Performance analysis of a hybrid photovoltaic/thermal (PV/T) collector with integrated CPC troughs

In the present investigation a theoretical analysis has been presented for the modelling of thermal and electrical processes of a hybrid PV/T air heating collector coupled with a compound parabolic concentrator (CPC). In this design, several CPC troughs are combined in a single PV/T collector panel. The absorber of the hybrid PV/T collector under investigation consists of an array of solar cells for generation of electricity, while collector fluid circulating past the absorber provides useful thermal energy as in a conventional flat plate collector. In the analysis, it is assumed that solar cell efficiency can be represented by a linear decreasing function of its temperature. Energy balance equations have been developed for the various components of the system. Based on the developed analysis, both thermal and electrical performance of the system as a function of system design parameters are presented and discussed. Results have been presented to compare the performance of hybrid PV/T collector coupled with and without CPC. Copyright © 1999 John Wiley & Sons, Ltd.     

Design concept and mathematical model of a bi-fluid photovoltaic/thermal (PV/T) solar collector

This paper presents an improved design of a photovoltaic/thermal (PV/T) solar collector integrating a PV panel with a serpentine-shaped copper tube as the water heating component and a single pass air channel as the air heating component. In addition to the electricity generated, this type of collector enables the production of both hot air and water, increasing the total efficiency per unit area compared to the conventional PV/T solar collector. The use of both fluids (bi-fluid) also creates a greater range of thermal applications and offers options in which hot and/or cold air and/or water can be utilized depending on the energy needs and applications. In this paper, the design concept of the bi-fluid PV/T solar collector is emphasized with 2D steady state energy balance equations for the bi-fluid configuration are developed, validated and used to predict the performance of the bi-fluid solar collector for a range of mass flow rates of air and water. The performance of the collector is then compared when the fluids are operated independently and simultaneously. The simulations indicate that when both fluids are operated independently the overall thermal and electrical performance of the solar collector is considered as satisfactory and when operated simultaneously the overall performance is higher. The bi-fluid PV/T solar collector discussed in this paper will add insights to the new knowledge of optimizing the utilization of solar energy by a PV/T solar collector and has potential applications in various fields.     

非晶硅太阳能光伏/光热空气集热器性能对比实验研究

文章设计了新型非晶硅太阳能PV/T空气集热器,该空气集热器能够解决传统太阳能PV/T热水器在高温波动情况下,晶硅电池热应力大的问题,同时避免了冬季管道发生霜冻的现象。文章通过实验对比,分析了非晶硅太阳能PV/T空气集热器、单独非晶硅光伏电池和传统太阳能空气集热器的能量效率和[火用]效率的差异。分析结果表明:非晶硅太阳能PV/T空气集热器的平均热效率为45.70%,比传统太阳能空气集热器的平均热效率降低了约25.88%;当空气质量流量增大至0.048 kg/s时,非晶硅太阳能PV/T空气集热器中的非晶硅光伏电池的平均电效率高于单独非晶硅光伏电池,它们的平均电效率分别为4.70%,4.54%;非晶硅太阳能PV/T空气集热器的总[火用]效率高于传统太阳能空气集热器的热[火用]效率和单独非晶硅光伏电池的电[火用]效率,非晶硅太阳能PV/T空气集热器总[火用]效率最大值为7.14%。文章的分析结果为非晶硅太阳能PV/T空气集热器的推广提供了参考。     

Feasibility study of a hybrid photovoltaic/thermal collector system in the climate of Jordan

This study is dedicated to investigating the feasibility of photovoltaic/thermal (PV/T) collectors' technology for application in Jordan. Simple parallel-plate collector configurations were simulated using COMSOL: rectangular fins, triangular fins, and wavy walls. The wavy-wall configuration was found the most efficient alternative in terms of heat transfer with respect to the pumping power and performance factor that took into account the comparison with a plain-wall parallel-plate collector. However, the performance of the plain-wall parallel plate preceded that of the wavy wall by increasing the Reynolds number and the water channel height. The plain-wall parallel-plate configuration was further investigated on HOMER as a 5 MW solar plant that provides energy to a 5-MW facility. One MW of its load is direct thermal load. Different solar plant designs were compared. The PV/T plant was found to be very much energy saving but not feasible due to its high initial cost. However, the PV/T plant was better than the PV when the cooling was not complete compromising on some electric energy in favor of heat generation. Further work on reducing the cost of the PV/T collector is required especially with regard to contact methods between the PV and the absorber plate and to the weight of the collector.     

