Integrating solar cells into double-skin facades for futureproof buildings An architectural concept featuring photovoltaic technology for use in retail premises
For this concept, the architects focused on retail buildings, a segment which has not yet fully engaged with the European Green Dealand where behaviours have not really changed. Their priority is still on attracting customers inside through permanently open doors and heated air curtains.
Since architectural solar glazing (or BIPV – building integrated photovoltaics) is still rarely used in retail applications, this concept features a facade element designed specifically for use in retail premises. The active solar glass element combines the latest crystal-clear photovoltaic technologywith a golden metallic film – delivering the perfect solution for tomorrow’s luxury retail outlets.
Not only will shops benefit from the electricity generated by this product, but they will also be protected from overheating thanks to the double-skin facade. The investment cost will be lowered by using the exact same glass element across the entire facade, or even across multiple projects. In fact, it can be ordered in large quantities, with spares kept in storage.
A closer look at the facade reveals multiple layers, the first of which, on the outside, is the glass itself. The second layer is the stripes created by the photovoltaic cells and the third layer is the bright white fritting, specially designed so as not to interfere with solar energy generation. Behind the multi-layer glass module, the building’s underlying steel structure is visible, but only indistinctly so, and changes appearance depending on the play of light and shadow throughout the day and as the seasons progress.
In front of the facade is a white glass panel embedded with LEDs forming the brand’s logo in a powerful post-COP 21 aesthetic that dovetails seamlessly with the luxury sector as represented by this wonderful custom glass gem.
The electrical magic of BIPV glass comes from photovoltaic cells sandwiched between two sheets of safety glass – but this energy-generating glass should not be confused with the conventional photovoltaic panels mounted on roofs.
BIPV solutions are suitable for both the vision and opaque parts of the building facade. In the vision parts, the solar modules provide transparency. They incorporate visible photovoltaic cells whose size and layout can be adjusted in accordance with the architectural project. These modules are generally installed in roofs, louvres, canopies, carports and so on. For the opaque parts of the façade, the modules are opaque and conceal the solar cells while allowing the sun’s rays to pass through. Some of these products can also be produced in an infinite number of designs and colours. Since they are intended for spandrels and cladding, their great advantage is they make the remaining vertical surfaces usable for generating energy. In large buildings, these opaque areas account for about 30% of the surface area.
For both newbuilds and renovation projects, you can find a BIPV solution that delivers an ideal combination of energy efficiency and attractive design that can be deployed seamlessly in building facades. With its SunEwat range of energy-generating glass solutions, AGC Glass Europe is currently the only major glassmaker that offers a complete vision and opaque glass solutions with embedded photovoltaic cells.
BIPV glass for a significant economic and environmental return
In addition to generating power, solar glass can also deliver optimal thermal and acoustic comfort for occupants. The payback period for a BIPV solution with a moderate return is between 6.5 and 10 years depending on the transparency required by the project1.
In addition, BIPV glass boasts environmental performance and efficiency ratings in line with nearly zero-energy building (NZEB) standards, which means it helps meet green building certifications such as BREEAM and LEED. Moreover, BIPV glass solutions have become an essential tool the construction sector can use to meet European Green Deal targets. The goal is to reach carbon neutrality by 2050, but there is an intermediate step: the sector must aim for a 55% reduction in greenhouse gas emissions by 2030 (compared to 1990 levels). This massive challenge is all the more important for the building sector, which accounts for 36% of total emissions in the EU. The only way to achieve this goal is to leverage electricity-generating facade solutions, which are increasingly efficient, affordable and aesthetically pleasing.
1. Depending on its transparency, BIPV glazing has an estimated power of 0.120-0.180 kWp/m2. Based on a southeast facing facade in Brussels that offers a moderate return, the yield should be 650 kWh/kWp per year. Over the course of one year, the facade therefore generates between 78 and 117 kWh (= 0.120 or 0.180 x 650). At an electricity price of €0.20/kWh (European average in the first half of 2021), the output is valued at between €15.6 and €23.4/m². Since the extra cost of BIPV glazing compared to standard glazing is about €150/m2, the payback period is between 6.5 and 10 years.
Your desire to use photovoltaic (PV) solutions may be driven by cost considerations, environmental performance and/or green certifications, such as LEED and BREEAM. In any case, a thorough solar study will allow you to accurately calculate the return on investment and meet the project’s energy specifications.
BIPV solar glass on vertical surfaces
Unlike warehouses, which can easily accommodate solar panels on their roofs, towers in urban areas have very little horizontal space – hence the need to make the most of vertical surfaces by using BIPV solar glass solutions, especially in spandrels. Based on a model of the building and its surroundings, the solar study examines the building’s sun exposure throughout the year, taking into account not only the negative impact of shading by external elements (skyscrapers, objects, trees, etc.) but also the positive impact of reflections (e.g. other glass surfaces). For each facade and the roof, the study indicates the potential power to be installed in kWp and the expected electricity output in kWh. Together with the cost of the installation, this kWh/kWp ratio is a valuable economic decision-making tool. While AGC Glass Europe can support you in the initial approach to a solar study, its specialised engineering partners, such as Sunsoak Design, carry out the in-depth study leading to a comprehensive solar balance.
