Building-integrated photovoltaics (BIPV) are solar materials that replace traditional building materials in parts of a building, such as the roof, windows, or walls. These materials are used in new buildings to generate electricity as a main or extra power source. They can also be added to older buildings to improve energy use. A benefit of BIPV compared to separate solar systems is that it can lower costs by reducing the need to buy and install other building materials and labor. Additionally, BIPV helps more people use solar energy when the building’s appearance is important, as it avoids the need for large, visible solar panels on the roof.

The term building-applied photovoltaics (BAPV) refers to solar systems added to buildings after they are built. Many installations labeled as BIPV are actually BAPV. Some companies and builders distinguish between BIPV used in new buildings and BAPV added later.

History

Photovoltaic (PV) systems for buildings first appeared in the 1970s. Solar panels with aluminum frames were attached to or placed on buildings, often in remote areas without access to electricity. In the 1980s, solar panels were added to rooftops and tested on buildings connected to the power grid in areas with large power stations. By the 1990s, building-integrated photovoltaic (BIPV) materials designed to be part of a building’s structure became available for sale. A 1998 study by Patrina Eiffert, titled An Economic Assessment of BIPV, suggested that Renewable Energy Credits (RECs) might one day have economic value. A 2011 report by the U.S. National Renewable Energy Laboratory noted that BIPV faces major technical challenges before its cost can compete with regular solar panels. However, many experts agree that widespread use of BIPV could help achieve the European goal for zero energy buildings by 2020. Despite its potential, challenges remain, such as the traditional practices in the building industry and fitting BIPV into crowded city areas. These studies suggest that successful long-term use of BIPV depends as much on government policies as on technological progress.

Forms

Most BIPV products use one of two technologies: Crystalline Solar Cells (c-SI) or Thin-Film Solar Cells. Crystalline Solar Cells are made from silicon wafers and usually work more efficiently than Thin-Film cells, but they cost more to make. These two technologies are used in five main types of BIPV products:

• Standard in-roof systems: These are strips of photovoltaic cells placed on roofs.
• Semi-transparent systems: These are used in greenhouses or cold areas where sunlight needs to enter the building while also being captured for energy.
• Cladding systems: These cover building walls vertically and come in many different designs.
• Solar Tiles and Shingles: These are the most common BIPV systems because they look like regular roof materials and can replace them easily.
• Flexible Laminates: These are thin sheets that can be attached to various surfaces, mostly roofs.

Except for flexible laminates, all other categories can use either c-SI or Thin-Film technologies. Thin-Film is only used in flexible laminates, making it ideal for designs that involve movement.

BIPV products can be used in many situations, such as sloped roofs, flat roofs, curved roofs, semi-transparent walls, skylights, shading systems, and external walls. Flat and sloped roofs are best for capturing solar energy. Roofing and shading systems are often used in homes, while wall and cladding systems are more common in businesses. Roofing BIPV systems currently have the largest share of the market and are more efficient than systems used on walls or cladding because they face the sun directly.

Building-integrated photovoltaic modules come in several forms:

• Flat Roofs: The most common type uses thin film solar cells attached to a flexible polymer module with an adhesive sheet between the solar module and the roof. Copper Indium Gallium Selenide (CIGS) technology now produces solar cells with 17% efficiency, and a UK company has created similar efficiency in TPO membranes.
• Sloped Roofs: Solar roof tiles are ceramic tiles with built-in solar modules. A Dutch company developed this technology in 2013. Solar shingles look like regular shingles but use thin film cells. They help protect roofs from damage by reducing condensation.
• Façades: These modules can be added to existing buildings, improving their appearance and value. They are placed on the building’s exterior over the current structure.
• Glazing: These are transparent or semi-transparent modules that can replace windows or skylights. They produce energy and improve thermal insulation.
• Photovoltaic Stained Glass: This uses colored glass to create solar panels that absorb specific light wavelengths. Technologies like perovskite, dye-sensitized cells, and plasmonic cells allow for colored panels. Researchers have tested colored panels with efficiencies up to 13.3% for blue light. Natural pigments from fruits and plants, such as maqui berries and spinach, are used in some low-cost solar cells. These cells have achieved a power conversion efficiency of 9.8%.

Transparent and translucent photovoltaics

Transparent solar panels use a tin oxide layer on the inside of glass to help carry electricity from the cell. The cell contains titanium oxide covered with a special dye that helps generate electricity when light hits it.

Most traditional solar cells use visible light and infrared light to create electricity. In contrast, new types of solar cells also use ultraviolet light. These cells can replace regular window glass or be placed on top of it. This allows for larger areas to be used, which could help combine power generation, lighting, and temperature control in one system.

Another name for transparent solar cells is "translucent solar cells" because they let about half of the light through. Like inorganic solar cells, organic solar cells can also be translucent.

