Direct Absorption Solar Collector Research Articles

A review study on the direct absorption solar collectors working with nanofluids

A review study on the direct absorption solar collectors working with nanofluids

ZrC–Au core-shell nanoparticles for efficient solar photothermal conversion

Nanoparticles (NPs) have attracted much attention recently because of their excellent photothermal properties. In particular, nanofluids (NFs) based on core-shell plasmon NPs have become the key to solar thermal utilization. This work proposed an ZrC–Au core-shell NP suitable for direct absorption solar collectors (DASCs). The optical properties of ZrC–Au core-shell NP are investigated based on the finite element method (FEM). The physical mechanism of its existence can be explained by the surface plasmon resonance and localized surface plasmon resonance of ZrC–Au core-shell NP. Meanwhile, the effect of core-shell size on the NP optical properties of ZrC–Au core-shell is investigated based on electromagnetic field distribution. In addition, the effects of length (H) and mass flow (ṁ) on the temperature rise and efficiency of the collector (η) are analyzed with DASC 2D simulation. Research shows that ZrC–Au core-shell NPs with t = 5 nm and r3 = 15 nm can effectively broaden the solar spectral absorption band, increase the absorption peak value, and the photothermal conversion efficiency (fv = 20 ppm, h = 15 mm) reaches 96 %, which is 15.89 % higher than Au NP. Meanwhile, the η of ZrC–Au NPs can be improved by ∼8.86 % compared with Au NPs under specific parameters (H = 2 cm, L = 20 cm, fv = 20 ppm, ṁ = 1 g/(s m)). Combined with the preparation possibility and economy of ZrC–Au core-shell NPs, the broad application prospect of this NP in DASC and other photothermal fields was analyzed.

Latent heat type nanofluid based on MXene and MoS2 modified hierarchical structured phase change nanocapsules for sustainable and efficient light-heat conversion

Recently, solar energy has garnered widespread attention due to its clean, pollution-free, and renewable characteristics. Among them, latent heat nanofluids (LHNF) are extensively employed in direct absorption solar collectors (DASC) because of their high heat storage density and efficient heat transfer efficiency. In this study, a novel LHNF was prepared through electrostatic interaction between phase change nanocapsules modified with MXene-MoS2 (hereafter named “n-22@SiO2-Ti3C2Tx-MoS2 MEPCN”) and ionic liquid, aiming at sustainable light-heat conversion. Phase change nanocapsules are obtained by encapsulating docosane (n-22) within an inorganic SiO2 shell and modifying it with Ti3C2Tx and MoS2 to improve the absorption of solar energy across the full spectrum. Research indicates that LHNF possesses high thermal stability, low viscosity, and high thermal conductivity. Furthermore, LHNF contains 4 % n-22@SiO2-Ti3C2Tx-MoS2 can achieve full spectral absorption at an optical path length of 0.005 m. The equilibrium temperature of LHNF-10 % under 1 Sun irradiation can reach 76.3 °C, with a light-heat conversion efficiency of 85.62 %. Its energy storage performance remains relatively stable under cycling conditions. In addition, the water evaporation rate of the fiber fabric coated with LHNF-10 % increased by 94.42 % compared to the untreated fabric, and this increase persisted even after sunlight was turned off. Its outstanding light-heat conversion performance is anticipated to confer application advantage in intermittent solar energy utilization, wearable fabrics, and biomedical materials.

Self-assembled Au-CQDs nanofluids with excellent solar absorption and medium–high temperature stability for solar energy harvesting

Nanofluids-based direct absorption solar collectors are promising candidates for medium–high-temperature solar energy harvesting. However, nanofluids’ complicated preparation process and undesirable high-temperature stability have hindered their practical applications. Herein, we propose a facile method for synthesizing gold/carbon quantum dots (Au-CQDs) nanofluids by directly carbonizing the base fluid and spontaneously assembling with Au nanoparticles (AuNPs) triggered by high temperatures. The results indicate that the self-assembled Au-CQDs nanofluids can maintain high stability at 110 °C for 100 h without precipitation and keep excellent photothermal conversion performance under 10 sun irradiation. The concentration and particle size of AuNPs are crucial factors affecting the self-assembly process. By modulating the microscopic morphologies of the self-assembled nanoparticles, the extinction coefficient of the prepared nanofluids is up to 88.7 % at a low loading of 30 ppm. The nanofluids can reach an equilibrium temperature of 50 °C under 1 sun irradiation, 10.4 °C higher than the base fluid due to the enhanced plasmonic effects and stability resulting from the CQDs dotted AuNPs. This work offers a new strategy to fabricate highly stable nanofluids with excellent light absorption properties for efficient solar thermal applications.

