Building Integrated Photovoltaics (BIPV) | WBDG

Introduction

One of the most promising renewable energy technologies is photovoltaics. Photovoltaics (PV) is a truly elegant means of producing electricity on site, directly from the sun, without concern for energy supply or environmental harm. These solid-state devices simply make electricity out of sunlight, silently with no maintenance, no pollution, and no depletion of materials.

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There is a growing consensus that distributed photovoltaic systems that provide electricity at the point of use will be the first to reach widespread commercialization. Chief among these distributed applications are PV power systems for individual buildings.

Interest in the building integration of photovoltaics, where the PV elements actually become an integral part of the building, often serving as the exterior weather skin, is growing worldwide. PV specialists and innovative designers in Europe, Japan, and the U.S. are now exploring creative ways of incorporating solar electricity into their work. A whole new vernacular of Solar Electric Architecture is beginning to emerge.

A PV skylight entryway
Courtesy of DOE/NREL

A Building Integrated Photovoltaics (BIPV) system consists of integrating photovoltaics modules into the building envelope, such as the roof or the facade. By simultaneously serving as building envelope material and power generator, BIPV systems can provide savings in materials and electricity costs, reduce use of fossil fuels and emission of ozone depleting gases, and add architectural interest to the building.

While the majority of BIPV systems are interfaced with the available utility grid, BIPV may also be used in stand-alone, off-grid systems. One of the benefits of grid-tied BIPV systems is that, with a cooperative utility policy, the storage system is essentially free. It is also 100% efficient and unlimited in capacity. Both the building owner and the utility benefit with grid-tied BIPV. The on-site production of solar electricity is typically greatest at or near the time of a building's and the utility's peak loads. The solar contribution reduces energy costs for the building owner while the exported solar electricity helps support the utility grid during the time of its greatest demand.

Description

Photovoltaics (PV) Technologies

There are two basic commercial PV module technologies available on the market today:

1. Thick crystal products include solar cells made from crystalline silicon either as single or poly-crystalline wafers and deliver about 10-12 watts per ft² of PV array (under full sun).

2. Thin-film products typically incorporate very thin layers of photovoltaicly active material placed on a glass superstrate or a metal substrate using vacuum-deposition manufacturing techniques similar to those employed in the coating of architectural glass. Presently, commercial thin-film materials deliver about 4-5 watts per ft² of PV array area (under full sun). Thin-film technologies hold out the promise of lower costs due to much lower requirements for active materials and energy in their production when compared to thick-crystal products.

A photovoltaic system is constructed by assembling a number of individual collectors called modules electrically and mechanically into an array.

Building Integrated Photovoltaics (BIPV) System

Building Integrated Photovoltaics (BIPV) is the integration of photovoltaics (PV) into the building envelope. The PV modules serve the dual function of building skin—replacing conventional building envelope materials—and power generator. By avoiding the cost of conventional materials, the incremental cost of photovoltaics is reduced and its life-cycle cost is improved. That is, BIPV systems often have lower overall costs than PV systems requiring separate, dedicated, mounting systems.

A complete BIPV system includes:

1. the PV modules (which might be thin-film or crystalline, transparent, semi-transparent, or opaque);
2. a charge controller, to regulate the power into and out of the battery storage bank (in stand-alone systems);
3. a power storage system, generally comprised of the utility grid in utility-interactive systems or, a number of batteries in stand-alone systems;
4. power conversion equipment including an inverter to convert the PV modules' DC output to AC compatible with the utility grid;
5. backup power supplies such as diesel generators (optional-typically employed in stand-alone systems); and
6. appropriate support and mounting hardware, wiring, and safety disconnects.

BIPV system diagram
Courtesy of Murdoch University Energy Research and Innovation Group

BIPV systems can either be interfaced with the available utility grid or they may be designed as stand-alone, off-grid systems. The benefits of power production at the point of use include savings to the utility in the losses associated with transmission and distribution (known as 'grid support'), and savings to the consumer through lower electric bills because of peak shaving (matching peak production with periods of peak demand). Moreover, buildings that produce power using renewable energy sources reduce the demands on traditional utility generators, often reducing the overall emissions of climate-change gasses.

