Building-integrated Photovoltaic Windows Research Articles

Quantifying the benefits of BIPV windows in urban environment under climate change: A comparison of three Chinese cities

Building-integrated photovoltaic (BIPV) windows are an effective way to increase distributed PV capacity in the urban environment. However, the effects of BIPV windows on an annual scale have not been rigorously studied. In this study, we compared their performances with different window-to-wall ratios, canyon aspect ratios, and orientations in three Chinese cities. Our results show that in Beijing, BIPV windows with the southward orientation have the highest potential for power generation of 44.7 kWh/(m2·yr), which is 1.5 times the potential in Shenzhen and Nanjing. Compared to clear windows, BIPV windows are advantageous when the window coverage is greater than 50 % in a shallow canyon. The highest electricity saving ratios are found in Beijing (29.7 %), followed by Shenzhen (26.3 %) and Nanjing (23.3 %). However, the electricity saving ratio decreases by over 10 % in deep canyons. Under future climate forcing, the saving potential of BIPV windows increases slightly in Nanjing and remain stable in Shenzhen and Beijing. The study also found that BIPV windows could increase canyon air temperatures by over 0.2 °C during winter days but slightly cool the canyon in summer. The findings guide BIPV application in the built environment and cast light on the construction of low-carbon neighbourhoods.

Transfer-printing a surface-truncated photonic crystal for multifunction-integrated photovoltaic window

Precise light manipulation is of paramount importance in improving the performance of semi-transparent organic photovoltaics (STOPVs) for their orientation toward building-integrated photovoltaic window. Nevertheless, one critically important issue for the integration of optical modulation with STOPV devices, lies in the damage from the harsh direct deposition steps to the intrinsic properties and long-term durability of STOPVs. Here a transfer-printing (TP) approach, in which photonic crystals (PC) films are deposited onto a self-adhesive and flexible matrix for their integration with STOPV devices, was first reported, enabling the resultant TPPC-STOPV devices with superior optical-related multifunction. In contrast to these devices based on direct-evaporated PC film, the non-encapsulated TPPC-STOPVs present an ultraviolet blocking (UVB) as high as 96%, an infrared rejection (IRR) of 92%, an enhanced power conversion efficiency (PCE) by 5% as well as superior long-term durability as 96% of its initial PCE. Their gifted superior UVB and IRR properties are individually on a par with those of the stat-of-the-art commercial optical films for smart solar window. This transfer-printing approach makes it possible to separate the high-energy fabrication of high-quality contacts from target optoelectronic devices, providing a wide range of possibilities for the integration of high-quality contacts with optoelectronic devices, including organic, silicon and perovskite optoelectronic devices, as well as their large-area flexible integration.

Experimental evaluation of daylighting performance and energy output of building-integrated photovoltaic (BIPV) panel in Bandung, Indonesia

Building energy use contributes up to 40% of total global energy use and increases by 8-10% every five years, encouraging the development of technology-based renewable energy sources. Building-Integrated Photovoltaic (BIPV) is a potentially relevant application of integrated PV in buildings which, it provides electricity cost savings, and increases the architectural attractiveness of a building. In contrast to conventional PV installations on building roofs, vertical PV installations are significantly influenced by the building orientation and the transparency of the PV. Study and analysis were conducted to implement BIPV windows in tropical climates using experimental measurement methods in energy output and indoor daylighting in four cardinal directions. This research was done by modelling a simple 2 × 2 × 1 m3 room with a PV solar window glazing made of Monocrystalline silicon 105Wp, placed on the roof of CADL Building, Institut Teknologi Bandung, Indonesia, for four days. The measurement results indicate that South is the most recommended orientation for installing BIPV windows for tropical areas in Bandung with the performance indicators for energy output = 564 Wh, DA300 = 100%, UDI250-750 = 93%, UDI100-3000 = 100%, and UDI>3000 = 0%. In contrast, West and East orientations are not recommended because of the significant difference in energy output and illuminance in the morning and the afternoon.

