Flat-plate Collector Research Articles

Solar energy harvesting from evacuated flat plate collector: Design, thermo-economic analysis, and off design performance

Adopting renewable energy technologies is becoming more and more popular, particularly in the industrial sector. Evacuated Flat Plate Collector (EFPC) is a promising technology which combines advantages of Flat Plate and Evacuated Tube Collector. It can be a potential device to be integrated into industrial process heating systems. In the current paper, the performance analysis of EFPC has been conducted for an operational textile factory through a validated mathematical model. Optimization of three design parameters, i.e., tube diameter, distance between tubes, and thickness of absorber plate is studied and their effect on four-important parameters, i.e., outlet temperature, overall heat loss coefficient, thermal efficiency, and exergy efficiency have been investigated. In energy and exergy analysis, the aforementioned four parameters are considered as performance indicators of EFPC and investigation is done into how fluid temperature at inlet, fluid flow rate, and variation of solar irradiance affects them. Collector performance in different seasons, i.e., summer, spring, and winter, has been examined using hourly radiation of an arbitrary day of that season. From economic analysis, it is found that up to 21.22% of the required heat can be supplied by EFPC, which ultimately contributes to reduce the cost of fuel up to 19.36 USD per day. Environmental analysis reveals that integration of EFPC can decrease CO2 emission significantly, up to 3.92 tons in summer, which will lead to a positive impact on the environment. Government and environmental organizations might be inspired to fund the installation by this fact which will increase feasibility of project.

Application of PEG-Fe3O4 nanofluid in flat-plate solar collector: An experimental investigation

In the present study, novel in-situ oxidation precipitation of ferrous hydroxide method is used to synthesized Fe3O4 nanoparticles and Polyethylene glycol 200 is used for covalent functionalization. Various characterizations tests (FESEM, EDX, XRD, FTIR, HRTEM) were performed, and the Polyethylene glycol treated Iron oxides functionalization was confirmed. Thermal conductivity, density, specific heat, and viscosity were experimentally assessed and validated using the correlations that were available. The corresponding improvements in thermophysical characteristics were 13.35%, 0.06%, 0.37%, and 20.9% at 0.1 wt% and 35°C. UV–vis spectroscopy and Zeta protentional was used to check the stability of nanofluids and found that nanofluid was stable for 30 days. A flat plate solar collector was experimentally installed, and the thermal performance of collector was calculated using ferrofluid under ASHRAE standard 93–2003 at different heat flux intensities (597,775,988 W/m2), mass flow rates ((0.0133, 0.0200, 0.0266 kg/s), inlet fluid temperature (30–50°C) and weight concentrations (0.025,0.05,0.075,0.1%). The highest thermal efficiency enhancement of 13.83% was noticed. Moreover, the ANSYS-CFD model was used for the numerical analysis of the thermal performance of flat plate collector at the same environmental conditions, and a maximum difference of 8.33% at 0.1 wt% was noticed in comparison with experimental data.

Investigation of the thermal performance and environmental impact of a forced circulation solar water heating system during the heating season

A thermal analysis of a forced circulation solar water heating system (SWHS) was carried out. Three different models were analyzed: SWHS without an auxiliary heater, SWHS with an auxiliary heater, and electric heater only. The study was carried out for the province of Mersin-Turkiye. Flat plate collectors with different structural properties were used in simulations, the best results were obtained with the collector with black chrome absorber coating. This system met 55% of the hot water requirement on the design day without requiring any auxiliary heater. During the season, 18.7% of hot water needs were met in January, 20.42% in February, 37.6% in March, 31.2% in November, and 20.5% in December. SWHS with an auxiliary heater, consumed 1130.3 kWh of electrical energy during the heating season, resulting in 540.3 kg of CO2 emissions. 33 % reduction in greenhouse gas (GHG) emissions is achieved with this system compared to a base system powered by electricity only. The hot water use profile is an essential factor in the design of the SWHS. Since the systems using fossil fuels can meet the needs of the users, energy storage techniques must be adapted to the SWHS to be an alternative.

