Building-integrated photovoltaics (BIPV) are photovoltaic systems that are built into the building envelope, and which have both construction and energy-generation functions. BIPV can substitute traditional envelope materials and can be built into walls, roofs, glazing systems, shading systems, and other building elements unlike building-applied photovoltaics (BAPV), which is mounted on existing surfaces31,32. In this respect, BIPV is not judged by the electricity generation, but also by the contribution to the envelope performance, architectural integration, and environmental response27; IEA PVPS Task 15, 2025). The most common groups of BIPV systems include those based on location and those based on optical or functional purpose. They are separated by application into roof-integrated and façade-integrated. BIPV that is built into the roof typically has a better solar exposure and tilt, whereas BIPV built into the facade, despite less incidence angles, has a larger available surface area in high-rise and dense urban buildings where the available roof area is smaller than the demand33. BIPV can be either opaque, semi-transparent or transparent by functionality. Panels and spandrels with cladding are generally clad with opaque systems, whereas windows, skylights, atria, and glazed curtain walls are usually clad with semi-transparent and transparent systems where the production of electricity should be balanced with the daylight transmission, visual connection, solar control, appearance of the facade, and comfort of the occupants34,35. The increased interest to BIPV is predetermined by the need to have low-carbon and energy-efficient buildings. Since the photovoltaic elements are integrated into the envelope, BIPV integrates the generation of renewable energy with material replacement and integration into the architecture, which is also known as one of its main benefits27; IEA PVPS Task 15, 2025). This is particularly important in facade application this multifunctionality is especially significant as the envelope has to meet the environmental, indoor-comfort, and architectural demands at the same time. BIPV integrated into the façade, however it cannot be viewed as an extension of traditional photovoltaics to the vertical plane. Once it is incorporated into the facade, it is conditioned by geometry, orientation, thermal relationships with the envelope, and general architectural reason25, reveal the enhancements of the architectural adaptability due to the differences in geometry, spacing, and system composition, whereas Cuce and Cuce8 reveal that the electrical performance is not only dependent on the irradiation, but also on the operating temperature, the tilt angle, and the passive heat dissipation. This is especially significant in façade-parallel applications, where envelope integration can increase thermal accumulation and decrease production if the heat is not suitably managed. Based on this, BIPV facade systems should be conceptualized as photovoltaic technologies and building-envelope systems whose functionality relies on the interaction of architectural design, climatic context, thermal performance, and functionality. This is needed prior to analyzing the individual benefits, drawbacks and performance issues of BIPV windows in semi-arid regions with dust. Figures 1, 2, 3, 4, 5 and 6.
Source: Authors’ own conceptual synthesis based on relevant BIPV literature.
Categorization of building-integrated photovoltaic (BIPV) systems based on type of integration and transparency of the building envelope.
Architectural advantages and architectural performance limitations of facade-integrated BIPV
Building-integrated photovoltaics (BIPV) are used to generate electricity and perform the envelope role, thus not being applied to existing surfaces, but instead replacing the standard material of facades or roofs31,32. This provides BIPV with a greater architectural and environmental impact than stand-alone PV in terms of on-site generation of renewable energy, material replacement, and envelope multifunctionality27; IEA PVPS Task 15, 2025). It is also particularly valuable in dense urban and high-rise settings since in many cases, rooftop photovoltaics cannot contribute as much due to the limited availability of a rooftop space, but the facade can offer a greater active area to the sun exposure33. BIPV is also flexible in terms of architecture, as the photovoltaic elements can be incorporated into the composition of the facade with a variety of transparency, geometry, distance, and surface rhythm instead of being perceived as independent technical elements25. BIPV can also be used in glazing to help regulate the environment (BIPV can act as a shading surface or solar filter, or a semi-transparent envelope layer that can balance the amount of daylight entering and the amount of electricity produced)7,34. Simultaneously, the BIPV embedded in facades has significant limitations, which make it different to rooftop PV. Vertical and near-vertical facades tend to work with less solar incidence, and thus performance is highly determined by the direction, the geometry of the facade, and climate33. Another significant drawback is thermal behavior since close envelope integration may limit heat dissipation; the operating temperature, tilt, and passive cooling conditions are thus another factor in BIPV performance7,8. Moreover, systems embedded in facades are very sensitive to the effects of shading, urban obstruction, and transparency, daylight, and optical quality which may decrease photovoltaic space or modify optical performance25,34. The trade-offs are especially high in semi-transparent and transparent BIPV, in which the production of electricity has to be compromised with visible-light transmission, solar control, and occupant comfort7,34. The cost, complexity of installation, maintenance, and long-term durability further restrict the wider adoption of the photovoltaic layer as the photovoltaic layer is required to be synchronized with waterproofing, structural integration, replacement strategy, and service access as a part of the building assembly13,27. In general, the concept of façade-integrated BIPV can be interpreted not as a renewable-energy system, but as an envelope technology of a building that can be considered in terms of its advantages and disadvantages as the result of the combination of energy performance, thermal performance, facade design and durability.
