Comparison of theoretical and real energy yield of direct DC-power usage of a Photovoltaic Façade system

Multifunctional façade components have nowadays become a significant research topic as a step towards developing energy-efficient buildings. This paper presents the performance evaluation of an experimental setup of a real fully decentralized façade-integrated photovoltaic (PV) system installed in a prototype façade, for direct DC power use. The goal of this evaluation was to test the system's ability to fulfill a pre-designed daily electrical load of 925Wh corresponding to a three-people office space under 100% decentralization. This was achieved by studying the operation under different weather conditions and the impact of the system design and components on its overall output. The evaluation of both the actual and theoretical system outputs indicates poor actual system performance in terms of low energy yield and unacceptable load fulfillment factor, which did not exceed 0.95. At the same time it revealed underutilized system potential which could be exploited theoretically with a proper system configuration. The results in this paper conclude that decentralized façade integrated PV systems can completely satisfy their designated applications if properly-designed and implemented, and provides a methodology which could be used in designing similar systems. Satisfactory fulfillment is shown to be achieved by having 30% additional PV and 9 times bigger storage capacities in this system.     

Performance of thin-film BIPV as double sloped pitched roof in buildings of Malaysia

Solar energy in built environments became more popular in the recent years emerging as building integrated photovoltaics (90° façade and 0° roof BIPV). However, in most cases, residential buildings have varying roof pitches instead of 0° roof. In this context, it is significant to assess the energy output and performance of double-sloped pitched roof thin-film BIPV at different angles and orientation. Results show that the performance of the BIPV inclined at 15° and east orientation is better among the other orientation and angles.     

Pilot study on building-integrated PV: Technical assessment and economic analysis

Building-integrated photovoltaics (BIPV) is an innovative green solution that incorporated energy generation into the building façade with modification on the building material or architectural structure. It is a clean and reliable solution that conserves the aesthetical value of the architecture and has the potential to enhance the building's energy efficiency. Malaysia's tropical location has a high solar energy potential to be exploited, and BIPV is a very innovative aspect of technology to employ the available energy. Heriot-Watt University Malaysia (HWUM) has a unique roof design that could be utilized as an application of the BIPV system to generate electricity, reducing the carbon footprint of the facility. Eight BIPV systems of different PV technologies and module types and with capacities of 411.8 to 1085.6 kW were proposed for the building. The environmental plugin software has been integrated with a building geometry modelling tool to visualize and estimate the energy potential from the roof surface in a 3D modelling software. Additionally, detailed system simulations are conducted using PVSyst software, where results and performance parameters are analysed. The roof surface is shown to provide great energy potential and studied scenarios generated between 548 and 1451 MWh yearly with PR range from 78% to 85%. C-Si scenarios offer the best economical profitability with payback period of 4.4 to 6.3 years. The recommended scenario has a size of 1085.5 kW and utilizes thin-film CdTe PV modules. The system generates 1415 MWh annually with a performance ratio of 84.9%, which saves 62.8% of the electricity bill and has an estimated cost of 901 000 USD. Installation of the proposed system should preserve the aesthetical value of the building's roof, satisfy BIPV rules, and most importantly, conserves energy, making the building greener.     

Design and assessment of a solar energy based integrated system with hydrogen production and storage for sustainable buildings

