Building Integrated Photovoltaic Thermal Research Articles

Experimental studies on summer performance and feasibility of a BIPV/T ethylene tetrafluoroethylene (ETFE) cushion structure system

An ethylene tetrafluoroethylene (ETFE) cushion structure integrated photovoltaic panels is proposed for solar energy utilization of cushion structures. It can maintain cushion operation by photovoltaic electricity and provide a way of collecting thermal energy due to enclosed cushions. An experimental mockup composed of a three-layer ETFE cushion and amorphous silicon photovoltaic panels (a-Si PV) has been developed and a series of experiments have been conducted in summer, especially under sunny and sunny to cloudy conditions. On the whole, the experimental results showed that this system operated smoothly and steadily. In this paper, two studies, i.e. one-day study and three-day study have been done to investigate system performance and feasibility.For energy, the average stored electricity was 61Wh and the average ratio of consumption electricity to output electricity under sunny condition was lower than that under sunny to cloudy condition. Meanwhile, an average temperature difference between air temperatures inside and outside of the cushion was 18.1°C. Therefore, system electricity feasibility and potential in solar energy utilization have been verified. For cushion structures, temperatures on structural ETFE membranes used to resist external loads were within the acceptable range and pressure performance was satisfactory. Therefore, structure feasibility has been demonstrated.This study reveals the technical feasibility of ETFE cushion structure integrated photovoltaic. It provides a way to expand the application of building integrated photovoltaic/thermal (BIPV/T) to cushion structures.

Efficiencies and improvement potential of building integrated photovoltaic thermal (BIPVT) system

Building integrated photovoltaic thermal (BIPVT) system has been designed to produce both electricity and hot water and later integrated to building. The hot water is produced at the useful temperatures for the applications in Malaysia such as building integrated heating system and domestic hot water system as well as many industrial including agricultural and commercial applications. The photovoltaic thermal (PVT) system comprises of a high efficiency multicrystal photovoltaic (PV) module and spiral flow absorber for BIPVT application, have been performed and investigated. In this study, it was assumed that the absorber was attached underneath the flat plate single glazing sheet of polycrystalline silicon PV module and water has been used as a heat transfer medium in absorber. Performances analysis of BIPVT system based on energy and exergy analyses. It was based on efficiencies including energy and exergy, and exergetic improvement potential (IP) based on the metrological condition of Malaysia has been carried out. Results show that the hourly variation for BIPVT system, the PVT energy efficiency of 55–62% is higher than the PVT exergy efficiency of 12–14%. The improvement potential increases with increasing solar radiation, it is between 98 and 404W. On the other hand, BIPVT system was produced primary-energy saving efficiency from about 73% to 81%.

Estimation of photovoltaic conversion efficiency of a building integrated photovoltaic/thermal (BIPV/T) collector array using an artificial neural network

Earlier studies have shown that the thermal efficiency of a solar thermal collector is influenced by the quality of coolant flow distribution within the array. The quality of flow distribution within a header/riser type fluid network is influenced by a number of parameters including the coolant mass flow rate, the direction of flow in the manifolds, and most importantly the geometry of the array. As a building integrated photovoltaic thermal (BIPVT) collector will be a made to measure product, meaning its dimensions will be dictated by the specific roofing and energy requirements of the customer, the issue of flow distribution and its effect on both thermal and photovoltaic performance raises some concern. In order to quantify the detrimental effect flow distribution may have on the photovoltaic output of a BIPVT array, a numerical approach was presented by authors in earlier work where factors known to influence flow distribution were varied. The authors demonstrated that photovoltaic output may be severely hindered if the issue of flow distribution is not adequately addressed. In this new study we use this numerical method to additionally show that photovoltaic output is not always improved by reducing the fin width W (by increasing the number of risers for each module) despite the theoretical rise in fin efficiency F as a consequence of flow distribution. Under certain scenarios it was shown that a single riser will in fact improve PV output and also reduce system installation cost and complexity. The combination of these new finding and results previously obtained by the authors highlights the need in selecting the optimal design parameters to meet the specific requirements of each installation. The numerical approach carried out to calculate PV output however was time consuming and computationally intensive and therefore not feasible to perform for each and every customer. To address this issue, the authors have proposed in this paper to train an artificial neural network which can be used to approximate the photovoltaic yield of an array of specified shape operating under parallel⧹reverse flow in the manifolds and also with one or two fluid channels cooling each string of cells. By approximating the yield for each scenario, the optimal configuration can then be chosen. It was found that the neural network can be successfully trained for this specific application offering a fast alternative to the original numerical approach.

