to solar irradiation for an extended period during a day causes asphalt pavements can reach to a considerable temperature. Consequently, they can be converted into an affordable solar collector by harvesting thermal energy. In recent years much effort and time have been devoted to improving the thermal performance of solar collectors. To this aim, the glazing strategy is a promising technique. The glass covers results in the reduction of heat loss and protecting the asphalt surface (absorber surface) from the outside environment. Little attention has been given to the glazing strategy in improving the performance of ASCs. The chief aim of the current investigation is a comparative assessment of the performance and heat dynamics of unglazed asphalt solar collectors with glazed asphalt solar collectors under field conditions. The evaluation was carried out using an experimental test-setup composed of an asphalt solar collector with a surface area of 1.2 m2 and a pipe network length of 12 m. Various sensors were utilized to monitor and measure the key parameters such as ambient conditions and working fluid temperature during the experimental runs. The experimental results prove that the glazing strategy is an effective method to improve the performance of ASCs. The constructed glazed ASC increases hot water temperature, meanly around 5 °C, and pavement temperature, meanly around 20 °C, while represents an improvement in the performance, near 10%, compared with the unglazed one. [ABSTRACT FROM AUTHOR]

• A novel straight-through all-glass evacuated tube collector. • High-quality borosilicate glass tube with good mechanical stability. • Better heat transfer properties than a Dewar-tube type ETC. A straight-through all-glass evacuated tube collector (ETC) made of high-quality borosilicate glass was developed for large-scale low and medium temperature solar hot water systems. It consists of an inner and outer tube without a free end and was shown to be mechanically stable with a thermal expansion coefficient of (3.3 ± 0.1) × 10−6 K−1. Due to turbulent conditions in the straight-through all-glass tube, a higher heat transfer rate could be achieved than in a Dewar-tube ETC, leading to increased heat extraction and decreased heat losses. The photo-thermal efficiency was improved, indicating that a straight-through tube could be more cost-effective. At the same time, active flow in the tube can result in a better water quality as the accumulation time in the tube was short. [ABSTRACT FROM AUTHOR]

• Gradient structure demonstrates an enhanced capillary effect. • Gradient structure can hinder water flow and inhibit heat convection loss. • An evaporation efficiency of 93.4% is achieved under 1 sun illumination. • Template method (Teflon-glass) is used to prepare gradient structured hydrogel. • Microgels are attracted by the Teflon plate showing gradient distribution. Solar interfacial evaporation is a promising way to generate clean water from seawater using clean, abundant, and sustainable solar energy. However, non-directionally moving water with high thermal conductivity acts inevitably as a medium for heat transfer from the surface to the bottom through heat convection, resulting in low energy efficiency and a low evaporation rate. Herein, a gradient structured composite hydrogel combining a desired functional differentiation is reported. The network sizes in the hydrogel continuously change, demonstrating an enhanced capillary effect and a direction-limited water supply capability, inhibiting the heat convection loss. In addition, the reported gradient hydrogel shows broadband light absorption, satisfactory mechanical properties under a saturated swelling state, an unusually higher water evaporation rate for brine compared with that for pure water, and an inherent ability to evaporate under both 1 sun illumination and dark environment. The proposed gradient channels to restrict the flow direction of liquid, and consequently the heat convection loss, will have an significant impact on the design of other efficient photothermal evaporation systems and even the field of mass and heat transfer. [ABSTRACT FROM AUTHOR]

• A novel external pressurized air receiver concept is presented. • Solar-thermal efficiency exceeding 80% modeled. • Radiative heat loss reduced through design. • Metallic pressurized air receiver that can withstand high solar flux. • Low pressure drop suggests suitability for integration Brayton Cycle. Combined cycle concentrating solar power (CSP) plants provide significant potential to achieve an efficiency increase and an electricity cost reduction compared to current single-cycle plants. A combined cycle CSP system requires a receiver technology capable of effectively transferring heat from concentrated solar irradiation to a pressurized air stream in a gas turbine. The novel spiky central receiver air pre-heater (SCRAP) technology is proposed to overcome barriers experienced to date. The SCRAP receiver is a novel metallic receiver technology aimed at pre-heating an air stream to about 800 °C, either prior to a combustion chamber or alternatively prior to a cascaded secondary non-metallic receiver system, capable of achieving elevated temperatures. A ray-tracing analysis demonstrated that the flux imposed on the absorber assemblies is dependent on the heliostat size. A thermodynamic computer model was developed to investigate the performance characteristics of the absorber assemblies (spikes) of the SCRAP receiver. The model was validated against an experimental test setup. Satisfactory agreement at various air flow rates was obtained. The thermal efficiency of the spikes was investigated and used to approximate the receiver's solar-thermal efficiency. The receiver is predicted to perform at solar-thermal efficiencies exceeding 80%. The geometric design of the receiver achieves a relatively low radiative heat loss, predicted at about 4–5%. A relatively large vulnerability to convective heat losses was identified. The pressure loss was found to be relatively low, compared to existing alternative receiver designs, with system pressure losses below 40 mbar achievable. [ABSTRACT FROM AUTHOR]