The current study investigates a holistically developed solar energy system combined with a ground-sourced heat pump system for stand-alone usage to produce power, heat, and cooling along with domestic hot water for residential buildings. An integrated system is proposed where three types of building-integrated photovoltaic plant orientation are considered and integrated with a vertical-oriented ground-sourced heat pump system as well as an anion exchange membrane electrolyser for hydrogen-based energy storage along with proton exchange membrane fuel cells. The ground-sourced heat pump system covers the heating requirements and exploits the available thermal energy under the ground. Hydrogen subsystem enables the integrated system to be used anytime by compensating the peak periods with stored hydrogen via fuel cell and exploiting the excess energy to produce hydrogen via electrolyser. The photovoltaic plant orientations are extensively designed by considering geometries of three different applications, namely, rooftop photovoltaic, building-integrated photovoltaic façade and photovoltaic canopy. The shading and geometrical losses of photovoltaic applications are extensively identified and considered. In addition, the openly available high-rise building load profiles are obtained from the OpenEI network and are modified accordingly to utilize in the current study. The building requirements are considered for 8760 h annually with meteorological data and energy usage characteristics of the selected regions. The integrated system is assessed via thermodynamic-based approach from energy and exergy points of views. In order to increase generality, the proposed building energy system is analyzed for five different cities around the globe. The obtained results show that a 20-floor building with approximately 62,680 m² residential area needs between 550 kWp and 1550 kWp of a photovoltaic plant in five different cities. For Ottawa, Canada, the overall energy and exergy efficiencies are found as 18.76% and 10.49%, respectively, in a typical meteorological year. For the city of Istanbul in Turkey, a 20-floor building is found to be self-sufficient by only using the building's surface area with a 495 kWp BIPV façade and a 90 kWp rooftop PV.     

Estimating thermal stress in BIPV modules

The thermal stress on building‐integrated photovoltaic modules (BIPV) in Espoo, Finland, was studied with field‐testing of amorphous silicon modules. Based on these results, the thermal stress at two other European locations (Paris and Lisbon) was estimated. The estimation procedure entailed thermal modelling of heat transfer in the façade with meteorological data as input. The results indicate that the thermal stress on BIPV modules in Lisbon is, in this case, approximately 50% higher that in Espoo and between 80 and 200% higher than in Paris, depending on the activation energy of the degradation process. The difference in stress between a BIPV module and a free‐standing module in Espoo was 50–200%. Copyright © 2006 John Wiley & Sons, Ltd.     

Assessment of fixed shading devices with integrated PV for efficient energy use

The use of external fixed shading devices to adjust solar influx radiation and to save energy is well known. However, fixed shading devices can reduce daylight availability, increase artificial light needs and block the beneficial winter solar radiation.This paper is part of a research on the characteristics of the optimum shading device. The aim is to investigate the balance between the energy needs for heating and cooling the space that the shading device is used for and the energy that is used for lighting the same space and the energy that the shading device can produce.In order to investigate the balance between the above mentioned parameters, thirteen types of fixed shading devices have been studied and categorized according to their energy performance, for a single occupant office room. The same office room is tested for two different Mediterranean latitudes in Athens and in Chania, Crete in Greece and for two different south facing windows’ sizes.The thermal behavior of the devices is assessed through computer simulation application and the daylight analysis is assessed with both computer simulation and physical modeling. Stable parameters were the internal loads in the office room, the south orientation of the façade and the type of glazing. Variable parameter was the type of the fixed shading device.The study shows that all shading devices with integrated south facing PV can efficiently produce electricity which may be used for lighting. The study highlights the fact that shading devices such as Surrounding shading, Brise–Soleil full façade and Canopy inclined double work efficiently against thermal and cooling loads and may be used to produce sufficient electricity and control daylight. The study defines the geometrical parameters that will be incorporated to the overall characteristics of the optimum fixed shading device and proposes new fields of development for the BIPV technologies.     

Sensitivity study of an opaque ventilated façade in the winter season in different climate zones in Spain

Energy efficient buildings need to take advantage of any renewable energy available. An opaque ventilated façade (OVF) is a kind of façade that absorbs solar energy and transfers it to the ventilation system. This way, the sensible ventilation load of the heating system can be reduced in the winter season. The energy saving of this system depends strongly on the weather variables, mainly solar radiation on the façade, ambient temperature and wind speed. In order to find the most convenient locations where the best OVF efficiency can be obtained, its performance has to be studied along a complete season. For this purpose in this study a sensitivity analysis with the most important weather variables was carried out and the energy saving values in 12 locations in Spain in the winter were evaluated using a numerical model previously validated with experimental data. The results showed that although the most influential weather variable was solar radiation, a combination of high temperatures and low wind speeds can also lead to important energy saving values. It was found that the most convenient locations for installing an OVF were those with low and medium winter severity climates, namely, in the southern and coastal regions of Spain (zones A3, B3, B4, C3 and C4).     

