Solar Thermal Performance Research Articles

A comprehensive numerical investigation of bi-dimensional analysis of PVT system using square channel absorber

Abstract This paper offers a comprehensive numerical investigation of PVT solar thermal performance using the Finite Difference Method (FDM) for both longitudinal bi-dimensional transient and steady state analysis, which is the unique aspect of this study. Likewise, a thorough analysis of the use of two distinct cooling absorber PVT solar collectors is conducted under realistic climatic conditions. The current modeling methodology can be considered a useful tool that enables rapid bi-dimensional PVT system analysis. The findings show that, in comparison to the PVT tube configuration (587 kWh/m2, 178 kWh/m2), the direct flow square channel has more yearly thermal and electrical gain outputs (608 kWh/m2, 196 kWh/m2). Furthermore, the design of directly flow channels has the advantages of easier integration and effective conduction heat transfer between the fluid and absorber panel. A good agreement between the measured and predicted data was obtained once the current results were compared with theoretical and experimental data in the literature. 

Honeycomb Cell Structures Formed in Drop-Casting CNT Films for Highly Efficient Solar Absorber Applications.

This study investigates the process of using multi-walled carbon nanotube (MWCNT) coatings to enhance lamp heating temperatures for solar thermal absorption applications. The primary focus is studying the effects of the self-organized honeycomb structures of CNTs formed on silicon substrates on different cell area ratios (CARs). The drop-casting process was used to develop honeycomb-structured MWCNT-coated absorbers with varying CAR values ranging from ~60% to 17%. The optical properties were investigated within the visible (400-800 nm) and near-infrared (934-1651 nm) wavelength ranges. Although fully coated MWCNT absorbers showed the lowest reflectance, honeycomb structures with a ~17% CAR achieved high-temperature absorption. These structures maintained 8.4% reflectance at 550 nm, but their infrared reflection dramatically increased to 80.5% at 1321 nm. The solar thermal performance was assessed throughout a range of irradiance intensities, from 0.04 W/cm2 to 0.39 W/cm2. The honeycomb structure with a ~17% CAR value consistently performed better than the other structures by reaching the highest absorption temperatures (ranging from 52.5 °C to 285.5 °C) across all measured intensities. A direct correlation was observed between the reflection ratio (visible: 550 nm/infrared: 1321 nm) and the temperature absorption efficiency, where lower reflection ratios were associated with higher temperature absorption. This study highlights the significant potential for the large-scale production of cost-effective solar thermal absorbers through the application of optimized honeycomb-structured absorbers coated with MWCNTs. These contributions enhance solar energy efficiency for applications in water heating and purification, thereby promoting sustainable development.

Double-layered phase change material microcapsules with enhanced solar thermal conversion performance and fire safety for buildings

Building energy saving is directly related to resource utilization optimization and residential comfort, which is important for the environment and production. At present, building energy saving is developing towards green, recyclable, and low-risk directions. Phase change materials, as effective energy storage materials, can pollution-freely regulate room temperature. Regarding the leakage, phase change materials are encapsulated into microcapsules. However, the flammability and slow thermal response of phase change material microcapsules hinder their application in building materials. Herein, novel double-layered phase change material microcapsules (D-MPCMs), with the inner poly melamine tetramethylene phosphonium sulfate (PMTMPS) shell layers and outer polydopamine (PDA) shell layers, are prepared by in-situ polymerization method, which are filled into epoxy resin (EP) coatings. This study is the first to use cross-linked flame retardants as the shells of microcapsules. The outer PDA shell layer improves the flame retardancy of microcapsules while overcoming the problem of slow thermal response rate. Thermogravimetric analysis and differential scanning calorimeter tests are considered to explore the thermal stabilities and properties of the resultant microcapsules. Results demonstrate that D-MPCMs have a residual mass of 10.8 % more at 600 ℃ and a faster thermal response rate. The study shows that the addition of the PDA shell layers not only reduces the total heat release from 64.29 MJ/m2 to 45.01 MJ/m2 but also enhances the solar thermal conversion performance which gives potential in the process solar energy storage design and fire safety design in actual building application of epoxy resin coatings.

