Direct Absorption Solar Collector Research Articles

Stable and environmentally benign nanofluids for direct absorption solar collectors based on natural deep eutectic solvents

Stable and environmentally benign nanofluids for direct absorption solar collectors based on natural deep eutectic solvents

The effect of ultrasonic waves on the structure, morphology, and thermal conductivity of graphene oxide as nanofluids for direct absorption solar collector application

This research aims to explore how ultrasonic waves affect the structure and morphology of graphene oxide (GO) as a nanofluid, influencing its thermal conductivity (TC), stability, and photo-thermal conversion properties. GO was rapidly synthesized under ultrasonic bath irradiation using modified and improved Hummers' methods. Ultrasonic irradiation creates different structural and morphological defects in the GO that depend on the sonication time. The relationship between the exposure time to ultrasound and the creation of structural and morphological defects in graphene oxide nanosheets was investigated using UV–Vis, FTIR, Raman spectroscopies, AFM, and TEM analysis. The study examined how the structure and morphology of graphene oxide nanosheets affect the thermophysical and photo-thermal conversion properties of nanofluids by comparing heat transfer and stability. The simultaneous characterizing of the structure and morphology indicates that TC and stability are related to the sonication time. Indirect sonication with low intensity can carefully control the oxidation reaction of GO. Sonication for 30 min creates GO nanosheets that yield stable nanofluids with a 32.31 % enhancement in TC, with no extra treatment needed. This particular nanofluid has excellent photo-thermal conversion properties thanks to its high optical absorption, good stability, and thermal conductivity. This can increase the solar-thermal conversion efficiency (η) up to 72.5 %, making it a promising candidate for use as the working fluid in direct absorption solar collectors (DASCs)

An Experimental Investigation on Synthesis, Characterization, and Photothermal Conversion Efficiency of Stable Aqueous Nanofluids Containing Multiwalled Carbon Nanotubes for Direct Absorption Solar Collectors

The nanofluids are the potential substitute in solar collectors as working fluids for better photothermal conversion efficiency. The present investigation focuses on the development of aqueous‐based nanofluids comprising multiwalled carbon nanotubes (MWCNTs) with and without surfactants to enhance the capacity of photothermal conversion in direct absorption solar collectors. To improve the stability of the nanofluid, the gum Arabic (GA) and polyvinyl alcohol (PVA) are used as the surfactants. The stable nanofluid was characterized using UV‐visible spectroscopy, zeta potential, fourier‐transform infrared spectroscopy, field emission scanning electron microscopy, and energy dispersive X‐ray spectroscopy (EDS) analysis. The results indicated that the thermal conductivity was enhanced by 94.57% and 91.19% for the MWCNT/GA/deionized (DI) water and MWCNTs/PVA/DI water based nanofluids in presence of surfactants at 90 °C and 0.02 wt%. The presence of surfactant in MWCNTs/DI water nanofluids exhibit excellent stability and enhanced MWCNTs dispersion. In the photothermal response analysis, the highest temperature of 62.8 °C, which is 16 °C higher than the base fluid, is obtained from 0.02wt% MWCNT/GA nanofluid. The highest efficiency of 27.94% is recorded when 0.02wt% MWCNT/GA nanofluid is used, which shows 71.24% enhancement as compared to the DI water after exposure of 30 minutes under solar irradiation. The use of MWCNTs/GA nanofluid as light‐absorbing working fluids in solar collectors is encouraged in the present investigation.

Photothermal Conversion Performance of Fe3O4/ATO Hybrid Nanofluid for Direct Absorption Solar Collector

In order to enhance the efficiency of direct absorption solar collectors, this study carried out an experimental analysis about the optical and photothermal conversion performance of Fe3O4, ATO (Antimony-doped tin oxide), and Fe3O4/ATO nanofluids with a total concentration of 0.1 wt%. According to the results of the experiments, Fe3O4 nanofluid outperforms ATO nanofluid in terms of optical absorption; nevertheless, at wavelengths shorter than 600 nm, it also shows significant scattering reflection. The solar-weighted absorption coefficient of Fe3O4/ATO nanofluid rose from 0.863 (mFe3O4/mTotal = 0.2) to 0.932 (mFe3O4/mTotal = 0.8) when the optical path length increased from 0.01 m to 0.06 m. Moreover, the Fe3O4/ATO hybrid nanofluid achieved a photothermal conversion efficiency of 0.932 when the mass ratio of Fe3O4 to total mass was 0.2, surpassing the efficiencies of 0.892 and 0.898 recorded for 0.1 wt% ATO and Fe3O4 nanofluids, respectively. When present together, the opposing optical characteristics of Fe3O4 and ATO boost photothermal conversion performance, which is anticipated to raise the efficiency of direct absorption solar collectors.

