Photovoltaic Thermal Module Research Articles

Bond graph modeling of a water-based photovoltaic thermal (PV/T) collector

This paper deals with photovoltaic-thermal (PV/T) collectors that combine photovoltaic (PV) module and solar thermal (ST) modules to provide heat and electricity simultaneously. The use of a PV/T system not only enhances PV efficiency but also allows to use solar thermal energy for various heating applications. The performance evaluation of the PV/T collectors had been investigated both theoretically and experimentally for the past few years. In this work, we consider a new water-based PV/T configuration by incorporating a tedlar layer and parallel tubes and further investigate its modeling. The aim is to develop a non-linear dynamic model which gives a realistic and reasonable performance of the system. The fundamental equations are determined for the thermal part using a bond graph approach which is a generic and general tool to represent thermal transfers. Simulations are given to highlight the usefulness of the proposed design and its modeling, considering the influence of some external factors (e.g. wind action) and internal geometrical parameters (e.g. insulator thickness). The results indicate that the rise in wind speed can reduce thermal efficiency from 70% to approximately 40%. The results also show that with an increase in insulator thickness, there is a sudden change in outlet temperature but thicknesses of more than 0.14 m is not required as the energy losses become constant. The assessment of the electrical and thermal performance of a PV/T collector is taken into consideration for a sample weather condition of southern France. Further, our results are compared to existing experimental and numerical ones from the literature on alternative PV/Ts design to validate and demonstrate the viability and consistency of our model.

Photovoltaic Thermal Module With Paraboloid Type Solar Concentrators

The article presents the results of the development and research of the solar photovoltaic thermal module with paraboloid type solar radiation concentrators. The structure of the solar module includes a composite concentrator, which provides uniform illumination by concentrated solar radiation on the surface of the cylindrical photovoltaic thermal photoreceiver in the form of the aluminum radiator with photovoltaic converters. When exposed in concentrated solar radiation, the electrical efficiency of specially designed matrix photovoltaic converters increases, and the heat taken by the heat carrier increases the overall efficiency of the solar module. Uniform illumination of photovoltaic converters with concentrated solar radiation provides an optimal mode of operation. The consumer can use the received electric and thermal energy in an autonomous or parallel power supply with the existing power grid.

Performance evaluation and economics of a locally-made stand-alone hybrid photovoltaic-thermal brackish water reverse osmosis unit

Abstract The performance of a developed brackish water reverse osmosis (BWRO) desalination unit integrated with a stand-alone hybrid photovoltaic-thermal (PVT) module was evaluated under the climatic conditions of Tehran (35.68° N latitude 51.42° E longitude). From the experimental results, the maximum surface temperature of the PV module and thermal efficiency of the PVT module were recorded as 60.38 ​°C and 83.7%, respectively at the set-point temperature of 50.00 ​°C for the thermostat, and under the average solar radiation of 971.34 ​W/m2. During the evaluation, the maximum average productivity of the BWRO unit was obtained as 13.98 ​L/h when temperature values of the PV module, soft water, and brackish feed water (BFW) were recorded as 52.94 ​°C, 28.97 ​°C, and 36.60 ​°C, respectively. From the results, it was also found that the temperature of BFW positively affects the PVT module’s thermal performance and improves the whole unit’s productivity. Also, water quality parameters of pH, TDS, EC, and DO for treated water were evaluated. The economic analysis of the system revealed that the cost of the produced freshwater for the BFW’s salinity of 15,000 ​ppm is 18.96% higher in comparison with 5000 ​ppm for all cases, indicating a closer value to freshwater cost of conventional large-scale RO plants.

