Evacuated Tube Solar Collector Research Articles

Assessment of a hybrid solar water heating system: environmental impact and economic viability

ABSTRACT Conventional methods of space heating are not only expensive but also environmentally harmful, as they emit greenhouse gases that contribute to global warming. To tackle this issue, a hybrid solar water heating system assisted by a solar evacuated tube collector has been developed at the Madhav Institute of Technology and Science in Gwalior, India. Experiments conducted from November to February 2022–23 (winter season) revealed promising results. Throughout the winter season, the system achieved a daily average effective solar heat collection of 2.85 kWh, with a daily average collector efficiency of 45.5%. The average coefficient of performance (COP) of the solar water heat exchanger was 3.5. Additionally, the system demonstrated an energy payback time of 1.2 years, shorter than that of conventional systems. Over its lifetime, the developed winter heating system is estimated to mitigate 127.9 tonnes of CO2 emissions, earning a carbon credit of $1408. Economic analysis further revealed a favorable benefit-to-cost ratio for the hybrid system, ranging from 3.13 to 3.36, with a payback period varying from 5.03 to 4.47 years for an inflation rate of 6–13%. These findings affirm the feasibility and efficacy of a solar-powered hybrid active winter heating system.

Exploration Of Key Approaches to Enhance Evacuated Tube Solar Collector Efficiency

Exploration Of Key Approaches to Enhance Evacuated Tube Solar Collector Efficiency

Use of carbon nanotubes in flat and evacuated tube solar collectors for thermal enhancement: A review

Solar thermal collectors (STCs) are a potential heating and cooling solution owing to their pollution-free nature and availability in many parts of the globe. Enhancing the thermal efficiency of STCs is crucial for optimizing energy conversion. In this respect, the purpose of this article is to provide an overview of the usage of carbon nanotubes (CNTs) for the enhancement of thermal performance in evacuated tube and flat plate solar thermal collectors. According to the research that was conducted earlier, it was discovered that the use of CNTs, both single-walled and multi-walled, results to increases the efficiency of a flat and evacuated solar thermal collector. In this article, the impact of carbon nanotubes (CNTs) was investigated in depth for their potential usage in flat and evacuated tube solar collectors (ETSCs). This review article offers a novel aspect based on extensive research that has been published in the past related to the impact of CNTs on the thermal performance of flat and ESTCs.

Thermodynamic analysis of an evacuated tube solar collector system for industrial building application: A case study

In this study, a modified solar-Organic Rankine Cycle (ORC) assisted hydrogen production system for two different scenarios was experimentally investigated. In the study, evacuated tube solar collector (ETSC), ORC system, proton exchanger membrane electrolyzer (PEMe) unit is discussed with a holistic perspective. The presented work includes energy and exergy analysis of solar-ORC assisted hydrogen production. According to scenario 1 (S-1), only the case of hydrogen production from the installed system is considered. According to Scenario 2 (S-2), the both electrical energy and hydrogen production from the installed system is examined. As a result of the study, the energy efficiency in S-1 and S-2 operating modes was calculated as 9.553% and 16.02%, respectively. Additionally, the highest exergy efficiency for both scenarios was calculated as 6.129% in the S-2 scenario. Furthermore, hydrogen production amount of the S-1 and S-2 scenarios was calculated as 743.1 kg/annual and 371.5 kg/annual, respectively.

Assessment of thermohydraulic performance and entropy generation in an evacuated tube solar collector employing pure water and nanofluids as working fluids

This study conducts a numerical comparison of the thermal performance of three distinct working fluids (pure water, TiO2, and SiO2 water-based nanofluids) within an evacuated tube solar collector using Computational Fluid Dynamics. The study evaluates thermohydraulic performance alongside global and local entropy generation rates, while considering variations in solar radiation values and inlet mass flow rates. Results indicate that nanofluids demonstrate superior performance under low solar radiation, exhibiting higher outlet temperatures, velocities, thermal efficiency, and exergy efficiency compared to pure water. However, at the higher solar radiation level, the efficiency of SiO2 water-based nanofluid diminishes due to its impact on specific heat. Furthermore, the entropy generation analysis reveals significant reductions with TiO2 water-based nanofluid in all the phenomena considered (up to 79 %). The SiO2 nanofluid performance aligns closely with pure water under high radiation value. This investigation offers valuable insights into the utilization of nanofluids in solar collectors across diverse operating conditions, emphasizing their pivotal role in enhancing overall performance.

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.

