BIPV vs. BAPV: Complementary Roles in Photovoltaic Buildings

Photovoltaic (PV) construction can be divided into two types based on the integration level of PV modules: Building-attached PV (BAPV) and Building-integrated PV (BIPV). Although BIPV has certain advantages in terms of cost and performance, its development is still in the early stages. BAPV, which can be directly installed on existing buildings, remains the mainstream form. In comparison to overseas markets, BIPV installations in Japan, France, Italy, and the United States have reached 3GW, 2.7GW, 2.5GW, and 0.6GW respectively, whereas in China, it was only 0.7GW in 2020, indicating significant potential for increased BIPV penetration in the future. Furthermore, from a business model perspective, BAPV retains more characteristics of PV products, with projects mainly led by PV manufacturing companies. On the other hand, BIPV is closely linked to the overall construction process, relying more on the EPC capabilities of construction companies, thereby bringing new growth opportunities to the construction sector. Overall, BAPV and BIPV complement each other's strengths and weaknesses, offering substantial growth opportunities for both PV manufacturers and construction firms in the PV construction industry.

Comparison of Installation Methods: Building-Attached Photovoltaic (BAPV) vs. Building-Integrated Photovoltaic (BIPV)

Photovoltaic (PV) applications in buildings represent a new frontier for solar energy generation. This technology integrates PV systems with the external structures of buildings, enhancing energy efficiency and reducing consumption, making it a crucial component in achieving low-energy passive buildings. 

Based on the degree of integration, building PV systems can be categorized into two types:

① Building-Attached Photovoltaic (BAPV): This refers to PV systems installed on existing buildings, utilizing idle spaces for energy generation. BAPV is commonly used in the retrofitting of existing structures.

② Building-Integrated Photovoltaic (BIPV): This involves PV systems that are simultaneously designed, constructed, and installed with the building itself, integrating seamlessly with the building's structure. BIPV systems not only generate electricity but also contribute to the building's aesthetic appearance.

Comparison of Construction Methods:

① BAPV: Typically, BAPV systems use special brackets to secure PV modules to the existing building structure. These systems primarily serve the function of energy generation without affecting the original functionality of the building, and they are considered "installation-type" solar PV buildings.

② BIPV: BIPV systems involve a one-time construction and investment approach, where PV system support structures, PV modules, and other electrical components are directly installed during the building's construction phase. BIPV systems not only generate electricity but also replace conventional building materials, serving both as a structural component and fulfilling the building's functional requirements.

Complementary Advantages and Disadvantages of BAPV and BIPV, with BIPV Offering Greater Economic Benefits

Building-Attached Photovoltaic (BAPV) and Building-Integrated Photovoltaic (BIPV) systems have complementary strengths and weaknesses. BIPV is generally more economical. According to calculations for a steel structure factory roof project by Polaris Solar PV Network, using a BIPV roof system can save approximately 164 RMB per square meter in material costs. Additionally, BIPV systems have a design lifespan of over 50 years, providing significant comprehensive economic advantages. A specific comparison is as follows:

1) Building Aesthetics

·BIPV: As an integrated photovoltaic system, BIPV is incorporated into the overall architectural design, resulting in a more cohesive and aesthetically pleasing building appearance.

·BAPV: Being a retrofitted system, BAPV is added post-construction, leading to a less cohesive appearance.

2) Roof Load-Bearing

·BIPV: The roof in BIPV constructions is a straightforward load-bearing structure, with clear force distribution, ensuring high safety.

·BAPV: Due to its retrofitted nature, the roof in BAPV systems experiences more complex loading conditions, which, under long-term wind load and deformation, may cause fatigue effects that could compromise structural safety.

3) Waterproofing

·BIPV: Uses hydrophobic glass panels combined with main water channels, waterproof seals, and other elements to form a comprehensive roof drainage system. Modular combinations of roof structure, flashing, and skylight bands can achieve superior waterproofing performance.

·BAPV: Does not inherently provide waterproofing; it relies on the existing roof to have adequate waterproofing capability.

4) Construction Difficulty

·BIPV: As a critical structural component, BIPV must meet high standards for waterproofing, insulation, and other architectural performance criteria, making installation more challenging.

·BAPV: Involves simply adding PV components to an existing roof, making the installation relatively straightforward.

5) Operation and Maintenance

·BIPV: Roofs are designed with modular PV panels, but maintenance requires ensuring that the roofing functions remain intact, which increases the complexity of operations and maintenance.

·BAPV: Maintenance can be performed directly on the roof with relatively easy disassembly and reassembly, making operations and maintenance less challenging.