Two-phase flow investigation in channel design of the roll-bond cooling component for solar assisted PVT heat pump application

The two-phase flow characteristics of the roll-bond cooling component were investigated to design and optimize the fluid channel pattern for higher thermal and electrical efficiencies. The CFD method was applied to evaluate the thermal, electrical, and hydraulic performance of the PVT (photovoltaic-thermal) module employing different patterns of roll-bond panel. The influence of uneven working temperature of solar cell units on the PVT module’s electrical efficiency was considered. Moreover, the proposed numerical model was validated by the experimental results. The optimized two-phase flow channel pattern was structured by hexagon-grid coupled fluid channel units with the one-way arrangement, and it showed significant improvement in temperature uniformity, thermal and electrical efficiencies, and hydraulic behavior. The feasibility analysis revealed that the optimized fluid channel pattern could reduce the PV module’s working temperature by up to 47.3 °C and improve its electrical efficiency by 46.5% on a typical summer day. In this circumstance, the average system COP was 4.37 and the average temperature difference of the PVT module was 4.6℃, while the average electrical and thermal efficiencies were 16.7% and 47.6%, respectively.

The study of heat control on PVT modules with a new leaf-like heat exchanger

The photovoltaic/thermal (PVT) collector is an eco-friendly technology that simultaneously converts solar energy into electrical and thermal energy. However, a high solar cell temperature seriously affects the electrical efficiency of the PVT collector, which is an urgent problem that needs to be addressed. Some traditional cooling technologies for PVT collectors were previously investigated, but they were inefficient in heat collecting performance. In addition, a nonuniform solar cell temperature distribution accelerates the aging of PVT modules, and this topic has only rarely been discussed. In the present study, a new leaf-like heat exchanger based on bionics was proposed to improve heat control of the PVT collector. A three-dimensional mathematical model was developed in COMSOL and validated by comparing modeling results with experimental data already available in the literature. The effect of different operating conditions on the performance of the new PVT collector was investigated. The results of this study show that the bifurcation angle of the leaf-like heat exchanger with a symmetrical configuration between 20° and 35° was characterized by a lower and more uniform temperature distribution on solar cells in comparison with conventional heat exchangers. Moreover, the average temperature of the solar cell cooled by the new leaf-like heat exchanger decreased by 5.31 °C, and the pressure drop associated with the leaf-like heat exchanger was only half the value of the pressure drop associated with a conventional heat exchanger at a mass flow rate of 0.0314 kg/s. Finally, the total efficiency of the new PVT collector was 4.36% higher than that of the conventional PVT collector.

Performance study on photovoltaic thermal building façade component in multi-energy generation during winter

Photovoltaic thermal systems have gained tremendous popularity in the production of electric and thermal energy. In this paper, the photovoltaic thermal modules for the building façade assisted by heat pump system is proposed which combines the photovoltaic modules with an evaporator part of the heat pump system to produce hot water and electrical energy. Also, the photovoltaic thermal panels are used to preheat the cold ambient fresh air without heat pump operation. The proposed system was constructed at the Institute of Building Energy, Dalian University of Technology, China to study the ambient fresh air heating characteristic, electrical power generation, and hot water generation through performance evaluation indices under natural weather conditions. It was found that the average electrical, thermal, and overall efficiencies are 8.8%, 26%, and 50%, respectively during the pre-heating of fresh air. While the average air temperature is 15.2°C inside an air gap. The average COP for water heating is 3.91 during the water heating mode. This study could be used as a guide for photovoltaic thermal solar-assisted heat pump systems on building envelopes in a multi-energy generation under different weather conditions. Practical application: The study considers the photovoltaic thermal modules for building façade not only to generate the electrical energy and pre-heated fresh air but also to generate the hot water when assisted with the heat pump system. This research could assist researchers and engineers in the field of photovoltaic thermal façade systems in multi-energy generation such as for the production of electricity, heated/cooled fresh air, and hot water generation.