Aspects and improvements of hybrid photovoltaic/thermal solar energy systems

Hybrid photovoltaic/thermal (PV/T or PVT) solar systems consist of PV modules coupled to water or air heat extraction devices, which convert the absorbed solar radiation into electricity and heat. At the University of Patras, an extended research on PV/T systems has been performed aiming at the study of several modifications for system performance improvement. In this paper a new type of PV/T collector with dual heat extraction operation, either with water or with air circulation is presented. This system is simple and suitable for building integration, providing hot water or air depending on the season and the thermal needs of the building. Experiments with dual type PV/T models of alternative arrangement of the water and the air heat exchanging elements were performed. The most effective design was further studied, applying to it low cost modifications for the air heat extraction improvement. These modifications include a thin metallic sheet placed in the middle of the air channel, the mounting of fins on the opposite wall to PV rear surface of the air channel and the placement of the sheet combined with small ribs on the opposite air channel wall. The modified dual PV/T collectors were combined with booster diffuse reflectors, achieving a significant increase in system thermal and electrical energy output. The improved PV/T systems have aesthetic and energy advantages and could be used instead of separate installation of plain PV modules and thermal collectors, mainly if the available building surface is limited and the thermal needs are associated with low temperature water or air heating.     

Parametric study of various configurations of hybrid PV/thermal air collector: Experimental validation of theoretical model

In this paper, an attempt has been made to evaluate the overall performance of hybrid PV/thermal (PV/T) air collector. The different configurations of hybrid air collectors which are considered as unglazed and glazed PV/T air heaters, with and without tedlar. Analytical expressions for the temperatures of solar cells, back surface of the module, outlet air and the rate of extraction of useful thermal energy from hybrid PV/T air collectors have been derived. Further an analytical expression similar to Hottel–Whiller–Bliss (HWB) equation for flat plate collector has also been derived in terms of design and climatic parameters. Numerical computations have been carried out for composite climate of New Delhi and the results for different configurations have been compared. The thermal model for unglazed PV/T air heating system has also been validated experimentally for summer climatic conditions. It is observed that glazed hybrid PV/T without tedlar gives the best performance.     

Design considerations for flat-plate-photovoltaic/thermal collectors

Several potentially useful features in the design of photovoltaic/thermal (PV/T) collectors are explored in order to determine their effectiveness and interaction. Based on a computer simulation of flat-plate PV/T collectors that is applicable to a wide range of designs, the present work focuses on air-type collectors employing single crystal silicon PV cells. Features explored center on two main areas: increasing the solar absorptance and reducing the infrared emittance. The results of the simulations can be summarized as follows: for PV cells covering greater than approximately 65% of the total collector area, a selective absorber actually reduces the thermal efficiency when used with a gridded-back cell. The requirements for the low emissivity coating are an infrared emissivity of less than 0.25 and a solar transmissivity of greater than 0.85. The optimum combination for an air PV/T was found to consist of gridded-back PV cells, a nonselective secondary absorber, and a high-trans-missivity/low-emissivity cover above the PV cells.     