Semi-transparent and transparent BIPV window technology
Semi-transparent and transparent BIPV windows are photovoltaic glazing systems that are able to transmit daylight, solar control and produce electricity on-site within a single façade element. In contrast to opaque PV modules, they work based on a multi-objective balance where electrical production has to be balanced with the visible light-transmittance, façade appearance, the visual comfort inside the building, and the control of solar gain7,34. The semi-transparent BIPV is generally developed by using controlled cell spacing, patterned deposition, or partial absorber coverage where some part of the visible spectrum could be permitted to pass through maintaining photovoltaic operation34. Transparent BIPV builds on this principle by spectral selectivity and optical routing, such as luminescent solar concentrator (LSC) principles and spectrally selective surfaces that separate non-visual radiation to photovoltaic areas while maintaining visible transparency10,11,29. These systems are also gradually being seen as multifunctional systems of facades, which can combine solar conversion, daylight control, and lower solar heat gain with the help of improved glazing assemblies, transparent conductive materials, and spectral filtering strategies9,34,36. They are also, however, still limited by the basic transparency efficiency trade-off, as increased visible transmittance tends to decrease photovoltaic performance. That is why37, claim that transparent PV glazing should be considered within the electric, thermal, and daylighting domains instead of assessing it based on the energy generation. On the facade aspect, these technologies are valuable as they add photovoltaic functionality into the glazed visual-sensitive areas without complete occupying the daylight or the exterior view. Nevertheless, their sensitivity to dust and abrasion, optical aging, and non-uniform fouling also makes them particularly vulnerable to such factors, as these may result in poor visual and photovoltaic performance7,34,37. This makes them of specially relevance to the study of dust-related loss of performance and secondary-layer strategies in semi-arid climates.
Soiling and climatic stressors in semi-arid dusty areas
The semi-arid areas present a difficult environment to BIPV windows since high levels of solar irradiation is combined with prolonged dryness, which is coupled with low rainfall and dusty environments. This generates good solar potential but accumulated soiling, especially on the glazing of the facades and minimal natural cleaning, which results in the simultaneous action of dust deposition, thermal loading, and high-intensity solar exposure on the photovoltaic envelope4,5. Regional and local sources, such as soil erosion, traffic, construction activity, and long-range transport of particulate matter determine dust behavior, which results in the formation of particles of various sizes, compositions, and optical effects2,5,6. In turn, the severity of soiling is determined by the properties of particles, roughness of the surface, moisture, wind regime, and duration of the exposure and thus differs depending on the location and facade exposure and climate4,5. Particularly tilt angle and orientation2, demonstrated that the dust has a considerable influence on the solar-glass transmittance and that the effect is dependent on the tilt, airflow, and exposure. Vertical surfaces can be not as susceptible to dust as low-slope surfaces; however, in dusty (low-rainfall) conditions, they are also vulnerable4,6. The adhesion of fine particles can be due to electrostatic forces, surface-energy forces, bonding by moisture, and surface irregularities, and the wind can be depositing and removing dust based on the aerodynamics of the facade and urban context2,5,6. This can cause an uneven deposition on the envelope in high-rise buildings. Thermal stress also interacts with dust, whereby it decreases optical transmission and changes radiative aspects of surfaces, which may enhance efficiency losses related to temperature when environments are hot and highly irradiated7. In general, soiling in semi-arid areas is an optical, thermal and facade-performance issue which is influenced by dryness, particle composition, wind, orientation, tilt angle and surface properties.
Effects of dust on the PV and BIPV window performance
Photovoltaic performance is degraded by dust deposition by both optical, electrical, and thermal mechanisms, and is particularly critical in glazing-based BIPV since surface transparency, solar transmittance and optical quality are directly affected. Scattered and reflected incident radiation reduces the energy reaching the active layer and decreases output due to the deposited particles absorbing it1,4. The effects of BIPV windows go beyond the electricity production to the transmission of visible light, daylight, visual quality, and solar-control performance of the facade7,34. The experimental evidences demonstrates that significant losses can be caused even at the lowest deposition levels4:, have found that a dust load of 4 g/m² can decrease electrical efficiency by up to 40%, thin layers of urban pollution have been observed to decrease it by up to 20%, and in some instances even 40%. This electrical response is not necessarily linear, as dust can have different effects on current, voltage, fill factor, and operating stability, but short-circuit current is frequently the most sensitive, and voltage may react less at moderate deposition4,5. At heavier and/or non-uniform fouling, though, the maximum power and the overall efficiency drops at a steeper rate, which becomes especially relevant when considering the case of façade-integrated BIPV glazing where wind-induced deposition, curvature of the facade and localized exposure can cause uneven patterns of soiling. Reported losses also vary widely with climate, rainfall, exposure period and tilt angle. According to4, average daily energy loss can be up to 4.4% and dry seasons can increase daily losses to 20% and efficiency decline in hot rainless climates can be as high as 0.2% per day the same as the productivity losses of 56.2% annually. In the literature reviewe, the daily losses of PV power are between 0.05% and 1.15% and monthly losses of efficiency may be more than 80% in extreme cases. The results per country are 17.4% monthly efficiency reduction in Egypt, 19.8% in Saudi Arabia, 13% in Mexico, 17% in Kuwait, 7% in another Saudi case, 60.6% in a severe Iranian case, 31–35% in productivity loss in Jordan, 0.4–0.8% in daily loss in Qatar which corresponds to 12–24% in monthly loss without cleaning, and 5.86% annual energy deterioration on Crete-greece4.