Performance analysis of natural and forced convection mixed mode UV tent house solar dryer for potato drying

ABSTRACT A solar dryer that uses solar radiation and a mixed mode of operation was installed. The dryer includes a flat plate collector with 1.12 m2 area covered by 5.0 mm glass. It has two trays for holding potato slices in the drying chamber. Meteorological data, including solar intensity, relative humidity, atmospheric temperature, and wind speed, were recorded. The initial moisture content of the potato slices, which were 2.5 mm thick, was 85.90%. In the forced convection drying mode, the moisture content decreased to 14.10% in 8 hours, while the natural convection mode required 14 hours to reach 14.75%. Forced and natural convection dryings were much faster compared to open sun drying. Air moves through the collector at a speed of 1.1 m/s during forced convection. The moisture ratio varied from 0.4750 to 0.0010 for forced convection drying and from 0.4095 to 0.02646 for natural convection drying. The maximum dryer efficiency was 32.95% for forced convection drying and 26.62% for natural convection drying. The little difference attained between natural and forced convections can be due to the fact that the experiments are not made in the same moment.

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

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

Sustainable Energy Progress via Integration of Thermal Energy Storage and Other Performance Enhancement Strategies in FPCs: A Synergistic Review

Flat plate collectors (FPCs) are the leading solar thermal technology for low-medium range temperature applications. However, their expansion in developing countries is still lacking because of their poor thermal performance. Improving the thermal performance of flat plate collectors (FPCs) is a crucial concern addressed in this review This study comprehensively discussed the performance improvement methods of FPCs, such as design modification, reflectors, working fluid, and energy storage materials, by covering current issues and future recommendations. Design factors such as coating and glass cover thickness, thickness of absorber plate and material, air gap between the glass cover and absorber plate, and riser spacing, along with insulation materials, are examined for their impact on FPC performance. Absorber design changes with selective coatings for improving the heat transmission rate between the working fluid and absorber are critical for enhancing collectors’ thermal output. The nanofluids utilization improved FPC’s thermal performance in terms of energetic and exergetic outcomes in the 20–30% range. Moreover, adding a heat storage unit extends the operating hours and thermal output fluctuations of FPCs. Research suggests that employing turbulators and nanofluids as heat transfer fluids are particularly effective for enhancing heat transfer in FPCs. This comprehensive review serves as a critical tool for evaluating and comparing various heat transfer augmentation techniques, aiding in the selection of the most suitable option.

Comparison between two LiBr–H2O absorption-compression chillers and a simple absorption chiller driven by various solar collectors: Exergy-economic performance and optimization

Although some studies have been conducted on various types of compressor-based absorption chillers (ACH), a comprehensive comparison of the performances of these configurations has not been made. In addition, selecting a proper solar collector in combination with the best compressor-based ACH is worthwhile as solar energy is widely available during the summer season. For this purpose, the exergy-economic performances of 12 LiBr–H2O chiller configurations are compared in the present study to produce 100 kW of cooling. The configurations are a single-effect ACH and two absorption-compression chillers (ACCH) driven by 4 collector types, namely, a flat plate collector (FPC), an evacuated tube collector (ETC), a parabolic trough collector (PTC), and a compound parabolic collector (CPC). In ACCH 1, a compressor is embedded between the evaporator and the absorber of the ACH. In ACCH 2, a compressor is employed between the generator and the condenser of the ACH. The outcomes of the research indicate the superiority of the PTC and ETC over the two other collector types in terms of exergy efficiency and economic performance, respectively. The highest exergy efficiency and lowest total cost rate are calculated as 4.8% and 23.58 $h−1, which are obtained by the PTC-driven ACCH 1 and ETC-driven ACCH 1, respectively. Nevertheless, the unit cost of cooling produced by these two layouts is too high compared to the other configurations. Hence, they cannot be selected as the best configuration. Instead, the ETC-driven ACCH 2 is selected as the best configuration since it brings about the lowest unit cost of cooling (20.45 $GJ−1), and it has acceptable values of exergy efficiency (4.11%) and total cost rate (29.3 $h−1).