Some solar cells that are not selective about the light they use become semi-transparent by placing small, opaque cells on a transparent base. This method reduces how efficiently they convert light into electricity while increasing how much light passes through.

Other non-selective solar cells use thin, visible-light-absorbing materials that are either very thin or have large gaps in their energy structure, allowing light to pass through. This creates semi-transparent solar cells, but it also means there is a balance between how much electricity they produce and how much light they let through.

Selective solar cells become transparent by using materials that only absorb ultraviolet or near-infrared light. These cells were first created in 2011. Although they let more light through, they are less efficient at converting light into electricity because of challenges like short distances for energy movement, difficulty making transparent electrodes without reducing efficiency, and the short lifespan of organic materials used.

Early attempts to make semi-transparent organic solar cells with very thin layers that absorbed visible light had efficiencies below 1%. However, in 2011, a type of transparent organic solar cell using a specific organic material and a fullerene receiver absorbed ultraviolet and near-infrared light with about 1.3% efficiency and let over 65% of visible light through. In 2017, researchers at MIT developed a way to apply transparent graphene electrodes to organic solar cells, achieving 61% visible light transmission and efficiencies between 2.8% and 4.1%.

Perovskite solar cells, which are promising for future use with efficiencies over 25%, have also shown potential as translucent solar cells. In 2015, a semi-transparent perovskite solar cell using a specific perovskite material and a silver nanowire mesh electrode allowed 79% of light at 800 nm wavelengths to pass through and had an efficiency of about 12.7%.

Government subsidies

In some countries, extra support, called subsidies, is given for building-integrated photovoltaics (BIPV) in addition to the existing payments for stand-alone solar systems. Starting in July 2006, France offered the highest extra payment for BIPV, which was an additional 0.25 euros per kilowatt-hour (kWh) on top of the 0.30 euros per kWh for regular solar systems. These subsidies are paid as a rate for electricity sent to the power grid.

• France: 0.25 euros per kWh
• Germany: 0.05 euros per kWh (façade bonus ended in 2009)
• Italy: 0.04–0.09 euros per kWh
• United Kingdom: 4.18 pence per kWh
• Spain: For systems up to 20 kilowatts (kW), 0.34 euros per kWh; for systems over 20 kW, 0.31 euros per kWh (based on RD 1578/2008)

• United States: Varies by state. For more details, check the Database of State Incentives for Renewables & Efficiency.

In March 2009, the Chinese government announced a subsidy program for BIPV projects, offering 20 yuan per watt for BIPV systems and 15 yuan per watt for rooftop systems. Later, the government introduced the "Golden Sun Demonstration Project," a subsidy program designed to support the growth of photovoltaic electricity generation and the use of solar technology. The Ministry of Finance, the Ministry of Science and Technology, and the National Energy Bureau shared the program details in July 2009. Qualified on-grid projects, including rooftop, BIPV, and ground-mounted systems, receive a subsidy equal to 50% of the total project cost, including transmission infrastructure. Qualified off-grid projects in remote areas may receive subsidies covering up to 70% of the total project cost. In mid-November, China’s finance ministry selected 294 projects totaling 642 megawatts, with costs of about 20 billion yuan (3 billion U.S. dollars), as part of the subsidy plan to increase the country’s solar energy production.

Other integrated photovoltaics

Vehicle-integrated photovoltaics (ViPV) work similarly for vehicles. Solar cells can be placed on parts of the car that get sunlight, like the hood, roof, and maybe the trunk, depending on the car's design.

Challenges

BIPV systems produce electricity at the location where it is used and are built into the structure of a building. The two most important measures of how well these systems work are their ability to generate power and their thermal properties. Traditional BIPV systems release less heat than rack-mounted PV systems, causing BIPV modules to operate at higher temperatures. These higher temperatures can damage the materials inside the modules, reducing their efficiency and leading to earlier breakdowns. Also, the performance of BIPV systems depends on weather conditions, and using the wrong type of BIPV system can lower the amount of energy they produce. In terms of heat management, BIPV windows can help reduce the need for cooling in buildings compared to regular clear glass windows, but they may increase the need for heating.

The high initial cost of BIPV systems is a major challenge for their use. In addition to the cost of buying BIPV components, the way BIPV systems are combined with building structures makes the design and construction process more complex, which increases overall costs. A lack of skilled workers who understand BIPV systems also raises labor costs during project development.

While many countries offer support for PV systems, few provide extra benefits for BIPV systems. BIPV systems must usually meet both building and PV industry standards, which makes their implementation more difficult. Additionally, government policies that keep traditional energy prices low reduce the advantages of BIPV systems, especially in countries where electricity is very cheap or heavily subsidized, such as in GCC countries.

Research shows that the public has limited knowledge about BIPV systems, and the cost is often seen as too high. Increasing public understanding through methods like policies, community activities, and example buildings may help BIPV systems develop more widely in the future.