Dynamic performance of a façade-based solar loop heat pipe water heating system

This paper reported a dedicated study of a novel façade-based solar loop heat pipe (LHP) water heating system using both theoretical and experimental methods. This system employs a modular panel incorporating a unique loop heat pipe that is able to serve as part of the building façade or a decoration layer of the façade, thus creating a façade integrated, low cost, highly efficient and aesthetically appealing solar water heating structure. Taking into account heat balances occurring in different parts of the system, e.g., solar absorber, heat pipes loop, heat exchanger and storage tank, a dedicated computer model was developed to investigate the dynamic performance of the system. An experimental rig was also established to evaluate the performance of such a prototype system through measurement of various operational parameters, e.g., solar radiation, temperatures and flow rates of the heat pipe fluid and water. Through comparison between the testing and modelling results, the model has been approved to be able to give a reasonable accuracy for predicting the performance of the LHP system. Two types of glass covers, i.e., double glazed/evacuated tubes and single-glazing plate, were applied to the prototype. It was found that for both covers, the heat pipe fluid temperature rose dramatically at the start-up operation and afterwards remained a slow but steady growth; while the water temperature remained a steadily growing trend throughout the operational day. The temperature rise of the circulated water at 1.6 l/min of flow rate was around 13.5 °C in the double-glazed/evacuated tubes based system and 10 °C in the single-glazing based system; correspondingly, their average solar conversion efficiencies were 48.8% and 36%, and the COPs were 14 and 10.5 respectively. In overall, the double-glazed/evacuated tubes based system presented a better performance than the single glazing based one.     

A state-of-the-art review of solar passive building system for heating or cooling purpose

The major portion of energy in a building is consumed by heating, ventilating, and air-conditioning (HVAC). The traditional heating and cooling systems contribute greatly to the emission of greenhouse gases, especially carbon dioxide. Four different ways, i.e., Trombe wall, solar chimney, unglazed transpired solar façade, and solar roof, are adopted for solar heating. Similarly, two major ways, i.e., evaporative cooling and building integrated evaporative cooling are adopted for cooling of the building. Therefore, an attempt has been made in this paper to compile the developments of solar heating and cooling technologies in a building.     

Development of the timber-glass upgrade module for the purpose of its installation on energy-inefficient buildings in the refurbishment process

The current research study presents the development of the upgrade module consisting of a timber frame structure with the optimal glazing size in the east-, south- and west-oriented façades for the purpose of energy-efficient refurbishment of the existing energy-inefficient buildings. Such construction module could open the way to simple installation onto the existing residential, public or office buildings of various shapes and ensure better energy performance of the refurbished buildings. The optimal glazing size of the east-, south- and west-oriented façades of the module with the optimal shape is determined by the glazing-to-wall area ratio where the sum total of the annual energy need for heating and cooling of the module is minimal. The sum of the annual energy is defined through an extensive parametric numerical analysis including variations regarding the module’s aspect ratio, the thermal transmittance of its envelope and the glazing size in its east-, south- and west-oriented façades. A parametric analysis carried out in the previously described manner leads to analytic functional dependence between the energy consumption and the module’s design parameters. It is therefore possible to make a fairly simple preliminary estimate of the annual energy need, in addition to defining the optimal floor plan shape of the module along with the optimal proportion of glazing in its east-, south- and west-oriented façades. The optimal proportion of glazing varies from 24 to 91% in the south-oriented façade, from 7 to 43% in the east and from 9 to 55% in the west façade, at the thermal transmittance of the thermal envelope 0.100 W/(m² K). The variation in the optimal glazing proportion of the module with the thermal transmittance of the thermal envelope 0.165 W/(m² K) ranges from 14 to 85% in the east, from 28 to 97% in the south and from 16 to 68% in the west-oriented façade. The presented research study permits a choice of the optimal module design with respect to baseline characteristics of the existing building and allows for a more systematic as well as energy-efficient refurbishment process.     

