Flat Plate Solar Collector System Research Articles

Noble MXene nanofluids' impact on solar collector effectiveness enhancement: a CFD numerical evaluation

The thermal flat plate solar collector (FPSC) is a versatile solar harvesting system that may be integrated into various designs and base fluids. This study presents a novel investigation of using nanofluids to transfer thermal energy in an FPSC system. Using the governing equations in CFD simulations, the performance of an FPSC is studied numerically. The base fluid has been defined as a 60:40 blend of ethylene glycol and water. The effects of three distinct volume fractions of MXene nanofluids in the 0.01–0.1% range on the efficiency are investigated. The numerical findings revealed that employing MXene nanofluid increases outlet temperature efficiency by about 5.83%, 6.06%, and 6.31% when 0.01%, 0.05%, and 0.1% volume fractions of nanofluids are used, respectively. The research aims to create a validated numerical model that can be used to assess the effectiveness of FPSC utilizing ethylene glycol and water or other nanofluids of any mass fraction as a working fluid. To examine the overall effectiveness of the FPSC, a numerical model was created using Solidworks software and ANSYS ICEM CFD. The numerical findings revealed that (i) increasing the proportion of MXene nanofluid in the FPCS enhances efficiency to 0.1% volume fraction, and (ii) MXene nanoparticles may be used in the solar collector to improve efficiency.

Exergy-based techno-economic and environmental assessments of a proposed integrated solar powered electricity generation system along with novel prioritization method and performance indices

This study focused on the two important gaps in the literature. The first is solar energy- powered electricity generation in a more economical way via the integration of flat plate solar collector (FPSC), an Organic Rankine Cycle (ORC), and an absorptional heat transformer (AHT) system. Another gap is advanced exergy analysis of the AHT cycle/ORC process based on renewable energy integration to reveal clues for improving the system. To close these gaps, a novel system including a lithium bromide AHT cycle-ORC with a FPSC system application was proposed in this study. In this proposed system, the temperature of the heat source for the ORC system was upgraded via an integration of the AHT and FPSC cycles. The main components of the AHT cycle are the condenser (ABScon), refrigerant cycle pump (P1), evaporator (EV), absorber (ABS), solution heat exchanger (SHX), absorbent cycle pump (P2), expansion valve (V), generator (Gen), ORC turbine (ORCT) and ORC condenser (ORCcon). To demonstrate the electricity production from solar energy in a more economical way thanks to the proposed system, a comparison was made with similar-scaled existing solar power plants. The results supported the main purpose of this study. The annual electricity production with the proposed system was calculated as 2601 MWh, with initial investment cost and payback period values of US$3.924 million and 4.531 years, respectively. The conventional and advanced exergy, exergoeconomic, environmental impact, and sustainability analyzes were also performed. Based on these, the novel performance parameters and prioritization method were proposed to assess the improvement potential of the system. The results indicated that SHX and FPSC had the highest exergy destruction rates (EDRs) of 23.711% and 21.849% over 5853.89 kW due to the stronger thermal and chemical reactions. Similarly, Gen, FPSC, and SHX had the highest ED cost rates (CRs) of 67.59%, 59.09%, and, 47.98%, respectively. Gen, V, and ORCcon were higher contributors to the exergy destruction rates of almost all the components. However, these showed an adverse manner for irreversibility activities. So, the temperatures of Gen and ORCcon should be optimized carefully. ABScon, P2, P1, ABS, Gen, ORCT, and ORCcon had high development priority to improve the whole system.

9E analysis of a flat plate solar collector system implementation: A new approach based on digital twin model coupled with global sensitivity analysis and multi-objective optimization

Flat plate solar collectors are technology with the most solar thermal energy field applications, and different studies based on artificial intelligence have been used to model these systems. This research study presents a 9E analysis based on a digital twin model coupled with global sensitivity analysis and multi-objective optimization of a solar system integrated with an array of flat plate solar collectors to satisfy residential hot water demand that represents a case study with different applications. A model based on artificial neural networks was trained, and a global sensitivity analysis using the Sobol method and a multi-objective optimization study using a genetic algorithm were also implemented. The main outcomes revealed that the digital twin model presented a high correlation above 0.99, and the 9E analysis reported a maximum value of 25.18% for thermal efficiency and 0.266% for exergetic efficiency. Also, a value of 1798.5 kgCO2/year was obtained for the amount of CO2 mitigated, $1342.9 USD for net present value, $0.0104 USD/kWh for levelized cost of energy, and 92.62, 0.519 kgCO2/year, $3.43, $1.34, and $0.00752 USD/year for energoenvironmental, exergoenvironmental, enviroeconomic energoenviroeconomic, and exergoenviroeconomic indicators, respectively. The methodology and the 9E analysis results provide a comprehensive approach that determines the optimal choice by analyzing the system's viability with different assessments and goes beyond the conventional analyses currently presented in the literature as it shows an untapped market potential for the best decision-making.

