Redefining Skylines: BIPV’s Role in Enabling the Era of Net-Zero Homes and Buildings
From static structures to dynamic Energy Hubs: What is Building-Integrated Photovoltaics (BIPV), how does it work, and how is it revolutionizing sustainable architectural design, paving the way to generating energy from every roof and façade
Written by Dafna Granot, Hadar Sharony and Ido Ginodi
Our buildings have always been a testament to human ingenuity, from ancient architectural wonders to today’s modern marvels. But what if our structures did more than stand tall and look impressive? What if they played an active role in our sustainable future? Building-Integrated Photovoltaics (BIPV) offers just that: a seamless blend of design and function, where our buildings take on two roles , serving as both permanent shelters and energy producers. As we strive for a greener future, it’s time to re-envision our skylines. Buildings can be more than static silhouettes against the sunset, they can also serve as dynamic contributors to our energy ecosystem.
Net-Zero Homes and Buildings
To mitigate global warming and support the transition to a carbon-neutral future, many regions have already adopted, or are in the process of creating action plans to deliver net-zero carbon homes and buildings. An effective way to do it is by relying heavily on renewable on-site energy generation, mainly through solar. But can a building generate enough energy to sustain its own needs? Clearly, it depends on the energy use pattern and its potential capacity to generate its own energy. The taller the building, the more energy it is expected to consume. A recent study from the University of Toronto claims that this goal is feasible only in buildings up to 10 floors.
But does this exhaust the potential? We believe that by diversifying the surfaces that are used to harvest energy through PV, (e.g. with solar façades, windows, carports and more), even taller buildings can generate significantly more energy.
Integrating PV into Buildings
Building-Integrated Photovoltaics (BIPV), refers to a photovoltaic element that replaces some of the traditional building materials while simultaneously producing electricity. BIPV is a different approach than the “traditional” PV installation, (which can more accurately be described as Building Applied Photovoltaics, or BAPV) and refers to a photovoltaic system that is applied on the building on top of the conventional construction and roofing.
BIPV can replace any part of the building envelope, though the most common application is roofing-integrated PV. Other common applications are carports, railings, pergolas, façades, semi-transparent curtain walls, and skylights. There are even ongoing developments in PV windows and outdoor flooring that may also present intriguing avenues for further exploration down the road.
Why BIPV?
Before we dive deeper into the technology and how it works, let’s first consider what drives the adoption of BIPV solutions, and the benefit over more traditional solar PV technologies:
- Eliminating redundant materials: BIPV reduces the need for some building materials by incorporating PV systems into the structure of the building itself, such as in the roofing, windows, or façade. This allows for construction savings and waste reduction, as it eliminates the need for both separate, traditional building materials and solar panel systems.
- Aesthetic Integration: With BIPV, architects can integrate solar power technology into building designs with heightened innovation and more aesthetic appeal.. This could foster more widespread adoption of solar power, as BIPV can be designed to blend seamlessly with the overall building appearance.
- Sustainability: BIPV supports the global push towards sustainable practices and reducing carbon footprints. Buildings account for 38% of greenhouse gas emissions worldwide, so maximizing available surface beyond rooftop PV can significantly decrease their energy demand, including the associated emissions.
- Energy Independence: Buildings equipped with BIPV can generate their own electricity, reducing their reliance on the power grid and potentially providing energy resiliency during power outages. For multi-story buildings, the available roof space for PV is usually not enough to provide the energy needs of the entire building, so leveraging other available real-estate with BIPV is the obvious complementary solution. In fact, in many buildings, BIPV is required to attain a net-zero goal.
- Regulations and incentives: Even though the majority of green building regulations worldwide do not yet require BIPV, the demand for on-site generation is growing. This cannot be addressed with rooftop solar alone. Some countries, most notably Switzerland and to some extent France, already have specific incentives for BIPV installations, that are more generous compared to typical PV installations.
Roofing BIPV is dominating the residential BIPV market; Façade installations prevail in commercial buildings
Instead of traditional roof tiles or shingles, equivalent products with an active photovoltaic layer can be installed, combining the properties of a roof with the capacity to generate power. Several companies already offer certain forms of such products, each compatible with a specific roof type according to the preferences of home and business owners in their regions: in the US, asphalt shingles dominate the residential market, while in western Europe it is mostly ceramic and slate tiles. In eastern and northern Europe metal panels prevail.
