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[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]

• 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]

• 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]

• 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]

• 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]

• 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]

• 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]

• 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]

• Single and two-phase flow model is developed for thermal performance of ETC. • The investigation is based on average data for varying seasonal conditions. • Overview of the applicability of solar collector for the location of Silchar. • Outlet temperature, overall heat loss coefficient etc are analysed. • Low mass flow rate favours the formation of vapor in the solar collector. The standard condition for evaluation of solar heating system considers solar insolation of 1000 W/m2 which provides a good estimation of the performance of the system, but not able to predict a realistic situation due to the fluctuating behaviour of solar insolation. Therefore, an attempt is made to simulate a practical condition for a solar heating system by varying solar radiation throughout the day as well as months of a year. Hourly solar insolation data are collected from web-based resource PVGIS for the region of Silchar, a north-eastern location in India. The results revealed that the temperature profile of the working fluid in the Evacuated Tube Collector is non-linear and the rise in temperature is more in the months of November-March than April-October. The outlet temperature is highest for the month of February and lowest in June which signifies that the system can be practically applicable in this region for water heating purpose, as it produces a higher temperature in winter days. Also, the daily analysis shows the efficiency of the system is very low during the morning and evening hours. Moreover, there is a possibility of obtaining a two-phase flow in the outer pipe under certain circumstances and this production of vapour is accompanied by a reduction in efficiency. The analysis shows that with radiation being fixed, inlet temperature and mass flow rate are the most dominant factors for two-phase flow. Present model also suggests an optimum mass flow rate beyond which the flow becomes two-phase and not desirable. [ABSTRACT FROM AUTHOR]

• Performance of DPSAH with two air passages has been experimentally investigated at Mosul city/Iraq. • Installing aluminum fins to the absorbing plate for improving the heater efficiency. • A comparison between natural and forced air circulation processes has been performed. • A better thermal performance can be achieved when DPSAH is operated under natural convection case. • Optimal system performance has been obtained in March around 1 PM for both cases. This work involves an experimental study on a trapezoidal Double-Pass Solar Air Heater (DPSAH) to analyse its performance under natural and forced convection cases for the purpose of comparison. The experiments have been conducted in winter and compared for each case in same time and weather conditions. The collector has been carefully designed and constructed to prevent as possible the heat losses. A uniform fins have been fixed on both sides of the absorber plate to enhance the heat exchange rate. Effects of solar radiation and air mass flowrate on DPSAH performance have been investigated. The results show that DPSAH produces higher efficiency when the system is operated under natural convection case in comparison to forced convection case. The maximum efficiency has been found equal to 73.5% and 65% for natural and forced convection, respectively. A significant temperature difference has been obtained under natural convection case compared to forced convection. The results confirmed that DPSAH with adding fins leads to considerable performance improvement compared to conventional DPSAH due to enhance the absorbing solar energy caused by increasing surface area. The increasing in air mass flowrate has inverse influence on the performance of DPSAH. For natural circulation case, the outlet, plate and glass temperatures have been always observed higher than the forced convection case. It is evident that type of heat transfer has considerably affect the system performance and consequently, the selection of air circulation process are required to be satisfactorily chosen according to the application to achieve the desired objective. [ABSTRACT FROM AUTHOR]

Parabolic trough is the most extended solar thermoelectric technology. Solar radiation is converted into heat and transferred to the heat transfer fluid in the solar receiver tubes. The thermal energy obtained feeds a conventional Rankine power cycle. The performance of the receiver tube can be broken down into three single components: the optical transmittance of the outer glass envelope or capability in transmitting the radiant energy; the optical absorptance of the metal tube or capability to absorb the radiation; and heat losses of the tube or capability to retain the heat which depends of inner tube coating emissivity and the vacuum between both tubes. In this paper a novel test bench implementing both thermal and optical measurement systems is described and compared with other systems referred in the literature. The results obtained from the evaluation of three different solar receivers with different diameters are presented. Optical measurements of transmittance and absorptance parameters are carried out in the wavelength range of 300–2500 nm. Optical evaluation of trough receivers at operating temperatures up to 450 °C is feasible. The receivers can be heated using a high intensity electric current flowing through the internal tube. Uniform Joule heating results a reliable heat losses measurement method at temperatures up to 650 °C. [ABSTRACT FROM AUTHOR]

The design lifetime of parabolic trough receivers is at least 25 years. However, depending on the specific operating conditions, this expected lifetime may be shortened. A periodic inspection of receivers mounted in a solar field is thus recommended. Several field methods with distinct depth of information and field throughput exist to estimate receiver thermal performance. This paper gives an overview of these field methods and presents the application of a transient infrared thermography method, which combines dynamic temperature measurements with a numerical heat transfer model in order to derive specific receiver heat losses and separate internal heat loss mechanisms. This method has been previously investigated under laboratory test conditions and is here applied under field test conditions for in-situ thermal measurements on mounted receivers. The transient thermography method allows a correct estimation of specific heat losses within a precision range below ±10% for all tested receivers under field test conditions. Relevant separation of heat loss mechanisms could be derived for evacuated PTRs with solar selective absorber coating, while partially biased diagnoses could be observed for partially or non-evacuated PTRs with highly emissive absorber coatings. Active thermography is considered as a relevant tool for receiver field inspection, in combination with a complementary field screening measurement technique. [ABSTRACT FROM AUTHOR]

Non-imaging collectors are of great interest to supply thermal energy for domestic and industrial applications at temperatures of 60–300 °C for their configuration of non-tracking of sun and wide range acceptance angle. In particular, cylindrical CPC with tubular absorber have attractive properties such as all side illuminating absorber and eliminating the back side heat losses. Due to steep angle at the end of reflector, CPCs tolerate truncations without any significant reduction on the performance. On the other hand, non-uniform temperature distribution around the absorber may cause undesirable temperature gradient and causes hot spot presence in which very intense solar radiation occurs. It is particularly important for solar concentrator hybrid with photovoltaic system. Non-uniform distribution of the solar irradiation on the PV cell surface results in uneven current distribution that reduces the electric output. In order to reduce the presence of hot spots on the receiver area, a cylindrical CPC was evaluated for different truncation level. The optical and thermal efficiency of the concentrator were evaluated to determine the optimum truncation levels. A detail analysis was carried out for average efficiency as function of incident angle and annual performance for different absorber surfaces such as gray and selective surface. In order to decide the uniformity of the solar illumination on the absorber, the heat flux and temperature distribution on the absorber were evaluated. The truncation was the most effective on the incident angle of 20°. The peak values of the heat flux distribution were selected to see clearly the intense heat flux reduction by truncation. In the case of 50% truncation, the maximum heat flux decreases by half as the average thermal efficiency decreases only by 2%. On the other hand, the annual performance of 50% truncated CPC having selective surface increases by 5% due to the improved acceptance angle. Moreover, different absorber materials including stainless steel, aluminum and copper were considered and the temperature uniformity was evaluated for the incident angles in which the most intense heat flux occurred. The stainless steel absorber showed the maximum difference on the surface temperatures of about 3.5 K. On the other hand, for the case of the concentrator having copper absorber with 50% truncated reflector, the surface temperature was almost uniform with less component cost, and with only slight reduction on the thermal performance. [ABSTRACT FROM AUTHOR]