CFD modeling of a triple‐walled direct absorption evacuated tube solar collector based on hybrid nanofluid/microencapsulated PCM

AbstractNowadays, direct absorption solar collectors are a new concept of solar collectors which have attracted special attention. The type of heat transfer fluid (HTF) has a significant influence on the efficiency of this kind of collector. Therefore, in this study, a wide range of working fluids including mono nanofluid ( and CuO), binary nanofluid, and especially the incorporation of a new hybrid combination of nanofluid and microencapsulated phase change material (MPCM), are used as the working fluids of a triple‐walled direct absorption evacuated tube solar collector. The computational fluid dynamics (CFD) method is used for simulating the collector and investigating the effect of different parameters including volume fraction, base fluid, mass flow rate, and type of absorber tube structure (double‐ and triple‐walled) on collector thermal performance. Results show that binary nanofluids of 0.06% /0.002% CuO/water and 0.06% /0.002% CuO/ethylene glycol (EG) have the largest working fluid temperature differentials equal to 48.31 and 66.5 K, respectively. It was inferred that, at the mass flow rate of 2.7 , the efficiency is obtained to be 60.29% employing binary/EG nanofluid, which is 8.68% and 15.31% higher than CuO/EG and /EG nanofluids, respectively. Inserting the hybrid CuO nanofluid/MPCM leads to an improvement of 1.14% and 1.22% in the efficiency of triple‐ and double‐walled collectors, respectively, with respect to the individual usage of the nanofluid. The thermal efficiency of the double‐walled structure is higher than triple‐walled considering all HTFs.

Performance evaluation and parameter optimization of tubular direct absorption solar collector with photothermal nanofluid

Photothermal nanofluids exhibit broad-spectrum absorption characteristics, rendering them highly promising for applications in direct absorption solar collector (DASC). A three-dimensional computational fluid dynamics (CFD) model is established to analyze the solar collection performance of a tubular DASC. Three distinct types of nanofluids used in direct solar absorption collector have been investigated, employing the Rayleigh scattering method to compute their optical parameters. The non-gray discrete ordinates radiation method is employed to solve radiation heat transfer within the glass wall and nanofluid. The findings reveal that graphite nanofluids exhibit the most favorable thermal performance among the tested nanofluids. The impact of different operating parameters, such as mass fraction and flow rate, on the thermal performance of the tubular DASC is elucidated through thermal and exergy efficiency analyses. The results indicate that thermal performance experiences only marginal changes when the mass fraction exceeds 50 ppm. Thermal efficiency increases with higher mass flow rates, while exergy efficiency displays an inverse relationship. This research contributes valuable insights that can guide the selection of suitable working mediums and the optimization of operational parameters for DASC system.

Effect of the irradiation intensity on the photo-thermal conversion performance of composite phase change materials: An experimental approach

Composite phase change materials (CPCM) containing photo absorbers are regarded as promising conversion and thermal energy storage materials for solar energy. Understanding the impact of irradiation intensity on the photo-thermal conversion process is of crucial significance for improving the photo-thermal conversion efficiency (PTCE) of CPCM. However, previous studies have overlooked the evolution of temperature patterns and the solid-liquid phase interface in CPCM, posing challenges in revealing photo-thermal conversion characteristics. In response to these challenges, the present study introduces an improved test method that integrates monitoring plane and infrared thermography. Paraffin/graphite nanoparticles CPCM are used as conversion and thermal storage material. The results show that the dominated heat transfer mode in different stages is different, and the natural convection within the liquid CPCM has enhanced the melting process. When the irradiation intensity is increased from 450 W/m2 to 1250 W/m2, the average temperature and average charging rate increase by 33.75% and 197.27%, respectively. At an irradiation intensity of 1050 W/m2, the CPCM achieves the highest overall PTCE of 42.40%, which is an 8.85% increase in contrast to the irradiation intensity of 450 W/m2. The results provide guidance for improving the PTCE of CPCM in the application of direct absorption solar collectors.