Results of CFD-simulation of a solar photovoltaic-thermal module

Currently, in the energy supply of agroindustrial complex facilities there is an increasing interest in the development of structures and engineering systems using renewable energy sources, including combined photovoltaic-thermal modules (PVT-modules), combining photovoltaic modules (PV-modules) and solar collectors in one design. The use of PVT-modules technology makes it possible to increase the electrical performance of solar cells due to their cooling during operation, while the use of PVT-modules integrated into the roofs and facades of buildings can significantly reduce the need for centralized electricity and heat supply. The purpose of this work is to develop a CFD model of a solar PVT module for producing an estimate of the thermal performance of a PVT module. Using the ANSYS Fluent software package, a CFD model of the PVT module was developed. The contours of the temperature distribution, the coolant pressure in the PVT module channel at different values of the coolant flow at the entrance to the PVT module were obtained. The paper presents the daily variation of thermal power and total insolation calculated using the solar calculator built into ANSYS. The verification of the developed CFD-model of the PVT-module showed the comparability of the calculated values with the data obtained analytically and experimentally - the relative error of the results was no more than ± 1%. ANSYS is an effective software package that allows simulating thermal processes in PVT-modules.

Optimization of a novel photovoltaic thermal module in series with a solar collector using Taguchi based grey relational analysis

The solar collectors absorb solar irradiation and then produce thermal energy; however, they cannot generate electrical power. Electricity and thermal energy can be produced by the photovoltaic thermal module, simultaneously, while the outlet temperature of the photovoltaic thermal module is not usually high enough to provide thermal requirements of a building such as hot water or space heating. This work proposes a novel compound system created by the connection of a solar collector in series with a photovoltaic thermal module to resolve the issue of low outlet temperature in the photovoltaic thermal module and lack of electrical power in solar collectors. To examine the feasibility of this novel compound system, the performance of four systems, including photovoltaic unit, flat plate solar collector, photovoltaic thermal module, and compound system are numerically compared using a transient three-dimensional model. A parametric analysis is also performed to examine the impact of different operating conditions on the power outputs of the compound module. Furthermore, Taguchi based grey relational investigation is employed to indicate the optimum values and the contribution of operating conditions. Taguchi based grey relational examination indicates that the optimum value of mass flow rate, solar radiation, coolant inlet temperature, ambient temperature and wind speed are 50 kg/h, 1000 W/m2, 24 °C, 28 °C and 1 m/s, respectively.

Influence of multiple factors on performance of photovoltaic-thermal modules

In this paper, an analysis of three-dimensional transient thermal transfer is presented to evaluate the performance of a photovoltaic thermal module with an optimize structural design, incorporating direct use of an aluminum collector as the substrate. The effect of cross-sectional geometries and ratios of size and spacing was considered to optimize the performance of a photovoltaic-thermal (PVT) module. The temperature, velocity and pressure distributions were demonstrated in a steady state model using a finite element method. Simulation results indicated the temperature of the PVT module was increased by the solar irradiation incident with the panel, yet overall decreased by an increased flow velocity. In this study, we examine seven types of media used as the medium to cool the PVT module, where water was preferred, due to its higher specific heat capacity. Further, for multiple interconnected PVT modules, connecting method in parallel and series resulted in pressure drop for the PVT module. In addition, the simulations were compared to experimental data providing validation of the estimated operating temperature in agreement with simulation results, and the outcomes will provide an indication for preferred assembly of PVT modules for application in building integration and future product design.

Investigational evaluation of a thin film photovoltaic module by incorporating phase change material: An experimental approach

The operating performance of the solar photovoltaic (SPV) modules is perturbed by the temperature, wind, soiling and relative humidity. Among these parameters, temperature puts the most negative impact on the output yield of the module. On increasing the temperature of the SPV module, the output power decreases drastically. The decrease in temperature affects the power output of the photovoltaic module and the average power yield drops down very sharply. In the present study, the experimental analysis of two 45-watt thin films photovoltaic module with similar characteristics has been carried out. One of the modules is used as the reference module and the second module is incorporate with phase change material at the backside to decrease the cell temperature. It was observed that the photovoltaic thermal module with phase change material (PV/T-PCM) combined system was producing a higher output power as compared to the reference SPV module. An increment of 1.55% in the electrical efficiency of SPV module was recorded during the study period. The thermal efficiency of the PV/T-PCM system was analysed at the constant flow rate of the water. A rise of 20 °C in outlet water temperature was recorded from the PV/T system. The hot water obtained was collected in the reservoir which can be used for low heat applications.