Effect of flow distribution on the photovoltaic performance of a building integrated photovoltaic/thermal (BIPV/T) collector

The phenomenon of non-uniform flow distribution and its influence on thermal performance within a traditional solar thermal collector is well known. Its effect on the photovoltaic conversion of a hybrid photovoltaic/thermal (PV/T) collector however has received little attention. In this study an investigation has been carried out to determine what effect flow distribution will have on the photovoltaic yield of a BIPV/T collector of various size. A three step numerical analysis was conducted to model flow distribution, temperature variation, and photovoltaic yield for a PV/T collector of various design (manifold sizes), geometric shape (aspect ratio), and operating characteristics (mass flow rate and flow direction in manifolds) in order to vary flow uniformity within the collector. The results revealed that flow distribution within the collector will have a significant influence on the photovoltaic performance of a hybrid PV/T collector. For the scenario where flow distribution was most uniform, photovoltaic performance was improved by over 9% in comparison to a traditional photovoltaic (PV) collector operating under the same conditions. For poor flow however, performance was only improved by approximately 2%. Parameters found to influence flow distribution include the manifold to riser pipe ratio where a ratio of 4:1 was found to be ideal and that increasing to a 6:1 ratio offered negligible improvement. Additionally it was found that array geometry (characterised by its aspect ratio in this study) plays an important role on both flow distribution and photovoltaic yield. This study has identified that the optimal mass flow rate is dependent on the shape or aspect ratio of the array.

A Study of Design Options for a Building Integrated Photovoltaic/thermal (BIPV/T) System with Glazed Air Collector and Multiple Inlets

In this paper, a prototype open loop air-based building integrated photovoltaic thermal BIPV/T system with a single inlet is studied through a comprehensive series of experiments in a full scale solar simulator recently built at Concordia University. A numerical control volume model is developed and validated based on the results from the experiments. Improved designs of the BIPV/T system with multiple inlets and other means of heat transfer enhancement are studied through simulations. Simulation results indicate that the application of two inlets on a BIPV/T collector increase thermal efficiency by around 5% and increase electrical efficiency marginally. An added vertical glazed solar air collector improves the thermal efficiency significantly, and the improvement is more significant with wire mesh packing in the collector.

A Simulation Study of Air-Type Building-Integrated Photovoltaic-Thermal System

The building-integrated photovoltaic-thermal (BIPVT) collector combines PV panels with solar thermal collectors that applies as a building envelope material to produce both thermal and electrical energy at the same time. The air based BIPVT system applied to buildings can be an outer layer to make building envelope double-layers, so that the thermal characteristics of a building with the envelope system could be different from normal walls due to the heat generated from PV panels. Therefore, the envelope of building with BIPVT system is different from that of existing building and may take different impact on the building energy loads. Also, the building energy performance varies according to the energy obtained from the system.This study aims to evaluate the electrical and thermal performance of the air type BIPVT system, and to analyze the energy performance of building with the air type BIPVT system applied as the building envelope. For this study, building models with BIPV and BIPVT were compared through TRNSYS simulation results.

A heat pipe photovoltaic/thermal (PV/T) hybrid system and its performance evaluation

Building-integrated photovoltaic/thermal (BIPV/T) system has been considered as an attractive technology for building integration. The main part of a BIPV/T system is PV/T collector. In order to solve the non-uniform cooling of solar PV cells and control the operating temperature of solar PV cells conveniently, a heat pipe photovoltaic/thermal (PV/T) hybrid system (collector) has been proposed and described by selecting a wick heat pipe to absorb isothermally the excessive heat from solar PV cells. A theoretical model in terms of heat transfer process analysis in PV module panel and introducing the effectiveness–number of transfer unit ( ɛ– NTU) method in heat exchanger design was developed to predict the overall thermal–electrical conversion performances of the heat pipe PV/T system. A detailed parametric investigation by varying relevant parameters, i.e., inlet water temperature, water mass flow rate, packing factor of solar cell and heat loss coefficient has been carried out on the basis of the first and second laws of thermodynamics. Results show that the overall thermal, electrical and exergy efficiencies of the heat pipe PV/T hybrid system corresponding to 63.65%, 8.45% and 10.26%, respectively can be achieved under the operating conditions presented in this paper. The varying range of operating temperature for solar cell on the absorber plate is less than 2.5 °C. The heat pipe PV/T hybrid system is viable and exhibits the potential and competitiveness over the other conventional BIPV/T systems.

Energy saving in buildings by using the exhaust and ventilation air for cooling of photovoltaic panels

A building integrated photovoltaic-thermal (BIPVT) setup has been developed for using the cooling potential of ventilation and exhaust airs in buildings for cooling the photovoltaic (PV) panels and also heating the ventilation air by heat rejection of PV panels. The setup has been tested numerically for the Kerman city located in Kerman province in the south of Iran. Results showed that, the exhaust and ventilation airs in heating ventilating air conditioning systems can be used as the cooling fluid of the PV panels and increase their efficiency. On the other hand, the heat rejection of the PV panels could provide some part of the ventilation air heating load.