Analyzing performance of a solar water heater using nano-ZrO2/water-based nanofluid

Solar-based residential water heaters have become the most cost-effective and sizable use of renewable energy in commercial and housing developments. In order to improve the performance of such components, the deployment of nanofluids have been proposed in recent times. This study in intended to examine the influence of employing a zirconium oxide/water-based (nano-ZrO2/water) nanofluid as the heat absorption medium on the performance of a flat-plate collector solar powered water heating system (SPWH). The weight percentage of nano-ZrO2 had been held constant as 0.5%, and a distinct discharge rate of 0.0185 kg/sec had been maintained during the investigation. The analysis was accomplished with the SPWH system during the month of August 2022. The outcomes demonstrate that, compared to employing the plain water as working medium, operating the SPWH with the nano-ZrO2/water nanofluid yielded much better results, in terms of the system's efficiency and the temperature of the water being discharged. The efficiency of SPWH was observed to be increased by 20.68% owing to the nano-ZrO2/water-based nanofluid at a discharge of 0.0185 kg/sec.

Feasibility Study of Theoretical Efficiency Calculation for Flat Plate Collectors in Solar Water Heating Systems

Solar energy stands as a paramount clean, abundant, and renewable power source holding remarkable potential to address our escalating energy needs. Among its crucial utilization methods, solar water heating systems integrating flat plate collectors (FPCs) emerge as vital contributors in harnessing and converting solar energy into utilizable heat. This study delves into the realm of FPCs' theoretical efficiency assessment, employing mathematical models and factoring regional weather conditions to meticulously evaluate the efficiency of single-glaze and double-glaze collector variants. The outcomes spotlight the single glaze collector's efficiency at 0.669 and the double glaze collector at 0.713, underscoring the discernible performance gap. In a landscape where industries, hospitals, residences in Kandahar, and comparable settings extensively depend on hot water, often derived from fossil fuel-driven heating, this research's implications hold particular relevance. By transitioning towards solar water heating, this study not only underscores a concrete method to curtail carbon emissions but also to significantly reduce energy expenses linked with conventional heating techniques. The findings beckon a departure from the status quo, emphasizing that cleaner energy options are attainable, even for regions demanding hot water requirements. As society navigates complex decisions concerning energy sourcing, embracing solar water heating stands as an auspicious stride towards a sustainable future, beckoning us to collectively embark on a path of energy-conscious choices for the greater good of our planet and the generations that will inhabit it.

A scalable phase change material-based system enhanced by multi-walled carbon nanotubes and fins for efficient solar water heating applications

Phase change material (PCM)-based harvesting and storage systems are promising solutions to solar energy's intermittence and non-uniformity issues. Previous efforts have focused on the absorption, conversion, and storage capability of PCMs. However, efficiently utilizing the stored thermal energy within PCMs remains challenging. Herein, we devise a facile and scalable PCM-based system with heat transfer and light absorption enhancement simultaneously by fins and multi-walled carbon nanotubes (MWCNTs) for solar water heating applications. Photothermal conversion experiments demonstrate that the water temperature of the PCM-based system with MWCNT and fins is up to 79.0 °C under the stationary condition, which is increased by 58.6 % and 55.2 % compared to the original composite and the MWCNT-doped one, respectively. Furthermore, numerical simulations indicate that fins act as a bridge between PCM and water, facilitating rapid heat transport and improving the thermal energy storage pattern, enabling efficient solar water heating. The water temperature can keep above 40.0 °C for 51 min at a flow rate of 11.34 l/h under ambient cooling conditions, and the maximum thermal efficiency is up to 89.2 %, which is higher than most flat plate and tubular solar collectors, demonstrating the superiority of the proposed system.

