Abstract To improve the comprehensive performance of the solar photovoltaic-thermal (PV/T) integrated system and address the issue of reduced conversion efficiency caused by increased PV temperature, this study establishes a three-dimensional transient model of a PV/T-phase change material (PCM) system with bionic fractal fins. Paraffin RT-42 (phase change temperature: 311–316 K) is selected as the PCM, and computational fluid dynamics (CFD) is employed to systematically investigate the effects of the presence or absence of PCM, fin structure, solar radiation intensity, and cooling water flowrate on system performance. The results show that the integration of PV/T and PCM significantly enhances the temperature uniformity of the PV, reducing the maximum temperature difference from 6 °C to 4 °C. Compared with the PV/T system, the thermal efficiency is improved by 24.82% and the electrical efficiency by approximately 5%. The bionic fractal fins outperform traditional straight fins in heat transfer enhancement by increasing the heat exchange area and constructing a multipath heat transfer network. When the solar radiation intensity increases from 600 W/m2 to 1000 W/m2, the system's thermal efficiency rises from 54.96% to 80.36%, while the electrical efficiency decreases from 14.38% to 13.39% due to PV temperature increase. The cooling water flowrate has a significant effect on system temperature regulation: at a flowrate of 0.1 m/s, the average PV temperature is 9.22 K lower than that at 0.01 m/s, and the electrical efficiency is improved by 5.2%. Thus, optimizing the thermal and electrical efficiency of the system can be achieved by adjusting the flowrate. This research provides a new technical path and theoretical support for improving the performance of PV/T systems.

Abstract This study proposes a combined thermal cycle by a Helium Brayton cycle at high temperatures (800–850 °C) on top of a water Rankine cycle. Thanks to its high thermal conductivity, helium is also an excellent heat transfer fluid, so that jet impingement heat transfer and enhancement can obtain high energy efficiency at solar receivers. NaCl is considered a phase change material (PCM) to meet the requirement of thermal storage, due to its suitable melting point of 801 °C, cost-effectiveness, and great reserves in nature. The studies focus on thermodynamic analysis of the power systems to obtain maximum energy conversion efficiency through optimizing system combinations and parameters of the power cycles. The studied systems with combined power cycles include: (1) simple Brayton and simple Rankine (SBSR) cycles, (2) reheated Brayton and simple Rankine cycles (RBSR), (3) reheated Brayton and reheated Rankine cycles (RBRR), (4) reheated Brayton and reheated Rankine cycle with precooling in front of gas compressor (RBRR + P), and (5) reheated Brayton and reheated Rankine cycles with recuperation in Brayton cycle (RBRR + RE). The results demonstrate that the combined system of the helium Brayton cycle and water Rankine cycle can attain a thermal efficiency in the range of 42% to 50% when the supplied helium gas temperature and pressure approach 800 °C and 8 MPa, respectively.

Abstract Solar thermoelectric generators (STEGs) integrating phase change materials (PCMs) have attracted increasing attention in the past few years. However, the study of synergistic effects of heat transfer of PCM and cooling condition of heat sink on thermoelectric generator (TEG) performance is not sufficiently in-depth. This study improves the fins arrangement in phase change energy storage devices through simulation and experiments to enhance heat transfer, while also considering the influence of a PCM container material. Additionally, we compared the effects of TEG numbers and cooling conditions on system efficiency. The results indicate that the parallel arrangement of heat-conducting fins in the phase change heat storage container can completely melt PCM within half an hour, while the S-shape arrangement still remains 20% and has not melted under the same conditions. On this basis, when the solar radiation intensity is 1.6 W/cm2, PCM-STEG with six TEGs can obtain 1895 J of electrical energy under water-cooling conditions at a temperature of 30 °C and a flowrate of 25 mL/min.