Enhancing indoor thermal comfort and sustainability: A solar-driven desiccant cooling and adsorption chiller system with environmental impact assessment

Addressing indoor thermal comfort in buildings located in hot and humid climates is a persistent challenge, demanding innovative cooling solutions that are both efficient and environmentally responsible. This paper introduces a new integration of a Phase Change Material (PCM)-based solar desiccant cooling system with an adsorption chiller, a setup designed to enhance indoor thermal comfort conditions while utilizing renewable energy sources. This research simultaneously leverages the heating and cooling capacities of the adsorption chiller, leading to an efficient system performance. The TRNSYS software is used to evaluate the system's behavior in a typical house with moderate cooling demand and characterized by high relative humidity. Two types of solar collectors, the evacuated tube and Wavy Direct Absorption Solar Collectors (WDASC), are evaluated to supply the required thermal energy, providing a comprehensive assessment of the system’s efficiency under different configurations. Additionally, the study conducts a comprehensive Life Cycle Assessment (LCA) to quantify the Global Warming Potential (GWP) of the systems. The results confirm the proposed system's capability to maintain indoor thermal comfort within acceptable Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) ranges. The evacuated tube collector showed marginally better performance (average PMV: 0.018, average PPD: 6.7 %) compared to the WDASC (average PMV: 0.075, average PPD: 7.3 %). Additionally, the evacuated tube collector demonstrates superior energy (75.68 %) and exergy (10.82 %) efficiencies compared to the WDASC. The system utilizing the evacuated tube collector surpasses the WDASC configuration, achieving a higher Coefficient of Performance (COP) of 0.47 compared to 0.41, and emitting lower GWP values of 0.0194 kg-CO2 per kWh of cooling capacity compared to 0.0201 kg-CO2. An analysis of Embodied Energy reveals that the adsorption chiller is the most significant contributor to lifecycle energy consumption, with a quicker Energy Payback Time (EPBT) for the evacuated tube system (2.75 years) compared to the WDASC system (3.94 years). This research thus contributes a highly efficient, sustainable, and environmentally friendly solution to the challenge of cooling in buildings, setting a new standard for future green building practices.

Direct Absorption Solar Collector: An Experimental Investigation of Al2O3-H2O Nanofluid over the Flat Plate at Different Tilt Angles, and Mass-Flow Rates

The escalating demand for solar thermal energy, coupled with the current inefficiencies in existing systems, underscores the critical need for innovative advancements in thermal storage solar collectors. The efficiency of solar collectors relies not solely on design effectiveness but also on the thermophysical properties, such as heat capacity and thermal conductivity, inherent in the working fluid. This study investigates a novel solar collector with a gross area of 0.36 m2, operating on the principle of direct absorption. Experimental investigations were done at various tilt angles (15°, 20°, and 30°) with respect to the horizontal, considering different flow rates and nanofluid settlement within the base fluids. The use of Al2O3 nanoparticles into the base fluid as water, exhibits significant positive effects on the thermophysical properties of the nanofluids, with a volume concentration of 0.003%. The efficiency of the solar collector was calculated across three mass flow rates (0.5, 1, and 1.33 L/min) at each tilt angle. Notably, the study reveals that the efficiency peaks at a 15° tilt due to an optimal flow configuration for maximum energy harvest across all three mass flow rates. Increasing the mass flow rate yields efficiency increments for all tilt angles (15°, 20°, and 30°), with 1 L/min emerging as the optimal mass-flow rate in most cases. This research not only addresses the immediate need for improved solar thermal technologies but also aligns with global sustainability goals, contributing to the IEA Net Zero Emissions initiative and supporting UN Sustainable Development Goals 7, 9, and 11. The paper also includes a critical literature review on the use of nanofluids in solar thermal collectors to improve thermo-physical properties and enhance solar efficiency. Additionally, the key findings regarding the influence and tilt angle on solar efficiency are discussed.