Energy and the economic estimation of three SWH systems under the Mediterranean climate conditions

This research is focused on the energy estimation of 3-SWH systems installed near each other. Two of them are active systems and the third is a passive one. In these systems are utilized heat pipe evacuated tube collectors with dry connection and flat-plate collectors. With the aim to perform the energy estimation of the systems, the mathematical model is built. Experimental data obtained from their database are used. The recorded data for the three considered solar water heating systems refer to a 1-year time period. Monthly values for the solar irradiation on tilted area of the collectors, temperatures, specific solar yields, and system efficiencies are shown in respective graphs. Referring to the considered climate conditions, where the annual solar irradiation on tilted area of the SWHS collectors is 1499 kWh/(m2·year), it was obtained that the system efficiencies are respectively 41.1 %, 51.6 %, and 51.5 %. To assess the differences between the 3-SWHS, the energy balances for the considered period are built. Also, even the economic estimation based on DPBP and NPV is carried out.

CFD coupled heat and mass transfer simulation of pineapple drying process using mixed-mode solar dryers integrated with flat plate and finned collector

The present research deals with the analysis of 3-dimensional computational models to analyze the airflow, temperature profile of dryer coupled with heat transfer of pineapple slices during solar drying. A finite element approach performed the simulations of mixed-mode solar dryers integrated with flat plate and finned collectors consisting of baffles and semicircular loops under forced convection using COMSOL Multiphysics software. The mass transfer of pineapple slices was also simulated to compare the moisture distribution inside the samples dried in both solar dryers. The dryer integrated with flat plate collector (FPSC) presented 2.5 h longer drying period than the finned collector assisted dryer to attain the 10% (wb) moisture of pineapples slices. The airflow pattern indicated inadequate air distribution inside the FPSC and generated two vortices contributing to dead zones and localized heating inside the drying chamber. The finned collector provided a more effective air distribution in the dryer. The sample's temperature was greatly affected by their position because of non-homogenous temperature distribution in FPSC-Dryer and finned collector integrated dryer presented more uniform temperature profile. The results are beneficial for the analysis of uniformity of airflow and temperature in the dryer, which is a deciding factor for homogeneity of drying.

Impact of spatial and annual solar variability on the economic viability of non-tracking solar heating systems

Solar energy is stochastic, varying with time and space, which is a risk factor hindering the deployment of solar heating systems (SHS) in industries. Little is known about the level of risk associated with SHS due to spatial and annual variation. This research thus seeks to quantify the level of risk due to spatial and annual weather variation. The novelty of the study is that it assesses the variability in energy production of different non-tracking SHS at different operating temperatures (60 and 100 °C), different locations, and different time series. The level of risk is quantified using the coefficient of variation (CV) and the z-score. The yearly energy gains are simulated for each collector using the solar collector energy output calculator. The weather data for each location is produced using Meteonorm for a typical meteorological year (TMY). To analyze the annual variability 3 TMYs were produced from the time range 1981–2020 and the spatial variation was analyzed for 9 different locations. In terms of the annual variation, the results show that the CV of the energy gain for all the SHS was between 13 and 26 %. The highest z-score for spatial energy variation was 1.6 and -1.9. Both results indicate a considerably low risk factor. Economic predictions considering 1 TMY showed an underestimation of 4 and 7 % on the levelized cost of heat (LCOH) when operating at 60 and 100 °C respectively. Furthermore, operating at high temperatures has a high variability risk compared to lower temperatures. In terms of the variability of each SHS the compound parabolic concentrator (CV-10) and evacuated tube collector (CV-11) are more stable compared to the solar air heater (CV-14) and flat plate collector (CV-18). Knowing the extent of variability and risk involved for each collector will help investors plan their entire portfolio.