A Comparative Study on Bifacial Photovoltaic/Thermal (Bpv/T) Modules with Various Cooling Methods

The bifacial photovoltaic/thermal (bPV/T) module is an emerging concept that can provide electricity and heat simultaneously taking advantage of both front and rear sides of the panel, therefore exhibiting a better performance compared to a conventional photovoltaic module or photovoltaic thermal module. In this study, four configurations of the bPV/T module with different cooling methods have been proposed, i.e., cooling performed at either the upper or the lower surface, in parallel (applied to both upper and lower surfaces having similar start/end points), and swinging air back and forth (by guiding the air over the upper and lower surfaces, respectively). The computational fluid dynamic software is used to numerically investigate the performance of the studied configurations, and a novel radiation model is used to study bPV/T modules in steady-state and transient conditions. This study demonstrates that Configuration (c) performs best if thermal energy/exergy is more important while Configuration (b) is a better option in terms of electrical output. The transient simulation shows that Configuration (b) can generate more power on sunny (134 W/m2) and cloudy (58 W/m2) days, while seasonal analysis shows that energy and exergy output of Configuration (c) can only reach 500 W/m2 and 110 W/m2 respectively in the summer.

Energetic and exergetic evaluation of a photovoltaic thermal module cooled by hybrid nanofluids in the microchannel

Since reducing the local temperature of the solar cell boosts the performance of a concentrating photovoltaic–thermal, a microchannel heat sink technique is employed. Two hybrid nanofluids, Water-Aluminum oxide-Carbon Nanotube (water-Al2O3-CNT) and Water-Silver-Zinc Oxide (water-Ag-ZnO), are selected as the working fluids. The numerical model is designed in ANSYS CFX environment and the energetic and exergetic performance of the unit are taken into account. Reynolds number and nanoparticles volume fractions are the main variables for this simulation. The outcome of this study shows that more effective reduction in the cell temperature is achieved by using hybrid nanofluids compared to the pure water, in particular at lower Reynolds numbers. In detail, at Reynolds number equal to 10, it is observed that the electrical efficiency for water-Al2O3-CNT and water-Ag-ZnO nanofluids grow by 3% and 2%, respectively. Likewise, the exergy efficiency of the Concentrating Photovoltaic–Thermal panel is remarkably enhanced by taking advantage of the hybrid nanofluids. Finally, it can be concluded that employing hybrid nanofluids in solar systems could technically yield a desirable performance.

A comparative performance evaluation and sensitivity analysis of a photovoltaic-thermal system with radiative cooling

Radiative cooling (RC) of solar cells has received growing attention in recent years primarily due to its passive nature as compared to the other active cooling techniques. By using novel high emittance materials, the RC technique can also be integrated with a photovoltaic-thermal (PVT) system, to eventually improve the system's total efficiency (electrical and thermal output) during the day and provide additional cooling power at night. To quantify the effect of enhanced RC in a PVT system, this study investigated the performance of a regular glass encapsulated PVT module, and a spectrally modified module by using a polydimethylsiloxane coating on top of the glass layer to simulate enhanced RC. An experimentally validated simulation model was developed for performance comparison. Furthermore, a sensitivity analysis was conducted to investigate the influence of varying input parameters on system output performance. Results show that during the day, solar cell operating temperature reduced by most 1.7 °C, and electrical efficiency and total exergy efficiency increased by 0.76% and 0.5%, respectively. As for nighttime, an additional 4–7 W/m2 cooling power can be obtained. Although some improvements, the potential gains achieved by integrating enhanced RC in PVT systems are not substantially large as compared to the regular glass encapsulation in commercial PVT modules, since glass naturally has a fairly high emittance in the atmospheric window.

