Performance of a building integrated photovoltaic/thermal (BIPVT) solar collector

The idea of combining photovoltaic and solar thermal collectors (PVT collectors) to provide electrical and heat energy is an area that has, until recently, received only limited attention. Although PVTs are not as prevalent as solar thermal systems, the integration of photovoltaic and solar thermal collectors into the walls or roofing structure of a building could provide greater opportunity for the use of renewable solar energy technologies. In this study, the design of a novel building integrated photovoltaic/thermal (BIPVT) solar collector was theoretically analysed through the use of a modified Hottel-Whillier model and was validated with experimental data from testing on a prototype BIPVT collector.The results showed that key design parameters such as the fin efficiency, the thermal conductivity between the PV cells and their supporting structure, and the lamination method had a significant influence on both the electrical and thermal efficiency of the BIPVT. Furthermore, it was shown that the BIPVT could be made of lower cost materials, such as pre-coated colour steel, without significant decreases in efficiency.Finally, it was shown that by integrating the BIPVT into the building rather than onto the building could result in a lower cost system. This was illustrated by the finding that insulating the rear of the BIPVT may be unnecessary when it is integrated into a roof above an enclosed air filled attic, as this air space acts as a passive insulating barrier.     

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     

Optimization of the photovoltaic thermal (PV/T) collector absorber

In an effort to reduce the cost of conventional fin and tube photovoltaic thermal (PV/T) collectors a novel mathematical analysis was developed which determines the optimum absorber plate configuration having the least material content and thus cost, whilst maintaining high collection efficiency.The analysis was based on the “low-flow” concept whose advantages include: improved system performance, smaller pump (less expensive with lower power consumption), smaller diameter tubes requiring lower thickness and thus cost of insulation, less construction power and time for the optimum absorber configuration.From the optimization methodology developed it was found that very thin fins (typically 50 μm) and small tubes (of 1.65 mm inside diameter for the risers, in the header and riser arrangement and 4.83 mm for the serpentine arrangement), with a tube spacing of 62 mm and 64 mm (both corresponding to 97% fin efficiency) and a mass of 1.185 kg/m² and 2.140 kg/m², respectively, can be used. This optimum serpentine absorber plate contains 40.50% less material content and mass, as compared to the serpentine prototype proposed by others. In one such design a mass of 3.596 kg/m² was used (with 10 mm diameter tubes, 95 mm tube spacing and 200 μm thick absorber).To predict the performance of the determined optimum configurations, a steady-state model (using the EES code) was developed. To validate the steady-state model two prototypes, one in Header and Riser and the other in Serpentine configuration, were built and tested. It was found from the experiments that there is a good agreement between the computational and the experimental results. Moreover, it was found that optimum PV/T configurations do indeed have thermal and electrical performance comparable to non-optimum ones of greater mass and cost.     

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.     

Low light conditions modelling for building integrated photovoltaic (BIPV) systems

The low irradiance efficiency of photovoltaic modules is important to the optimization of BIPV systems. When photovoltaic modules are integrated into a building, architectural design considerations compete with maximizing photovoltaic energy production. As a result, BIPV arrays are often not facing south and are frequently mounted vertically. Under these conditions, a greater portion of the total sunlight striking the array is diffuse or at high angles of incidence. In northern latitudes a significant amount of the total yearly energy is produced at low light levels.A grid-connected array of BIPV modules integrated into the BCIT Technology Centre building in Burnaby, B.C. was used for assessing the accuracy of an energy performance model developed for BIPV systems. The BIPV system uses AC modules and a computerized data acquisition system for monitoring the performance of modules and inverters. The performance model was developed from analysis of the open circuit voltage, maximum power point voltage and maximum power point current of the individual modules comprising the BIPV array.The algorithm for calculating power output of the photovoltaic array is derived from the ideal diode equation using the single diode model of a photovoltaic cell. An empirically derived parameter modifies the equation. Once the parameters for different module technologies are established, it is possible to compare their annual performance in a BIPV system.     

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.     