BIPV vs. BAPV: Comprehensive cost comparison

Comparison ltems	BIPV System	BAPV System
Aluminum-magnesium-manganese Roof Panels	/	Including vertical lock-edge aluminum-magnesium-manganese roof panels and aluminum alloy T-type supports, about ￥200/㎡
System Bracket Accessories	Including supporting light pot camphor strips, aluminum alloy strips, rubber sealing strips, fixings, etc. about ￥0.6/W*120W/㎡=￥72	Including clamps, guide rails, fixings, etc. about ￥0.3 /W*120W/㎡ = ￥36
Photovoltaic Power Generation Module unit Board	Including photovoltaic panels and Ming alloy frames, about 120W/㎡'* ￥ 2.8 /W= ￥336	Including photovoltaic panels and Ming alloy frames, about 120W/㎡* ￥ 2.8 /W = ￥336
Comprehensive Cost (material price)	System bracket accessories + photovoltaic power generation component unit board =￥408 /㎡	Aluminum-magnesium-manganese roof panels + System bracket accessories + photovoltaic power generation component unit board = ￥572 /㎡
Unit Cost (yuan/square meter)	408	572
Conclusion	The use of photovoltaic building integrated roof system can save materials ￥160 /㎡

Data by Polaris Solar PV Network

BIPV vs. BAPV

Comparison ltems	BIPV System	BAPV System
Building appearance	Incorporated into the overall design of the building, without losing beauty	Late installation, poor integrity
Design Life	Lifespan can reach more than 50 years	20-25 years
Roof Stress	The roof is a simple roof with clear structural stress and high structural safety	Complex stress, long-term wind load and deformation may produce fatigue effects, affecting structural safety
Waterproofness	The roof drainage svstem is formed by hydrophobic glass panels, main water tanks.waterproof seals, etc. The roof structure, flashing edging, light strips, etc. are modularly composed to avoid leakage hazards	No need to provide waterproofing ability, only the existing roof needs to have waterproofing ability
Construction Difficulty	Hiah installation accuracy, undertakes roof waterproofing, heat insulation and other functions,and has great construction difficulty	Construction in two phases, low difficulty in component installation
Operation and Maintenance	The roof is modularly desianed and installed with a single battery module as a unit. While inspecting and repairing, it is also necessary to consider whether the roof functions complete, and the operation and maintenance are difficult	Can be directly inspected and repaired on the roof, disassembly and assembly are relatively convenient, and operation and maintenance are easy

Data by Polaris Solar PV Network

Technical Systems: Crystalline Silicon and Thin-Film as Main Component Materials

Photovoltaic (PV) cells are the foundational core components of PV power generation systems. They are primarily categorized into crystalline silicon solar cells and thin-film solar cells based on the materials used. Crystalline silicon cells dominate the market share, while thin-film cells are expected to see increased penetration due to the growth of photovoltaic building applications.

1) Crystalline Silicon Cells: Crystalline silicon solar cells have developed over several decades, leading to a mature technological system with continuously improving photoelectric conversion efficiency. The industry has also rapidly expanded, significantly lowering marginal manufacturing costs. In the current PV industry, crystalline silicon cells hold over 95% of the market share due to the economic cost advantages brought by economies of scale and their high conversion efficiency. Among them, monocrystalline silicon cells are characterized by high photoelectric conversion efficiency and high manufacturing costs, while polycrystalline silicon cells have slightly lower conversion efficiency but are inexpensive to produce and do not suffer from significant efficiency degradation. Before 2017, polycrystalline cells held a market share as high as 73%. Since 2017, the introduction of new production technologies has significantly reduced the production costs of monocrystalline silicon, and the increased penetration of PERC technology has substantially improved the conversion efficiency of monocrystalline silicon, which now accounts for approximately 90% of the crystalline silicon cell market.

2) Thin-Film Cells: Thin-film cells have not yet achieved a large market scale due to their relatively lower photoelectric conversion efficiency. However, they exhibit strong low-light performance, making them significantly more effective than crystalline silicon modules in some non-south-facing BAPV/BIPV projects. Additionally, because thin-film cells have a better temperature coefficient, they can maintain performance in extreme high-temperature conditions, effectively compensating for the shortcomings of crystalline silicon. Crystalline silicon cells are primarily available in deep blue and light blue colors, which are somewhat monotonous and cannot meet the diverse color needs of photovoltaic buildings. In contrast, thin-film cells offer the advantage of adjustable color, with current market products covering almost all common color schemes. Furthermore, thin-film cells are relatively lightweight, reducing construction difficulty and the manufacturing costs of support structures when using thin-film PV modules.