Hybrid solar thermal/photovoltaic‐battery energy storage system in a commercial greenhouse: Performance and economic analysis

AbstractPerformance and economic analyses of a hybrid solar thermal/photovoltaic‐battery energy storage (ST/PV‐BES) system for a commercial greenhouse were developed. One of the objectives of the study is to evaluate the best configuration of photovoltaic (PV) and solar thermal (ST) modules, and battery energy storage size to have the minimum levelized cost of energy. The system was economically optimized. Moreover, to assess the influence of economic parameters such as ST system cost, PV system cost, natural gas price, electricity price, and large renewable procurement (LRP) rate, a series of sensitivity analyses were undertaken. The results showed that the ST system cost and natural gas price were the most effective parameters on both levelized cost of energy and payback period. The role of future evolution of electricity, fuel cost, and financial incentives (LRP rate and carbon tax) in the economic performance of the system were also analyzed.

Theory of concentration distribution over the surface of axisymmetrical receiver in cylindrical parabolic mirror solar energy concentrator

This work is devoted to develop the theory of concentration distribution of radiation over the receiver surface in cylindrical parabolic concentrator of radiation with axisymmetrical (cylindrical) radiation receiver has been studied. The results will make it possible to estimate concentration distribution over the radiation receiver surface and to associate output characteristics of concentrator unit for various combinations of design parameters at the stage of engineering, to choose the best combination of such parameters and to optimize reflecting surface and radiation receiver. Photovoltaic module with cooling or without it, solar collector, photovoltaic thermal module, etc. may be applied as radiation receivers. Mathematical physics equations have been deduced that describe the specifics of incident radiation flux reflection from the concentrator’s surface and falling onto that of radiation receiver. Concentration distribution has been estimated, for various concentrator design parameters and various positions of receiver axis in relation to the focus of reflecting surface, on the symmetry plane. The most effective concentrator designs characterized by 100% optical efficiency correspond to options where the focus of concentrator’s reflecting surface is located inside radiation receiver. Analysis of design options using the developed theory is shown on examples for given values of average concentration ratio (2, 6, 8, 10, 15, 20, 50), as well as radius of radiation receiver, half concentrator aperture and distance between the focus line and the symmetry axis of radiation receiver in cross-section.

Roofing Solar Panels of Planar and Concentrator Designs

Solar roofing panels fulfill both building protective functions and energy generating ones. The composition of the substrate of the solar roofing panel includes secondary raw materials, which has a positive effect on the environment. To increase the electrical efficiency and also to obtain thermal energy in the form of warm water, it was proposed to create a photovoltaic thermal roofing panel. For this purpose, the presented article describes the method of creating a three-dimensional model of solar photovoltaic thermal modules in a computer-aided design system. The article also proposes a method for manufacturing a prototype body for a solar roofing panel, manufactured using additive technologies, which will significantly reduce costs at the initial stage of creating a prototype due to the possibility of operational changes to a three-dimensional model followed by printing a modified and optimized model. To reduce the number of photovoltaic cells and the cost of a solar roofing panel, it is proposed to use a solar concentrator in the panel.

Cross sectional geometries effect on the energy efficiency of a photovoltaic thermal module: Numerical simulation and experimental validation

The operating temperature influences both the electrical efficiency and thermal efficiency of a photovoltaic thermal (PVT) module. In this paper, a simplified thermal transfer model is used to search for the optimal structure of a high efficiency PVT module. For an aluminum collector with a given thickness, the optimal ratio between size and spacing and cross sectional geometry of the flow channels has been found with numerical simulations using computational fluid dynamics (CFD). The temperature distribution of the PVT module constructed with an aluminum collector is found to be more uniform than the conventional sheet-tube PVT module, due to using an improved thermal transfer mode based on the surface contact. To evaluate the impact of cross sectional geometry, the operating temperatures, electrical and thermal efficiencies of two PVT modules designed with rectangle and arch geometries are examined under outdoor conditions. Measured experimental intercept values of instantaneous thermal efficiencies are close to simulation results, demonstrating the utility of the approach as a reference for a new generation of PVT modules in future.