Building-integrated photovoltaic (BIPV) systems: A science mapping approach

<abstract> <p>Solar energy is one of the most important renewable energy sources due to its wide availability and applicability. One way to use this resource is by building-integrated photovoltaics (BIPV). Therefore, it is essential to develop a scientific map of BIPV systems and a comprehensive review of the scientific literature that identifies future research directions. For that reason, the bibliometric research methodology enables the quantification and evaluation of the performance, quality and influence of the generated maps and their elements. In this regard, an analysis of the scientific production related to BIPV, indexed from 2001 to 2022, was carried out using the Scopus database. This was done using a scientific mapping approach via the SciMAT tool to analyze the co-occurrence of terms through clustering techniques. The BIPV was integrated with the themes of buildings, investments, numerical models, office buildings, photovoltaic modules, roofs, solar cells and zero-energy buildings. As photovoltaic technology progresses, the production of flexible PV elements is increasing in lieu of silicon substrate-based PV elements, and this is of current scientific interest. The evaluations of BIPVs in various climatic contexts are encouraging in warm and sunny climates. BIPVs demonstrated high-energy generation, while in temperate climates, BIPV windows exhibited a reduction in heating and cooling loads, indicating notable efficiency. Despite significant benefits, BIPVs face challenges such as upfront costs, integration complexities and durability concerns. Therefore, silicon solar cells are considered a cross-cutting theme within the BIPV research field. It is highlighted that this study provides a comprehensive scientific mapping and critical review of the literature in the field of BIPV systems. This bibliometric analysis not only quantifies the performance and quality of the generated maps but also identifies key thematic areas that have evolved.</p> </abstract>

Understanding BIPV performance with respect to WWR for energy efficient buildings

Globally, the building sector absorbs 40% of energy, which is expected to reach double or triple by 2050. Building-integrated Photovoltaic (BIPV), known to the use of PV to replace long-established building envelopes such as windows, roofs, and walls which will create energy while simultaneously protecting the inside the structure from the harsh outside environment. The study utilizes Application of BIPV, as a fenestration component in various commercial structures around the United States of America. The paper addresses the dual functionality of PV on fenestrations which not only is an on-site energy generator but also decreases thermal transmittance. To comprehend the significance of BIPV across the United States, five different temperature zones were taken into account: Atlanta, Chicago, Los Angeles, Miami, and Phoenix round out the top five. The component chosen for BIPV is the dye-sensitized solar cell. Using the WINDOW Tool, two alternative BIPV models were computationally created, where the first type of window had two panes with Dye-Sensitized Solar Cells (DSSC) filled between The second model was a three-pane window as opposed to a window with two panes with DSSC and Inert gas filled between the first and second, second and third, and so forth. Three different commercial buildings were considered for the study, from the reference building. Another parameter of variability was introduced such as the Window to Wall Ratio (WWR) [1]. East, West, and South faces of the structure, the most commonly utilized WWR, such as 40%, 60%, and 80%, were taken into consideration. The potential for energy savings was assessed for Every one of these combinations of building type, climate/cities, WWR, and BIPV windows. The study finds an answer, in Triple glazed windows as the most efficient solution in the case of the small building.

Building energy performance of DSSC BIPV windows in accordance with the lighting control methods and climate zones

This study was aimed at analyzing the total energy consumption associated with different lighting control methods when dye-sensitized solar cell (DSSC) building-integrated photovoltaic (BIPV) windows were installed in office buildings in various climate zones. The total energy consumption and power generation efficiency of the DSSCs were analyzed to determine the power generation efficiency standards that could facilitate energy conservation within a target building. Notably, the energy required for heating, cooling, and lighting and power generation efficiency of DSSCs can be influenced by the climate. Thus, four climate zones in the United States were considered to perform a comparative analysis. The total energy consumption of the buildings was analyzed using DesignBuilder, a computer simulation program, and three window types were compared: Low-E, DSSC-R, and DSSC-Y. In general, DSSCs consume a considerable amount of lighting energy because of their low visible light transmittance. To decrease the lighting energy consumption, three lighting control methods were considered, and the corresponding total energy consumption was analyzed. The energy consumption can be minimized using the linear/off lighting control method. The energy consumption associated with Low-E can be further decreased by enhancing the power generation performance of the DSSCs. Specifically, when the power generation efficiency of DSSC-R is more than 13%, the overall energy consumption is lower than that of Low-E in all climates. The presented findings can guide the development of power generation efficiency standards for DSSC BIPV windows.

