Research | Adaptive Design of BIPV Curtain Walls

 

 

01 

The Inevitability of BIPV Curtain Wall Development

 

Definition of Photovoltaic Power Generation

Photovoltaic power generation utilizes the photovoltaic effect of semiconductor interfaces to directly convert light energy into electrical energy. Components capable of generating the photovoltaic effect are known as photovoltaic components.

/ Photoelectric Conversion Diagram /

 

BIPV Definition

Building-Integrated Photovoltaics (BIPV) refers to the integration of photovoltaic components into the building's envelope, such as roofs, curtain walls, and sunshades. This allows the building envelope to fulfill its functions of insulation, shading, etc., while also generating electricity through photovoltaic components. BIPV systems require simultaneous design, construction, and acceptance with the building.

 

Significance of BIPV

Photovoltaic energy systems are mainly divided into centralized photovoltaic energy systems and distributed photovoltaic energy systems. Centralized photovoltaic energy systems are mainly photovoltaic power plants built in concentrated areas such as deserts, Gobi deserts, mountains, and water surfaces. The electricity generated is directly fed into the national grid, which supplies power to long-distance loads through high-voltage transmission systems. Application forms include large-scale ground power stations, agricultural photovoltaic integration, forestry photovoltaic integration, and water photovoltaic integration projects. Centralized photovoltaic voltage levels are high, generally 35 kV or 110 kV grid connection, characterized by large land area, long transmission distance, large investment, and long construction period. Distributed photovoltaic energy systems, on the other hand, refer to smaller photovoltaic power generation systems installed on-site or near the electricity consumption site, generally built on buildings near users, allowing for on-site power generation, grid connection, conversion, and use, solving the problem of power loss during voltage boosting and long-distance transmission. Distributed photovoltaic voltage levels are low, generally 380V grid connection, characterized by small land area, short transmission distance, small investment, and short construction period. Distributed energy systems can be further divided into BAPV (Building-Added Photovoltaic Systems) and BIPV (Building-Integrated Photovoltaic Systems). BAPV is often installed separately on the roofs of buildings, while BIPV comes in various forms, such as building photovoltaic curtain wall integration, photovoltaic skylight integration, and photovoltaic sunshade integration.

Under the current state of social development, the centralized construction of ground photovoltaic power plants in cities is clearly unrealistic. The BIPV distributed photovoltaic system can utilize city building facades to install photovoltaics, effectively reducing greenhouse gas emissions during building construction and use with lower marginal investment, without requiring additional urban land resources. It simultaneously lowers energy bills, offsets material costs, and reduces electricity transmission losses.

/ Centralized Photovoltaics /

/ BAPV Illustrative Photo /

/ BIPV Illustrative Photo /

 

Development of BIPV in China

Domestic BIPV development has been rapid, thanks to relevant photovoltaic policies. From 2008 to the present, there have been two approvals of electricity prices, two bidding authorizations, eight releases of benchmark electricity prices (guiding electricity prices), eleven electricity price documents, and thirteen electricity price adjustments. Through adjustments and improvements to regulations on electricity prices, the safety of BIPV systems has been further enhanced, promoting the healthy development of the BIPV industry.

/ Domestic Photovoltaic Development Process (Policy Perspective) /

 

02

Current Status, Issues, and Improvements of BIPV Curtain Wall Technology

 

Current Status of BIPV Technology

A conventional BIPV system consists of a photovoltaic array (photovoltaic components—power generation equipment, photovoltaic brackets, etc.), an inverter (power conversion equipment), a grid-connected busbar cabinet (grid connection equipment), and a local load (power consumption equipment). A grid connection system is set up according to the owner's needs and connected to the grid.

/ BIPV Grid-Connected (Local On-site Use) System /

 

The most important part of a photovoltaic system is the photovoltaic cell. Photovoltaic cells can be broadly classified into silicon-based cells, non-silicon-based cells, and new concept cells, with monocrystalline silicon cells, cadmium telluride, and copper indium gallium selenide thin-film cells being the most common on the market.