Enhanced electrical performance for heterojunction with intrinsic thin-layer solar cells based photovoltaic thermal system with aluminum collector

Crystalline silicon heterojunction with intrinsic thin-layer photovoltaic (HIT-PV) module produces more output power, compared with the c-Si photovoltaic module. However, it presents a risk of overheating in hot weather. In this paper, we used a new cooling design of the heterojunction with intrinsic thin-layer photovoltaic thermal (HIT-PVT) module to lower the temperature using laminated encapsulation of an aluminum collector in outdoor climates. The measured electrical, thermal and total efficiencies of a HIT-PVT system can catch up to 17.47%, 34.71% and 52.18%, respectively. Moreover, comparing with HIT-PV module, the output power of the HIT-PVT module was enhanced by 5.58% with coolant circulation, and the converted electrical energy can be increased by 9.81% with the designed HIT-PVT module. In addition, the primary energy savings of the new HIT-PVT and HIT-PV systems were 79.77% and 43.71%, respectively.

Theoretical analysis on efficiency factor of direct expansion PVT module for heat pump application

Direct expansion solar assisted PVT (photovoltaic/thermal) heat pump is a combination of PVT technology and heat pump technology, which can improve the comprehensive conversion efficiency of solar energy, and it is suitable for solar heating applications. In this paper, the efficiency factor of direct expansion PVT module employing roll-bond panel has been theoretically derived, modified, and validated by experimental results. Moreover, the efficiency factor could be used to design, evaluate, and optimize the thermal performance of direct expansion solar assisted heat pump systems. In addition, parameter analysis of four evaporator unit types has been conducted, and the recommendation values of each parameter have also been presented. The simulation results show that the roll-bond evaporator (fluid channel width: 10 mm) with hexagon and rectangle patterns have better temperature distribution uniformity than grid and linear types, and their temperature differences are both 0.038 °C while their dimensionless pressure losses are 0.109 and 0.230, respectively. To specifically design different kinds of PVT collector/evaporator or direct expansion evaporators, a novel design method for roll-bond evaporator is proposed, and a combination of hexagon and grid types is recommended for PVT module. Moreover, the recommendation fluid channel width of the roll-bond panel is 8 mm to 13 mm while the scaling ratio is 0.8 to 1.2. The modified efficiency factors are 0.521, 0.564, 0.549, and 0.342 of hexagon, grid, rectangle, and linear types when the fluid channel width is 10 mm, respectively.

A new method for evaluating nominal operating cell temperature (NOCT) of unglazed photovoltaic thermal module

Photovoltaic thermal (PVT) modules convert solar energy into electricity and heat. Unlike that of normal photovoltaic modules, the nominal operating cell temperature (NOCT) of PVT modules, which is used to evaluate the temperature and electrical power output, is unknown because it depends on the mass flow rate and inlet temperature of the working fluid in the module. In this paper, a new method for calculating the NOCT of PVT modules with water as the working fluid is presented. Four unglazed identical PVT modules in series were tested outdoors with various mass flow rates. The tests, which were similar to solar collector tests, were conducted from 8:30 to 16:30 on clear-sky days in Chiang Mai, Thailand, and the water inlet temperature of the first PVT module of the system was varied from 27 to 60 °C. The correlation between the NOCT of the unglazed PVT module, based on (Tfi−Ta)∕IT, and the water mass flow rate, ṁ, was determined. The calculated PVT module temperature determined with the new NOCT method agrees well with the experimental data, and 96% of the calculated results deviate only by up to ±10% from the experimental data.