Analysis of ultra-high concentration solar cells integrated with a confined microjet impingement cooling

The high solar concentration levels result in an intense influx of energy onto the concentrated triple-junction solar cell, leading to elevated temperatures that can degrade the cell’s performance and overall lifespan. This necessitates the development of innovative and efficient cooling strategies to mitigate temperature-induced losses and ensure optimal energy conversion. This study introduces an innovative micro jet impingement cooling system designed for ultrahigh concentrated solar cells, addressing the critical challenge of temperature management under high solar concentration levels. Furthermore, structural modifications were proposed, including reducing ceramic layer thickness to decrease the thermal resistance and using thermal interface materials to improve the cell temperature uniformity. A three-dimensional computational fluid dynamics model was developed to evaluate the proposed system’s performance and compare it with the traditional jet impingement heat sink. The model was verified and validated using empirical data in the literature. In addition, the Response Surface Method was employed to provide a comprehensive understanding of the system’s behavior under various weather conditions and cooling fluid effects. The results showed that concentration ratio and direct normal irradiance significantly affect the system’s performance. Moreover, the new cooling system maintains temperatures below the recommended operating temperature. Finally, the environmental assessment indicated substantial energy payback time reductions at 20,000 Suns, which is significantly lower than at 1000 Suns. The CO2 emissions analysis shows a marked potential for emissions mitigation, particularly at higher CRs and longer sunshine hours. These insights offer a comprehensive overview of ultrahigh concentrated solar cell thermal system performance, highlighting its efficiency and environmental sustainability in solar energy applications.

Ultrablack surface with omnidirectional high absorption.

Black surface plays an important role in solar-thermal conversion systems and space optical systems. Despite the significant efforts in developing a black surface with strong broadband absorption, realizing scalable omnidirectional high absorption ultrablack surfaces remains challenging. Here, we report an ultrablack surface based on a structural black paint (SBP), realized by femtosecond (fs) laser fabrication of high aspect ratio microstructure mold followed by mold transferring on black paint coating. The SBP exhibits extremely low hemispheric reflectance (R < 1.2%) in the solar spectrum at a normal incident angle; even at an 80° incident angle, the SBP also has good anti-reflection performance (R < 9%). Based on such properties, we further show the enhanced solar-thermal performance over commercial black paints. Our approach holds promises for scalable and cost-effective manufacturing of ultrablack surface, with potential applications in solar-thermal conversion efficiency improvement and space optical system stray light suppression.

Thermal energy storage using phase change material for solar thermal technologies: A sustainable and efficient approach

Over-exploitation of fossil-based energy sources is majorly responsible for greenhouse gas emissions which causes global warming and climate change. To mitigate these challenges renewable energy sources, especially solar thermal technologies, can play a decisive role. United Nations also proposes steps to attenuate the adverse effects of fossil-based energy and climate change through Sustainable Development Goals (SDG7 and SDG8). Solar thermal technologies have seen a huge capacity expansion around the globe in previous decades because of their inherent advantages. However, solar energy faces crucial limitations of fluctuating intensity and time-dependent availability. This decreases solar thermal system performance and makes solar thermal technologies time-dependent. To overcome these challenges, integrating phase change material (PCM) in solar thermal technologies makes a sustainable approach to enhance the efficacy, productivity, and utilization rate of solar thermal technologies. In this manuscript, the sustainable approach of integrating PCM in solar thermal technologies was reviewed. This includes literature on PCMs which covers classification, properties, importance, and limitation. Comprehensive data on the integration of PCM with solar thermal technologies such as solar water heating, solar desalination, solar cooking, solar dryers, solar PV/T, solar ponds, solar chimneys, and solar power plants were reported explicitly in terms of the type of PCM, efficiency and their productivity. In addition, the effect of PCMs integration in solar thermal technologies was analyzed in terms of mitigation of CO2 emissions and economic analysis at different locations around the World.