Numerical evaluation of an optically switchable photovoltaic glazing system for passive daylighting control and energy-efficient building design

Adaptive control of solar heat gain and visible light transmission through windows is perceived to be a potential measure for enhancing energy conservation and visual comfort in buildings. In this study, a novel versatile window, named Building Integrated Photovoltaic (BIPV) smart window, was proposed to offer simultaneous improvement of daylighting control, on-site electricity generation and building energy efficiency, compared to traditional BIPV windows with static optical properties. The key components of the proposed system include an optically switchable thermotropic layer made of Hydroxypropyl Cellulose (HPC) hydrogel, crystalline-silicon photovoltaic cells, clear glass and low-emissivity (low-e) glass covers. The thermotropic layer can respond to heat by autonomously changing its visible and near-infrared optical properties, with which the amount of solar radiation into building spaces can be manipulated and thus the risks of excessive solar heating and illumination can be prevented. Apart from excellent solar modulation, the BIPV smart window can collect a proportion of the light scattered from the thermotropic layer and concentrate it onto the integrated PV cells for extra electricity generation. An innovative methodology has been proposed to predict the optical, thermal and electrical properties of the BIPV smart window under varying ambient conditions. Numerical simulations have been carried out in EnergyPlus to predict the window's performance when it is applied to an office-type environment in the climate of Nottingham, the UK. The influence of different window design scenarios, in terms of Window-to-Wall Ratio (WWR), orientation and transition temperature, has been investigated. It was found that using the BIPV smart window can achieve an annual energy saving of 36.6% but also a more comfortable indoor luminous environment, compared to the counterpart BIPV window (with no thermotropic layer integrated), when installed in the south-oriented office with a WWR of 25%.

Dynamic coupling of a heat transfer model and whole building simulation for a novel cadmium telluride-based vacuum photovoltaic glazing

In recent years, building-integrated photovoltaic (BIPV) windows have drawn attention from both the building industry and academic society. As a multifunctional application of photovoltaic technologies, semi-transparent BIPV panels can generate renewable energy in situ and play the role of typical windows. Unlike those PV windows made by crystalline silicon solar cells, the semi-transparent cadmium telluride (CdTe) photovoltaic (STPV) windows can admit natural daylight with a certain degree of transmittance without any shading. Therefore, it can provide better visual comfort to occupants. However, typical BIPV windows are not suitable for cold regions due to inadequate thermal insulation. To improve the thermal performance of the BIPV glazing, a novel CdTe-based vacuum PV glazing (VPV) is developed with a highly integrated three-layer structure. To fully understand the dynamic heat transfer process and thermal behaviour, this study developed a mathematical heat transfer model for the CdTe-based VPV. The dynamic heat transfer model was validated with laboratory tests. To investigate the whole year performance of the VPV, a dynamic coupling approach is proposed to integrate the transit heat transfer model with a whole building simulation model conducted by EnergyPlus to obtain more accurate simulation results. Comparing the simulation results of the decoupled and coupled methods, it was found that EnergyPlus tends to slightly underestimate the cooling energy consumption and overestimate the heating energy consumption to a considerable level. Therefore, the dynamic coupling approach is more reliable than the EnergyPlus model, especially in the heating-dominated regions.