Design of a Building Integrated Photovoltaics (BIPV) System

BIPV systems should be approached to where energy conscious design techniques have been employed, and equipment and systems have been carefully selected and specified. They should be viewed in terms of life-cycle cost, and not just initial, first-cost because the overall cost may be reduced by the avoided costs of the building materials and labor they replace. Design considerations for BIPV systems must include the building's use and electrical loads, its location and orientation, the appropriate building and safety codes, and the relevant utility issues and costs.

Steps in designing a BIPV system include:

1. Carefully consider the application of energy-conscious design practices and/or energy-efficiency measures to reduce the energy requirements of the building. This will enhance comfort and save money while also enabling a given BIPV system to provide a greater percentage contribution to the load.

2. Choose Between a Utility-Interactive PV System and a Stand-alone PV System:

   • The vast majority of BIPV systems will be tied to a utility grid, using the grid as storage and backup. The systems should be sized to meet the goals of the owner—typically defined by budget or space constraints; and, the inverter must be chosen with an understanding of the requirements of the utility.
   • For those 'stand-alone' systems powered by PV alone, the system, including storage, must be sized to meet the peak demand/lowest power production projections of the building. To avoid over sizing the PV/battery system for unusual or occasional peak loads, a backup generator is often used. This kind of system is sometimes referred to as a "PV-genset hybrid."

3. Shift the Peak: If the peak building loads do not match the peak power output of the PV array, it may be economically appropriate to incorporate batteries into certain grid-tied systems to offset the most expensive power demand periods. This system could also act as an uninterruptible power system (UPS).

4. Provide Adequate Ventilation: PV conversion efficiencies are reduced by elevated operating temperatures. This is truer with crystalline silicon PV cells than amorphous silicon thin-films. To improve conversion efficiency, allow appropriate ventilation behind the modules to dissipate heat.

5. Evaluate Using Hybrid PV-Solar Thermal Systems: As an option to optimize system efficiency, a designer may choose to capture and utilize the solar thermal resource developed through the heating of the modules. This can be attractive in cold climates for the pre-heating of incoming ventilation make-up air.

6. Consider Integrating Daylighting and Photovoltaic Collection: Using semi-transparent thin-film modules, or crystalline modules with custom-spaced cells between two layers of glass, designers may use PV to create unique daylighting features in facade, roofing, or skylight PV systems. The BIPV elements can also help to reduce unwanted cooling load and glare associated with large expanses of architectural glazing.

7. Incorporate PV Modules into Shading Devices: PV arrays conceived as "eyebrows" or awnings over view glass areas of a building can provide appropriate passive solar shading. When sunshades are considered as part of an integrated design approach, chiller capacity can often be smaller and perimeter cooling distribution reduced or even eliminated.

8. Design for the Local Climate and Environment: Designers should understand the impacts of the climate and environment on the array output. Cold, clear days will increase power production, while hot, overcast days will reduce array output;/p>

   • Surfaces reflecting light onto the array (e.g., snow) will increase the array output;
   • Arrays must be designed for potential snow- and wind-loading conditions;
   • Properly angled arrays will shed snow loads relatively quickly; and,
   • Arrays in dry, dusty environments or environments with heavy industrial or traffic (auto, airline) pollution will require washing to limit efficiency losses.

9. Address Site Planning and Orientation Issues: Early in the design phase, ensure that your solar array will receive maximum exposure to the sun and will not be shaded by site obstructions such as nearby buildings or trees. It is particularly important that the system be completely unshaded during the peak solar collection period consisting of three hours on either side of solar noon. The impact of shading on a PV array has a much greater influence on the electrical harvest than the footprint of the shadow.

10. Consider Array Orientation: Different array orientation can have a significant impact on the annual energy output of a system, with tilted arrays generating 50%–70% more electricity than a vertical facade.