Optimal design of a multi-generation system based on solar and geothermal energy integrated with multi-effect distillatory

In this study, an optimal system is designed to meet the needs of fresh water, heating, cooling and electricity. Four modes were simulated in MATLAB to provide the requirements of a hotel. The combined cooling, heating and power (CCHP) with multi-effect distillation through thermal vapor compression (MED-TVC) was used as the base mode. Geothermal wells (Geo) were employed to convert the renewable energy of the earth into heat and electricity. Also, the flat plate collectors (FPC), photovoltaic panels (PV) were utilized to gain the sun's radiant energy and convert it into heat and electricity. An organic Rankine cycle (ORC) has been used to convert the obtained geothermal energy into electricity. The genetic algorithm has been used for optimal design. In the case of base, base + Solar, base + Geo and base + Solar + Geo 21, 24, 24, 27 design parameters were considered respectively. The total annual cost (TAC), in which the effects of pollution were included, was considered as the objective function in the optimal design. As the innovation of this work, the use of geothermal and solar energy with desalination process combined with CCHP was mentioned, which was not done in previous works. For a case study, the annual needs of a hotel in Bandar Abbas, Hormozgan province, Iran were considered and the TAC obtained results for base, base + Solar, base + Geo and base + Solar + Geo modes were 1.2789×106$/year, 1.0950×106$/year, 5.8048×105$/year and 5.1436×105$/year , respectively. It was found that in the mode of using solar energy, geothermal energy and solar and geothermal energy, the objective function was improved 14.38%, 54.61% and 59.78%, respectively, comparing to the base mode.

A detailed investigation of an evacuated flat plate solar collector

The evacuated flat plate collector is a pioneering solar device for operation at medium temperatures (<200 °C) with high efficiency and without the need for tracking. The goal of this investigation lies in the detailed parametric analysis of an efficient evacuated flat plate collector and its daily performance for the city of Athens (Greece). The parametric analysis presents the instantaneous thermal and exergy performance of the collector for different inlet temperatures, solar irradiation levels, ambient temperatures, specific mass flow rates and the number of riser tubes. The daily analysis presents results for the thermal and exergy performance of the collector for different daily profiles of solar irradiation and ambient temperatures using real weather data. Also, the main innovation of this study lies in the development of a correlation of the daily useful output by taking into account the operating temperature level, the daily irradiation level and the mean ambient temperature. According to the yearly analysis, the optimum exergy efficiency is found at 13.33% for operation at 125 °C and the respective thermal efficiency is found at 47.24%. For this case, the levelized cost of energy and exergy were calculated at 0.0274 €/kWh and 0.1043 €/kWh respectively.

Evacuated tubes solar air collectors: A review on design configurations, simulation works and applications

One of the primary components of solar energy utilization systems is evacuated tube solar air collectors (ETSACs). The irradiance is absorbed by these collectors, which is then transformed into thermal energy at the absorbing surface before being transmitted to the air passing through the collectors. This type of collector outperforms flat plate collectors in terms of reducing heat loss through conduction and convection and also during cloudy days; thus, ETSACs are the most preferred collectors to be applied for space heating, crop drying, and industrial applications. This review focuses on a summary of design configurations, simulation works, and applications of ETSACs in order to understand the influence of the thermal performance of ETSACs so that these collectors can be applied more effectively. Studies on the use of nanofluids as thermal performance enhancers and phase change materials as thermal storage media can be considered to enhance the thermal performance of ETSACs.

Assessment of the Trilateral Flash Cycle potential for efficient solar energy conversion in Europe

The potential of the Trilateral Flash Cycle (TFC) for the efficient conversion of solar energy to power in Europe is assessed in this work. A numerical analysis of a Solar-TFC thermal power unit is performed, by applying an in-house numerical model. Flat Plate Collectors (FPC) and Evacuated Tube Collectors (ETC) are modeled as solar heat sources. Particular focus is on the technological bottleneck of the TFC, i.e. two-phase expansion, by applying a novel two-phase expansion numerical model. Annual simulations are performed with the total efficiency of the Solar-TFC maximized at each time step. The annual total efficiency of the Solar-TFC, exergy efficiency, and thermal efficiency of the TFC can be as high as 5%, 5.3%, and 11%, respectively. ETCs increase the economic viability of the Solar-TFC, particularly as the annual electricity output increases. The Levelized Cost of Electricity (LCOE) of the modeled unit is estimated in the range of 0.25 and 0.75 €/kWh, which can be further reduced by increasing the collectors’ area. The Solar-TFC unit can reduce, on an annual basis, the CO2 emissions by 2.5–47 kg per m2 of solar collectors, with the carbon footprint reduction depending on the collectors’ efficiency and the installation location.