Experimental Analysis of a Polygeneration System: Assessment of the Thermal Sub-System

In this paper, the experimental results of the thermal sub-system of a reliable and cost-effective polygeneration solar system are presented. This polygeneration system produces heating, cooling, and electricity from solar energy, which is used in an existing test building. Heat is generated in four evacuated tube solar collectors (ETCs). The heat may be used for space cooling through a variable geometry ejector (VGE) heat pump. In order to reduce the mismatches between generation and consumption, two thermal storage tanks were added. The performance of a new thermal storage, with 400 L, able to store both sensible and latent heat, was tested. The heating performances of the test building were assessed. Ejector cycle tests were also performed, and the variation of the cooling coefficient of performance (COP) was calculated for different flow rates. For heating, the results showed that the heat storage was capable of heating the test building for 8 h, with temperatures between 22 °C and 26 °C. All results showed that this polygeneration prototype could be capable of meeting the heating and cooling needs when applied to a real building.

Multi-objective optimization and long-term performance evaluation of a hybrid solar-hydrogen energy system with retired electric vehicle batteries for off-grid power and heat supply

This paper presents a novel off-grid hybrid renewable energy system integrated with hydrogen production and retired electric vehicle (EV) batteries for combined power and heat supply to a small rural community. The system consists of photovoltaic (PV) panels, evacuated tube solar collectors, a proton exchange membrane fuel cell (PEMFC), an alkaline electrolyzer, compressed hydrogen storage tanks, and reused lithium-ion batteries from EVs. A new battery model is developed in the Transient System Simulation Program (TRNSYS) to capture the capacity degradation of retired batteries. A two-stage energy management strategy is proposed to regulate power flow and maximize solar energy utilization. The system is optimized for minimum power supply disruption, hot water supply disruption, energy waste, and annualized costs over a 20-year lifetime using a multi-objective NSGA-II algorithm coupling MATLAB and TRNSYS. Optimization results reveal tradeoffs between the competing objectives. Dynamic simulations show the water tank temperature fluctuates between 20 and 100 °C with mean values dropping slightly in later years due to battery degradation. Energy waste from components rises in later years for the same reason. The replacement interval for a retired EV battery module is around 2.5 years. The integrated system proves feasible for off-grid combined power and heat supply using solar energy and retired EV batteries as storage, though battery degradation impacts long-term performance.

A data-driven model for a liquid desiccant regenerator equipped with an evacuated tube solar collector: Random forest regression, support vector regression and artificial neural network

The application of a solar-assisted liquid desiccant air-conditioning system equipped with evacuated tubes, focusing on the assessment and comparison of various artificial intelligence (AI) models is investigated. Specifically, Support Vector Regression (SVR), Multi-Layer Perceptron Artificial Neural Network (MLP-ANN), and Random Forest Regression (RFR) models are assessed for predicting key performance indicators: mass removal rate, efficiency, and effectiveness. Additionally, different optimizers within the Artificial Neural Network (ANN) framework—such as Adam, Stochastic Gradient Descent (SGD), and RMSprop—are systematically examined and tuned. The study encompasses the selection of the most suitable AI model for each target variable, considering parameters such as ambient temperature, solar radiation, timestamp, airflow rate, and initial solution concentration as influential factors in the modeling process. It is found that the best predictor model for effectiveness is SVR with RBF kernel. For MRR and efficiency, it is MLP-ANN with respectively AdamW and NAdam optimizers. The disparity of prediction of the MRR, efficiency and effectiveness target are respectively 0.72%, 1.07% and 0.5%, on average, indicating a precise prediction. Furthermore, including timestamps as model inputs significantly boosts accuracy, an aspect often neglected in prior research, leading to a noticeable minimum 5% rise in the R2 score.

Energy performance analysis of solar assisted gas-fired boiler heating system for floating roof oil tank

An innovative solar assisted gas-fired boiler heating system for floating roof oil tank is proposed to achieve the low carbonization of the conventional crude oil heating method. However, the dynamic energy transport performance of the proposed heating system affected by the key engineering parameters (crude oil capacity load, mass flow rate of heat transfer fluid (HTF), crude oil initial temperature) is unclear, which hinders the engineering application of this technology. In this regard, a simulation platform for solar assisted gas-fired boiler heating system for floating roof oil tank is established, and the above mentioned engineering parameters are investigated. The results show that under the condition of combined heating of evacuated tube solar collector (ETSC), phase change heat storage tank (PCHT), and auxiliary heat source (AHS), the system can achieve stable operation by means of controllers. With the increase of crude oil capacity load, the time for the crude oil to reach its design temperature is delayed, and up to 84.21% time lag is recorded. Apart from the contribution of AHS, the maximum annual heat supply of 43.37% is provided by PCHT and ETSC, presenting good energy-saving potential. Increasing HTF mass flow rate and crude oil initial temperature is a good strategy to reduce the output of AHS, in which the annual heat supply proportion of AHS decreases by 2.25% and 2.05%, respectively. The operating stability of proposed system is enhanced under the condition of higher HTF mass flow rate, compared to the 3.5 kg/s HTF mass flow rate, the safe reserve time increases by 31.44% for 7 kg/s and 34.24% for 14 kg/s HTF mass flow rate, respectively.