11. Reduce Building Envelope and Other On-site Loads: Minimize the loads experienced by the BIPV system. Employ daylighting, energy-efficient motors, and other peak reduction strategies whenever possible.

12. Professionals: The use of BIPV is relatively new. Ensure that the design, installation, and maintenance professionals involved with the project are properly trained, licensed, certified, and experienced in PV systems work.

In addition, BIPV systems can be designed to blend with traditional building materials and designs, or they may be used to create a high-technology, future-oriented appearance. Semi-transparent arrays of spaced crystalline cells can provide diffuse, interior natural lighting. High profile systems can also signal a desire on the part of the owner to provide an environmentally conscious work environment.

Application

Photovoltaics may be integrated into many different assemblies within a building envelope:

• Solar cells can be incorporated into the facade of a building, complementing or replacing traditional view or spandrel glass. Often, these installations are vertical, reducing access to available solar resources, but the large surface area of buildings can help compensate for the reduced power.

  Additional reading:
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• Photovoltaics may be incorporated into awnings and saw-tooth designs on a building facade. These increase access to direct sunlight while providing additional architectural benefits such as passive shading.

• The use of PV in roofing systems can provide a direct replacement for batten and seam metal roofing and traditional 3-tab asphalt shingles.

• Using PV for skylight systems can be both an economical use of PV and an exciting design feature.

APS Factory in Fairfield, California
Courtesy of Kiss + Cathcart

Intercultural Center, Georgetown University in Washington, DC

Relevant Codes and Standards

Publications

Additional Resources

Computer-Based PV Design and Sizing Tools

• PV F-Chart—Provides analysis and rough sizing of both grid-connected and stand-alone PV systems.
• PVFORM—Offers simulation of grid-connected and stand-alone systems, including economic analysis. Available from Sandia National Labs, Albuquerque, NM.
• TRNSYS—Simulation system for renewable energy applications; originally for solar thermal, now has extensions for PV and wind.
• PV Planner —A spreadsheet analytical tool for grid-connected applications from the Center for Energy and Environmental Policy, University of Deleware.
• HOMER—Hybrid Optimization Model for Electric Renewables (HOMER) is a design optimization model that determines the configuration, dispatch, and load management strategy that minimizes life-cycle costs.
• PVnode—Calculates the electric behavior of large and inhomogeneously illuminated PV arrays. Available from D. Stellbogen, ZSW Baden-Wurttemberg Hessbruhlstr., 21c, D-70565 Stuttgart, Germany.

Other

• Solar-Estimate.org is a free public service offering solar estimating tools and is supported by the Department of Energy and the California Energy Commission.

Training Courses

State of the Industry and Key Domestic Markets

Market segments actively being pursued

Based on responses received, a variety of product segments were identified as being pursued in the United States. The list includes:

• Roofing products:
  • Roofing systems with commodity solar modules
  • Monocrystalline roofing panels on slopped roofs
  • Standing seam metal roofs
  • Solar shingles
  • Solar tiles
  • Integrated roofing membrane on rooftop with solar
• Covering/Shading products:
  • Parking lot coverings
  • Solar carports with charging stations
  • Awnings
  • Sunshades
  • Solar laminates (without framework) on solar canopies, carports, awnings
• Glass products:
  • Power generating PV windows
  • Opaque solar modules and semitransparent solar modules
  • Building glazing
  • Spandrel
  • Curtain walls
• Vertical products:
  • Cladding
  • Building façades
  • Vestibules
  • Wall-integrated PV
• Other areas:
  • High-performance building envelopes
  • Fiberglass pultruded parts for window reinforcement
  • CIGS panels for building façades, partial window replacements, indirect light awnings
  • Power electronic solutions for rooftop and façades
  • Electrical panels, subpanels, breakers
  • Building microgrids (solar+ESS+EV charging+EMS+VPP operation)
  • Characterization and validation of products