Convective Heat Transfer Coefficients in a Building-Integrated Photovoltaic/Thermal System

This paper presents an experimental study for the development of convective heat transfer correlations for an open loop air-based building-integrated photovoltaic/thermal (BIPV/T) system. The BIPV/T system absorbs solar energy on the top surface, which includes the photovoltaic panels and generates electricity while also heating air drawn by a variable speed fan through a channel formed by the top roof surface with the photovoltaic modules and an insulated attic layer. The BIPV/T system channel has a length/hydraulic diameter ratio of 38, which is representative of a BIPV/T roof system for 30–45 deg tilt angles. Because of the heating asymmetry in the BIPV/T channel, two average Nusselt number correlations are reported as a function of Reynolds number: one for the top heated surface and the other for the bottom surface. For the top heated surface, the Nusselt number is in the range of 6–48 for Reynolds numbers ranging from 250 to 7500. For the bottom insulated surface, the Nusselt number is in the range of 22–68 for Reynolds numbers ranging from 800 to 7060. This paper presents correlations for the average Nusselt number as a function of Reynolds number; this correlation is considered adequate for the design of BIPV/T systems where forced convection dominates. Local Nusselt number distributions are also presented for laminar and turbulent flow conditions.

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.

Predicting the performance of amorphous and crystalline silicon based photovoltaic solar thermal collectors

BIPVT is an application where solar PV/T modules are integrated into the building structure. System design parameters such as thermal conductivity and fin efficiency, type of cells, type of coolant and operating conditions are factors which influence the performance of BIPVT. Attempts have been made to improve the efficiency of building-integrated photovoltaic thermal (BIPVT). A new design concept of water-based PVT collector for building-integrated applications has been designed and evaluated. The results of simulation study of amorphous silicon (a-Si) PV/T and crystalline silicon (c-Si) module types are based on the metrological condition of Malaysia for a typical day in March. At a flow rate of 0.02 kg/s, solar radiation level between 700 and 900 W/m 2 and ambient temperature between 22 and 32 °C, the electrical, thermal and combined photovoltaic thermal efficiencies for the PV/T (a-Si) were 4.9%, 72% and 77%, respectively. Moreover, the electrical, thermal and combined photovoltaic thermal efficiencies of the PV/T (c-Si) were 11.6%, 51% and 63%.

Development of photovoltaic thermal technology in recent years: a review

Photovoltaic/thermal (PV/T) technology developed quickly in recent years with new configuration designs and methods for energy efficiency improvement. This paper presents a review of the development of PV/T technology, mainly focusing on the past 5 years, including commercial PV material properties, PV/T collector configurations, building-integrated photovoltaic thermal (BIPVT) collectors and concentrating PV/T collectors as well as a PV/T heat pump system. From the literature review, it can be found that PV/T technology has a great potential for energy savings and further work should be focused on the reduced cost, improved efficiency and stabilized operation and control strategy. Copyright The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com, Oxford University Press.

Modeling, design and thermal performance of a BIPV/T system thermally coupled with a ventilated concrete slab in a low energy solar house: Part 1, BIPV/T system and house energy concept

This paper is the first of two papers that describe the modeling, design, and performance assessment based on monitored data of a building-integrated photovoltaic-thermal (BIPV/T) system thermally coupled with a ventilated concrete slab (VCS) in a prefabricated, two-storey detached, low energy solar house. This house, with a design goal of near net-zero annual energy consumption, was constructed in 2007 in Eastman, Québec, Canada – a cold climate area. Several novel solar technologies are integrated into the house and with passive solar design to reach this goal. An air-based open-loop BIPV/T system produces electricity and collects heat simultaneously. Building-integrated thermal mass is utilized both in passive and active forms. Distributed thermal mass in the direct gain area and relatively large south facing triple-glazed windows (about 9% of floor area) are employed to collect and store passive solar gains. An active thermal energy storage system (TES) stores part of the collected thermal energy from the BIPV/T system, thus reducing the energy consumption of the house ground source heat pump heating system. This paper focuses on the BIPV/T system and the integrated energy concept of the house. Monitored data indicate that the BIPV/T system has a typical efficiency of about 20% for thermal energy collection, and the annual space heating energy consumption of the house is about 5% of the national average. A thermal model of the BIPV/T system suitable for preliminary design and control of the airflow is developed and verified with monitored data.