Tilt angle is one of the aspects that are still significant4, refer to Egyptian experiments that found that deposited dust reduced to 15.84 g/m² at 0 o of tilt and 4.48 g/m² at 90 o of tilt, with a loss of permeability between 52.54% and 12.38%; they also note that the voltage can be reduced by over 6% Though near vertical BIPV facades can hold less dust than low slope ones, they are susceptible in dusty urban conditions where there is little rainfall and cleaning is not done too often. A thermal penalty is also caused by dust, which alters surface radiative behavior and raises local surface temperature, which further decreases efficiency4[,7. Dust under hot semi-arid conditions must be understood, in other words, that it is a coupled optical-electrical-thermal degradation process and that it is a key determinant of the operational and architectural performance of BIPV windows7,8.
Current dust mitigation measures of PV and BIPV glazing
Dust-reduction strategies of photovoltaic systems can be broadly classified into cleaning, surface-treatment and protective-layer methods, although their applicability to façade-integrated BIPV glazing is less favorable than to other systems, where transparency, access, durability, and long-term optical performance are all critical4,5. The most established cleaning technique is manual cleaning, but it is not as effective because of the labor requirement, use of water, re-soiling, and ineffectiveness on high-rise facades15,16. Regularity can be enhanced with automated and robotic cleaning, although they cannot be applied to the architecturally complex glazed facades and create the additional cost and maintenance burden4,14.
Surface-treatment methods are more compatible with glazing. Anti-soiling, anti-reflective, textured, hydrophobic, and self-cleaning surfaces are designed to minimize the adhesion or loss of dust or transmission loss of optical quality. The anti-soiling coatings in desert environments were found to improve performance18, the textured and anti-reflective glass surfaces were identified to be promising but highly conditional on climate, durability, and exposure17,38. The anti-UV and anti-scratch treatments are also applicable since the retained transmittance and long-term stability are vital in exposed glazing systems22,23,24.
Strategies to enhance the retained performance are operation-and-maintenance strategies, which enhance cleaning schedules, inspection, monitoring, and service planning, and modular façade strategies which could enhance access and replacement control15,16,35,39. One more direction that is more facade-oriented is the application of protective or optically functional secondary layers that are placed in front of the active glazing and that can help to minimize direct dust exposure as well as have an effect of optical and thermal performance. Overall, cleaning, coatings, and O&M methods only partially solve the issue of soiling, which explains the need to pay more attention to the secondary-layer methods of facades-integrated BIPV windows to dusty semi-arid environments.
Thermal-responsive and protective secondary-layer materials
Thermal responsive and protective secondary-layer materials are becoming more applicable to BIPV windows since they help overcome two long-standing constraints of the facade, namely thermal accumulation and surface degradation. High irradiance and ambient temperature increase the operating temperature of photovoltaic and decrease the efficiency in hot climates, and outer glazing should also be able to withstand ultraviolet exposure, abrasion, dust impact, and weathering (Liu and Wu, 2022;7. Research on adaptive glazing including thermotropic and electrochromic systems demonstrates that additional functional layers can be used to control solar transmission and minimize overheating and still maintain daylight functionality, which applies to BIPV since operating temperature has a direct impact on electrical yield and envelope characteristics8. This rationale is also backed by photovoltaic thermal-management studies Hamdan40 found better performance with passive cooling, and41, considered finned phase-change-material systems to control thermal variation in time. Façade studies also support the added outer layers. The retrofit double glazing was also found to be a significant envelope intervention by42,43,44,demonstrated that the conditions of cavities in the double-skin facades may change the air temperature, surface temperature, airflow, and overall thermal performance45,46, also proved that the performance of multi-layer facades is also determined by airflow, heat exchange, and the structure of the layers, rather than the properties of the PV materials in photovoltaic applications. Durability is also ensured by protective layers22,23,24, demonstrate that retained transmittance, UV resistance, and abrasion durability are the key factors in the long-term operation in extreme arid conditions. Overall, secondary layers could be seen as the aspects of the facade performance, which have the potential to moderately control heat, retain optical quality, and enhance the operational stability of semi-arid BIPV glazing.