In terms of markets served, most of the respondents indicated a focus on residential or commercial buildings. This was an almost equal split, with slightly more responses giving preference to commercial buildings and the majority pursuing both markets. It was noted by some respondents that their strategy is to initially target commercial buildings and then move to the residential market, as they see more difficulties for the residential segment due to less willingness of owners to pay and lack-of-standardization concerns for BIPV products. Some special segments of the commercial building market, like government buildings, educational facilities, hospitals, manufactured houses, and agricultural facilities were also identified by the respondents as being of interest and of their primary focus. The following segments were specifically mentioned:

• Residential buildings (single and multi-family)
• Commercial buildings
• C&I buildings
• MUSH market: municipalities, universities, schools, hospitals
• Government buildings, higher education, healthcare sector
• Manufactured houses at the factory level
• Agriculture and greenhouses
• Playscapes

In terms of new buildings or retrofits, the vast majority of respondents mentioned being involved in both sectors with few of them only focusing on new buildings.

Market segments best aligned with commercialized BIPV products

A variety of information was provided with respect to the alignment of commercialized BIPV products and market segments. Some responses viewed the topic from the customer market segment perspective and others from the side of the BIPV product and application. It was also noted that, assuming availability of various BIPV products, the type of BIPV should be dictated by the aspect ratio of the building. Larger roof areas (like in warehouses) would naturally be a better fit for rooftop solar, while taller, skinnier buildings (like high-rise office or residential buildings) would be better fit for glazing or façade products.

Overall, most of the respondents considered the extended commercial building market to be best aligned with commercialized BIPV products. This market includes high-end commercial office and retail buildings (which have fewer cost constraints and can use the technology as marketing point), educational facilities, such as schools, colleges, and universities (which consider educational and research benefits of incorporating new technologies, especially in the science and technology sectors), hospitals, hospitality buildings, and warehouse facilities (which consider weight issues and reduced need for puncture of membrane roofs). New construction commercial projects seem to have the most potential.

The residential building market seems to be interested in the appeal of aesthetics of BIPV compared to tradition rooftop PV products. Development of more aesthetically pleasing products would be the best strategy for alignment with this market, though cost is also a significant factor. Multi-family homes and high-rise buildings seem to be the most promising segments. New constructions seem to be perceived as better aligned compared to retrofits.

In terms of products, roofing products are perceived to be best aligned with the market, both for commercial and residential applications. Power generating windows and other glass products are secondary, with more appeal on in commercial applications. However, responses indicate that most of the existing products need further development as they might not be fully aligned with the market needs. Another product category identified is shading elements, awnings, and in particular carports and parking shade covers.

Respondents also provided some insights about differences between the U.S. markets and markets in Europe or elsewhere in the world. It was noted that in the United States, residential and commercial roofs for new constructions align well with existing BIPV products in the space, but elsewhere in the world, many more commercial products are available for building façades for high-rise buildings, offices, government buildings, educational facilities, sports arenas, airports, and public areas. In Europe, there have been large commercial projects integrating BIPV glass as well as several small-scale commercial projects integrating BIPV walls and façades.

Largest market opportunities for BIPV

A variety of information was provided on the market opportunities for BIPV products. Like in the previous question, some responses viewed the topic from the customer market segment perspective and others from the side of the BIPV product and application.

Respondents perceived the largest market opportunities for BIPV to be in the commercial sector; however, residential applications were also considered to present great opportunities. In the commercial segment, corporate offices, retail buildings, storefronts, public buildings, government buildings, educational facilities, hospitals, and light industrial facilities were specifically identified as promising. Opportunities for older buildings with large power needs at places where the grid infrastructure is older were mentioned as well as applications that combine conventional rooftop solar with additional BIPV elements. For the residential sector, multi-family housing and low- and mid-rise buildings with a high ratio of wall-window to roof area were considered the largest opportunities. Incorporation of BIPV into manufactured housing and modular construction production lines was also identified as a promising opportunity. In terms of location, it was mentioned that the state of California would provide a large market opportunity because of the state requirements with respect to climate change and clean energy.