Performance of Polymer Composite Constituted Cabinet Dryer Integrated within a Solar Flat Plate Collector

Generally, solar dryer cabinets are made up of sheet metals that are heavy, costly, tend to rust over time, and possess the high heat rate to the outer atmosphere. In order to overcome these drawbacks, this research urges to develop a natural fiber reinforced polymer-based cabinet dryer, specially designed and fabricated for the purpose of solar drying. Nylon is used as the matrix material and Prosopis juliflora in particulate form is used as the natural fiber reinforcement. The dryer cabinet was designed at industrial scale to dry 5 kg of ginger at a single setting. This work also studies the efficiency of the polymer composite cabinet integrated with a flat plate solar collector system that is coated with copper and black chrome attached to corrugated fins in between the absorber plate and storage medium. The FRP chamber was compartmented in its interior with aluminium perforated sheets and experimentation was performed to determine the efficiency of the composite cabinet based on reduction of heat loss from the system. The performance of the coating, storage medium materials, and overall storage efficiency were also studied. The FRP cabinet resulted in a moisture level less than 8.5% within 4–7 days. Exergy studies showed 75% efficiency and energy studies gave 25.5 kJ/kg peak readings of drying efficiency for a period ranging between 11 and 12 hours. This was a 75% increment in energy efficiency. Thermal degradation of the FRP material was found to be stable up to 300°C. The overall weight of the constructed polymer cabinet was 25% lesser than the conventional systems.

Performance evaluation of a hybrid thermoelectric generator and flat plate solar collector system in a semi-arid climate

This study investigates the performance of a hybrid system that combined thermoelectric generators (TEG) with a solar flat plate collector system (SFPC) to turn more renewable energy into useable energy under normal operating and environmental conditions. A multi-month case study was first time conducted to explore the performance of SFPC with and without TEGs under the cold climatic conditions of Abha, Saudi Arabia. The result demonstrates that the heat losses from the rear surface of the SFPC's absorber plate were effectively utilized by TEGs, thereby decreasing overall heat losses and increasing the SFPC's overall thermal efficiency. Further, it was found that adding TEGs at the rear surface of SFPC's absorber plate improves thermal efficiency and exergy efficiency by 8.4% and 1.3%, respectively. The hybrid TEG-SPFC system can turn waste heat into useable electricity, with a peak power output of 2.2 W at midday. Maximum power was generated around midday, when the temperature differential between the upper and lower layers of TEGs was greatest. In addition, it was noticed that the thermal efficiency of the SFPC diminishes when the inlet water temperature rises. A hybrid TEG-SFPC system's exergy efficiency depends on ambient temperature variation and solar irradiance.

Performance assessment of solar and desiccant aided building air-conditioning system

Indoor thermal comfort significantly influences people’s health, happiness and consequently the output at the workplace. Here, a systematic simulation study on a conventional vapor compression-based building cooling system integrated with desiccant assisted dedicated outdoor air system (DOAS) is performed using EnergyPlus software for warm and humid climate zones. Impact of using desiccant material in the DOAS, on the cooling load requirement of the building, coefficient of performance (COP), and energy consumption of the system is discussed. The building design is well-validated with the available guidelines. Desiccant assisted system supplies dehumidified air inside the building space which affects the evaporator performance. A flat plate solar collector system is used to supply the hot air to regenerate the desiccant material. Electric energy savings in desiccant assisted system can be achieved up to 5.5 %, whereas, the COP of the system is not found to be significantly affected even though thermal load demand reduces by nearly 13.5 % by the proposed modification.