Proposed secondary-layer BIPV facade air cavity design
Existing literature shows that ventilated double-layer design is more appropriate in BIPV windows as compared to sealed cavity47, reasoned that ventilated double BIPV windows have the highest potential of energy-saving and climatic flexibility whereas48, found operation by natural ventilation to be the most suitable in hot climates in BIPV double-skin facade that includes an outer semi-transparent PV layer, an inner glass layer, and an intermediate cavity. Accordingly, the current study uses a compact front ventilated air cavity between the secondary protective outer layer and the BIPV glazing/window rather than a deep occupiable double-skin façade49, presented dimensional guidance and established that the greatest change in PV temperature was observed when the spacing was increased between 0.05 m and 0.15 m, and suggested an engineering range of about 0.10–0.15 m. according to that, the present study will use a cavity depth of 100–150 mm with 120 mm as the nominal value to balance the ventilation performance, the compactness of the facade and constructability. Architecturally, based upon detailing of the cavity, it is suggested that the cavity be proposed as a laterally enclosed vertical air gap with screened bottom and top openings, rather than a fully sealed or fully exposed open-joint structure. An open cavity would enhance the direct ingress of dust, but a complete seal would undermine the passive ventilation and add technical complexity50, substantiate this principle with the help of a screen-covered top-and-bottom ventilated cavity, and51, also confirm the appropriateness of solar double-skin facades in warm weather. Based on this, the proposed system will be a naturally ventilated, laterally enclosed front cavity with a screened top and bottom opening and nominal depth of 120 mm within a defensible range of 100–150 mm.
Customization of Façade, multi-layered systems and performance assessment
Photovoltaics integrated into facades are subject to architectural, environmental and technical limitations that make the customization of photovoltaics to be a defining performance determinant and not a design concern. In contrast to stand-alone PV, BIPV facades have to react to energy production, daylighting, envelope structure, visual expression and construction rationality. According to25, geometry, transparency, spacing, and system composition are thus considered to be the variables of enhancing the architectural flexibility and lowering the conflict between energy and facade design goals. These variables affect solar exposure, self-shading, day light penetration and the general envelope character especially in high rises and urban environments25,33. The optimization of BIPV should thus be considered at the scale of facade-assembling instead of being considered at the material level. This reasoning is more significant in multi-layer systems. Research on the development of glazing demonstrates that outer layers, cavities, interlayers, and inner glazing together can control the solar transmission, heat gain, optical quality, and environmental resilience52. Therefore, a secondary layer in front of BIPV glazing, whether protective, thermal-responsive, or optically functional, should be perceived as a component of a larger strategy of facade-engineering and not as an independent addition. It is backed by the fact that facade studies have shown that retrofit double glazing can serve as a substantial envelope intervention and cavity conditions in the double-skin facades have a significant impact on airflow, temperature, and thermal behavior42,43,44,45,46, also demonstrate that electrical and thermal performance in photovoltaic multi-layer facades is also dependent on airflow, heat exchange, cavity conditions, and the arrangement of the layers. The most recent developments on modular and prefabricated facades further underline the fact that performance is connected with constructability, maintenance accessibility, replacement strategy, and long-term operation35,39. That is why the BIPV window systems must be considered not only in terms of electricity production, but also in terms of electrical, optical, thermal, environmental, and architectural aspects, such as daylight, solar control, usability, and compatibility with design34,37. In general, the literature upholds a multi-criteria, multi-layer BIPV systems assessment framework based on the facade scale25,26,28,35,39,42,43,44,53,54.
Study gap and rational of the present research
The literature review indicates that the field of BIPV has advanced in the definition of the technology, integration of the facade, transparent photovoltaic glass, dust-related loss-mechanisms, and mitigation strategies4,25,27,34. Similar facade investigations also prove that secondary transparent materials, ventilated cavities and photovoltaic multi-layers assemblies can have a dramatic impact on thermal and electrical performance at the architecture scale42,45. Nevertheless, they do not provide enough integration that is required for the specific case of BIPV windows in dusty semi-arid environment. The primary gap is not the lack of the available knowledge, but the inability of the integration between the existing research directions. The existing literature on dust mitigation primarily focuses on the conventional PV, cleaning, or coating instead of the facade-integrated BIPV glazing4. In comparison, semi-transparent and transparent BIPV are studied in terms of transparency, daylighting, and thermal behavior, whereas dust is not considered a key performance variable of the facade7,34. Similarly, the significance of added layers and cavity behavior is established by facade-layer studies, but fail to directly test a front secondary layer in front of BIPV glazing as a combined strategy of dust-protective, thermal, optical and facade-performance in semi-arid environments.