Experimental study of parabolic trough collector in series having a concentric copper tube in evacuated tube for air heating

ABSTRACT Currently, the utilization of solar energy for domestic purposes, particularly in applications such as space heating and hot water, is constrained to flat plate collectors and evacuated tubes due to its compact size, absence of tracking mechanisms, low maintenance, and cost-effectiveness. The objective of this study is to evaluate the practical effectiveness of a locally developed parabolic trough collector system through experimentation. In this configuration, two parabolic trough collectors with one-ended evacuated tubes and inner concentric copper tubes for double pass airflow were connected in series, exhibiting an average air temperature within the range of 130.22°C to 166.72°C, which indicates its potential for use in industrial and domestic applications. Solar intensity, thermal performance, and pressure drop were determined after the first evacuated tube (intermediate point) and after the second evacuated tube. The experiments were carried out on six separate days, with three distinct airflow rates of 0.0056 kg/s, 0.0038 kg/s, and 0.0021 kg/s. Results discovered that the maximum air temperature reached was 210.5°C. The maximum thermal efficiency observed was 39.31%, with an overall average thermal efficiency of 30.56%. Further, the maximum pressure drop achieved was 510 Pa at 0.0056 kg/s.

Artificial intelligence vision technology application in sustainability evaluation of solar-driven distillation device

The process of transforming brackish water into freshwater utilizing solar thermal energy is referred to as solar-driven distillation device, or solar still. Such device without fossil fuel provides significant environmental and health benefits by reducing air pollutants and remedying brackish water. The yield of purified water from conventional solar stills remains insufficient, prompting the necessity for research to enhance it by understanding the coupling effect between steam flow, heat transfer, and mass transfer. As such, computer-aided brackish water treatment comparison of the hemispherical solar still and other multi-slope solar stills is conducted in this paper, and an automatic steam&heat flow detection algorithm is developed to solve the problem of difficult data acquisition for gas-liquid transport processes. Firstly, double slope, four slope, and hemispherical solar stills are exposed to the sun in outdoor experiments, therefore the solar thermal performance of each still is analyzed through pairwise comparisons. Secondly, a large amount of experimental image data is input into neural network for training, and by continuously adjusting network parameters, the network can accurately recognize different types of images. Finally, the image to be recognized is input into the trained neural network, which outputs the category labels of the image to achieve automatic image recognition. Based on the data above, the best structure of solar-driven device is hemispherical structure, due to that the hemispherical solar still possesses the best performance in terms of distilled water yield, energy efficiency, exergy efficiency and energy payback.

Simulation of Effect a Variable Height of Porous Absorber on Ventilation Solar Chimney Performance

The improvement in solar chimneys' thermal performance and thermal behavior that can be achieved by adding metal foam has been tested in computational work. The flow and heat transfer governing equations for solar chimney models were solved using computational fluid dynamics (CFD). It was solved using the control volume numerical method in ANSYS FLUENT 14.5. It is used to construct a finite volume modeling technique for solving the governing equations and the radiation heat transfer equations. With standard flat absorber plates, the results showed that heat transmission was increased by the inclusion of metal foam (10 PPI), leading to an increase in air velocity at the solar chimney of around 13.3%. The highest average air velocity with 10 PPI drops by 54.4% as the height of the absorber plate changes from 5 cm to 25 cm respectively.

Multi-Scale Superhydrophobic Surface with Excellent Stability and Solar-Thermal Performance for Highly Efficient Anti-Icing and Deicing.

Ice accretion can significantly impact the efficiency and safety of outdoor equipment. Solar-thermal superhydrophobic surface is an effective strategy for anti-icing and deicing. However, droplets easily turn to the Wenzel state during the icing and melting cycle processes, significantly increasing the adhesion and making the droplets difficult to remove from the surface. In this work, a triple-scale solar-thermal superhydrophobic surface is prepared on stainless steel 304 by etching, in situ oxidation, and spin-coating TiN nanoparticles for highly efficient deicing and anti-icing. The multi-scale structure enabled the droplets to recover the Cassie state completely after melting. The contact angle decreased from 162.5° to 136.7° during the icing process and gradually increased to 162.1° during the melting process. In addition, metal oxides and TiN nanoparticles enabled the superhydrophobic surface to exhibit a high solar absorptivity ( = 0.925). The synergistic effect of the superhydrophobicity and the solar-thermal performance endowed the designed multi-scale surface with excellent anti-icing and deicing performance. This work contributed to the practical development of anti-icing and deicing applications based on solar-thermal superhydrophobic surfaces.