Commercial buildings also take advantage of roofing BIPV, one of the most notable examples being the Google campus at the Silicon Valley, which features dragon-scale solar roof tiles manufactured by the French company SunStyle.
The selection and quality of BIPV products are growing, with companies such as GAF in the US offering an integrated solar shingle roof, and Autarq in Europe offering solar roof tiles. The cost parity of these products with roof + typical PV installations is within reach and many companies claim to be close to cost parity (10%-20% more expensive).
Façade installations can be custom-made for the modules in the building to blend in with the architecture, while maximizing production. This method is more popular in commercial buildings, notably office and public buildings. Products include opaque claddings of various kinds (usually colored) and semi-transparent curtain walls.
BIPV is typically installed as part of the construction of new buildings, or during a renovation process (e.g., re-roofing, façade renovation). In some cases, a new photovoltaic façade is applied to an existing building over the old façade, giving it a fresh look and adding power generation capabilities. These installations are still often referred to as BIPV, even though they do not meet the technical criteria of replacing construction material.
BIPV technologies and key trends
In the past, BIPV products mainly included standard modules that were modified for integration with the building envelope. The result was usually not very aesthetically appealing and only suitable for a very limited number of buildings. The attempt to impose mandatory regulations for these standardized building products did not yield success and failed to gain market traction.
In recent years, the BIPV market sought to adapt the products to the building’s needs, as technological developments made it possible to produce PV construction materials that resemble traditional materials. All types of roofs, for example, can be made from PV materials without compromising the desired look and feel: from metal roof panels to asphalt shingles, and even ceramic or slate tiles. facades of any texture, color and transparency level are also available, enabling architects to fully incorporate PV into the entire building material while enhancing their aesthetic appeal.
BIPV products are now constructed using different types of solar cells, each having its own advantages and challenges:
- Crystalline Silicon (c-Si) is the ultimate choice in terms of efficiency, which can be as high as 22%-23%. The c-Si cells are usually incorporated between two layers of glass, and the top glass layer is sometimes printed to obtain different colors or mimic other materials (while reducing the efficiency by 10–20% due to suboptimal light absorption). The high efficiency and versatile design made c-Si the prevalent technology in opaque BIPV products, mainly roof tiles and facades (vast majority of the BIPV roofs and ~50% of the BIPV facades). C-si can also be used for semi-transparent BIPV modules, such as curtain walls, canopies and skylights. To obtain partial transparency, cells are dispersed across the glass module, so that part of the light can pass through. The efficiency drops as the gap between the cells widens. In these kinds of modules, the cells are usually visible, and the glass is not colored.
- A-Si (amorphous Silicon) is a thin-film material made of non-crystalline Si layer. Encapsulating a-Si between two layers of glass results in uniform semi-transparent PV modules, where the cells are almost invisible. The transparency level can be adjusted between 10%-90%, and multiple colors can be achieved by adding a colored layer or having the glass printed. A-Si modules are an attractive solution for semi-transparent facades and skylights, but their efficiency is much lower than that on c-Si BIPV modules (usually <10%, the exact number depends on transparency level).
- Other thin-film materials such as CIGS and CdTe are also found in BIPV modules, as they are lightweight and easy to apply on buildings. However, they offer inferior efficiency compared to c-Si. Thus, thin-film based BIPV modules are less common today than the various Si-based options, but still exist in many colors and transparency levels.
- 3rd generation PV materials such as organic PV (OPV) can also be found among the commercially available BIPV products. They offer a uniform look and can come in many colors and transparency levels. However, their efficiency is still low (<10%), and they are less common than a-Si products. Perovskites are also projected to enter the market of semi-transparent, colored BIPV modules in the coming years.
Apart from the cell technologies, improved aesthetics and customization trends led to higher diversification in the BIPV: BIPV modules now come in any shape and size: from small tiles of ~0.2m² to huge façade panels measuring up to 12m². The electrical characteristics also vary widely: the power can be as low as 10W for small tiles, up to ~350W for in-roof large panels, while power density depends on cell technology, transparency level, and color and is usually between 30W/m² and 200W/m². Some modules, especially thin-film-based ones, have high voltages, as much high as 250V. Even among the ‘standard tiles’ maximum STC power, voltage and current ratings vary greatly.