Effect of Silicon Oil with Nano Particles in Direct Absorption of Solar Thermal Collectors

We discussed about various aspects of solar energy, including its growth due to technological advancements and government support. It explores the utilization of solar energy in different climatic conditions, techno-economic analyses for hydrogen production, and solar-assisted biomass conversion. The section on Solar Thermal Collectors highlights different collector types, their efficiencies, and environmental impacts. The Nano Platelets section delves into the use of graphene nanoplatelets in direct absorption solar collectors, their structure, stability, and potential applications. Additionally, the paragraph touches on the application of graphene in coatings, cement-based composites, and nanocomposites, showcasing their impact on thermal and electromagnetic properties. The discussion extends to silicon oil-based materials, detailing their use in engine bearing alloys, transformer insulation, and environmental considerations. The findings emphasize the multifunctional benefits of graphene and nanocomposites in enhancing various properties, making them promising for future energy solutions. Keywords: Solar Energy, Solar Thermal Collectors, Thermal Nano Platelets, Silicon Oils.

Field study of a direct absorption solar collector with eco-friendly nanofluid

The concept of direct absorption solar collector (DASC) was introduced in the 1970s. Multiple laboratory studies proved that nanofluid-based DASCs presented a fruitful alternative to conventional solar collectors. However, due to environmental and cost limitations of nanofluids, there are few records of real-size DASCs operating in field conditions. Filling the gap, we report a 5-month seasonal field study for a full-scale DASC with an eco-friendly and low-cost nanofluid. Throughout the experiments, the DASC competed with a commercial flat-plate solar collector mounted in the exact location. The results showed that the commercial collector had an average daily efficiency of about 65.9%, while the direct absorption collector had a daily efficiency of 57.7% to 86.1%. The most important parameters influencing the efficiency of the DASC are the flow rate and the extinction coefficient of the nanofluid. They alter the efficiency by 9.2% and 6.2%. Finally, the article briefly notes the technical and economic features of the DASC operation.

Real‐time thermal performance investigation of a thermal energy storage integrated direct absorption solar collector under tropical climate

AbstractIn the last two decades, metallic particles of nano sizes (~10−9 m) have been tested profoundly in volumetric absorption solar collectors (VASC) due to their excellent optical properties and broadband absorption in the entire solar spectrum. However, very limited studies are available for understanding the performance of integrated energy storage VASC systems using nanofluids. For the experimental work presented here, a hybrid nanofluid of gold nanoparticles in Azadirachta indica leaves extract has been synthesized by chemical route. The prepared hybrid nanofluid has shown good absorption in 400 to 700 nm wavelength range and hence achieved high photo‐thermal conversion efficiency for tested VASC system. Furthermore, commercially available paraffin wax is used as a phase change material (PCM) in thermal energy storage (TES) and further integrated with VASC to analyze the thermal performance of the system even after sunshine hours. The real‐time experiments were conducted using different working fluids, and at three mass flow rates, that is, 0.008 kg/s, 0.016 kg/s, and 0.033 kg/s, respectively, during mild winter days in the tropical climate of India. The study revealed a photo‐thermal efficiency enhancement of about 17.1% when hybrid heat transfer fluid was used in the VASC system with TES as compared to base fluid water but without TES. During the heating period, the maximum thermal gain of the hybrid nanofluid was observed to be about 15°C higher than the ambient temperature at mass flow rate of 0.033 kg/s. Thermal efficiency enhancement of about 23.8%, 24%, and 24.1% was observed with hybrid nanofluid compared to base fluid water at a mass flow rate of 0.008 kg/s, 0.016 kg/s, and 0.033 kg/s, respectively, when PCM was kept inside the tank. Furthermore, a maximum zero loss efficiency of 83.8% was estimated at an optimal mass flow rate of 0.033 kg/s for the TES‐integrated VASC system.