Improved PV/T solar collectors with heat extraction by forced or natural air circulation

The photovoltaic (PV) cells suffer efficiency drop as their operating temperature increases especially under high insolation levels and cooling is beneficial. Air-cooling, either by forced or natural flow, presents a non-expensive and simple method of PV cooling and the solar preheated air could be utilized in built, industrial and agricultural sectors. However, systems with heat extraction by air circulation are limited in their thermal performance due to the low density, the small volumetric heat capacity and the small thermal conductivity of air and measures for heat transfer augmentation is necessary. This paper presents the use of a suspended thin flat metallic sheet at the middle or fins at the back wall of an air duct as heat transfer augmentations in an air-cooled photovoltaic/thermal (PV/T) solar collector to improve its overall performance. The steady-state thermal efficiencies of the modified systems are compared with those of typical PV/T air system. Daily temperature profiles of the outlet air, the PV rear surface and channel back wall are presented confirming the contribution of the modifications in increasing system electrical and thermal outputs. These techniques are anticipated to contribute towards wider applications of PV systems due to the increased overall efficiency.     

Performance improvement of PV/T solar collectors with natural air flow operation

The electrical efficiency of a photovoltaic system drops as its operating temperature rises and PV cooling is necessary. The photovoltaic/thermal (PV/T) system is a relatively recent type of solar collector where a circulating fluid of lower temperature than PV module extracts heat from it, cooling the module to improve its output power while the solar pre-heated fluid provides sensible heat. In the present work, air cooling of a commercial PV module configured as PV/T air solar collector by natural flow is presented, where two low cost modification techniques to enhance heat transfer to air stream in the air channel are studied. The considered methods consist of thin metal sheet suspended at the middle or fins attached to the back wall of the air-channel to improve heat extraction from the module. A numerical model was developed and validated against the experimental data obtained from outdoor test campaigns for both glazed and unglazed PV/T prototype models studied. The validation results show good agreement between predicted values and measured data and thus could be used to study analytically the performance of these PV/T air collectors with respect to several design and operating parameters. The modified systems present better performance than the usual type and will contribute to better performance of integrated PV systems for natural ventilation applications in buildings, both space cooling and heating.     

Exergetic optimization of a solar photovoltaic thermal (PV/T) air collector

In this paper, an exergetic optimization has been developed to determine the optimal performance and design parameters of a solar photovoltaic thermal (PV/T) air collector. A detailed energy and exergy analysis has been carried out to calculate the thermal and electrical parameters, exergy components, and exergy efficiency of a typical PV/T air collector. The thermal and electrical parameters of a PV/T air collector include solar cell temperature, back surface temperature, outlet air temperature, open‐circuit voltage, short‐circuit current, maximum power point voltage, maximum power point current, etc. An improved electrical model has been used to estimate the electrical parameters of a PV/T air collector. Furthermore, a new equation for the exergy efficiency of a PV/T air collector has been derived in terms of design and climatic parameters. A computer simulation program has been also developed to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Moreover, the simulation results obtained in this paper are more precise than the one given by the previous literature, and the new exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature. Finally, exergetic optimization has been carried out under given climatic, operating, and design parameters. The optimized values of inlet air velocity, duct length, and the maximum exergy efficiency have been found. Parametric studies have been also carried out. Copyright © 2010 John Wiley & Sons, Ltd.     

An improved thermal and electrical model for a solar photovoltaic thermal (PV/T) air collector

In this paper, an attempt is made to investigate the thermal and electrical performance of a solar photovoltaic thermal (PV/T) air collector. A detailed thermal and electrical model is developed to calculate the thermal and electrical parameters of a typical PV/T air collector. The thermal and electrical parameters of a PV/T air collector include solar cell temperature, back surface temperature, outlet air temperature, open-circuit voltage, short-circuit current, maximum power point voltage, maximum power point current, etc. Some corrections are done on heat loss coefficients in order to improve the thermal model of a PV/T air collector. A better electrical model is used to increase the calculations precision of PV/T air collector electrical parameters. Unlike the conventional electrical models used in the previous literature, the electrical model presented in this paper can estimate the electrical parameters of a PV/T air collector such as open-circuit voltage, short-circuit current, maximum power point voltage, and maximum power point current. Further, an analytical expression for the overall energy efficiency of a PV/T air collector is derived in terms of thermal, electrical, design and climatic parameters. A computer simulation program is developed in order to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Finally, parametric studies have been carried out. Since some corrections have been down on thermal and electrical models, it is observed that the thermal and electrical simulation results obtained in this paper is more precise than the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency and overall energy efficiency of PV/T air collector is about 17.18%, 10.01% and 45%, respectively, for a sample climatic, operating and design parameters.     