Fe3O4/Au@SiO2 nanocomposites with recyclable and wide spectral photo-thermal conversion for a direct absorption solar collector

The Fe3O4-based photothermal materials have been widely applied for the recycling of heavy metal nanoparticles to avoid secondary pollution in the utilization of solar energy owing to excellent magnetic properties. However, the narrow absorption band of Fe3O4 or metal nanoparticles limits their capacity for solar energy harvesting. In this paper, a recyclable and wide spectral photo-thermal conversion system (Fe3O4/Au@SiO2) based on Fe3O4 nanospheres and SiO2-modified Au nanorods (NRs) is prepared. Owing to the strong coupling effect between Fe3O4 and different Au NRs, the wide and strong absorption band from 400 nm to 1100 nm is obtained. Under the influence of magnetic field, the temperature change of nanofluids (NFs) at different positions can be controlled. When the concentration is 0.0467 vol%, the solar energy absorption fraction reaches 96.50 %. Besides, the photothermal performance of Fe3O4/Au@SiO2 NFs at different flow rates is investigated and the results show that temperature rise decreases as increasing flow rate. Finally, a water evaporator device based Fe3O4/Au@SiO2 NFs is developed. The maximum water evaporation rate of 2.6 kg m−2 h−1 can be reached and the movement of evaporator on water can be operated using magnetic field, showing great photothermal conversion performance and recovery potential in practical applications.

A Nanorod With Near-Perfect Absorption for Efficient Utilization of Solar Thermal Energy

Solar thermal utilization faces a significant challenge, with efficient photothermal conversion being the primary issue. Although plasma nanofluid-based direct absorption solar collectors have shown potential in providing excellent sunlight capture capabilities, their narrow-band absorption limits their efficient photothermal conversion. This study proposes an alternative solution by introducing gold nanorods that achieve nearly perfect absorption across 300–1100 nm. The study demonstrates that the spectral absorption capacity of nanorods remains unaffected by their size and material at specific concentrations and depths. The analysis of the electromagnetic distribution at the resonance absorption peak reveals that the nanorods exhibit a “lightning rod” effect and surface plasmon resonance, leading to significant absorption. Additionally, the study investigates the effect of five common plasma nanomaterials on the nanorods’ optical absorption properties. The results show that titanium nitride-based nanorods exhibit broad-spectrum absorption and require only a small concentration and depth to achieve a 95% solar weighted absorption fraction. This research provides a valuable guide for the efficient photothermal conversion of plasma nanofluids, enhancing their potential for solar thermal systems.

Optically manipulated nitrate-salt-based direct absorption solar collectors for a photothermal energy harvesting system

This study introduces a nitrate-salt-based direct absorption solar collector (DASC) for a photothermal energy harvesting system with efficient solar energy harvesting and the reduction of thermal radiation loss. Investigations of the optical properties of snow-like solid-state binary nitrate salt in solar and thermal infrared (IR) spectral regions were first conducted in this study. Research revealed that the solid-state binary nitrate salt showcases high solar reflectivity (>90 %) and infrared emissivity (∼0.85), leading to a cooling power of 36.4 W m−2. This implies pure solid salt cannot gain energy from solar illumination. To tackle this, the proposed system incorporated nano graphite and a hot mirror. Consequently, the absorbed solar energy increased from 67.6 W m−2 to 898.7 W m−2, resulting in a heating power of 794.0 W m−2 under AM 1.5G solar irradiance. With the proposed approaches, melting the salt with lowest solar concentration ratio of 15 (∼12.5 kW m−2) was achieved.

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

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

Experimental study of a direct absorption solar collector with stationary nanofluid

In this study, an experimental assessment of the performance of carbon black nanofluids in a direct absorption solar collector was conducted. Unlike traditional direct absorption solar collectors, the laboratory setup in the present work utilized stationary nanofluids for solar absorption, which later heated a secondary fluid (water). This approach enabled the elimination of the need for pumping nanofluids within the system, thus reducing pumping costs and maintenance requirements. The efficiency of various nanoparticle concentrations was investigated and evaluated under identical conditions. Among the six nanofluids examined in the experimental analysis, ranging from 0.0015 to 0.05 wt.%, the most effective concentration was found to be 0.01 wt.% with a thermal enhancement of 42%, as compared to the reference distilled water values.

Broad-band absorption and photo-thermal conversion characteristics of rGO-Ag hybrid nanofluids

In the current paper, the thermo-physical, optical and photo-thermal conversion characteristics of reduced graphene oxide nanosheets and silver nanoparticles suspended in water and water + ethylene glycol solution (1:1) were experimental investigated under indoor conditions. The results indicated that the hybrid nanofluids have a good solar absorption in both visible and near-infrared regions (220–1400 nm). Comparing transmission spectra and extinction coefficients of rGO-Ag/water and rGO-Ag/W + EG hybrid nanofluids it is found that the use of rGO-Ag/W + EG hybrid nanofluid is much more beneficial than the rGO-Ag/water nanofluid in solar applications. The rGO-Ag /water and rGO-Ag /W + EG hybrid nanofluids with 0.10 wt% exhibit a relative increase in the temperature difference by about 21 % and 37 % compared to the base fluids and also stored energy values of 4989 J and 5432 J respectively, after an irradiation time of 60 min. This study emphasized the solar potential of rGO-Ag hybrid nanofluids for improving the direct absorption solar collectors performance.

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.

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.

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.