The variety of colors and visual effects featured by many BIPV products can be achieved in several ways. Some of the more prevalent methods include:
- Digital ceramic printing (DCP)- the most versatile method, enables to create any kind of color or design on the panel. Used by companies to achieve unique, custom-made modules.
- Interferential coating- uses a multi-layer coating on the glass to achieve color, with relatively high efficiencies for dark tones.
- Colored foils- the simplest method, with direct integration at the module level.
- Colored PV-active layer- in some 3rd generation PV materials (e.g., perovskites, OPV, DSSC), the active layer itself can be tuned during production to achieve certain colors and transparency levels. Aside from OPV, these products are not commercially available in the BIPV market yet but are expected to be in the coming years.
Towards Solar on Every Building
BIPV can be applied on to any building. This includes both buildings that are common for retrofit installations today (detached & semi-detached residential houses, C&I buildings), as well as applications and segments that, until now, did not adopt standard retrofit installations. This includes:
- High-rise buildings (both residential MDU’s and office buildings) that have insufficient roof area but high vertical facades.
- Private homes and C&I buildings, where owners refrained from installing rooftop solar for aesthetic value.
- Historic buildings in areas with strict conservation-led construction codes.
As BIPV is typically applied in new-builds or during renovations, the potential market certainly includes any building that is going through construction or renovation (especially roof or façade replacement).
In the US residential market alone, there are ~85M rooftops excluding multi-dwelling units, with an average of another 1 million single-family homes being built every year, meaning one million new roofs are installed each year. 80% of these roofs are composed of asphalt shingles. A typical asphalt shingle life span is 15–20 years, leading to 5 million re-roofings/year. This amounts to over 6 million roof installations each year, in contrast to 700,000 retrofit PV installations installed in residential homes in 2022. A mere 10% integration of BIPV during the re-construction or re-roofing process could double the annual the amount of residential PV installations in the US.
While determining figures for the European market are more challenging, it is assumed that the potential is roughly equivalent. With over 50 million detached and semi-detached existing residential roofs, the number of rooftops that require renovation in order to achieve their energy efficiency goals is staggering. In Germany alone, an estimated 500,000 rooftops (across all segments and applications) need to be renovated each year.
While BIPV rooftops dramatically increase the total existing PV potential, BIPV facades are an entirely new, mostly untapped market. Researchers calculate that through the implementation of BIPV on facades, all energy demands of buildings in European cities can be met. Switzerland, for example, estimates the potential from facades alone at 17TWH/yr.
While the total number of BIPV installations so far is hard to assess, as installations are documented simply as PV installations, some estimations do exist for the global BIPV market. These range from 2–5GW/year, with the following regional divisions:
- China: local entities estimate that the current market is 0.5–2GW/y, and project that in a few years it will become a >10GW/y market
- Europe: projected to reach 500MW in 2023 (€1B market), some estimate already 1–2 GW/y today. The growth rate of European BIPV companies is 62% on average. Switzerland is leading, with already 12% of PV installations being BIPV in 2019 (and a steady growth since)
- North America: a sub-1GW market
Though academic estimations for the BIPV market size in coming years are generally conservative, in the range of 4GW/y (~$8B), market research companies have much higher estimations, resulting in $10B-$90B market value by 2030.
Adoption challenges
Despite its great potential, mass adoption of BIPV solar rooftops and facades was very limited until recently, especially outside Europe. Despite vigorous past efforts by numerous stakeholders, including Tesla Solar, BP Solar and Dow Chemicals, the American BIPV market failed to gain traction. According to NREL, Less than 1% of PV installations in the residential sector are building-integrated. Only a few thousands of BIPV solar roofs were installed in the US up to 2022, amounting to a mere few dozens of MWdc. Facades projects lagged with very few installations.
The slow uptake can be explained by a number of factors:
- BIPV technology was still considered immature, paired with the need for customizability resulted in a higher cost gap that was not economically competitive. In many cases, BIPV installations did not even provide a return on investment within the system’s lifetime.
- The visual appeal was lacking until recent years, and different building styles had extremely limited options.
- Safety of the different solutions. The confidence and safety of firefighters and first responders is crucial. While in traditional builds, the hazards were known and the unexpected was always a factor; BIPV introduces new considerations as an additional electric power generator covering the building’s envelope.