An evaluation on thermal performance of CPC solar collector

The main objective of this work is the investigation and improvement of thermal performance of evacuated CPC (Compound Parabolic Concentrator) solar collector with a cylindrical absorber. Modified types of this solar collector are always combined with the evacuated glass envelop or tracking system. The conventional stationary CPC solar collector has been compared with the single axis tracking CPC solar collector in outlet temperature, net heat flux onto the absorber and thermal efficiency. Numerical model has been analyzed based on the irradiation determined actually and the results have been calculated to predict the thermal efficiency. Based on the comparison of the measured and calculated results, it is concluded that the numerical model can accurately estimate the performance of solar collectors. The result shows the thermal efficiency of the tracking CPC solar collector is more stable and about 14.9% higher than that of the stationary CPC solar collector.     

Advancement in solar photovoltaic/thermal (PV/T) hybrid collector technology

This article presents an overview on the research and development and application aspects for the hybrid photovoltaic/thermal (PV/T) collector systems. A major research and development work on the photovoltaic/thermal (PVT) hybrid technology has been done since last 30 years. Different types of solar thermal collector and new materials for PV cells have been developed for efficient solar energy utilization. The solar energy conversion into electricity and heat with a single device (called hybrid photovoltaic thermal (PV/T) collector) is a good advancement for future energy demand. This review presents the trend of research and development of technological advancement in photovoltaic thermal (PV/T) solar collectors and its useful applications like as solar heating, water desalination, solar greenhouse, solar still, photovoltaic-thermal solar heat pump/air-conditioning system, building integrated photovoltaic/thermal (BIPVT) and solar power co-generation.     

抛物面聚光太阳能PV/T系统的热电性能分析

建立了带有散热翅片的聚光太阳能PV/T热电联产系统内部传热过程的一维稳态数学模型,对传热过程进行了数值模拟,分析了空气质量流速、入射光强度、聚光比、环境温度、上部通道高度及翅片参数对系统的空气温度、电池板温度及系统热、电效率的影响.结果表明:随着入射光强、聚光比的增加,空气出口温度和电池板温度都会增加,系统热电总效率增加;通过增空气流量可以有效降低电池温度,提高电池的光电转换效率和系统的总能量利用效率;吸热板背面的翅片可以强化通道内空气的传热过程,降低电池板的温度,系统效率可增加约2%;在相同的光照条件下,人口空气温度越低,上部通道越窄,系统热效率越高.研究结果为聚光太阳能PV/T热电联产系统的设计和运行提供了理论依据.     

Study of a new concept of photovoltaic–thermal hybrid collector

This work represents the second step of the development of a new concept of photovoltaic/thermal (PV/T) collector. This type of collector combines preheating of the air and the production of hot water in addition to the classical electrical function of the solar cells. The alternate positioning of the thermal solar collector section and the PV section permits the production of water at higher mean temperatures than most of existing hybrid collectors. These higher temperatures will allow the coupling of components such as solar cooling devices during the summer and obviously a direct domestic hot water (DHW) system without the need for additional auxiliary heating systems. In this paper, a simplified steady-state two-dimensional mathematical model of a PV/T bi-fluid (air and water) collector with a metal absorber is developed. Then, a parametric study (numerically and experimentally) is undertaken to determine the effect of various factors such as the water mass flow rate on the solar collector thermal performances. Finally, the results from an experimental test bench and the first simulation results obtained on full scale experiments are compared.     