Modelling the effect of BIPV window in the built environment: Uncertainty and sensitivity

BIPV (building-integrated photovoltaic) window has been proven as a promising technology to increase renewable energy and reduce environmental effects of the building. The effect of BIPV window in the built environment could change significantly with the window configuration, building materials, and urban landscape, which have a large variability within cities. In this study, we adopted a newly developed building energy model coupled with a single-layer urban canopy model (BEM-SLUCM) to characterize the uncertainties of BIPV window effect at the neighbourhood scale in a hot desert climate city, Phoenix, USA. Using an advanced Markov chain Monte Carlo algorithm, extensive simulations were conducted to quantify the sensitivity of extreme outdoor microclimate, building cooling load and renewable energy generation to various input parameters. Results show that the canyon aspect ratio, window coverage, and power generation efficiency are pivotal to maximize the electricity generation by BIPV window. Canyon air temperature and building cooling load are highly sensitive to momentum roughness length above canyon, thickness of building envelope, air conditioning setpoint temperature, and canyon aspect ratio. This indicates a strong dynamic interaction between building's indoor space and the surrounding canyon environment. In contrast, thermal and optical properties of BIPV window have negligible effects on the urban thermal environment. Findings in this study reveal key mechanisms that regulate the urban microclimate and building energy consumption, provide guidance for BIPV applications in the built environment, and shed new lights on the sustainable design of urban neighbourhoods.

Quantum dot assisted luminescent hexarhenium cluster dye for a transparent luminescent solar concentrator

A luminescent solar concentrator (LSC) is a solar-light harvesting device that concentrates light on a photovoltaic cell placed at the edge of an LSC panel to convert it into electricity. The nano-sized inorganic–organic cluster complex (dMDAEMA)4[Re6S8(NCS)6] (this refers to RMC where dMDAEMA is 2-dimethyl amino ethyl methacrylate) is a promising candidate for LSC luminophores due to its downshifted broad photoluminescence suitable for photovoltaic cells. However, the low quantum yield (QY) of RMC limits the performance. Here, zinc-doped CuGaS/ZnS core/shell quantum dots (ZQD) were used as energy transferring donor with high QY to improve the performance of the LSC. The two metal chalcogenide luminophores, RMC and ZQD, are chemically suitable for dispersion in an amphiphilic polymer matrix, producing a transparent waveguide with suppressed reabsorption and extended harvesting coverage of the solar spectrum. We achieved an ηopt of 3.47% and a PCE of 1.23% while maintaining greater than 80% transparency in the visible range. The high performance of this dual-dye LSC with suppressed reabsorption, and scattering losses is not only due to uniform dispersion of dyes in a polymer matrix, but also energy transfer from ZQD to RMC. This report suggests a new possibility for promising various multi-dye LSCs for use in building-integrated photovoltaic windows.

Impact of BIPV windows on building energy consumption in street canyons: Model development and validation

Photovoltaic components have been increasingly integrated into the façades of buildings as a means to enhance their energy efficiency in recent years, yet the impact of using building-integrated photovoltaic (BIPV) windows in street canyons has been rarely studied due to the lack of modelling tools. In this study, we developed a new parametrization scheme for BIPV windows, and incorporated it into building energy simulations coupled with a single-layer urban canopy model. Evaluation against in-situ measurements and EnergyPlus simulation suggests that the coupled model is able to reasonably capture the diurnal profiles of BIPV window temperature, building cooling load, and outdoor microclimate. A set of simulations were conducted to examine the impact of BIPV windows on summertime building energy consumption and outdoor air temperature in different street canyons. Compared to clear glass windows, BIPV windows can reduce canyon air temperature and building cooling load. Temperature reduction is found to increase with window coverage but does not change significantly with canyon geometry. Savings on cooling energy consumption vary between 9.16% and 63.71% for the studied neighbourhood in Phoenix, US, but tend to be higher for open street canyons with north–south orientation and large window-to-wall ratios. The coupled model takes into account the dynamic interactions between building energy consumption and the outdoor microclimate, thus providing insight into the benefit of using BIPV windows at the neighbourhood scale.