- Sales Channels differ than those in the general PV industry, with a tendency to be controlled by building companies, contractors, and architects who may lack familiarity with the BIPV offering on the market and often-times do not possess the necessary expertise of how to seamlessly integrate the products in the buildings.
- Lack of supportive regulation — most countries still do not have favorable regulation for BIPV installations. While some countries are starting to regulate PV mandates, they still do not incentivize BIPV systems. Rather, they require a minimal system capacity that can be easily met with a few panels on the rooftop. Even the leading Green Building standards do not offer additional points for BIPV installations over retrofit, even though BIPV minimizes material use over typical PV installations.
- Trust and awareness — previous attempts left many in the industry skeptical towards the adoption potential, and many homeowners are not aware of new available possibilities.
Why now?
Over the past few years, there have been massive developments in the BIPV industry, leading to steady growth in installations. We believe the BIPV market is at a turning point, poised to transition from a niche application to a firmly established and popular solution in the coming years.
The main reasons for that are:
- Technological advancements that led to the introduction of higher efficiency, better-looking products for all the building segments and materials.
- Cost reduction of products, following the massive PV cost reduction of the last decade, led to BIPV becoming increasingly competitive, closing the gap with traditional roofing + retrofit PV installations in the case of roofs, and lowering the premium over traditional cladding materials in case of facades. Payback times for systems varies, but is often in the range of 4–10 years; an appealing solution compared to traditional roofs and facades, which never generate revenue to return the initial investment required to build them.
- Until recently, most players in the BIPV industry were specialized PV companies or startups, attempting to introduce a new product to the market and gain market share but with limited brand awareness. Recently, two new kinds of players emerged with the power to transform the market:
- Building and roofing companies, such as GAF in the US, BMI across Europe, Creaton in Germany, Ediliance in France, BP2 in Poland, and more. These companies already have established channels with stakeholders and customers for installing BIPV (new construction/renovation). As they introduce new BIPV products into their lineup, they not only address the sales channel challenge but also present the BIPV option to customers planning to construct or renovate buildings, who might not currently be aware such options exist.
- Mass module manufacturers, such as JA Solar, Longi, and Canadian Solar are entering the BIPV market with a variety of new products for roofs and facades. With the cost reduction power and the established sales channel of the solar manufacturing giants, BIPV is poised to be increasingly available to a much broader audience.
The role of power electronics in unlocking the potential of BIPV
As BIPV gains momentum, technical issues need to be addressed for it to tap its full potential. Some of these issues are relevant for all BIPV installations, and some are specific to certain product lines or applications:
- High mismatch between panels: especially in façade applications, where panels cover the building envelope, the panels are positioned in different orientation, tilts, and heights. This results in high imbalance between the amount of sunlight that hits each panel, and consequently the power output. In many cases, BIPV installations involve several types of panels (different sizes, colors and/or transparency levels) in the same roof or façade, which can result in high mismatch if not addressed properly. This could significantly compromise the BIPV system’s lifetime PV production.
- Structural shading: Since BIPV systems are installed on non-traditional surfaces, shading from one part of the building may adversely affect solar protection from other parts of the building.
- Non-traditional electrical characteristics: In the case of solar tiles, individual tiles generate lower output than solar panels. In other cases, mainly in thin-film based large façade cladding or curtain walls, currents can be as low as 1–2A, as opposed to around 250V in solar panels. These challenges require smart solutions to minimize cabling and alleviate electrical installation complexity.
- Complex electrical design: Designing a BIPV system that is integrated into the building envelope is significantly more complex than designing a traditional rooftop or ground-mount PV array. Uneven string lengths and multi-faceted strings can compromise system performance and reduce overall system production.
A two-fold approach is needed to overcome these challenges:
Pairing the BIPV with Module Level Power Electronics (MLPE), such as SolarEdge’s Power Optimizers, can mitigate these challenges. Power optimizers use Maximum Power Point Tracking algorithms to maximize the amount of power each module produces individually, regardless of the weaker performing modules in the string (due to shading, location, or module type mismatch). As façade installations can still be costly, maximizing module-level production is crucial in order to drive the BIPV industry forward.