(Digital Presentation) Electrodeposition and Characterization of a Selective Coating on Aluminum for Scale-up in Thermo-Solar Applications

Flat-plate solar collector systems are devices used to convert solar energy to thermal energy. These devices require a selective coating that absorbs all sunlight but does not emit energy in the near IR; hence, a multilayer system of metal/IR-reflector/metal oxide is often used. Many substrates are used, including metals such as copper, stainless steel, and aluminum. Aluminum is an interesting substrate for its lower cost and good optical properties. Electrodeposited materials have gained importance in the industry for the easy handling and good results in scale-up. However, in general it is difficult to electrodeposit onto aluminum due to the ever-present thin insulating oxide film. In this work, we propose an adherent interlayer film based on copper, which is electrodeposited onto aluminum, and serves as a basis for the subsequent electrodeposition of a selective coating consisting of bright nickel and the absorber film of electrodeposited black nickel. Solar collectors based on aluminum substrates and this electrodeposited selective coating are specifically useful for thermo-solar applications at low to medium temperature.Electrochemistry studies including cyclic voltammetry, rotating disk cyclic voltammetry, and galvanostatic curves are carried out for all the different layers. The properties of the coatings are subsequently characterized by reflectance spectra using UV-Vis, NIR and IR spectrophotometers equipped with integrating spheres. The solar absorptance is calculated by weighting the reflectance spectrum against the solar radiation spectrum ASTM G173-03. The thermal emittance is calculated weighting the reflectance spectra against the black body radiation function at 100 °C. The morphology and homogeneity of the film are evaluated with scanning electron microscopy, and energy dispersive spectroscopy. X-ray photoelectron spectrometry is used to determine the film composition. The crystalline structure of the films is studied by X-ray diffraction and Raman measurements. The second and third layer, bright nickel, and black nickel, respectively, are electrodeposited on top of the Cu layer using a previously reported method. We characterize the selective coating electrodeposited onto aluminum/Cu/bright nickel and show that this is a viable technology for the fabrication of low-cost and high efficiency flat plate solar collectors. In addition, we demonstrate the scale-up of the electrodeposition process, and characterize the performance of a complete flat-plate solar collector device of 1.8 m2 gross area.AcknowledgementsThe authors gratefully acknowledge CONACYT, Módulo Solar S.A. de C.V. and IER-UNAM for funding through the Mexican Center for Innovation in Solar Energy (CeMIE-Sol), Project P-81.

Heat Transfer Analysis of Nanostructured Material Flow over an Exponentially Stretching Surface: A Comparative Study

The objective of the present research is to obtain enhanced heat and reduce skin friction rates. Different nanofluids are employed over an exponentially stretching surface to analyze the heat transfer coefficients. The mathematical model for the problem has been derived with the help of the Rivilin–Erickson tensor and an appropriate boundary layer approximation theory. The current problem has been tackled with the help of the boundary value problem algorithm in Matlab. The convergence criterion, or tolerance for this particular problem, is set at 10−6. The outcomes are obtained to demonstrate the characteristics of different parameters, such as the temperature exponent, volume fraction, and stretching ratio parameter graphically. Silver-water nanofluid proved to have a high-temperature transfer rate when compared with zinc-water and copper-water nanofluid. Moreover, the outcomes of the study are validated by providing a comparison with already published work. The results of this study were found to be in complete agreement with those of Magyari and Keller and also with Lui for heat transfer. The novelty of this work is the comparative inspection of enhanced heat transfer rates and reduced drag and lift coefficients, particularly for three nanofluids, namely, zinc-water, copper-water, and silver-water, over an exponentially stretching. In general, this study suggests more frequent exploitation of all the examined nanofluids, especially -water nanofluid. Moreover, specifically under the obtained outcomes in this research, the examined nanofluid, Ag-water, has great potential to be used in flat plate solar collectors. Ag-water can also be tested in natural convective flat plate solar collector systems under real solar effects.

Area Optimization of a Flat Plate Collector for Meeting the Air Conditioning Load of an Office Building Using a Solar Vapor Absorption System

A solar single effect vapor absorption system is designed to meet the cooling demand of an office building having a floor area of 100 m2. The absorption system operating parameters are optimized using Genetic algorithm to maximize the coefficient of performance (COP). The solar insolation at a location is used as the heat source for the absorption refrigeration generator heat input. The monthly total global radiation at the location for a particular year is found. The insolation profile of a representative day of the year is the input source for the sizing of the solar flat plate collector. Also, the ambient temperature variation profile is used to dynamically simulate the system performance. The refrigeration system is integrated with the solar collector and storage tank to meet the varying cooling load. The total generator load required to meet the cooling load profile of the building is found from the vapor absorption system model in Matlab. The solar flat plate collector system is modelled in such a way that the energy output from the solar collector matches the generator load required. The hot water temperature to generator (heat supplied) is kept constant at 85°C. The generator load required to meet the varying cooling load is achieved by controlling the solution pump flow rate in absorption system. The optimal area of the collector required for meeting the total generator load is found as 14.6 m2. The storage volume required in the storage tank is 0.48 m3. In the solar collector, a variable water flow system profile is used to maintain the constant temperature required in the generator.