Modeling, design and thermal performance of a BIPV/T system thermally coupled with a ventilated concrete slab in a low energy solar house: Part 2, ventilated concrete slab

This paper is the second of two papers that describe the modeling and design of a building-integrated photovoltaic–thermal (BIPV/T) system thermally coupled with a ventilated concrete slab (VCS) adopted in a prefabricated, two-storey detached, low energy solar house and their performance assessment based on monitored data. The VCS concept is based on an integrated thermal–structural design with active storage of solar thermal energy while serving as a structural component – the basement floor slab (∼33 m 2). This paper describes the numerical modeling, design, and thermal performance assessment of the VCS. The thermal performance of the VCS during the commissioning of the unoccupied house is presented. Analysis of the monitored data shows that the VCS can store 9–12 kWh of heat from the total thermal energy collected by the BIPV/T system, on a typical clear sunny day with an outdoor temperature of about 0 °C. It can also accumulate thermal energy during a series of clear sunny days without overheating the slab surface or the living space. This research shows that coupling the VCS with the BIPV/T system is a viable method to enhance the utilization of collected solar thermal energy. A method is presented for creating a simplified three-dimensional, control volume finite difference, explicit thermal model of the VCS. The model is created and validated using monitored data. The modeling method is suitable for detailed parametric study of the thermal behavior of the VCS without excessive computational effort.

Modeling of energy performance of a house with three configurations of building-integrated photovoltaic/thermal systems

A theoretical and experimental study of energy performance of three different open loop air heating building-integrated photovoltaic/thermal (BIPV/T) systems that utilize recovered heat for home heating is presented. The configurations are: Configuration 1: base case of unglazed BIPV with airflow under it; Configuration 2: addition of 1.5 m vertical glazed solar air collector in series with Configuration 1; Configuration 3: addition of a glazing over the PV. The model developed has been verified against experimental data from a solar research house for Configuration 1. Obtained relationships for BIPV/T system exiting air temperature as function of solar irradiance and air speed in PV cavity may be used for developing fan airflow control strategies to achieve desired outlet air temperature suitable for different applications. For Configuration 1, preheated air is suitable for HVAC system and domestic hot water (DHW) preheating. Higher outlet air temperatures of the PV cavity suitable for DHW might be achieved by utilizing Configurations 2 or 3. With Configuration 2, significant outlet air temperatures are achieved in winter along with enhanced thermal efficiency making it suitable for coupling with a rockbed heat storage. Finally, Configuration 3 significantly reduces electricity production and may lead to excessively high PV panel temperatures.

Life cycle cost assessment of building integrated photovoltaic thermal (BIPVT) systems

The present paper deals with an analysis of the building integrated photovoltaic thermal (BIPVT) system fitted as rooftop of a building to generate electrical energy higher than that generated by a similar building integrated photovoltaic (BIPV) system and also to produce thermal energy for space heating. A thermodynamic model has been developed to determine energy, exergy and life cycle cost of the BIPVT system. The results indicate that although the mono-crystalline BIPVT system is more suitable for residential consumers from the viewpoint of the energy and exergy efficiencies, the amorphous silicon BIPVT system is found to be more economical. The energy and exergy efficiencies of the amorphous silicon BIPVT system are found to be 33.54% and 7.13% respectively under the composite climatic conditions prevailing at New Delhi. The cost of power generation is found to be US $ 0.1009 per kWh which is much closer to that of the conventional grid power.

Experimental and numerical investigation on thermal and electrical performance of a building integrated photovoltaic–thermal collector system

An experimentally validated computational fluid dynamics (CFD) model of a novel building integrated photovoltaic–thermal (BIPV/T) collector is studied to determine the effect of active heat recovery on cell efficiency and to determine the effectiveness of the device as a solar hot water heater. Parametric analysis indicates that cell efficiency can be raised by 5.3% and that water temperatures suitable for domestic hot water use are possible. Thermal and combined (thermal plus electrical) efficiencies reach 19% and 34.9%, respectively. A new correlation is developed relating electrical efficiency to collector inlet water temperature, ambient air temperature and insolation that allows cell efficiency to be calculated directly.

Optimizing the energy and exergy of building integrated photovoltaic thermal (BIPVT) systems under cold climatic conditions

Building integrated photovoltaic thermal (BIPVT) system has the potential to become a major source of renewable energy in the urban environment. In this paper, the system has been used as the roof top of a building to generate higher electrical energy per unit area and to produce necessary thermal energy required for space heating. One-dimensional transient model has been developed using basic heat transfer equations. On the basis of this model, an analysis has been carried in order to select an appropriate BIPVT system suitable for the cold climatic conditions of India. The PV performances, net energy gain and exergy of the building are determined. The results show that for a constant mass flow rate of air the system connected in series gives a better performance whereas for a constant velocity of air flow the system connected in parallel gives a better performance. The BIPVT system, fitted on the rooftop in an effective area of 65 m 2, is capable of annually producing the net electrical and thermal exergies of 16,209 kW h and 1531 kW h, respectively, at an overall thermal efficiency of 53.7%.

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.