Abstract Solar energy is a prominent renewable energy source, with photovoltaic (PV) systems offering sustainable solutions. However, the efficiency of PV panels declines with rising temperatures. This study tackles this limitation by integrating a hybrid composite phase change material (CPCM) made of LiNO3-NaNO3-NaCl and coral beach sand (8:2 ratio) with a PV system for real-time thermal energy storage. Heat capture is facilitated by a 12.7 mm copper pipe beneath the PV panel, with water circulating at 2.4 l/min. The thermophysical properties of the CPCM were analyzed using X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and thermogravimetric analysis, focusing on phase transitions and melting-solidification behavior. Results showed an 8 °C reduction in PV panel temperature, increasing power output from 22.3 W (standard panel) to 24.8 W. The CPCM achieved a thermal energy storage capacity of 30 kJ and a maximum temperature of 63.6 °C. This enhanced the electrical efficiency of the PV system by 1.2%, yielding an overall efficiency of 12%, while thermal efficiency reached 70%. The exergy efficiency also improved by 1.5%, achieving 9.2% compared to the standard panel. These findings underscore the CPCM's potential to enhance the performance of PV systems by simultaneously improving thermal management and energy efficiency.

Abstract This study focuses on experimentally investigating the performance of two generations of internal helically ribbed tubes during single-phase heat transfer of water inside the tube, where boiling or condensation of refrigerant occurs outside the tube. The design parameters of the two generations of enhanced tubes include differences in internal helical rib height, helix angle, number of ribs per turn, and rib base thickness. This includes a smooth tube (Tube-1) as well as Tube-2 through Tube-8 representing the first generation of internal helically ribbed tubes from the 1990s, and Tube-9 through Tube-19 representing the second generation of internal helically ribbed tubes that are in widespread use now. With the maturity of tube manufacturing processes, the number of ribs per turn and the helix angle of the second generation of internal helically ribbed tubes have been increased. This helps in increasing the tube's heat transfer area and enhancing the turbulence intensity of the fluid. The increase in the number of ribs per turn also disrupts the development of the fluid boundary layer, reducing its thickness, thereby reducing its thermal resistance and further improving the heat transfer rate. Furthermore, based on previous single-phase empirical correlations, a novel heat transfer correlation capable of predicting the heat transfer factor of the 18 tested tubes with an uncertainty ranging from −20% to 20% has been successfully fitted to the experimental data. Results of this research should provide a reliable body of data for optimized design of heat exchangers used in a variety of industries and especially in high-temperature solar energy applications.

Abstract Recent studies show that solar air heaters (SAHs) with artificial roughness significantly outperform conventional designs with only minor modifications. In this study, the absorber plate of SAH is modified with a rib-fin roughness profile due to its high potential to induce turbulence in the airflow. This 2-dimensional numerical analysis investigates fluid flow, heat transfer characteristics, and entropy generation per unit volume. The Reynolds number (Re) is varied from 4000 to 18,000, while the relative roughness pitch (P/e) is considered at three values: 8, 10, and 12. The governing equations are solved using the finite volume method and the renormalization group (RNG) k–ε model. The thermo-hydraulic performance parameter (THPP) is calculated using the average Nusselt number (Nu) wand friction factor (f), while total entropy generation per unit volume is determined using entropy generation due to friction and entropy generation due to heat transfer, helping to achieve an optimal solar air heater design. For the current rib-fin solar air heater, the maximum THPP is found to be 1.67, and the minimum entropy generation is 0.01605 W/m3 K. Correlations for the Nu and f are developed as functions of the Re and relative roughness pitch (P/e).

Abstract This study explores the use of solar energy to drive a novel multigeneration system that includes, power, heating, cooling, and hydrogen production. The proposed system undergoes a thorough evaluation from three essential perspectives: Energy, Exergy, and Economics. Unlike previous studies, in the proposed system, Ammonia-LiNO3 operated absorption refrigeration cycle is integrated with the Steam Rankine cycle (SRC), organic Rankine cycle (ORC), and proton exchange membrane (PEM) electrolyzer. The influence of climatic conditions; solar flux and ambient temperature is examined on exergy efficiency of sub-systems and the overall system. The system yields a net power generation of 640 kW, a cooling production rate of 425 kW, heating output of 4190 kW, and a hydrogen production rate of 160 kg/hr. These outcomes of sub-systems are associated with cost rate of 6.20 $/hr and pay-back period of 6.02 years at the baseline operation. The proposed multigeneration system achieved energy and exergy efficiencies of 23.31% and 6.25%. The solar flux experiences a positive effect on electricity generation and rate of hydrogen production. The exergy efficiency of sub-systems producing hydrogen, cooling, heating, and elec-tricity generation is obtained as 66.25%, 34.5%, 29.3%, and 69%, respectively, at ambient temperature of 25°C. The exergy efficiency of overall system increases approximately by 65% with increase of ambient temperature from 5 to 40°. Exergy analysis determined tower-solar collector responsible for highest destruction of solar exergy (47.34%), although main energy loss occurs in multigeneration system. The proposed system appears to be superi-or to conventional solar-based multi-carrier energy systems from exergy perspective.