Thermodynamic investigation of a solar-driven organic Rankine cycle with partial evaporation

The partial evaporation organic Rankine cycle (PE-ORC) is an emerging technology for the efficient exploitation of low-temperature heat sources. The purpose of the present study is the energy and thermodynamic analysis of a solar-fed PE-ORC with a solar field of evacuated flat plate collectors coupled to a sensible storage tank. The studied PE-ORC operates with the environmentally friendly working fluid R1233zd(E) with variable evaporation percentage in the expander inlet. The thermodynamic investigation is done with a validated model in Engineering Equation Solver, and the transient analysis is performed with the TRNSYS tool by coupling it with the thermodynamic model. According to the dynamic analysis, the annual electrical yield is found at 6243 kWh, while the maximum obtained value is found at 3.81 kW. Moreover, the annual mean solar field efficiency was calculated at 45.0%, the annual mean thermodynamic cycle efficiency at 8.71% and the annual mean system efficiency at 3.68%.

Enhanced Performance of Nickel–Cobalt Oxides as Selective Coatings for Flat-Plate Solar Thermal Collector Applications

Solar thermal collectors represent a practical option to capture energy from the sun, providing low-cost domestic and industrial heating and decreasing the dependency on fossil fuels. Spinel-type metal oxides show interesting physicochemical properties and so can be used as active materials for converting solar energy to electrical, chemical, and heat energy. We report the synthesis and characterization of nickel–cobalt mixed metal oxides used as an active phase in selective paints for solar absorber coatings applied to a domestic flat collector. The nickel–cobalt mixed oxides crystallized in the cubic phase related to the spinel structure, exhibiting good thermal stability and reproducibility. These mixed oxides presented oxidation states (2+ and 3+) for both nickel and cobalt. The coatings fabricated from the selective paints based on nickel–cobalt mixed oxides showed a solar absorptance value of 94%, while for the commercial paint Solkote®, the value was 93%. A representative coating based on the NiCo2O4 composition was evaluated for the first time in a domestic-type flat solar collector for water heating under real operating conditions, achieving an outstanding performance that competes with that of commercial collectors. The potential application of nickel–cobalt mixed oxides in solar collectors opens up new opportunities for future innovations and developments in functional absorber coatings.

Study and Characterization of a Spherical Solar Collector. Part II: Comparative Analysis with Flat-Plate Devices

The paper analyses the performance of a spherical solar collector compared to the efficiency of a flat-plate solar collector, which is the type of solar collector that does not use a tracking system in collecting solar radiation for energy conversion. Spherical solar collector benefits from a constant value of the angle of incidence, which optimizes the solar radiation that strikes the absorber of the solar device and maximizes the energy collection. Besides, the spherical geometry has a larger area for equal dimensions, width, and length. The combined effect of a larger surface and a higher value of the effective solar radiation onto the surface of the absorber increases the energy collection and the performance of the solar device. We developed a theoretical analysis to obtain the algorithm to determine the collected solar energy, which increases when using the spherical solar collector. A simulation runs to calculate the predicted values. We developed experimental tests in a spherical solar collector of 1.05 m in diameter, and in a flat-plate solar collector of 1.94 m × 1.025 m. to validate the simulation. The comparative analysis shows that a spherical solar collector generates more energy than a flat-plate one of the same absorbing surface by a factor of 2.09, and 7.75 times more if the width and height of the flat-plate collector equals the diameter of the spherical one.