Techno-Economic Assessment of Evacuated Flat Plate Solar Collector System for Industrial Process Heat

Techno-Economic Assessment of Evacuated Flat Plate Solar Collector System for Industrial Process Heat

Simultaneous Production of Solar Thermal Heat and Power for Industrial Applications

Currently most of the energy production is supported by fossil fuels, however, renewable sources contribution on worldwide demand of energy has been in constantly growth. One of the main challenges in the use of solar thermal energy in industrial processes is their cost, especially when is compared to energy generation by fossil fuels. This cost delimits the investment payback time for a thermo-solar installation to be feasible. This fact makes crucial the development of methodologies for the integration of solar energy for large-scale industrial applications. This work deals with the thermo-economic evaluation of the heat and power production through a low-temperature flat-plate solar collector system. Also, strategies were developed to increase energy efficiency by evaluating different process integration scenarios. The proposed strategies for energy efficiency combined with renewable energy were applied to an integrated solar thermal energy system into a 1G and 2G (first and second generation) bioethanol process from sugarcane. It was found that to replace the fully process heat and power with low-temperature solar thermal energy, a heat recovery network ? ?? ?????? of 5 °C, a heat duty of 131 kW and a supply temperature of 105 °C are required. All these results lead to a cost of 0.2112 USD/kWh of the integrated system. The power system operates independently by mean an Organic Rankine Cycle and the heating system is supplied by a solar collector network with a cost of 0.0477 USD/kWhele.

The effects of the use of hybrid and mono nanofluids on thermal performance in flat‐plate solar collectors

Since considerable amount of energy is spent in water heating processes in the world, solar energy systems are of great importance while heating water. Amongst these systems, flat-plate solar collector systems have an extensive area of use in residences. Therefore, nanofluid system has been investigated in order to enhance the efficiency in water heating through flat plate solar collectors and to benefit from solar energy more effectively. A simplified model has been taken into consideration to design the model of this system and complete the analyzes more rapidly. To identify the accurateness of the model, comparisons have been made against an experimental and a numerical study; and, a decent convergence to the experimental data has been obtained. Nanofluids used in the system have been applied in hybrid structure. The analysis has been conducted for the case of that two different nanometer-sized metal nanoparticles (SiO2 and Cu) are mixed in water-based base fluid with different volume concentrations. Influences of nanofluids in different volume fractions on thermal performance have been investigated and compared against water and each other. In the system having 30° angle, diversified flow rates and heat fluxes have also been evaluated. It is concluded that water-based nanofluids enhances thermal performance; and, amongst these, the nanofluid including Cu nanoparticles augments thermal performance much better. To avoid precipitation problems within the system, thermal performance has been increased by virtue of using nanofluids with lower volumetric concentrations in hybrid form by adding certain amount of Cu nanoparticle instead of using high volumetric concentrations of SiO2 nanoparticles. In comparison to water, these nanofluids we utilized have increased thermal performance in the rates of 2.03% (2%SiO2 + 1%Cu-H2O), 3.218% (1%SiO2 + 2%Cu-H2O), 0.943% (3%SiO2-H2O), 4.076% (3%Cu-H2O), 4.083% (3%SiO2 + 2%Cu-H2O), 4.935% (2%SiO2 + 3%Cu-H2O), 1.569% (5%SiO2-H2O), and 6.508% (5%Cu-H2O).