Abstract It is important to analyze the variables influencing the performance of the solar chimney power plant (SCPP) according to output power as well as efficiency. The most important of these variables is the geometric dimensions, solar radiation intensity, and ambient temperature. In this experimental and numerical study, a prototype with variable dimensions was manufactured. A theoretical study was presented by creating a numerical model that helps in analyzing the governing equations, such as the continuity, momentum, and energy equations, in addition to the turbulence model equations (k–ε). The calculations show the influence of chimney height, diameter, solar collector diameter, inlet collector gap, temperature, and solar radiation on the SCPP performance. These variables were also tested experimentally, and the effect of each variable on the efficiency and output power was demonstrated. The maximum velocity was at the turbine exit, about 18.5 m/s in the case of the Spanish model, while it was 2.2 m/s for the present prototype. The maximum temperature value was 333 K for the Spanish model at a collector radius ratio of 3. The maximum output power was 156 mW for the Spanish model. For the current prototype, the maximum airflow temperature was 67 °C when the chimney height was 3 m; by decreasing the chimney height to 2.5 and 2 m, the maximum temperature decreased to 63 and 54 °C, respectively, which are about 6.5% and 19% deterioration. The results show that the relationship between the output power and any of the geometric dimensions is direct. The overall efficiency relationship is direct with the height and diameter of the chimney and inverse with the diameter of the collector and the height of the collector entrance. The output power rises with increasing solar radiation and slightly drops with increasing ambient temperature. The reliability of the numerical solution was verified by comparing the numerical and experimental results, as well as the data of the Spanish model. The agreement was satisfactory, with the mean percentage error (MPE) not exceeding 1.5% for all performance parameters.

Abstract Photovoltaic (PV) systems convert solar energy into electricity with about 20% efficiency, while the remaining 80% dissipates as heat, reducing performance. Maintaining PV cells near 25 °C is crucial to avoid efficiency losses. This study explores a novel passive cooling design, photovoltaic perforated wavy-shape fins (PV-PWSFs), using ansys fluent simulations under solar irradiance (400–1000 W/m2) and airflow speeds (0.5–2.5 m/s). The PV-PWSFs system significantly reduced average PV temperatures, cooling them to 57.8 °C at 1000 W/m2, compared to 64.5 °C for photovoltaic perforated straight-shape fins (PV-PSSFs) and 83.3 °C without fins. At higher airflow speeds, the system achieved even lower temperatures, reaching 47.7 °C at 2.5 m/s. This cooling enhanced PV efficiency to 12.79% and boosted power output by 15.6% at 1000 W/m2. The wavy fins increased heat dissipation by enlarging the surface area and promoting turbulent airflow for improved convective cooling. Perforations facilitated better airflow distribution, reducing hotspots and ensuring uniform panel temperatures. Additionally, the study also analyzed the effects of fin wavelength and amplitude on performance. A wavelength of 10 cm and an amplitude of 1.5 cm provided optimal cooling by balancing heat transfer enhancement and flow resistance. These findings demonstrate that the PV-PWSF design effectively reduces operating temperatures, enhancing both the performance and lifespan of PV systems.

Abstract It is widely known that photovoltaic technology has been massively distributed over the last decade despite its low-efficiency ratio. Dust deposition reduces this efficiency even more lowering the energy production and reducing module performance. In this work, we developed an artificial vision algorithm based on CIELAB color space to identify dust over panels in an automatic way. The proposed algorithm uses a series of images of soiled panels and creates a simulation with a known soiling coefficient to compare with the real ones. All the images were taken directly by drones or cellphone cameras. The results prove satisfactory with a maximum error of approximately 4.14% with respect to visual inspection and a resolution of 4.4%. The algorithm is independent of training and uses the soiling over the panel to create the simulation so that it could be valid at any location.