Photovoltaic glass for the vision parts of a building
Photovoltaic glass modules in spandrels are opaque, with concealed solar cells. But you may be wondering about the usefulness of transparent modules incorporating visible PV cells. They are also suitable for the vision parts of the building: windows, skylights, canopies, carports, etc. The size of the modules can be customised as can the layout of the solar cells.
Since windows are meant to let light in and provide occupants with a view of the outside world, replacing standard window panes with solar glass can lead to discomfort. However, increasing the transparency of the window by reducing the number of PV cells in the solar module might no longer be cost-effective. This means you will have the delicate and difficult task of striking the right balance between comfort and profitability. By contrast, in other parts of the building (e.g. the atrium), where too much natural light causes excessive heat, BIPV solar glass could reduce transparency and save on air-conditioning costs while generating power.
Whether used in spandrels or the vision parts of the building, you can be confident that BIPV solar glass offers enormous economic and environmental potential.
1. Building-integrated photovoltaics glass products with built-in PV cells.
Energy-saving glass combined with BIPV solar glass
Stopray Vision – for the vision part of the facade – is a colour-neutral range of solar control glass products developed by AGC Glass Europe. Thanks to an outstanding selectivity2 of around 2, it combines excellent protection from excessive heat (low solar factor3) with high light transmission. In addition, Stopray Vision features a particularly low Ug-value, preventing heat loss. In both winter and summer, Stopray Vision delivers substantial energy savings.
To further improve a building’s energy efficiency, consider using BIPV solar glass for the spandrels. Stopray Active – part of AGC’s SunEwat range – features photovoltaic (PV) cells embedded behind a Stopray Vision coating and can seamlessly match the facade’s vision elements (windows) to deliver an aesthetically superb project while also generating electricity. This kind of fully integrated facade contributes towards compliance with nearly zero-energy building standards and helps earn credits for green certifications, such as BREEAM and LEED. Moreover, the payback period for the BIPV solution should be less than 10 years, as demonstrated in the article entitled BIPV Glass and Carbon Neutrality. If the BIPV solution is not cost effective for a poorly oriented facade, a uniform appearance can be maintained across the entire project by specifying the same glass panels without built-in PV cells.
Curtain walls: electrical components
In a curtain wall, you must take into account the fact that double or triple BIPV glazing requires some space for the electrical components. The box housing the glazing’s electrical components along with the connectors and cables cannot emerge from the back of the insulating glass unit as is the case in a conventional photovoltaic panel, since that would allow the insulating gas inside the glazing unit to escape. As a result, the small electrical components should ideally be positioned on the upper edge of the glazing unit. Bear this in mind when designing your facade so as to integrate the electrical components seamlessly into the curtain wall.
Building-integrated photovoltaics glass with built-in PV cells.
Ratio of light transmission to solar factor.
Percentage of solar energy transmitted through the glass. The lower the solar factor, the better it protects against heat.
In their proposal for a ‘solar esplanade’, Sunsoak’s architects examined the feasibility of building true solar farms in an urban environment. With that challenge in mind, how big should an urban solar farm be, what technologies should it incorporate and how should it be deployed architecturally?
In the URbAN WAVES concept, a museum and convention centre are built underneath a public space in order to preserve the form and shape of that space. The challenge lies in making it accessible and ensuring sufficient light inside the facility. In this kind of complex, it is the roof which is the visible part, which forms its identity. Access to the roof and the glass canopy over it can be prevented by a recessed area running all around the building, in the form of steps punctuating the esplanade. In other words, this is a great opportunity to incorporate an elegant, large-scale solar farm, featuring ethereal shimmering colours created by a combination of BIPV technologies. We will use three different products from the Active Glass range to create a play of colours and reflections, like one might see rippling on the surface of a lake:
Vision Square: single translucent glazing fitted with visible solar cells or pixels;
Stopray Active: highly reflective active glass in which we’ll see reflections of the sky and city;
Lacobel T Active blue: slightly matt active glass with a smooth, light blue coating, adding a second blue tone to the ensemble.
In that spirit, we designed a project taking the form of a floating plane, punctuated by waves of solar materials and surmounting a lake that will add its brilliance to the multiple reverberations from the glazings radiating out in all directions. The result: an architecturally integrated solar project that will ultimately become an urban design object. It will be right in the middle of the esplanade – replacing the foundation one might typically see – and will act like a mirror, or even a mirage when approaching the museum. Above all, it will be a signal, a totem of the energy transition currently in progress.
The project to upscale renewable energy installations in urban areas is directly linked to the European climate strategy and its 2050 targets under the European Green Deal, a resolution adopted by the European Parliament in January 2020.
Winning industrial competitiveness
SunEwat is our range of BIPV glazing which integrates photovoltaic (PV) cells and thereby generates electricity. “AGC Glass Europe has been marketing SunEwat for almost ten years,” says Daphné Stassen, Project Manager at the AGC Technovation Centre. “Our in-house manufacturing model was not, by its very manual nature, able to withstand the constraints of competitiveness.”