A prototype photovoltaic/thermal system integrated with transpired collector

Building-integrated photovoltaic/thermal (BIPV/T) systems may be utilized to produce useful heat while simultaneously generating electricity from the same building envelope surface. A well known highly efficient collector is the open-loop unglazed transpired collector (UTC) which consists of dark porous cladding through which outdoor air is drawn and heated by absorbed solar radiation. Commercially available photovoltaic systems typically produce electricity with efficiencies up to about 18%. Thus, it is beneficial to obtain much of the normally wasted heat from the systems, possibly by combining UTC with photovoltaics. Combination of BIPV/T and UTC systems for building facades is considered in this paper - specifically, the design of a prototype façade-integrated photovoltaic/thermal system with transpired collector (BIPV/T). A full scale prototype is constructed with 70% of UTC area covered with PV modules specially designed to enhance heat recovery and compared to a UTC of the same area under outdoor sunny conditions with low wind. The orientation of the corrugations in the UTC is horizontal and the black-framed modules are attached so as to facilitate flow into the UTC plenum. While the overall combined thermal efficiency of the UTC is higher than that of the BIPV/T system, the value of the generated energy - assuming that electricity is at least four times more valuable than heat - is between 7% and 17% higher. Also, the electricity is always useful while the heat is usually utilized only in the heating season. The BIPV/T concept is applied to a full scale office building demonstration project in Montreal, Canada. The ratio of photovoltaic area coverage of the UTC may be selected based on the fresh air heating needs of the building, the value of the electricity generated and the available building surfaces.     

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.     

Practical application of building integrated photovoltaic (BIPV) system using transparent amorphous silicon thin-film PV module

An analysis has been carried out on the first practical application in Korea of the design and installation of building integrated photovoltaic (BIPV) modules on the windows covering the front side of a building by using transparent thin-film amorphous silicon solar cells. This analysis was performed through long-term monitoring of performance for 2 years. Electrical energy generation per unit power output was estimated through the 2 year monitoring of an actual BIPV system, which were 48.4 kWh/kWp/month and 580.5 kWh/kWp/year, respectively, while the measured energy generation data in this study were almost half of that reported from the existing data which were derived by general amorphous thin-film solar cell application. The reason is that the azimuth of the tested BIPV system in this study was inclined to 50° in the southwest and moreover, the self-shade caused by the projected building mass resulted in the further reduction of energy generation efficiency. From simulating influencing factors such as azimuth and shading, the measured energy generation efficiency in the tested condition can be improved up to 47% by changing the building location in terms of azimuth and shading, thus allowing better solar radiation for the PV module. Thus, from the real application of the BIPV system, the installation of a PV module associated with azimuth and shading can be said to be the essentially influencing factors on PV performance, and both factors can be useful design parameters in order to optimize a PV system for an architectural BIPV application.     

Performance analysis of a double-pass photovoltaic/thermal (PV/T) solar collector with CPC and fins

The use of PV/T in combination with concentrating reflectors has a potential to significantly increase power production from a given solar cell area. A prototype double-pass photovoltaic-thermal solar air collector with CPC and fins has been designed and fabricated and its performance over a range of operating conditions was studied. The absorber of the hybrid photovoltaic/thermal (PV/T) collector under investigation consists of an array of solar cells for generating electricity, compound parabolic concentrator (CPC) to increase the radiation intensity falling on the solar cells and fins attached to the back side of the absorber plate to improve heat transfer to the flowing air. Energy balance equations have been developed for the various nodes of the system. Both thermal and electrical performance of the collector are presented and discussed.     

Performance of a concentrating photovoltaic/thermal solar collector

The performance of a parabolic trough photovoltaic/thermal collector with a geometric concentration ratio of 37× is described. Measured results under typical operating conditions show thermal efficiency around 58% and electrical efficiency around 11%, therefore a combined efficiency of 69%. The impact of non-uniform illumination on the solar cells is investigated using purpose built equipment that moves a calibrated solar cell along the line of the receiver and measures short circuit current. The measured illumination flux profile along the length shows significant variation, despite the mirror shape error being less than 1 mm for most of the mirror area. The impact of the illumination non-uniformities due to the shape error, receiver support post shading and gaps between the mirrors is shown to have a significant effect on the overall electrical performance. The flux profile transverse to the receiver length is also investigated. Peak flux intensities are shown to be around 100 suns. The impact on efficiency due to open circuit voltage reduction is discussed.     

Equilibrium thermal characteristics of a building integrated photovoltaic tiled roof

Photovoltaic (PV) modules attain high temperatures when exposed to a combination of high radiation levels and elevated ambient temperatures. The temperature rise can be particularly problematic for fully building integrated PV (BIPV) roof tile systems if back ventilation is restricted. PV laminates could suffer yield degradation and accelerated aging in these conditions. This paper presents a laboratory based experimental investigation undertaken to determine the potential for high temperature operation in such a BIPV installation. This is achieved by ascertaining the dependence of the PV roof tile temperature on incident radiation and ambient temperature. A theory based correction was developed to account for the unrealistic sky temperature of the solar simulator used in the experiments. The particular PV roof tiles used are warranted up to an operational temperature of 85 °C, anything above this temperature will void the warranty because of potential damage to the integrity of the encapsulation. As a guide for installers, a map of southern Europe has been generated indicating locations where excessive module temperatures might be expected and thus where installation is inadvisable.     