Visual Comfort Analysis of Semi-Transparent Perovskite Based Building Integrated Photovoltaic Window for Hot Desert Climate (Riyadh, Saudi Arabia)

Buildings consume considerable amount of energy to maintain comfortable interior. By allowing daylight, visual comfort inside a building is possible which can enhance the occupant’s health, mood and cognitive performance. However, traditional highly transparent windows should be replaced with semitransparent type window to attain a comfortable daylight inside a building. Evaluation of visual comfort includes both daylight glare and colour comfort analysis. Building integrated photovoltaic (BIPV) type windows are promising systems and can possess a range of semitransparent levels depending on the type of PV used. In this work, the semitransparent Perovskite BIPV windows was investigated by employing daylight glare analysis for an office building located in Riyadh, KSA and three wavelength dependent transmission spectra for colour comfort analysis. The results showed that the transmissions range between 50–70% was optimum for the comfortable daylight for south facing vertical pane BPV-windows. However, excellent colour comfort was attained for the transmission range of 90% which provided glare issues. Colour comfort for 20% transparent Perovskite was compared with contemporary other type of PV which clearly indicated that wavelength dependent transmittance is stronger over single value transmittance.

Monte-Carlo optical model coupled with Inverse Adding-Doubling for Building Integrated Photovoltaic smart window design and characterisation

Building Integrated Photovoltaic (BIPV) glazings are promising technologies with the benefits of electricity generation, solar shading and building energy savings. A new approach is to integrate BIPV windows with thermotropic materials such as Hydroxypropyl Cellulose (HPC) hydrogel, which offers adaptive advantages for the systems to respond to time-varying weather conditions but also enhances the PV electricity generation. To design such systems, knowledge of the temperature-dependent scattering properties of the selected thermotropic materials is of significance. In this study, a Building Integrated Photovoltaic (BIPV) smart window system consisting of a thermotropic membrane synthesised using HPC and gellan gum gelling agent for electricity generation and also solar control has been designed and investigated. An advanced optical model, which combines a Monte-Carlo ray-tracing technique with an Inverse Adding-Doubling (IAD) method, has been developed for characterising the thermotropic membrane in terms of angular scattering distribution under various membrane temperatures and HPC concentrations. Then the developed optical model has been validated by comparison with experimental measurements. Subsequently, the validated optical model has been used to design and optimise the proposed BIPV smart window. The effects of HPC concentration, geometric concentration ratio, thermotropic membrane thickness and glass refractive index on PV power outputs have been evaluated. Finally, a prototype of the BIPV smart window with a 6 wt% HPC membrane has been manufactured and tested under indoor conditions. From the experimental tests, it was found that the total transmittance of the double-pane glass sample with a 6 wt% HPC membrane layer decreases from approximately 90%to 14%, when the membrane temperature increases from 27 °C to 56 °C. The measured short-circuit current for the prototype BIPV smart window is up to 1.15 times higher than that of its counterpart system with a similar PV area but no membrane.

Status of BIPV and BAPV System for Less Energy-Hungry Building in India—A Review

The photovoltaic (PV) system is one of the most promising technologies that generate benevolent electricity. Therefore, fossil fuel-generated electric power plants, that emit an enormous amount of greenhouse gases, can be replaced by the PV power plant. However, due to its lower efficiency than a traditional power plant, and to generate equal amount of power, a large land area is required for the PV power plant. Also, transmission and distribution losses are intricate issues for PV power plants. Therefore, the inclusion of PV into a building is one of the holistic approaches which reduce the necessity for such large land areas. Building-integrated and building attached/applied are the two types where PV can be included in the building. Building applied/attached PV(BAPV) indicates that the PV system is added/attached or applied to a building, whereas, building integrated PV (BIPV) illustrates the concept of replacing the traditional building envelop, such as window, wall, roof by PV. In India, applying PV on a building is growing due to India’s solar mission target for 2022. In 2015, through Jawaharlal Nehru National Solar Mission, India targeted to achieve 100 GW PV power of which 40 GW will be acquired from roof-integrated PV by 2022. By the end of December 2019, India achieved 33.7 GW total installed PV power. Also, green/zero energy/and sustainable buildings are gaining significance in India due to rapid urbanization. However, BIPV system is rarely used in India which is likely due to a lack of government support and public awareness. This work reviewed the status of BIPV/BAPV system in India. The BIPV window system can probably be the suitable BIPV product for Indian context to reduce the building’s HVAC load.