Experimental performance of a Fresnel-transmission PVT concentrator for building-façade integration

A building-façade integrated concentrating photovoltaic-thermal system has been designed, constructed and experimentally characterised. Comparative performances with a non-concentration reference unit have been conducted to analyse the differential outputs. The concentrating system consists of double-side reflective strips which concentrate the incident beam towards a static photovoltaic-thermal receiver. The reflectors are placed vertically at the façade and track the sun by rotating axially. The concentrating reflector outperforms the reference one in both, thermal and electrical power. The thermal output of the concentration module almost doubles the reference one and the electrical power registered is more than 4.5 times in the case of the concentrating configuration.     

‘State-of-the-art’ of building integrated photovoltaic products

During the last decades, the photovoltaic (PV) modules and their associated architectural materials are increasingly being incorporated into the construction of the building envelope such as façade, roof and skylights in the urban centers.This paper analyzes the-state-of-the-art of the PV elements and construction materials which are advertised as BIPV-products at the most important companies in the world. For this purpose 136 companies and 445 PV elements have been investigated and analyzed from a technical and architectural point of view. Also, the study has been divided into two main groups according to industry which producing the product: BIPV-Modules, which comes from the PV modules manufacturers and consist of standard PV-modules with some variations in its aesthetic features, support or dimensions; and PV-Constructions Elements, which consist of conventional constructive elements with architectural features intentionally manufactured for photovoltaic integration. In advance for conclusions, the solar tile is the most common PV-constructions element, the Si-crystalline is the most widely used PV technology, and the BIPV-urban furniture is the fastest growing market experienced in recent years. However, it is clear the absences of innovative elements which meet at the same time both the constructive purpose as the quality standards of PV technology.     

Experimental study on flame height and temperature profile of buoyant window spill plume from an under-ventilated compartment fire

Fire experiments were carried out in a scale model, consisting of an 0.8 m cubic fire compartment with six window like geometries and an attached 3 m (wide) × 5 m (high) façade wall. A propane porous gas burner with controlled fuel supply rate was the fire source. Gas temperature profiles were measured inside the compartment and near the façade wall. The outside spill flame heights were recorded by a CCD Digital camera. Temperature and flame heights are correlated with heat release rate and the window geometry using physically non-dimensional analysis. The steady gas temperatures inside the compartment are determined by an overall energy balance between the heat release rate inside the compartment and the wall conduction and opening radiation heat losses using an effective overall heat loss coefficient. Flame heights on the façade are non-dimensionally correlated by the excess fuel heat release rate outside the enclosure and a characteristic length scale for the window. These results agree with previous results in the literature. Vertical gas temperatures near the façade wall outside the enclosure are non-dimensionally correlated with the total convective heat flow rate above the flames and the same characteristic window length scale as the flame height, with the additional necessary determination of a virtual origin of the convective flow above the flame. These results and correlations are new and a significant improvement over previous results in the literature.     

Environmental payback time analysis of a roof-mounted building-integrated photovoltaic (BIPV) system in Hong Kong

This paper reports the investigation results of the energy payback time (EPBT) and greenhouse-gas payback time (GPBT) of a rooftop BIPV system (grid-connected) in Hong Kong to measure its sustainability. The 22 kWp PV array is facing south with inclined angle of 22.5°. The hourly solar irradiance and ambient air temperature from 1996 to 2000 were used as weather data input. The annual power output was found to be 28,154 kWh. The embodied energy for the whole system in the lifespan was 205,816 kWh, including 71% from PV modules and 29% from balance of system (BOS). The percentage of embodied energy for silicon purification and processing reached 46%. The EPBT of the PV system was 7.3 years, and the GPBT was estimated to be 5.2 years considering fuel mixture composition of local power stations. This paper also discussed the EPBTs for different orientations, ranging from 7.1 years (optimal orientation) to 20.0 years (west-facing vertical PV façade). The results show that the ‘sustainability’ of a PV system is affected by its installation orientation and location. Choosing locations and orientations with higher incident solar irradiance is one key for the sustainability of BIPV technology applications.     