Honeycomb-like porous copper with pleated surface for supporting phase change material with enhanced thermal conductivity and solar thermal storage performance

Paraffin wax (PW) is concerned in the field of thermal storage because of its high thermal storage density, but it generally has problems such as low thermal conductivity, poor shape stability, and low solar absorption, which limit its application in solar thermal storage and thermal management. In this study, a honeycomb-like 3D porous Cu skeleton with a pleated surface was prepared by the salt template method, and the phase change composites (PCCs) were prepared using this 3D thermal conductive skeleton to support PW. The honeycomb-like porous structure with pleated surface has positive effects on the shape stability and solar-thermal conversion of PW. The thermal conductivity, leakage resistance, and solar-thermal conversion efficiency of the PCCs were significantly improved. Among them, the thermal conductivity of PW@PSHCPC2 reached 3.3 Wm−1 K−1, which was 16.5 times higher than that of PW, and the solar-thermal conversion efficiency reached 89.2 %, and a stable current of 61.8 mA was generated in the solar thermal power generation experiment. These results show that these PCCs have great potential for applications in several fields such as solar thermal storage, waste heat recovery, solar power generation, and electronic thermal management.

Enhanced performance of photovoltaic thermal module and solar thermal flat plate collector connected in series through integration with phase change materials: A comparative study

The decline in photovoltaic cell efficiency due to temperature elevation, coupled with solar energy's inherent intermittency, presents challenges for solar systems, including photovoltaic panels and solar thermal (ST) collectors. The integration of phase change materials (PCMs) emerges as a promising solution to enhance thermal energy storage and regulation, thereby improving system performance and sustainability. This study investigates the performance of series-connected photovoltaic thermal (PVT) and ST systems with integrated PCMs from energy and exergy viewpoints, utilizing a 3D transient numerical simulation. The proposed system's performance is compared with that lacking a PCM across various heat transfer fluid mass flow rates. Suitable PCM selection based on melting temperature is explored, along with PCM layer thickness and nanoparticle augmentation. The research highlights that PCM integration effectively regulates PV cell temperature, enhancing electrical power and exergy rate. While increasing the mass flow rate improves thermal and electrical power, it reduces the thermal exergy rate. Comparing different PCMs (RT28 HC, RT35 HC, and RT44 HC), the RT28 HC PCM provides the lowest temperature of PV cells and the best electrical performance during the day. Moreover, increasing PCM layer thickness results in lowering PV cell and outlet temperatures and storing more heat. Nanoparticles added to PCMs lead to a marginal improvement in energy and exergy, especially for the system with RT28 HC. This analysis emphasizes PCM integration's role in enhancing solar thermal system performance, highlighting the importance of considering the PCM's melting temperature for effective thermal energy management.

Parametric investigation of the solar-thermal performance of tensile membrane roofs in hot-desert climates

Parametric investigation of the solar-thermal performance of tensile membrane roofs in hot-desert climates

Analytical and experimental study of hybrid photovoltaic–thermal–thermoelectric systems in sustainable energy generation

A new hybrid system, known as photovoltaic–thermal–thermoelectric (PVT-TE), has been proposed to enhance the conversion efficiency of PV cells by incorporating an intelligent thermal management system, which leverages the dual functions of thermoelectric (TE). This study aims to explore the potential for creating a hybrid system that is more efficient and offers improved performance than standalone photovoltaic thermal (PVT) systems. The key parameters for the creation of a hybrid system were analysed, and the theoretical and experimental results were compared to validate the model. The performance of the PVT-TE collector was evaluated through a steady-state analysis using a one dimensional (1D) mathematical model. Energy balance equations were solved using Microsoft Excel and inverse matrix method. Experiments on PVT and PVT-TE collectors were examined at a solar radiation intensity of 593.16 W/m2. The air mass flow rate was set at 0.009, 0.021, 0.039, 0.069 and 0.095 kg/s for specific radiation intensity. The thermal and electrical performance of the hybrid system was higher than that of the conventional PVT system. The PVT-TE system combines photovoltaic and thermoelectric components, including a thermoelectric module and an air collector. The integration improves system efficiency and performance, surpassing previous research efforts. The PVT-TE system with an air collector has innovative features including efficient thermal-electric conversion, integrated component utilisation, and air collector integration. The overall efficiency of the hybrid system was 7.05%–31.13% higher than the theoretical values and 9.64%–34.83% higher than the experimental values. The increase in the output power of the hybrid system was also higher by 32.59%–55.93%. The findings indicate that the integration thermoelectric (TE) with PV cells has the potential to enhance solar thermal systems' performance. This study provides the basis for further analysis and optimisation of PVT-TE hybrid systems.