/ Cell Classification /

 

Problems and Solutions in the BIPV Implementation Process

Poor Architectural Effects: Crude, Unaesthetic, and Disharmonious

Solution Strategies——From the perspective of architectural design, photovoltaics should be comprehensively considered in the initial design stage, combining photovoltaic performance to achieve coordination between appearance and power generation. From the perspective of components, the photovoltaic panels should be optimized. From the construction perspective, the construction procedures and standards should be clearly defined to control the project effects with high-quality requirements.

Insufficient Safety: Insufficient safety in connection structures, components, and electricity

Solution Strategies——Further improve the standards for the integration of building and related professions with photovoltaics. For structural safety, double-glass panels are used, and reinforcing layers are added as needed to protect panel safety (such as hail-prone areas). Wind-lifting prevention measures should be installed in coastal areas and other areas with high wind pressure. For electrical safety, DC arc detection and component-level rapid shutdown measures should be implemented.

Building Physics Indicators Do Not Meet Standards: Light transmittance and shading effects do not meet standards

Solution Strategies——Comprehensive shading measures can be considered during building design, such as adding indoor shading measures, to reduce the shading parameter requirements of photovoltaic panels and expand the range of photovoltaic panel selection; photovoltaic panels can also be integrated with electrochromic glass to achieve dynamic control of the indoor environment through integrated components; green building design can also be coordinated to adjust the parameters of other parts of the project to relax the restrictions on photovoltaic parts. In the building facade lighting parts, when integrating photovoltaics, the adverse effects on lighting should be analyzed, and the lighting coefficient and light reduction coefficient should be reasonably configured to meet the building's lighting needs.

Power Generation Less Than Planned: Unreasonable system design and component selection

The power generation calculation formula is as follows:

Q = Luminous Flux × Sarea (Photovoltaic Area) × Rβ (Effective Illumination Coefficient) × ηsystem (System Efficiency) × ηmodule (Panel Efficiency) × Time

According to the calculation formula, the main factors affecting energy efficiency are lighting conditions, installation tilt angle, photovoltaic component performance, and grid connection system efficiency. Therefore, to ensure the power generation of the BIPV system, the following measures should be taken:

Solution StrategiesWhen estimating the initial power generation, various situations during use should be fully considered to reduce the photovoltaic power generation; and when designing the photovoltaic system, components that are resistant to PID should be selected as much as possible, and the climatic conditions and site characteristics of the usage site should be comprehensively considered to select photovoltaic components, and at the same time, the system should be simplified as much as possible to avoid excessively long cables and reduce system losses.

 

Focus Points in BIPV Implementation

Safety Design—Selection of Panel Laminate and Glass.BIPV photovoltaic panels are usually used in complex environments. During design, not only the effects of loads such as wind pressure and snow pressure must be considered, but also the effects of environmental temperature changes caused by power generation on the panels. To ensure the safety of the panels during use, appropriate and safe glass thickness and interlayer should be selected. According to the "Technical Specifications for the Application of Solar Photovoltaic Systems in Civil Buildings," laminated glass should use PVB or other anti-penetration films. At the same time, the type and thickness of the glass should be reasonably selected through calculation.

/ PVB Vs. EVA /

 

Preventing Overheating—Ventilation and Cooling Design.When the BIPV photovoltaic system is running, the photovoltaic panels will generate heat; therefore, during the design of the BIPV system, appropriate ventilation and other cooling measures should be taken to avoid a decrease in power generation efficiency due to excessively high temperatures.

/ Power Reduction Caused by Excessive Temperature, Photovoltaic Ventilation /

 

Long Lifespan—Reducing Hot Spot Effects.During the discussion of photovoltaic solutions in the initial plan, shadow analysis should be carried out, and photovoltaic systems should be arranged in locations with little or no shadowing as much as possible to reduce hot spots and avoid affecting photovoltaic power generation; when refining the photovoltaic solution, attention should be paid to the selection of photovoltaic panels, and photovoltaic chips with small hot spot effects, such as cadmium telluride, should be selected as much as possible, so that even if there is shading on the panel, the temperature near the shaded part is relatively low and safer; after the photovoltaic system is put into use, regular cleaning of the photovoltaic panels should be paid attention to in order to avoid dust, fallen leaves, etc., from shading the photovoltaic panels.