When viewing opportunities from the BIPV product perspective, three product categories were identified as being the most promising in the market:

• Roofing products
• Glass products (windows, glazing)
• Shade elements (awnings, carports, sunshades)

Regarding PV glass and power generating windows, respondents explicitly mentioned the stacking benefits of glass capturing infra-red light and thus also reducing heat transferred into the building.

Respondents also noted that a comprehensive market characterization and assessment is necessary, as the market opportunity will be eventually defined by the adoption and market-pull for these products, not by the theoretical availability of BIPV products that could replace a particular building element. Another view presented was the perspective of using the energy generated to offset the cost of the building element that is required by the building.

Marketing and sourcing of current BIPV products

Respondents approached this topic from various different angles and provided different types of information related to marketing strategies, manufacturing locations, industry composition, and PV cell technologies mostly used by BIPV products. Some respondents noted that marketing efforts are very limited and are done on a project-per-project basis, and this is considered a contributing factor to the limited uptake of BIPV technologies.

• Marketing and sourcing strategies: A typical marketing approach treats BIPV as architectural products that are marketed and sourced as offerings within the construction materials industry. Therefore, marketing starts from approaching architects, engineers, or real-estate developers via a product advertising strategy. Typical media and avenues include:
  • major architectural magazines, websites, or other digital media;
  • social media venues;
  • trade shows, home and garden shows, green building shows, architectural conferences, sustainability expos;
  • networking into specific target market segments.

In cases where developers or designers are more familiar with BIPV products, sourcing would follow the pattern of an interested architect or building developer reaching out to a BIPV product vendor. BIPV products are often marketed as elements of total-building approaches to achieve high LEED or similar scores. They are offered by the supplier to real-estate developers and architects with a promise of return on investment based on the electrical cost offset from the generated electricity as well as on applicable local incentives. Non-electrical benefits, such as acoustics, thermal, safety glazing, or UV light blocking, are also listed but often not included as part of the economic consideration. The dual-use and aesthetic aspects of BIPV compared to traditional PV products is another marketing point typically used.

• Manufacturing locations: Locations mentioned in responses include the United States (mainly for assembly), Canada, and China. Companies seem to have interest in having manufacturing in the U.S. as they believe it could allow them to better serve their customers.
• Industry composition: Respondents perceive the BIPV industry in the U.S. to be highly concentrated with only 5-6 major players, most of them providing roofing products. There is also a number of smaller companies or start-ups, some of which are also focusing on other products (windows, glass, façades, curtainwalls, shading elements, carports, etc.). It was mentioned that the number of startup companies in the U.S. is very small in comparison to Europe, where there are over 30 small companies producing and marketing various BIPV products. There are also cases of big roofing, construction, and window companies that begin to acquire and partner with BIPV companies and then integrating them with their existing offerings and channels.
• PV cell technologies: Cell technologies considered for BIPV products are based on silicon or other thin-film technologies, such as amorphous silicon, (a-Si), multicrystalline silicon (mc-Si), polycrystalline silicon (pc-Si), copper indium gallium diselenide (CIGS), cadmium telluride (CdTe), or organic PV (OPV) cells. Monocrystalline silicon (c-Si) is also used in roofing products, like in solar shingles.

Domestic manufacturing opportunities

There is a growing interest in U.S. manufacturing, as evidenced by the number of foreign-owned companies that have opened or are opening plants in the U.S., in addition to U.S.-owned companies that already have manufacturing facilities. The U.S. has established itself as a leader in the manufacturing of rooftop-integrated solar, but other companies could be incentivized to develop manufacturing capabilities that include PV integrated into windows, building façades, and other substrates. In addition, a growing number of innovative BIPV ideas have emerged across smaller companies and startups in the United States. Respondents, however, have noted that currently there are insufficient economic incentives for the development of domestic manufacturing of BIPV products and their respective supply chains in the United States. Tax incentives or grants to support BIPV manufacturers who wish to manufacture in the U.S. and for businesses to procure these products could be a driver for adoption.