Energy and exergy analysis of waste heat and solar energy assisted for hydrogen production system: A case study

In the presented study, the focus is on the exergy efficiency of a textile factory that has the potential to optimize itself using solar energy and waste heat. Two distinct scenarios are considered in this study. In Scenario 1 (S-1), the whole system components operate solely for hydrogen production, while in Scenario 2 (S-2), the whole system components are utilized for both electricity, heat water and hydrogen production. For the harnessing waste heat, a 25 kW capacity Organic Rankine Cycle (ORC) system, 20 evacuated tube solar collectors (ETSC) for solar energy utilization, and a water electrolyzer for hydrogen production are employed. As a result of the thermodynamic analysis of the whole system, the energy and exergy efficiency is calculated as 5.17 %, 2.63% and 39.32%, 21.74%, respectively, according to the S-1 and S-2 scenarios. Furthermore, considering S-1 and S-2 conditions, hydrogen production amounts to 5197 kg/annual and 2209 kg/annual, respectively.

Improving solar still performance with heat pipe/pulsating heat pipe evacuated tube solar collectors and PCM: An experimental and environmental analysis

This study comparatively assesses the efficiency of various single-slope solar stills employing thermosyphon and pulsating heat pipe evacuated solar collectors, integrated with phase change material. The evaporator of the thermosyphon/pulsating heat pipe system is affixed to the evacuated tube, while the condenser is immersed in water to assist the transfer the solar irradiation heat energy. Paraffin wax is utilized as the PCM, positioned at two filling ratios within the thermosyphon/pulsating heat pipe evacuated tube at two filling ratios of 50 % and 100 %, to investigate its impact on water production during periods of low solar irradiation. The thermal energy of the solar radiation stored in the PCM and remove it to the thermosyphon/pulsating heat pipe system. The findings demonstrate that the highest daily freshwater production was 2248 ml/m2, showcasing a notable 40.7 % increase in productivity compared to conventional solar stills (CSSs). Moreover, the system employing pulsating heat pipe and full PCM showcased significant reductions in CO2, SO2, and NO emissions, approximating 19.53 tons, 117.1 tons, and 449.2 tons, respectively. Additionally, solar stills utilizing heat pipes (SSTHP) and solar stills employing pulsating heat pipes (SSPHP) exhibited energy efficiencies of 19.4 % and 20.3 %, respectively. Furthermore, the exergy-economic factors for CSS, SSTHP, and SSPHP were approximately 1.27 kWh/$, 1.56 kWh/$, and 1.62 kWh/$, respectively.

Thermal performance of two evacuated tube solar collectors with flat heat pipes

To promote the transition to clean heating methods in rural areas and improve solar energy utilization efficiency, two new types of solar water collectors with evacuated tubes, namely finned and finless collectors, are constructed with multi-channel flat tubes and flat micro-heat pipe arrays, and comparison experiments are conducted. By integrating with multi-channel flat tubes, the micro-heat pipe arrays, which function as the central heat transfer component, are capable of attaining effective thermal transmission. The multi-channel flat tubes have a substantial surface area available for heat transfer with the thermal fluid, while the evacuated tubes exhibit superior thermal insulation performance. The structural discrepancy between the two collectors lies in the presence or absence of louvered fins attached to the flat heat pipes inside the evacuated tubes. The comparative analysis of the two collectors includes time constant, thermal resistance analysis, distribution of temperature, normalized temperature difference, pressure drop, and actual operation effect under different conditions. The average thermal efficiency of the finless collector (59.4 %) is lower than that of the finned collector (78.2 %) on a typical experimental day. Then, further investigations are conducted to explore the effects of heat transfer fluid volume flow rate and inlet temperature on the thermal performance of finned solar water collector. With the heat transfer fluid volume flow rate of 120 L/h and the inlet temperature at 15 °C, the finned collector can achieve its maximum thermal efficiency of 86.4 %.