The Optimum Performance of Building Integrated Photovoltaic (BIPV) Windows Under a Semi-Arid Climate in Algerian Office Buildings

Recently, Building Integrated Photovoltaic (BIPV) windows have become an alternative energy solution to achieve a zero-energy building (ZEB) and provide visual comfort. In Algeria, some problems arise due to the high energy consumption levels of the building sector. Large amounts of this energy are lost through the external envelope façade, because of the poorness of the window’s design. Therefore, this research aimed to investigate the optimum BIPV window performance for overall energy consumption (OEC) in terms of energy output, heating and cooling load, and artificial lighting to ensure visual comfort and energy savings in typical office buildings under a semi-arid climate. Field measurements of the tested office were carried out during a critical period. The data have been validated and used to develop a model for an OEC simulation. Extensive simulations using graphical optimization methods are applied to the base-model, as well as nine commercially-available BIPV modules with different Window Wall Ratios (WWRs), cardinal orientations, and tilt angles. The results of the investigation from the site measurements show a significant amount of energy output compared to the energy demand. This study revealed that the optimum BIPV window design includes double-glazing PV modules (A) with medium WWR and 20% VLT in the southern façade and 30% VLT toward the east–west axis. The maximum energy savings that can be achieved are 60% toward the south orientation by double-glazing PV module (D). On the other hand, the PV modules significantly minimize the glare index compared to the base-model. The data extracted from the simulation established that the energy output percentages in a 3D model can be used by architects and designers in early stages. In the end, the adoption of optimum BIPV windows shows a significant enough improvement in their overall energy savings and visual comfort to consider them essential under a semi-arid climate.

Controlling the visibility of embedded silicon solar cells in building-integrated photovoltaic windows using surface structure modification and metal-oxide back coating

In this paper, we demonstrate a simple and effective method to control the visibility of embedded silicon solar cells in building-integrated photovoltaic (BIPV) windows by surface structure modification and metal-oxide back coating. The surface structure modification by etching the front glass in BIPV modules and the use of a thin niobium pentoxide (Nb2O5) film as a back coating enable the silicon solar cells to be hidden from view without a serious loss in the power efficiency. By employing the etched front glass and Nb2O5 back coating, silicon solar cells embedded in the BIPV module exhibited power conversion efficiency of 15.23% and fill factor of 65.05%. We also investigate the origin of the improved photovoltaic performance of the solar cells in the BIPV modules. The surface modification of the front cover glass of the BIPV windows enhances the light absorption in the solar cells, which results in the improved photovoltaic performance degraded by a metal-oxide back coating. We believe that the proposed surface modification which induces light trapping and anti-reflection into the cover glass of the BIPV modules with a metal-oxide back coating film is a promising and practical solution for the successful integration of BIPV windows with high efficiency and invisibility.

Photo-Carrier-Guiding Behavior of Vertically Grown MoS2 and MoSe2 in Highly Efficient Low-Light Transparent Photovoltaic Devices on Large-Area Rough Substrates.

Two-dimensional MoX2 (X = S, Se) films were vertically grown on highly rough transparent conducting F-doped SnO2 glass substrates for the first time and successfully used as photogenerated carrier-guiding layers (CGLs) in transparent hydrogenated amorphous silicon (a-Si:H) thin film solar cells (TFSCs). The MoSe2 CGL layers could be grown at 530 °C using thermally cracked small Se-molecules on transparent FTO glass substrates and significantly improved cell performance. A transparent cell transmitting 26.0% of visible light with a 20 nm-thick vertically grown MoSe2 CGL showed an outstanding power conversion efficiency of 27.1% at a light intensity of 0.16 mW cm-2 (500 lx; corresponding to normal indoor irradiation). The shunt resistance (Rsh) of the TFSCs reached 32,000 Ω at a light intensity of 7 mW cm-2. An Rsh value this large is essential for low-light photovoltaic (PV) devices to prevent the dissipation of photogenerated carriers. These results strongly demonstrate that transparent a-Si:H-TFSCs with vertically grown MoX2 films should find wide use in building-integrated PV windows or indoor PV applications, as they can generate power even in very low-light environments.