Corrosion analysis and performance investigation of hybrid MXene/C-dot Nanofluid-Based direct absorption solar collector

Nanofluids having exceptional thermo-optical characteristics can enhance the performance of direct absorption solar collectors (DASC). Conventional nanofluids have either high optical properties or thermal properties. In this study, carbon quantum dot (C-dot) nanomaterial with high stability and optical absorption along the UV range, and MXene nanoparticles with high thermal conductivity and absorption along visible and near-infrared (NIR) spectral range was selected for synthesizing a hybrid nanomaterial with synergistic thermo-optical properties. Hybrid MXene/C-dot nanofluid exhibits higher stability, thermal conductivity, and complementary absorption properties of individual nanomaterials. A two-step method was used for the synthesis of nanofluids using water as the base fluid. Thermal conductivity, UV–Vis-NIR spectroscopy, and stability analysis were conducted on nanofluids, and the concentration was optimized for corrosion study and application in direct absorption parabolic trough collector (DAPTC). Optimised concentrations of C-dot, MXene, and hybrid nanofluids were 0.15 wt%, 0.1 wt% and 0.15 wt%, respectively. The corrosion study states that copper electrodes dipped in the hybrid nanofluid exhibited the least corrosion rate of 0.6 mm/year with an anticorrosion efficiency of 64.5 % over DI water. Thermal efficiency and entropy generation in the system with different HTFs were measured and compared with that of the base fluid. The study shows that C-dot and MXene/C-dot nanofluids were producing the highest efficiencies of 50.5 % and 47.5 % at a flow rate of 1.2 lpm. This study shows that hybrid MXene/C-dot nanofluid exhibited exceptional thermal stability, reduced corrosion effects, and considerable enhancement in photothermal conversion efficiency of the DASC.

Investigation of annual thermal performance and techno-economical analyses of direct absorption solar collector by using nanofluids

In this study, the annual thermal performance and techno-economic analyses of a direct absorption solar collector (DASC) using nanofluids were investigated. According to the results of numerical analysis the difference between the specific heat gains was 126.5 W/m2, where difference for annual energy saving or enhancement for solar energy converting to useful was 224 kW/m2a. To sum up utilization of MWCNTs (0.05%) based nanofluids as heat transfer fluids in PTC supported the 13,5% of thermal efficiency in comparison of water. Furthermore, when nanofluids are used as a heat carrier in a solar collector, the cost of 1 kWh of thermal energy is 0.029 $/kWh, and when water is used, it is 0.034 $/kWh. The payback period of the initial investment amount of the nanofluid solar collector is 3.96 years, where the interest rate of the bank is calculated at 23%, and the payback period of the initial investment amount of the water solar collector is 3.99 years.

Heat collection characteristics of nanofluids in direct absorption solar collector with built-in rotors

As for the uneven heating of the working medium in direct absorption solar collector (DASC),this paper proposed the method of optimizing the flow pattern in DASC by inserting combined rotors into the collector tube to improve the heat collection performance. The working medium used in this paper is Chinese ink nanofluid. The heat collection performance of the collector was studied, and the enhanced mechanism was explained through simulations. Results demonstrated that inserting rotors improved the temperature rise rate in the circuit, and the temperature of the medium after inserting rotors increased by about 56 % compared with that before inserting rotors when the mass fraction of nanoparticles was 0.2 %. In some cases, a small number of rotors can achieve an enhancement effect similar to that of enormous rotors, and improve the economic performance of the system. The numerical simulation results showed that the high-temperature medium in the plain tube is concentrated near the light side, while the medium in the centre and backlight side of the tube cannot easily absorb solar radiation. After rotors were inserted into the tube, the back-side and light-side media were displaced and mixed by the turbulence of rotors, which can improve heat collection.

Comparative assessment of direct absorption solar collector performance in different climates

Energy supply and environmental protection by reducing pollutants are among the main challenges these days. As a clean and sustainable source, solar energy is capable of generating thermal and electrical power. In this regard, Iraq is one of the regions with high solar energy harvesting potential. A numerical model was developed and validated by experimental findings in MATLAB software. This model, which also included geometrical and optical characteristics, was developed using information from four cities representative of different climates in Iraq: Baghdad, Samawa, Mosul, and Al-Qa'im. This study examined the effects of climate on the performance of direct absorption parabolic solar collectors used for energy production in Iraq. According to the results, solar collectors in Samaveh provide the highest thermal energy efficiency (up to 66.5%). Even thoth, the highest exergy efficiency is found in Al-Qa'im (36.21%). From an environmental point of view, the collector in Al-Qa'im has the highest CO2 mitigation (2.73 kg per m2 of collector) every year. As compared to other cities, Al-Qa'im and Samawah have a high thermal efficiency and solar intensity, which can lead to more water and energy savings.