The effect of nonuniform fluid flow distribution on the thermal performance of solar collector

In the design of solar collector, every effort is made to provide an uniform fluid flow distribution among the flow channels of the collector. Economical and space considerations, however, may make the uniform fluid flow distribution through the solar collector unrealistic. If the fluid flow distribution is not uniform, the thermal performance of the solar collector may deteriorate. A numerical method is developed for determination of the deterioration of thermal performance of solar collector due to this flow nonuniformity effect. Using several typical fluid flow maldistribution models, the collector efficiency and its deterioration are determined for various collector design and operating conditions.     

A photovoltaic/thermal (PV/T) collector with a polymer absorber plate. Experimental study and analytical model

A polymer solar heat collector was combined with single-crystal silicon PV cells in a hybrid energy-generating unit that simultaneously produced low temperature heat and electricity. The PV/T unit was tested experimentally to determine its thermal and photovoltaic performance, in addition to the interaction mechanisms between the PV and thermal energy systems. Thermal efficiency measurements for different collector configurations are compared, and PV performance and temperature readings are presented and discussed. An analytical model for the PV/T system simulated the temperature development and the performance of both the thermal and photovoltaic units.     

基于纳米流体的光伏热联用装置及其理论分析

利用纳米流体对太阳能辐射分频吸收与高效传热的性能,结合太阳能直接吸收(DAC)技术、菲涅尔聚光技术,构建了基于纳米流体的新型聚光太阳能光伏热联用(CPV/T)装置,并建立了装置的物理模型和能量平衡模型。采用计算流体力学方法进行模拟仿真和对比实验,分析了不同流速及流体工质下光伏组件及纳米流体的温度场。研究结果表明:基于纳米流体的CPV/T装置能够充分利用纳米流体辐射分频吸收与高效传热特性,取得对太阳能光伏组件冷却的更好效果,也获得了更高的光热部分流体出口温度;与仅背板冷却的普通光伏热装置相比,流体出口温度有较大幅度的提升,从而提高了光热部分的利用能级。     

Experimental study on a new hybrid photovoltaic thermal collector

A calorific energy is generated during the photovoltaic conversion of the solar module which increases the temperature of the cell and will causes a fall of its electric output. This phenomenon is due, on one hand to the partial unabsorptive solar radiation which constituted the origin of the cells heating and on the other hand, with the Joule effect caused by the passage of the photo electrical current generated in the external circuit. This heating, harmful for the photovoltaic cells output involved many research efforts to limit its effects by evacuating this heat. There was also the idea to exploit this phenomenon by the combination of the photovoltaic module with a thermal system to form the photovoltaic-thermal hybrid collector (PVT) which will generate at the same time electricity and heat. In this paper we described the design of a new type of PVT collector through its experimental study. This novel collector constitutes a new technical approach to maximize the total output of conversion with lower cost compared to the traditional hybrid collectors.     

小型菲涅尔式CPV/T集热器光热特性研究

为充分利用建筑屋顶,解决光伏光热一体化(PV/T)集热器光电转换效率的高温减益问题,并提高太阳能综合利用率和集热品位,文章构建了一种基于太阳光谱分频利用技术的光伏/光热模块分离式的小型聚光式PV/T集热器。通过建立其光/电/热理论分析模型及TracePro/Fluent数值仿真模型,以南京地区气象数据为例,综合分析其光/电/热性能,结果表明:该集热器以与安装地纬度等值的倾角南北轴向放置时,其年均光学效率为64.97%,工质出口温度为90℃时的系统光电/光热效率分别为12.47%,40.09%,系统综合热效率达72.91%,且其结构简单、外形轻薄,有望实现与普通建筑的有效结合。     

Modelling of a hybrid photovoltaic thermal collector based on CdTe

A few years ago, silicon photovoltaic panels had yields of 10 to 18%, which made them interesting because is not profitable enough (too expensive to energy conversion yield too low).But recently, thin film technology appears to increase the efficiency and reduce the cost. For application in hybrid collectors, various types of solar photovoltaic hybrid collectors (PVT) based on new materials for solar cells have been developed as the binary semiconductor, ternary and quaternary materials and organic. CdTe is a the most appropriate binary materials for use in photovoltaic structures in thin layers, this material can produce a high yield of about 15% and is also known by a direct band structure gap of a value of 1.45 eV and a very high absorption coefficient (>105 cm^–1 in the visible). In this work we present the modeling of a hybrid photovoltaic thermal collector based on the thin films solar cells of CdTe, and then we made the determination of the temperature levels of the various layers through the development of the energy balance sheet involves heat exchange between the different components of the collector and to study its electrical and thermal performance, and finally compare their efficiency with it of the PVT collector based on monocrystalline silicon.     

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.