Available remodeling simulation for a BIPV as a shading device

A building integrated photovoltaic system as a shading device is used as an application and remodeling model. This study applies the simulation program SOLCEL and the computational fluid dynamics method to cases with solar irradiance components analysis and a ventilated double façade remodeling of the BIPV. For the validation of the theoretical work, experimental results of the Samsung Institute of Engineering and Construction Company building are used with a wind velocity of the weather data of Suwon area, Korea, where the real building is located. A photovoltaic system can be used only to generate electricity, but if a photovoltaic module can be used as an element of a double envelope, it could be more useful at the point of view of renewable energy usage and night insulation. Increase of PV module surface temperature is negative for power generation by installing PV module as an element of double envelope. A reasonable combination between renewable energy usage and power generation should be well analyzed for better usage of natural energy to design a BIPV.     

Influence of a building’s integrated-photovoltaics on heating and cooling loads

Building integrated photovoltaics (BIPV) has the potential to become a major source of renewable energy in the urban environment. BIPV has significant influence on the heat transfer through the building envelope because of the change of the thermal resistance by adding or replacing the building elements. Four different roofs are used to assess the impacts of BIPV on the building’s heating-and-cooling loads; namely ventilated air-gap BIPV, non-ventilated (closed) air-gap BIPV, closeroof mounted BIPV, and the conventional roof with no PV and no air gap. One-dimensional transient models of four cases are derived to evaluate the PV performances and building cooling-and-heating loads across the different roofs in order to select the appropriate PV building integration method in Tianjin, China. The simulation results show that the PV roof with ventilated air-gap is suitable for the application in summer because this integration leads to the low cooling load and high PV conversion efficiency. The PV roof with ventilation air-gap has a high time lag and small decrement factor in comparison with other three roofs and has the same heat gain as the cool roof of absorptance 0.4. In winter, BIPV of non-ventilated air gap is more appropriate due to the combination of the low heating-load through the PV roof and high PV electrical output.     

An experimental investigation on temperature profile of buoyant spill plume from under-ventilated compartment fires in a reduced pressure atmosphere at high altitude

Buoyant fire plume over a building façade spilled from the window of an under-ventilated compartment fire poses a serious fire hazard of flame spread to upper floors, a process in which the high plume temperature is the key parameter. In order to specify its counteracting fire safety design and regulations, the façade plume temperature profiles have been studied and correlated in the past. However, those correlations are all specified at normal atmospheric pressure conditions at sea level, which is needed however to be extended for conditions at low pressure such as in high altitudes. To investigate the effect of low atmospheric pressure on temperature profile of buoyant spill plume, a knowledge which has never been revealed, scale model experiments were carried out correspondingly at two different altitudes (Hefei city: 50 m, 1 atm; Lhasa city: 3650 m, 0.64 atm). Both the lateral (in the direction normal to façade) and vertical (along facade) temperature profile of the spill plume are measured. It is found that the lateral decay of temperature in the reduced pressure atmosphere is much faster than that in the normal pressure condition, but they can be converged and correlated by a proposed non-dimensional equation. For a given total heat release rate, the temperature of the spill plume near the façade wall is much higher in the reduced pressure atmosphere than that in the normal pressure condition at the same height, suggesting that the fire safety regulations to counteract the vertical fire spread to upper floors need to be specified more rigorous in high altitude. Based on the correlation of vertical temperature profile, it is found that the air entrainment of the buoyant spill plume is weaker in the reduced pressure atmosphere, being about 0.8 times of that in the normal pressure condition. Finally, the vertical temperature profile is collapsed non-dimensionally with this entrainment change accounted for. These results and findings at low pressure provide a significant supplement over previous results in the literatures, as well as application of current fire protection measure settings to high altitude locations with considerably reduced atmospheric pressure.     