In general, it is ideal to manufacture components as close to the market as possible as this reduces costs and speeds up development. The impact to the cost of the final product could be lowered, if the bulk of the raw materials and final assembly are completed domestically or regionally (especially if tariffs are considered). It is customary for the building industry to use local manufacturing and source materials locally, so it would be meaningful for BIPV to follow the same paradigm. Many building materials used in such products are large and heavy enough that makes sense to produce domestically and even regionally throughout the country to reduce transportation costs and logistics, which could account for 10-15% of the cost, in some cases.  Other benefits include manufacturing to order, reduced inventories, on time delivery, quick deployment within the region, quality control, and the ability to better meet various sustainability requirements, while also ensuring supply chain security. It was also identified that cybersecurity of BIPV systems, as it pertains to their electronics and control hardware and software, provides another argument for domestic production.

The roofing industry lends itself to domestic manufacturing, with shipping costs being a major reason. The main challenge to the development of BIPV roofing is sourcing of materials and manufacturing of the non-industry standard-size solar roof tile. There currently exists very limited domestic capability for this need. The specific glass used in PV modules is made only in Asia today and is difficult and costly to source. Manufacturing equipment and facilities do not currently exist for specific solar tile sizes, and this not only increases cost but also lengthens development time. This creates needs and opportunities for developing domestic manufacturing capabilities.

Glass is also produced close to the consumption site due to high transportation costs because of the brittleness and weight of the product. Most windows are manufactured domestically, and insulated glass units (IGUs) follow this same pattern. IGUs are primarily ordered and manufactured regionally/domestically, due to custom specifications, sizes, and lead times. By extension, it is reasonable to conclude that solar windows and other glazing-based PV products are well-suited for domestic manufacturing. Solar windows are unlikely to be exported globally from a single manufacturing site as this could be cost prohibitive. If the integrated photovoltaic function does not involve fabricating semi-transparent solar cells over the entire window area, but rather only employ commercial solar cells (e.g. crystalline Si based) outside the window viewing area and thin-film coating techniques, then it is very feasible to integrate the photovoltaic window manufacturing/assembly alongside the existing window manufacturing facilities. It could also seamlessly integrate into the existing IGU supply chain (glass fabricators can apply PV coatings), which further ensures domestic manufacturing and that the revenue uplift from the value-added BIPV window product is captured domestically as well. Semitransparent OPV power generating windows also have a significant opportunity for domestic manufacturing.

Respondents also identified a few additional, more specialized opportunities for domestic manufacturing, such as cadmium telluride (CdTe) as the semiconductor for PV modules, pre-engineering and assembly of unitized curtainwall panels, manufactured homes incorporating BIPV, and emerging products that rely on advanced manufacturing like quantum dots.

Advantages to regionalization of product manufacturing with end markets

Respondents described a variety of advantages that regional BIPV product manufacturing would provide. Such benefits pertain to:

• Development of a stable domestic supply chain less susceptible to political interruption or other disruptions.
• Reduction of transportation costs.
• Reduction of carbon footprint.
• Improvement in the pace of product development.
• Decrease in product lead times.
• Reduction in inventories.
• Enhancement in customer perception.
• Local sales support and logistics.
• Creation of more local jobs.
• Creation of regional educational opportunities.
• Fostering of innovation.
• Enhancement in community engagement and relations.
• Fulfilling regional architectural preferences that are best addressed with local production.
• Capturing market share by calibrating products and applications to meet specific regional customer environmental characteristics.
• Customization of locally manufactured products to regionally specific building code requirements.

It was also noted that this topic should be more thoroughly addressed within an economic framework that will consider factors like the costs of building and operating regional manufacturing facilities, the cost and availability of raw materials at a distributed scale, projected long-term product demand per region, the ability of a smaller manufacturing facility to adapt to new products and production equipment, and how the latter stacks up against projected savings in transportation and breakage costs.