/ Sunlight Shadow Analysis /

/ Photovoltaic Panel Cleaning /

Comparison of Hot Spot Effects of Monocrystalline Silicon (left figure, maximum temperature 113.7℃) and Cadmium Telluride (right figure, maximum temperature 72.6℃)  

/ Comparison Chart of Photovoltaic Panel Hot Spot Effects /

 

Easy Maintainability—Electrical Design and Wiring.During the initial photovoltaic electrical design, the electrical system maintenance and inspection plan after the system is put into use should be considered, and the cable troughs and bridge plates for laying photovoltaic cables should be placed in the ceiling, etc., where maintenance and inspection are convenient, as much as possible.

/ BIPV Wiring Scene /

 

03

Evolution Process and Inspiration of BIPV Curtain Walls

 

BIPV Evolution Process

First-generation BIPV: 1980s - 1990s

First-generation BIPV products mainly installed traditional glass curtain wall solar panels on the exterior of buildings. The advantages of these products are easy installation and maintenance; the disadvantages are that the appearance is not beautiful enough and cannot meet the design requirements of architects.

Second-generation BIPV: 2000s - 2010s

Second-generation BIPV products began to integrate solar panels into the appearance of buildings to achieve better appearance. Examples of these products include solar roof tiles and solar glass. These products are more aesthetically pleasing but more costly.

Third-generation BIPV: 2010s to present

The focus of third-generation BIPV products is to achieve higher energy conversion efficiency, lower costs, and integrate more functions. These products are mainly integrated into the exterior walls, windows, roofs, and balconies of buildings. Currently, the cost of third-generation BIPV products is gradually decreasing, making them more attractive and more widely used in the construction industry.

 

Inspiration

BIPV has gradually evolved from single photovoltaic components to integration with other components, forming a composite component orientation. BIPV components are no longer limited to power generation; they can also be combined with building shading, waste heat utilization, and other technologies to reduce the impact of photovoltaics on building effects and expand the dimensions of building energy saving. From integrated design orientation to composite component orientation, BIPV can further optimize design, control overall building energy saving, and reduce building material costs. (For example, photovoltaic and electrochromic glass integration, i.e., photovoltaic electrochromic integration, combines power generation and light regulation functions; photovoltaic and phase change material integration, i.e., photovoltaic phase change material integration, combines power generation and temperature regulation functions.)

/ Photovoltaic Electrochromic Integration /

/ Photovoltaic Phase Change Material Integration /

 

04

BIPV Curtain Wall Adaptability Integration Cases

 

BIPV under Integrated Design Orientation

The photovoltaic system is expanded from a single façade replacement element to deeply intervene in many aspects such as indoor ventilation and lighting control and building completion effects, forming integrated design content.

[Practical Cases]

Lingang Top Science and Technology Experimental Building:The first "scientists' Community" urban unit in the country—the World Leading Scientists Community (WLA) Artificial Intelligence Laboratory. This project is an ultra-low energy consumption building that adopts a photovoltaic shading integration strategy. A cadmium telluride BIPV system is installed in the light-transmitting top part, combining power generation, lighting, and shading functions, and the shading coefficient can be reduced to 0.2, with an annual total power generation of approximately 310,000 kWh.

/ Lingang Top Science and Technology Experimental Building Scene /

/ Photovoltaic Panel Structure /

/ Effects of Photovoltaic Panels with Different Defilming Rates /

 

Lingang D07-02 Project:Ultra-low energy consumption building, using photovoltaic integration strategy, a dark gray monocrystalline silicon façade interlayer photovoltaic curtain wall BIPV, rooftop photovoltaic BAPV, etc., are set. The total photovoltaic area is approximately 4,000 square meters, with an annual total power generation of about 540,000 kWh.

/ Lingang D07-02 Project /

/ Dark Gray Monocrystalline Silicon Panel /

 

Jiangnan Emerging Industry Concentration Zone Electronic Information Industry Park:The integrated photovoltaic strategy for the comprehensive industrial park project includes cadmium telluride photovoltaic curtain walls (BIPV) and rooftop photovoltaics (BAPV), with a photovoltaic application area of approximately 18,000 square meters on the facade.