Feasibility analysis of solar photovoltaic array cladding on commercial towers in Doha,Qatar – a case study

Building-integrated photovoltaic (BIPV) technology has become a major area of research due to environ-mental concerns. This article studies the feasibility of cladding high-rise towers in Doha with solar photovoltaic modules. Specifically, the case of the Qatar Financial Centre (QFC) is discussed. The major aim of the work is to evaluate the technical feasibility, economic impact and environmental effects of using photovoltaic panels on commercial towers in Qatar. Experimental data on solar irradiance and the effect of shading on the QFC Tower are presented. Numerical calculations are done using solar pathfinder software. The studies show that, although there is a significant amount of saving in CO₂ emission by using BIPV on towers in Doha, the payback period is still very long due to the cheaper cost of grid electricity in Qatar and poor conversion efficiency of PV panels. The complete system layout is presented and viable solutions are investigated.     

Double skin facades (DSF) and building integrated photovoltaics (BIPV): A review of configurations and heat transfer characteristics

This article presents the state of the knowledge on the thermal analysis of double skin facades with integrated photovoltaic (PV) panels called the Building Integrated Photovoltaics (BIPV) in terms of the published studies carried out on these systems. The idea of integration of the PV panels by replacing building elements, increase the prospects of the renewable energy systems. Taking also into account the need to use more renewable energy systems in buildings, the investigation of the BIPV systems to improve their performance is of a great importance. The literature studies are separated into experimental and theoretical for naturally ventilated systems and mechanically ventilated with external means e.g. fan use. It is concluded that most researchers studied the systems with mechanical ventilation rather than the systems with natural ventilation because the latter are more complex in terms of the air flow behaviour in the air duct. Additionally, various researchers proposed Nu number correlations and convective heat transfer correlation under several assumptions and conditions every time, for different range or Ra number which are presented and compared in this paper.     

Experimental operating cell temperature assessment of BIPV with different installation configurations on roofs under Mediterranean climate

The presence of an air gap between a photovoltaic (PV) module and roof facilitates ventilation cooling under the device and consequently reduces cell temperature and improves its performance. In case of rack-mounted PV installation, the Nominal Operating Cell Temperature (NOCT) method could be effectively used to predict the temperature of the module for various environmental conditions.Many countries, for esthetic purposes, offer economic advantages (tax deductions, incentives, etc…) for the installation of building integrated photovoltaic modules (BIPV), with water-tightness capability and adequate mechanical resistance in order to substitute tile covering or part of it. Nevertheless, poor or absent ventilation under BIPV panels could cause them to overheat and reduce their efficiency. Lack of validated predictive tools for the evaluation of BIVP energy performance could be another barrier to their widespread application.In this study, we investigated the thermal performance of PV modules installed in a real scale experimental building over a traditional clay tile pitched roof in Italy for almost one year (from August 2009 to June 2010). One PV module was rack-mounted over the roof covering with a 0.2 m air gap; the others were fully integrated and installed at the same level of the roof covering (one with an air gap of 0.04 m, the other mounted directly in contact with the insulation).Temperature and heat flux measurements for each panel, and environmental parameters were recorded.Two temperature prediction models, NOCT model and SNL (Sandia National Laboratory) model were used to predict BIPV temperature and energy efficiency so that their suitability for BIPV could be evaluated. SNL model takes into account also the wind speed.Experimental results demonstrate that even though the rack-mounted PV module constantly maintains cell temperature below that of the other full-building integrated modules, due to the presence of a higher air gap, the difference in the energy produced by the BIPV modules estimated for the entire monitoring period is less than 4%.The two predictive models, NOCT and SNL, cause the differences in predicted and calculated temperature up to 10 °C. However, subsequent percentage variations on the energy predicted compared to that arising from the temperature measured generally turn out to be lower than 5%.An optimization of empirical coefficients used for calculations based on the SNL method allows for the reduction of this value below 2.5%.