Modified mica-supported phase change materials for efficient solar thermal conversion and thermal energy management

To improve the solar thermal conversion performance of composite phase change materials and further practical applications, the rational design and realization of excellent thermal properties, electrical properties, shape stability, and fast response to solar energy are essential. Three-dimensional layered composite phase change materials loaded with paraffin wax were prepared by vacuum impregnation method using polyethylene glycol grafted nanocellulose modified mica as the carrier. The prepared materials exhibited high bulk resistivity (1.47 × 1013 Ω cm), excellent thermal conductivity (1.3 W/m K), outstanding solar energy conversion efficiency (98.3%), good thermal stability and reusability. It was noteworthy that the thermal conductivity of the composite was improved by 619.05% compared to pure paraffin. The three-dimensional layered structure of directional stacking and the polyethylene glycol-linked heat transfer channels greatly improved the thermal conductivity of the composite phase change material. These findings provide ideas for designing innovative materials that combine energy storage and other functional properties.

Comparative capacities of residential solar thermal systems versus F-chart model predictions and economic potential in an equatorial-latitude country

One popular simulation tool for predicting solar thermal (ST) performance is the F-chart model, which has not been validated for the conditions in equatorial-climate countries. In this work, the performance of two ST systems (evacuated tube collectors (ETCs) and flat plate collectors (FPCs), widely used for supplying domestic hot water (DHW) was assessed and compared with F-chart simulation results. The energy demands were simulated by scheduling hot water discharges and measuring the backup energy requirements to fulfil DHW needs. Then, the difference between the calculated solar fraction using the F-chart model and the measured solar fraction was obtained. Both the measurements and simulations showed that the ETC systems performed better than the FPC systems in a city located on the Ecuadorian highlands with distinct climate conditions. The results showed that ETC systems are, on average, up to 18.5% more efficient than FPC systems. A comparative economic analysis was carried out considering that domestic water heating systems are backed up with liquified petroleum gas (LPG) or electricity, both with and without state subsidies. However, due to the higher cost of ETC technology compared to FPC technology, and despite ETC’s higher efficiency than FPC’s, only US$0.34 per month can be saved on average because of the impact of energy subsidies. Thus, the FPC technology seems more profitable, under the mentioned conditions, because of its lower capital costs. With backup systems powered by unsubsidized energy, the two technologies are nearly comparable. The ETC technology appears suitable only under the unsubsidized electricity scenario. The novelty of this research is that real ST systems installed under similar conditions are integrated, the operation of ST technologies for DWH is simulated, and the different inclinations and orientations of solar collectors are considered. The results are compared with simulations from the F-chart model, and each system is economically assessed.

Efficient solar thermal energy utilization and storage based on phase change materials stabilized by MOF@CuO composites

Solar thermal conversion technology employing phase change composites is an available strategy for solar thermal energy utilization and storage. In this work, a novel metal-organic framework (MOF)-based phase change composites were successfully constructed through vacuum impregnation method. The stearic acid (SA) was served as phase change materials, and the SA-modified MOF (HS) with CuO derived from MOF (HS@CuO composites) was assembled to be support materials, which composed the SA/HS@CuO phase change composites. HS@CuO composites could well prevent the SA leakage over phase change point and endowed the phase change composites outstanding form stability (SA loading rate: 71.8 %) and thermal storage ability (ΔHm: 158.24 J/g). Furthermore, the SA/HS@CuO possessed greatly strengthened thermal conductivity (improved by 3.8 times over SA) and extraordinary solar thermal conversion performance (η: 95.9 %). These results powerfully suggest that the innovative phase change composites own promising potentials in not only solar energy utilization and development but also thermal storage and management fields.