Carbon counter electrode mesoscopic ambient processed & characterised perovskite for adaptive BIPV fenestration

In this work, carbon counter electrode perovskite was developed at the laboratory environment and building integrated photovoltaic (BIPV) window application using this material was investigated. At 1 sun (1000 W/m2) continuous incident solar radiation from an indoor simulator, this particular type of perovskite had 8.13% efficiency. Average solar and visible transmittance of this perovskite BIPV window was 30% and 20% respectively. Solar heat gain for different incident angle was evaluated for this perovskite glazing. For the University of Exeter, Penryn (50.16° N, 5.10° W) UK location, solar heat gain coefficient (SHGC) or solar factor (SF) varied from 0.14 to 0.33 at the highest and lowest incident angle respectively. Overall heat transfer coefficient (U-value) of 5.6 W/m2K was realized for this glazing while calculation was performed by window performance analysis programme, WINDOW 6.0. Daylight glare control potential of this glazing was investigated using subjective rating methods and comfortable daylight penetrated through glazing in a typical cloudy condition. Colour properties of this material showed that 20% visible transmittance is threshold limit, and below this value colour or visual comfort using this glazing is not achievable.

High-efficiency white-light solar window using waveguide glass plate

A high-efficiency white-light solar window is proposed for building-integrated photovoltaic (BIPV) applications. In the solar window, incident light is scattered at a waveguide plate and guided into GaAs cell arrays at the edges of the window frame. The optical characteristics of the waveguide plate are designed and evaluated using a ray-tracing simulation, and the solar window is fabricated and assembled with three-dimensional printing. The solar window exhibits an almost constant transmittance, with an average of about 21.6% in the visible range of 400–800 nm and a color rendering index of about 97.8 for sunlight, which is a neutral color that does not distort the colors of indoor objects under sunlight through the window. The solar window achieves a geometric concentration gain of 1.14 and edge collection ratio (ECR) of about 27.0%, which is constantly obtainable regardless of the incident angle of sunlight, and it exhibits an efficiency of 6.368%, a very high value for conventional transparent solar cells and modules. The method for optimizing the window efficiency and effective indoor illuminance by increasing the size of the solar window is also presented. These results can contribute to the further development of high-performance and large-area BIPV windows.

Experimental Investigation of Overall Energy Performance in Algerian Office Building Integrated Photovoltaic Window under Semi-Arid Climate

Building integrated photovoltaic (BIPV) energy has now become one of the most significant renewable energy alternatives for providing natural daylight and clean energy. As such, this study was conducted for the first time in Algeria to experimentally evaluate the BIPV window energy and lighting energy savings of a typical office building under the semi-arid climate condition. Apart from using the Energy Plus and Integrated Environment Solution-Virtual environment (IES-VE) energy simulation tools in the experimental validation, the daylighting control method and the dynamic Useful Daylight Illuminance (UDI) were also utilized to analyse the daylighting performance as well as the lighting energy of BIPV windows with different transparency levels at various cardinal orientations. The field measurements had revealed the overall energy model to be consistent and in good agreement with the EnergyPlus and the IESVE simulation models, where the tested PV module was found to have provided not only a 20% Visible Light Transmittance (VLT) of uniformed daylight with low illuminance level, but also thermal comfort and a considerable amount of clean energy. The simulated results had demonstrated a substantial improvement in cooling energy and glare reduction of the PV modules as compared to the base-model, where the only BIPV window configuration was achieved good area of UDI 300-700 lux is facing the South orientation and 30% VLT. In conclusion, the application of the thin film BIPV windows with different transparency and orientation levels can thus be regarded as an effective solution for minimizing the lighting energy consumption through its energy production instead of daylighting utilization.