An adaptive short-term forecasting method for the energy yield of flat-plate solar collector systems

The number of large-scale solar thermal installations has increased rapidly in Europe in recent years, with 70% of these systems operating with flat-plate solar collectors. Since these systems cannot be easily switched on and off but directly depend on the solar radiation, they have to be combined with other technologies or integrated in large energy systems. In order to most efficiently integrate and operate solar systems, it is of great importance to consider their expected energy yield to better schedule heat production, storage and distribution. To do so the availability of accurate forecasting methods for the future solar energy yield are essential. Currently available forecasting methods do not meet three important practical requirements: simple implementation, automatic adaption to seasonal changes and wide applicability. For these reasons, a simple and adaptive forecasting method is presented in this paper, which allows to accurately forecast the solar heat production of flat-plate collector systems considering weather forecasts. The method is based on a modified collector efficiency model where the parameters are continuously redetermined to specifically consider the influence of the time of the day. In order to show the wide applicability the method is extensively tested with measurement data of various flat-plate collector systems covering different applications (below 200°Celsius), sizes and orientations. The results show that the method can forecast the solar yield very accurately with a Mean Absolute Range Normalized Error (MARNE) of about 5% using real weather forecasts as inputs and outperforms common forecasting methods by being nearly twice as accurate.

Multi-objective search group algorithm for thermo-economic optimization of flat-plate solar collector

This study aims to develop a multi-objective version of the search group algorithm (SGA) called the multi-objective search group algorithm (MOSGA) to help determine thermo-economic optimization of flat-plate solar collector (FPSC) systems. Search mechanisms of the SGA were modified to determine non-dominated solutions through mutation, generation, and selection stages. Authors also mined the Pareto archive with a selection mechanism to maintain and intensify convergence and distribution of solutions. The study tested the proposed MOSGA with well-known multi-objective benchmark problems. Results were compared with outcomes from conventional algorithms using the same performance metrics to validate the capability and performance of the MOSGA. Afterward, MOSGA was applied to find the best design parameters to simultaneously optimize thermal efficiency and the total annual cost of FPSC systems. Four case studies were conducted with four different working fluids (pure water, SiO2, Al2O3, and CuO nanofluids). Optimization results obtained by the MOSGA were analyzed and compared with solutions provided by other algorithms. The findings revealed relative improvement in thermal efficiency and reduced annual cost for all nanofluids compared to pure water. Thermal efficiency was improved by 2.2748%, 2.4298%, and 2.7948% for SiO2, Al2O3, and CuO case studies, respectively, compared to pure water. Meanwhile, TAC rates were increased by 2.4111%, 2.3403%, and 2.9133% for these case studies, respectively. Comparative results also demonstrated that MOGSA was robustly effective and superior in the selection of appropriate design parameters of FPSC systems.

Modelling of a flat plate solar collector system using response surface methodology

Abstract: In this study, performance analysis of flat plate solar collector has been carried out analytically.
 A comprehensive mathematical modelling of thermal performance is modelled using Response Surface Methodology and optimal geometrical and thermodynamic parameters are predicted pertaining to optimum performance of the system. In this study a model was developed for evaluating and predicting the efficiency, outlet temperature and performance of a flat plate solar collector considering the hour angle, day and input temperature as input parameters.
 In the cause of the work it was found that the days and months close to the beginning of the year (January, February, March and April) yielded higher outlet temperature and solar radiation due to dry season, while the months at the middle of the year showed lower outlet temperature and solar radiation due to the rainy season. The months towards the ending of the year also showed higher outlet temperature and solar radiation respectively.

Application of Generalized Regression Neural Network in Predicting the Thermal Performance of Solar Flat Plate Collector Systems

Abstract This study presents a smart neural network (NN) model for estimating the thermal performance of a transient nature solar flat plate collector system (SFPCS). For this purpose, a series of experimental studies are conducted through four successive days with three different arrangements of SFPCS (standalone, series, and parallel). Experimental results of such arrangements are then used for designing a generalized regression neural network (GRNN) model. The GRNN architecture proposed in this study consists of four inputs (mass flowrate, solar irradiance, fluid temperature difference, and collector area) and two dependent outputs (power output and efficiency of SFPCS). Such GRNN architecture is trained, tested, and validated with real-time experimental transient datasets for each arrangement individually. The results of the GRNN model are in good agreement with experimental datasets. The overall accuracy of the developed GRNN model in predicting the performance of standalone, series, and parallel connected SFPCS is 98%.

Modelling of a flat plate solar collector system using response surface methodology

In this study, performance analysis of flat plate solar collector has been carried out analytically.
 A comprehensive mathematical modelling of thermal performance is modelled using Response Surface Methodology and optimal geometrical and thermodynamic parameters are predicted pertaining to optimum performance of the system. In this study a model was developed for evaluating and predicting the efficiency, outlet temperature and performance of a flat plate solar collector considering the hour angle, day and input temperature as input parameters.