Preparation of n-OD@PMMA/PDA photothermal conversion microencapsulated phase change material and application of the suspensions in DASC

A novel photothermal conversion microencapsulated phase change material (PDA-MPCM) was successfully prepared, contained n-octadecane (n-OD) as the core material, polymethyl methacrylate (PMMA) as the middle layer, and polydopamine (PDA) as the shell material. The incorporation of PDA enabled PDA-MPCM can obtain excellent photothermal conversion efficiency (73.92 %) and maintain good thermal energy storage capacity (1570 J kg−1 K−1). The PDA-MPCM suspension (PDA-MPCMS) prepared by the two-step method has a long time dispersion stability (more than 72 h) and an ultra-low transmittance (close to 0) in the wavelength range of 200–650 nm. To investigate the photothermal conversion ability of suspension, the stuffy bask experiments were carried out under the real sunlight in the direct absorption solar collector (DASC) with PDA-MPCMS. The experimental results showed that the peak temperature rise of 0.10 wt% PDA-MPCMS was 27.80 % higher than that of the base fluid, and the zero-loss collector efficiency reached 93.6 %. The PDA-MPCMS are expected to play an important role in promoting solar applications.

Prediction of radiation characteristics of solar collectors with multiple geometrical configurations based on Monte Carlo considering absorption element

This paper presents a study on the optical properties of direct absorption solar collector (DASC) modules with different geometrical configurations considering absorption elements. Three DASC module models, namely flat plates, circular tubes, and tri-prisms, were established and solved using the Monte Carlo method and Mie theory. The accuracy of the results was well verified with the reference data. The results show that the DASC with Si absorption elements exhibited higher absorbance than the DASC with TiO2 absorption elements. It is observed that SiO2@Ni nanofluid exhibited the highest absorbance and lowest reflectance, while TiO2 nanofluid displayed the lowest absorbance and highest reflectance. The absorbance of the nanofluids decreases and the reflectance of systems increases with the increasing particle size of the nanofluid. At incident light angles of 0° and 15°, tri-prism collectors outperform other geometric configurations of collectors. At 30° and 45°, circular tube collectors perform best. At 60° and 75°, flat plate collectors show superior performance. Overall, the tri-prism collector using SiO2@Ni nanofluid coupled with Si absorption elements can improve the efficiency of solar energy utilization compared to the other types of solar collectors.

Numerical investigation of the photo-thermal characteristics of a direct absorption solar collector using Monte Carlo and finite volume methods

Numerical investigation of the photo-thermal characteristics of a direct absorption solar collector using Monte Carlo and finite volume methods

Effect of hollow structure on solar thermal applications of Au nanodiscs

Plasmonic nanoparticles (PNPs) with hollow structures have shown great potential for enhancing optical absorption. While spheres or cylinders are commonly used for PNPs, the study of hollow PNPs for direct absorption solar collectors is limited. This research investigates the impact of three different hollow structures (cylindrical – Case 1, square – Case 2, and trigonal – Case 3) on the optical absorption properties of Au nanodiscs. The findings demonstrate that the presence of hollow structures significantly enhances the photothermal conversion efficiency of Au nanodiscs. Specifically, Case 1, Case 2, and Case 3 exhibit photothermal conversion efficiencies that are 17.9%, 22.0%, and 16.8% higher, respectively, compared to standard Au nanodiscs. Notably, Case 2 demonstrates the highest optical absorption capacity and photothermal conversion efficiency among the three hollow structures. Through optimization, Case 2 achieves a remarkable photothermal conversion efficiency of 97.6%. Meanwhile, we also investigated the effect of continuously sharpening the hollow edges on the optical absorption properties of the nanodiscs. The continuous sharpening of the hollow core hampers both the enhancement of optical absorption properties and photothermal conversion properties in Au nanodiscs. Therefore, this research provides valuable theoretical insights for utilizing plasmonic nanoparticles with hollow structures to enhance photothermal conversion.