Wood Lamella-Inspired Photothermal Stearic Acid-Eutectic Gallium-Indium-Based Phase Change Aerogel for Thermal Management and Infrared Stealth.

Eutectic Gallium-Indium (EGaIn) liquid metalis an emerging phase change metal material, but its low phase transition enthalpy and low light absorption limit its application in photothermal phase change energy storage materials (PCMs) field. Here, based on the dipole layer mechanism, stearic acid (STA)-EGaIn-based PCMs which exhibit extraordinary solar-thermal performance and phase change enthalpy are fabricated by ball milling method. The wood lamella-inspired cellulose-derived aerogel and molybdenum disulfide (MoS2 ) are used to support the PCMs by the capillary force and decrease the interfacial thermal resistance. The resulted PCMs achieved excellent photothermal conversion performance and leakage proof. They have excellentthermal conductivity of 0.31W m-1 K-1 (this is increased by 138% as compared with pure STA), and high phase change enthalpy of187.50 J g-1 , which is higher than the most of the reported PCMs. Additionally, the thermal management system and infrared stealth materials based on the PCMs are developed. This work provides a new way to fabricate smart EGaIn-based PCMs for energy storage device thermal management and infrared stealth.

Scrutinization of Solar Thermal Energy and Variable Thermophysical Properties Effects on Non-Newtonian Nanofluid Flow

Nanofluids generate high values of convection heat transfer coefficients, low specific heat, and density, which improve the solar thermal energy performance by making it work effectively. By utilizing nanotechnology and solar thermal radiation, the modern world is moving in the direction of new technologies. Therefore, this research is communicated to explore the significance of solar thermal energy, variable properties on non-Newtonian nanofluid flow. However, to exemplify the fluid transport features of the Casson nanofluid (CF), the Buongiorno nanofluid model was utilized. Also, the Lie-group technique is used in the framework to develop similarity variables that will be used to reduce the number of independent variables in partial differential equations (PDEs) and is solved numerically by using the weighted residual Galerkin method (WRGM). The graphical findings revealed that when the variable viscosity parameter is increased, the fluid temperature decreases, while the presence of the solar radiation parameter has the opposite impact. Additionally, when the non-Newtonian parameter approaches infinity, the Casson fluid obeys the viscosity law. The report of this study will be of benefit to thermal and chemical engineering for nanotechnology advancement. KEYWORD: Solar Thermal Energy, Nanofluids, Non-Newtonian, weighted residual Galerkin method (WRGM).

Investigation on the enhancement of optical and solar thermal harvesting performance of water with Fe3O4 nanoparticle and external rotating magnetic field

In this study, the light absorption characteristics and solar heat harvesting performance of water by adding Fe3O4 nanoparticles (NPs) were experimentally investigated under different external magnetic field (MF) strengths, and rotating MF speeds. As a result, the photothermal conversion efficiency (PTCE) of Fe3O4 NF exhibits higher light absorption characteristics than water at all concentrations. The PTCE of the Fe3O4 NF at the optimal concentration of 0.075 wt% was 90%, which was 45.6% higher than that of the base liquid. The optimal performance of 0.075 wt% of Fe3O4 NF was presented at an external MF strength of 500 Gauss and rotating MF speed of 200 rpm, resulting in a high PTCE of 96.1%, which was significantly higher than that of base liquid. Furthermore, it increased by approximately 6.73% compared to the PTCE of 0.075 wt% Fe3O4 NF without an external MF. The Fe3O4 NPs are reacted by the external MF and arranged on the MF line. As the external MF rotates, the Fe3O4 NPs move to form convection in the working fluid, improving the temperature uniformity of the working fluid. Therefore, the PTCE of the working fluid can be improved by adding Fe3O4 NPs into water and using external rotating MFs, which can significantly improve the performance of direct absorption-type solar collectors.