Building thermal load management through integration of solar assisted absorption and desiccant air conditioning systems: A model-based simulation-optimization approach

Performance of standalone air-conditioning systems is affected while simultaneously handling both sensible and latent building loads. Model-based simulation and optimization is one of the best ways to analyze system's performance under load fluctuations at the initial design stages. Therefore, in the current study, seasonal transient simulations of an Integrated Absorption Desiccant System are carried out using TRNSYS to handle sensible (10.94 kW peak) and latent (4.44 kW peak) cooling load separately. Radiant cooling with chilled water from an absorption chiller mainly handles sensible cooling load, while the latent load is achieved by a solid desiccant dehumidification system. Initially, key components of the system are modeled in TRNSYS including a flat plate solar collector system, desiccant wheel, heat recovery wheel, and absorption chiller. Afterwards, the integrated model is coupled with GenOpt to optimize the solar fraction and thermal coefficient of performance by varying collector area, flow rate in the collector loop, flow rate in load side loop, and volume of storage tank. The resulted optimized value of solar fraction is 57.50%, and COPth is 0.55 for standalone absorption system, whereas the solar fraction of 56.20%, COPth of 1.52 are achieved for IADS. In addition, the effects of load variation in terms of sensible to latent load ratio on regeneration heat required for both IADS and conventional desiccant system are also analyzed. A critical value of load ratio of 0.75 is also observed in terms of heat regeneration requirements to compare the both systems. The proposed approach and analysis will be very helpful for HVAC designers for optimal system performance through separate load handling, especially at the initial design stage.

Fabrication and Performance Evaluation of Integrated Solar-Driven Membrane Distillation System with Serpentine-shape of Flat Plate Solar Collector for Seawater Desalination

Solar-powered membrane distillation (SPMD) system has gained its popularity in desalination application for past decade credit to the system efficiency in producing pure water and the utilization of renewable energy. However, most of the past SPMD works used commercial solar thermal collector (STC) as the thermal energy supply to the feed solution and the study only focused on the performance of the system in terms of flux and salt rejection. In this work, a self-made flat plate solar collector (FPSC) with the serpentine-shape pipe was designed and fabricated to study the effect of the STC towards the membrane performance. Before testing, a simulation work of the fluid flow inside the serpentine-shape pipe of the FPSC was analyzed using NX 10.0 computer-aided design simulation. After that, the efficiency of the self-made FPSC system was tested directly to sunlight in order to identify the maximum irradiance and the temperature of the feed solution. Due to the fluctuation of solar irradiance, the experimental setup of the SPMD system was tested using a solar simulator, and the performance was compared with the membrane distillation (MD) system without integration with FPSC system. Based on the simulation data, it can be concluded that the heat losses across the pipe are due to the slower fluid velocity and sudden pressure drop, which attributed to centripetal force and pressure differences. Meanwhile, the outdoor evaluation data showed that the temperatures of collector and water inside the feed tank could reach up to 84°C and 64°C, respectively when the maximum irradiance of 938 W/m2 was applied. For the performance evaluation between with and without the self-made FPSC system, it can be seen that only marginal difference can be observed for the permeate flux and salt rejection with an average difference of 6.06% and 1.29%, respectively.

Study on the hysteresis characteristic of solar thermal storage system

The thermal storage efficiency is one of the important indicators for evaluating the operation of solar thermal storage system. Affected by the thermal inertia of the system, the analysis of the relationship between the thermal storage efficiency and solar radiation, which is inadequate at the smaller time scale. This paper measured the operation of a flat plate solar collector system, studied the hysteresis characteristics of the system’s collector efficiency changes with solar radiation, took a numerical solution method for the actual lag time of the system and finally obtained the actual influence rule of solar radiation on the collection efficiency per minute. The results show that the solar collector’s efficiency change lags behind the solar radiation by 27 min; combined the lag time, the relationship between the modified thermal storage efficiency and solar radiation also were analysed; initially the modified storage efficiency per minute increases with the solar radiation, then gradually decrease after reach a certain value, due to the overall system temperature is higher and the system temperature rise is smaller when the solar radiation is large enough; the varying curve conforms to quadratic function. It provides theoretical support and practical reference for contrasting and evaluating the thermal storage efficiency changes with solar radiation in a smaller time scale.