/ Jiangnan Emerging Industry Concentration Zone Electronic Information Industrial Park /

/ Cadmium Telluride Photovoltaic Curtain Wall (BIPV) Corresponding Model /

 

Xinquiao Airport Phase II:Targeting a three-star green building rating, a photovoltaic integration strategy is employed, with photovoltaics installed in multiple locations to balance power generation, lighting, and shading functions: 2384mm*1304mm monocrystalline silicon panels are installed on the top of the boarding bridge; 1200mm*1200mm laminated hollow cadmium telluride photovoltaic curtain walls are installed on the facade; 900mm*3600mm laminated hollow cadmium telluride photovoltaic skylights are installed on the top of the terminal building, integrating power generation, lighting, shading, and insulation; and 3600mm*1200mm laminated cadmium telluride photovoltaic louvers are installed on the terminal building facade, providing indoor shading while generating photovoltaic power.

/ Xinquiao Airport Phase II Renderings  /

/ Boarding Bridge BIPV Curtain Wall /

/ Terminal Building BIPV Shading Louvers, BIPV Skylights /

/ BIPV Curtain Wall Diagram /

 

BIPV under Component Compound Guidance

Photovoltaic products should be liberated from the constraints of energy components, while also being combined with architectural details and optimized for usage needs. Photovoltaic components under this guidance typically have multiple functions.

[Practical Cases]

New Pavilion Pavillon Novartis:The Swiss Novartis Pavilion's zero-energy media facade, where "the media skin becomes a zero-energy facade." A photovoltaic lighting integration strategy is used, with a total of 10,000 diamond-shaped organic photovoltaic panels and 30,000 embedded LEDs. The electricity generated by the organic photovoltaic panels powers the LED light show, combining power generation, floodlighting, and information transmission functions. The LEDs not only emit light outwards but also towards the metal casing below—allowing their light to reflect and flicker through the translucent solar modules, further improving photovoltaic power generation.

/ Photovoltaic Lighting Integration /

/ Test Sample /

/ Completed Project /

 

05

Summary

 

With the development of deep integration technology between photovoltaics and buildings, and the continuous upgrading of energy-saving and low-carbon standards, in the field of building skins, BIPV (Building-Integrated Photovoltaics) and BIPV/T (Building-Integrated Photovoltaics/Thermal) technologies will be more widely used.To promote the development of BIPV, it is necessary to improve the integration degree of photovoltaic curtain walls,The following technologies are worthy of attention:

Further improving the aesthetic coordination of photovoltaic integrated buildings——Optimizing the performance of photovoltaic panels to meet different building requirements; optimizing photovoltaic junction boxes, cables, and other components to minimize their visibility while ensuring safety.

Photovoltaic panel overheating resistance——Photovoltaic panels are prone to overheating during photoelectric conversion, which reduces photoelectric conversion efficiency and power generation. To ensure building appearance and photovoltaic output, research on the overheating resistance of photovoltaic panels needs attention.

Efficient and safe use of photovoltaics under shading conditions——When photovoltaic panels are partially shaded, they are prone to local overheating, posing a safety hazard. For safe use of photovoltaic systems, components with low hot spot effects should be considered during photovoltaic integration design; at the same time, the photovoltaic electrical system should have corresponding shutdown measures to prevent local electrical faults from affecting the overall system.

Measures to improve photovoltaic component and system efficiency——Employ measures such as automatic tracking to increase the annual irradiance of components and automated cleaning to reduce power generation losses, ensuring photovoltaic system power generation.

Other——In addition to the four points mentioned above, the physical performance and economic value of BIPV systems are also bottlenecks in the adaptive development of BIPV, requiring further research.

In summary, BIPV skin design is not a passive process of complying with regulations, but an active process of creating a new type of energy-producing skin. Reasonable use of BIPV skin design can effectively reduce carbon emissions during the building's life cycle, achieving a truly "positive energy building"  .

/ Building Type Development /