Comparison of crystalline silicon and thin-film cells in the field of building photovoltaics

	Crystalline silicon Solar Cells	Thin-Film Solar Cells
Power per Unit Area	A crystalline silicon photovoltaic power station with a roof area of 1,000 square meters has a capacity of approximately 100 kW.	A thin-film photovoltaic power station with a roof area of 1,000 square meters has a capacity of approximately 70 kW.
Low-Light Performance	Crystalline silicon solar cells have relatively poor low-light performance. For example, in a southern Chinese city, crystalline silicon PV modules installed facing directly south achieve only 59% of their maximum efficiency under suboptimal light conditions.	Thin-film solar cells have strong low-light performance and are less sensitive to installation angles. They generate electricity for longer periods in low-light conditions compared to crystalline silicon cells, making them more suitable for non-south-facing installations, curtain walls, and BlPV projects in cloudy or cold regions.
Temperature Coefficient	The temperature coefficient is relatively high. When the operating temperature exceeds 25°c, the maximum power output decreases by 0.40-0.45% for each 1°c increase.	The temperature coefficient is relatively low, When the operating temperature exceeds 25℃, the maximum power output decreases by only 0.19-0.21% for each 1°C increase.
Color Diversity	The color options are mainly in shades of blue, such as deep blue and light blue.	Thin-film modules can be produced in various colors as needed.
Module Weight	The modules are relatively heavy.	They are relatively lightweight, reducing roofing construction difficulty and costs. Additionally, when used in curtain wall applications, thin-film Py modules require less structural support and incur lower costs compared to crystalline silicon modules.

Source by 2021 Crystalline silicon, thin-film and perovskite BIPV technology and market forum

Overall, crystalline silicon and thin-film technological systems play complementary roles in the field of photovoltaic buildings. Thin-film technology holds a distinct advantage in specific photovoltaic building projects, such as non-south-facing roofs, curtain walls and customized scenarios. According to a 2018 study by the Fraunhofer Institute for Solar Energy Systems in Germany on European BIPV projects, approximately 90% of roof BIPV projects use crystalline silicon technology, while about 56% of façade BIPV projects utilize thin-film technology.

Classification and characteristics of the main technical systems of photovoltaic cells

Technological System	Specific Materials	Photoelectric Conversion Efficiency	Advantage	Disadvantage
Crystalline Silicon Solar Cells	Monocrystalline silicon	16% - 18%	Long lifespan (generally up to 20-30 years), high photoelectric conversion efficiency	High production cost, long production time, poor low-light performance
	Polycrystalline silicon	14% - 16%	High light stability, low cost, simple production, and no obvious efficiency decline	Poor low-light power generation performance
Thin-Film Solar Cells	Amorphous silicon	6% - 9%	Mature technology, low manufacturing threshold	Limited photoelectric conversion efficiency
	Copper indium gallium selenide (ClGS)	11%	Low production cost, low pollution, no decline, good low-light performance, high photoelectric conversion efficiency	The technology is highly sensitive to elemental ratios, and the structure is complex, requiring extremely stringent processing and preparation conditions
	Cadmium telluride (CdTe)	9% - 12%	Low manufacturing cost, high conversion efficiency, low-temperature coefficient (excellent performance at low temperature), good low-light effect	The scarcity of raw materials and the toxicity of cadmium necessitate a large-scale recycling system, making large-scale applications difficult

Source by  Research on the application of solar photovoltaics in buildings, Overview of the development of copper indium gallium selenide thin-film solar cell industry

BAPV (Building-Attached Photovoltaic) is currently the mainstream form of building photovoltaics. From the current industry landscape, BAPV remains the dominant form of building-integrated photovoltaics. This is primarily because the construction of new buildings is limited each year, and the standards for BIPV are not yet fully established. Even if BIPV were to be adopted immediately, it would still take 3-5 years until the buildings reach the capping stage before BIPV can be used. In contrast, retrofitting existing rooftops is relatively easier, and the abundance of existing rooftop resources makes it more suitable for the rapid development of distributed photovoltaics at this stage.

Compared to Mature Overseas Markets, BIPV Has Significant Potential for Increased Penetration in the Future. In developed countries, building-integrated photovoltaics (BIPV) began earlier, with many countries implementing various incentive policies and development plans as early as the late 20th century. For instance, Germany, Italy, Japan, and the United States have all established "Solar PV Roof Programs," setting clear targets for building PV installation capacities in the coming years. As of 2018, according to a report by the BIPVBOOST organization, Japan had the highest cumulative BIPV installation globally, with a capacity of 3 GW, followed by France (2.7 GW), Italy (2.5 GW), and the United States (0.6 GW). In contrast, China's cumulative BIPV installation was only 0.1 GW (approximately 0.7 GW by 2020).

When comparing the historical installation capacities of developed regions, China's current total BIPV installation is equivalent to the levels Japan and Europe reached around 5 to 10 years ago. This trajectory indicates that the market in China is far from mature, and there is substantial room for BIPV penetration to increase in the future.