Numerical Heat Transfer Analysis of Evacuated Tube Solar Collector Using MXene/Soyabean Oil Nanofluid

This study focuses on investigating the thermo-hydraulic performance and entropy generation rate of an evacuated tube solar collector using MXene/Soybean oil as a working nanofluid by means of Computational Fluid Dynamics (CFD). A complete 3-D geometry is considered using three different kinds of working fluids (water, soybean oil and MXene/Soybean oil-0.025 wt.%, 0.075 wt.%, and 0.125 wt.%) for five different mass flow rates (0.02475 kg/s, 0.04818 kg/s, 0.0717 kg/s, 0.0952 kg/s, and 0.1188 kg/s) under same solar radiation (925W/m2). The results revealed that MXene/SO-0.125 wt.% at 0.0717 kg/s showed the best thermo-hydraulic performance because it achieves the balance between a high heat transfer coefficient and a low-pressure drop. However, MXene/SO-0.125 wt.% has been shown to have the highest entropy generation rate compared to other loadings because thermal efficiency is directly proportionate to the entropy generation rate. Therefore, the final recommendation for the best working fluid is MXene/SO 0.075 wt.% at 0.4818 kg/s because it attains good thermal efficiency, low entropy generation rate, and when compared to water has shown the highest improvement of 31.1%.

Statistical analysis of the vacuum solar collector using the analysis of ‎variance method

Space and weight constraints, as well as the time lag between energy generation and consumption, ‎are major obstacles to expanding solar water heating systems into existing structures with limited ‎space. It is possible to collect heat with this small, evacuated tube collector (ETC). It was found ‎that the air inside the glass tube has poor thermal conductivity. An experimental and numerical ‎study was performed on an evacuated tube solar collector, incorporating a heat tube with ‎cylindrical fins to increase the contact surface between the air and the fin surface. Statistical ‎analysis software is used to verify the results in practice. The temperature data was investigated ‎using SPSS under the same flow conditions. These figures are from experiments examining the ‎effect of variable volumetric flow rate, boost type, and variance analysis on temperature ‎distribution. When analyzing the results of the trials, a significant threshold of 95% was used. ‎Therefore, we compare the calculated significance to a value of 0.05 to evaluate the efficacy and ‎capabilities of the components. The reliability and validity of the model depend on the presence of ‎two components. If the resulting value is less than the significance level (0.05), then the model can ‎be considered robust and efficient (flow rate and optimization type). If the estimated value is ‎greater than that, the variables do not affect system performance. Flow rate and type of ‎enhancement are the two factors considered in the analysis of variance.

Thermal Performance Analysis of U-pipe Evacuated Tube Solar Heater System with and without PCM

The study presents a comprehensive thermal performance analysis of a U-pipe Evacuated Tube Solar Collector (U-ETSC) system, integrated with Phase Change Material (PCM), for satisfying water demand in domestic applications. The innovative approach of incorporating PCM aims to enhance the system's efficiency during night or off-sunny hours, addressing a common limitation in solar heater systems. The research primarily focuses on the impact of varying mass flow rates of the heat transfer fluid (HTF) on the thermal dynamics of the system. Experimental results reveal that as the mass flow rates of HTF increase from 0.5 to 1 and then to 1.5 liters per minute, there is a notable change in the phase transition times of the PCM. Specifically, the melting time of the PCM is increased by 13% and 16% for the respective flow rates, suggesting a delayed response in energy absorption. Conversely, the solidification time of the PCM is reduced by 16% and 18% respectively, indicating a faster release of stored thermal energy. This behavior underscores the PCM's significant role in stabilizing the system's thermal output during varying solar intensities. The findings of this study highlight the potential of integrating PCM in U-ETSC systems to achieve a more consistent and reliable supply of hot water for domestic purposes, especially during periods when solar irradiance is low or absent.

Performance investigation of drying Ashwagandha roots in a forced convection-evacuated tube indirect solar dryer

In this research work, experiments are conducted on drying Ashwagandha using an evacuated tube solar collector (ETSC) in India. The drying process performance parameters are evaluated. Experiment results obtained in drying of Ashwagandha using ETSC are compared with results obtained in open sun drying (OSD). ETSC dryer consumes 16 hours to reduce initial moisture content of 61.2% (db) to final moisture content of 8% while OSD consumes 24 hours of drying time to reach the final and safe moisture content. The average drying rate in ETSC and OSD processes are 0.004 and 0.0023% d.b min−1, respectively. Average efficiencies of the air heater and drying cabinet are 52% and 35%, respectively. From thin-layer mathematical modelling, Page and Two-Term models are the best fit for ETSC and OSD, respectively. After drying, OSD samples have the highest colour change than OSD. Total phenolic contents are 32.35 ± 1.4 and 21 ± 2.1 of the solar and OSD samples, respectively.