Design and simulation of a low concentrating photovoltaic/thermal system

The advantages of photovoltaic/thermal (PV/T) collectors and low solar concentration technologies are combined into a photovoltaic/thermal system to increase the solar energy conversion efficiency. This paper presents a prototype 11X concentration rate and two axis tracking system. The main novelty is the coupling of a linear Fresnel concentrator with a channel photovoltaic/thermal collector. An analytical model to simulate the thermal behaviour of the prototype is proposed and validated. Measured thermal performance of the solar system gives values above 60%. Theoretical analysis confirms that thermal conduction between the PV cells and the absorber plate is a critical parameter.     

Optimal design of orientation of PV/T collector with reflectors

Hybrid conversion of solar radiation implies simultaneous solar radiation conversion into thermal and electrical energy in the PV/Thermal collector. In order to get more thermal and electrical energy, flat solar radiation reflectors have been mounted on PV/T collector. To obtain higher solar radiation intensity on PV/T collector, position of reflectors has been changed and optimal position of reflectors has been determined by both experimental measurements and numerical calculation so as to obtain maximal concentration of solar radiation intensity. The calculated values have been found to be in good agreement with the measured ones, both yielding the optimal position of the flat reflector to be the lowest (5°) in December and the highest (38°) in June. In this paper, the thermal and electrical efficiency of PV/T collector without reflectors and with reflectors in optimal position have been calculated. Using these results, the total efficiency and energy-saving efficiency of PV/T collector have been determined. Energy-saving efficiency for PV/T collector without reflectors is 60.1%, which is above the conventional solar thermal collector, whereas the energy-saving efficiency for PV/T collector with reflectors in optimal position is 46.7%, which is almost equal to the values for conventional solar thermal collector. Though the energy-saving efficiency of PV/T collector decreases slightly with the solar radiation intensity concentration factor, i.e. the thermal and electrical efficiency of PV/T collector with reflectors are lower than those of PV/T collector without reflectors, the total thermal and electrical energy generated by PV/T collector with reflectors in optimal position are significantly higher than total thermal and electrical energy generated by PV/T collector without reflectors.     

A numerical investigation of a photovoltaic thermal (PV/T) collector

The photovoltaic thermal collector can provide thermal and heat power at the same time.In this paper, a photovoltaic/thermal sheet and tube collector has been numerically investigated. The paper focuses on the development of a hybrid solar collector PV/T. This model will be applied to optimize the operation of the PVT collector in the semi-arid climate. A mathematical model has been developed to determine the dynamic behavior of the collector, based on the energy balance of six main components namely a transparent cover, a PV module, a plate absorber, a tube, water in the tube and insulation. It has been validated by comparing the obtained simulation results with experimental results available in literature, where good agreement has been noted. Using our developed model, the heat and electrical power of sheet and tube collector has been analyzed for four typical days of year with the meteorological parameters of Monastir, Tunisia. Furthermore, the effect of solar radiation, the inlet water temperature, the number of glazing covers and the conductive heat transfer coefficient between plate absorber and PV module have been involved to identify their influence on the thermal and electrical efficiencies. The monthly thermal and electrical energies is also evaluated.     

System performance studies on a photovoltaic/thermal (PV/T) air heating collector

A computer simulation model is presented for the analysis of a solar photovoltaic/thermal (PV/T) hybrid collector with air as heat transfer fluid and algorithm for making quantitative prediction regarding the performance of the system is described. Thermal efficiency curves for the solar PV/T hybrid collectors corresponding to various type of absorbers have been derived. In order to appreciate the model, numerical calculations have been made for evaluating the system performance corresponding to typical climate of Delhi, India     

Performance evaluation of a hybrid photovoltaic thermal (PV/T) (glass-to-glass) system

In this paper, an attempt is made to evaluate the thermal performance of a hybrid photovoltaic thermal (PV/T) air collector system. The two type of photovoltaic (PV) module namely PV module with glass-to-tedlar and glass-to-glass are considered for performance comparison. The results of both PV modules are compared for composite climate of New Delhi. Analytical expression for solar cell, back surface, outlet air temperatures and an overall thermal efficiency are derived for both cases. It is observed that hybrid air collector with PV module glass-to-glass gives better performance in terms of overall thermal efficiency. Parametric studies are also carried out.