An example of the role of MLPE in façade installations, first presented at NREL’s “PV Everywhere” workshop in August 2023, is shown here: the office for Environment and Energy in Basel, Switzerland, covered with BIPV cladding of all four facades and paired with SolarEdge’s optimizers and inverters. The mismatch (the gap between the average panel‘s production and the worst panel’s production) is high, even within the same string on the same façade: up to 82% total energy loss and 68% power mismatch!
The details are shown below: the power of the weakest link in the string (blue line) is much lower than that of most of the panels. If not connected through Power Optimizers, production from all panels would have dropped to the level of the lowest-producing one, hence lowering total production by 82%.
In addition to the benefits of maximizing solar production, Power Optimizers offer state-of-the-art built-in safety technology that meets stringent global safety requirements designed to reduce the DC voltage to touch-safe levels in the event of an emergency. Furthermore, Power Optimizers provide high-resolution monitoring at the module-level, enabling faster detection of failures and more efficient troubleshooting.
Designing for maximum production: Proper system design that takes into account inverter sizes, string lengths, and allocation between facades and minimizing cabling can help fulfill the production potential of the building.
Looking at these different use cases emphasizes the benefit of SolarEdge’s MLPE
BIPV Commercial façade and roof MDU project in Brazil (in planning)
- Rooftop typical system: SE33.3K inverter — 85 PV modules and P1100 (2:1) optimizers
- Front façade BIPV: 3X SE9200H inverter — P601 (3:1) optimizer
Roof BIPV Residential Project in Germany
The roof tiles are replaced by PV modules aesthetically fitted into the existing roof structure and color.
Two strings cross multiple irradiance levels with different power modules
- 33 modules 190 watt
- 23 modules 140 watt
- 32 modules 150 watt
- 11 modules 110 watt
What’s next?
SolarEdge is working closely with BIPV partners such as Blachprofil2 (BP2), which uses monocrystalline cells applied on roof elements for residential applications. Their FIT VOLT integrated photovoltaic panels are perfectly visually matched to modular FIT roof panels. BP2 adopts the SolarEdge solution for optimal yield, reliability, and safety of their unique methodology.
Closing thoughts
The future energy is exciting: homes, buildings and campuses on the fringe of the grid will operate as bi-directional nodes on a software defined energy network. These energy nodes will present a ‘stiffened’, more predicable net-load to the grid, all the while optimizing for profit and decarbonization through both optimal local dispatching and strategic participation in energy markets. Nodes of different types (residential, C&I/SMBs, utility scale plants) will be able to interact with each other, opening the door for new business models, including peer-to-peer applications.
A hallmark of this new energy landscape is the Net-Zero Node. Alas, in many cases, Net-Zero Homes and Buildings will require more clean energy than what their roof size can accommodate. While retrofitting a PV/PV+Storage system on existing buildings is the industry standard, there are significant gains to be reaped by integrating these infrastructure products much earlier in the process (BIPV/BI-Storage), towards balancing the ‘net-zero equation’.
BIPV is a potential and promising key to promote a future where “PV from every roof” is a benign, straightforward decision.
These ‘built in’ applications are very challenging in terms of environmental conditions, shading, blockage & multi-facet effects (“the urban jungle”). MLPE is uniquely positioned to perform well under these circumstances, and new technologies need to be developed to unlock the full potential of renewables in this environment
Uri Sadot, Roy Shkoury and Rafael Fleischman participated in the research and analysis for this article.
Sources
- Feasibility of achieving net-zero energy performance in high-rise buildings using solar energy
- Gholami, H.; Nils Røstvik, H.; Steemers, K. The Contribution of Building-Integrated Photovoltaics (BIPV) to the Concept of Nearly Zero-Energy Cities in Europe: Potential and Challenges Ahead. Energies 2021, 14, 6015.
- BIPV cost competitiveness and future developments in Europe, BIPV boost, 2023
- Spring 2023 solar industry update, NREL
- Building integrated photovoltaics: a practical handbook for solar building’s stakeholders, Supsi & Becquerel institute, 2020
- National Survey Report of PV Power Applications in SWITZERLAND, PVPS, IEA, 2019
- BIPVBoost public reports
- Bonomo, P., et al. “BIPV products overview for solar building skin (subtopic 6.3/Building, infrastructure and landscape applications).” 33rd European Photovoltaic Solar Energy Conference and Exhibition. 2017.
- Schweizer Hausdächer und -fassaden könnten jährlich 67 TWh Solarstrom produzieren