Investigation of thermal performance and charging/discharging characteristics of finned coaxial evacuated tube collector filled with phase change material

Present numerical model simulates the charging (melting), discharging (solidification) and heat transfer phenomenon of a phase change material (PCM) filled in the finned type coaxial evacuated tube solar collector. Thermal performance of the proposed evacuated tube has been predicted with Paraffin wax as the PCM. Solar radiation data measured on March 13, 2022 at Srinagar (Garhwal), Uttarakhand, India (latitude 30.2247° N and longitude 78.7986° E) has been applied as heat flux (450–965 W/m2) on wall of the evacuated tube. Heat transfer fluid (HTF) at the varying inlet temperature flows through the tube and absorbs heat, consequently its temperature increases. Results predict that during the charging process, 90 % of the PCM was melted by 11:30 AM for 0.0063 kg/s mass flow of the HTF having inlet temperature of 303 K. For the same operating conditions, maximum temperature rise achieved by HTF is ≈ 30 K at 14:00 PM. In the absence of solar radiation, discharging process (during 18:00 to 23:00 PM) of the PCM occurs that liberates the heat which is carried by HTF. Hence, heating of the HTF is continued during this period, however, outlet temperature continuously drops as night progresses. For the considered inlet temperature of the HTF = 303 K, maximum and minimum outlet temperatures were found to be 316.87 K and 307.55 K respectively. Furthermore, mass flow rate of the HTF significantly affects the melting rate of the PCM. At the mass flow rate of 0.0063 kg/s, 99.36 % of the PCM was melted by 12:30 PM. Whereas, till 14:00 PM, only 91.68 % and 70.54 % of the PCM melts when mass flow rate increases to 0.016 kg/s and 0.026 kg/s respectively. Findings also confirm that by increasing the HTF inlet temperature from 288 K to 308 K, melting period of the PCM is reduced by 40 %. Hence, it may be concluded that varying intensity of the solar radiation has significant effect on the performance of the evacuated solar tube. Moreover, the performance also depends on various other operating parameters.

Theoretical cost and energy optimisation of a 4th generation net-zero district heating system with different thermal energy storage technologies.

A model was used to simulate and optimise a speculative district heating (DH) system for an existing urban area in Loughborough, UK. Heat was supplied using only renewable heat sources (RHS) with long and short duration thermal energy storage (TES) systems used to address mismatch between heat generation and demand. For an 18-month simulation period, a) building heat loads, b) heat generated, c) heat flow to and from stores, and d), heat losses from the stores and network were calculated using hourly weather data, network and building characteristics. RHS included evacuated-tube solar thermal collectors (ETSTCs), and ground and air source heat pumps powered by electricity generated by solar-photovoltaic (PV) and Wind turbines (Wind). The effect of long-term TES system volume and charging temperature on the calculated DH system cost per dwelling, and the calculated DH system energy efficiency was assessed. The minimum cost of the DH system was obtained by modifying the capacity of installed Wind and PV, while ensuring that heat demands were met in every hour of the simulation. A minimum cost per dwelling of £12,278 was predicted with an energy efficiency of 84.84 % for a long term TES volume of 15,000 m3 and temperature of 60 °C.

Solar-Powered Adsorption-Based Multi-Generation System Working under the Climate Conditions of GCC Countries: Theoretical Investigation

In this study, transient modelling for a solar-powered adsorption-based multi-generation system working under the climatic conditions of the Gulf Cooperation Council (GCC) countries is conducted. Three cities are selected for this study: Sharjah in the United Arab Emirates, Riyadh in Saudi Arabia, and Kuwait City in Kuwait. The system comprises (i) evacuated tube solar collectors (ETCs), (ii) photovoltaic-thermal (PVT) solar collectors, and (iii) a single-stage double-bed silica gel/water-based adsorption chiller for cooling purposes. A MATLAB code is developed and implemented to theoretically investigate the performance of the proposed system. The main findings of this study indicate that among the selected cities, based on the proposed systems and the operating conditions, Riyadh has the highest cooling capacity of 10.4 kW, followed by Kuwait City, then Sharjah. As for the coefficient of performance (COP), Kuwait City demonstrates the highest value of 0.47. The electricity generated by the proposed system in Riyadh, Kuwait City, and Sharjah is 31.65, 31.3, and 30.24 kWh/day, respectively. Furthermore, the theoretical results show that at 18:00, the overall efficiency of the proposed system reaches about 0.64 because of the inclusion of a storage tank and its feeding for the adsorption chiller. This study analyzes the feasibility of using a combination of ETCs and PVT collectors to drive the adsorption chiller system and produce electricity in challenging weather conditions.