AGC has therefore formed partnerships with companies specialising in the manufacture of PV modules which produce SunEwat exclusively for its needs. This is a win-win situation according to Bassel Glore, Sales Director of Active Glass. “These partners have the necessary automated mass production lines, expertise and skills. On our side, we contribute the sales force and the knowledge of the glass and buildings industries.” In this way, AGC can now offer SunEwat solutions which, in addition to contributing to the achievement of the ZEB (Zero Energy Building), can cover their cost (payback) in less than 10 years. This is something of a novelty in the world of BIPV, a term over which we now prefer the ‘energy-generating façade’ concept.
AGC has therefore formed partnerships with companies specialising in the manufacture of PV modules which produce SunEwat exclusively for its needs. This is a win-win situation according to Bassel Glore, Sales Director of Active Glass. “These partners have the necessary automated mass production lines, expertise and skills. On our side, we contribute the sales force and the knowledge of the glass and buildings industries.” In this way, AGC can now offer SunEwat solutions which, in addition to contributing to the achievement of the ZEB (Zero Energy Building), can cover their cost (payback) in less than 10 years. This is something of a novelty in the world of BIPV, a term over which we now prefer the ‘energy-generating façade’ concept.
Transparent and opaque range
In line with current market trends, the SunEwat range has been given a strong boost with the launch of two lines: one transparent and the other opaque.
“In addition to the existing SunEwat, made up of square PV cells and renamed Square, the transparent range now also features SunEwat Stripe, the cells of which form thin horizontal stripes, offering greater transparency and a more refined aesthetic,” explains Bassel. This glazing can occupy all the “vision” parts of the building and is generally installed on roofs, louvres, canopies, carports, etc. On the other hand, the new opaque range makes it possible to use the rest of the vertical surface area of buildings for electricity generation, since it is intended for spandrels and cladding.
It features three products, all of which conceal cells while allowing the sun’s rays to pass through. “The key here is to reduce as much as possible the loss of light that impacts PV cells,” explains Daphné.
Artlite Active is laminated glazing integrating, in front of the PV cells, a pre-printed film that can depict an infinite number of designs with no colour limitations. Lacobel T Active, to be launched soon, masks the cells with a coat of paint. Its performance depends on the choice of colour. Finally, Stopray Active integrates a coating with the same optical properties (reflection, tint) as conventional Stopray glazing, while enabling the optimisation of light transmission (energy).
A SunEwat solution that is fully operated on a building covers around 50% of its energy consumption.
Market-driven development
All these developments are the result of the electronics and surface treatment (painting, coating) expertise available at the AGC Technovation Centre. “As a researcher, my role is, with the help of my colleagues in the relevant internal departments, to find solutions to the customer needs that our marketing managers report to us,” explains Daphné. “By ensuring that these solutions are achievable and industrially feasible at reasonable and sustainable costs.”
Thanks to these exclusive patented products, AGC is today the only major glass-maker to offer a complete solution, in vision glass and spandrels, for energy-generating façades. “We achieved this result by listening to the market and adapting our offering to the demand using R&D.”
Representing a grass roots movement comprising more than 200 European BIPV value chain partners (ranging from academia to SMEs), ISSOL and AGC Glass Europe handed over a letter to Commissioner Simson calling for more and better recognition of BIPV in EU policies.
Did you know that if all louvres on the European Commission’s Berlaymont building in Brussels were fitted with BIPV, as much as 3.09 GWH/year could be generated? That’s equivalent to the annual electricity consumption of around 800 households! At current electricity prices, this would yield a return of €3,223,240 over 10 years, easily outstripping the original investment.
On top of that, there are many new and innovative applications of BIPVwhereby photovoltaic cells can be embedded in building materials, thus helping to transform the entire stock of EU buildings into a de facto power generator. To be able to achieve the objectives of the Renovation Wave – e.g. renovating 35 million buildings by 2030, creating up to 160,000 additional green jobs in the construction sector, slashing buildings’ greenhouse gas emissions by 60% and reducing buildings’ energy consumption – we must aim for the mass deployment of all kinds of solar applications – including BIPV – not just on roofs but also on building facades.
“To reach EU targets for energy efficiency in buildings and ensure an increasing share of renewable energies we need as much photovoltaic as possible, and roofs are just not enough. We need to look beyond the roof to the rest of the building. That’s where BIPV as a technology for facades comes in.”
NIELS SCHREUDER (PUBLIC AFFAIRS & COMMUNICATION AT FLAT GLASS LEADER AGC GLASS EUROPE)
BIPV can be added to existing building facades by way of aesthetically attractive, non-intrusive renovation. This creates European and local green jobs; more so than with standard PV products. The EU BIPV value chain is ready to contribute and is calling on the European Union to recognise and specifically mention BIPV as readily available solutions in EU policies and in the upcoming revisions of energy-related European directives.
“BIPV’s potential is huge and can replace any conventional building material, even on protected cultural heritage buildings. Incorporating BIPV building materials in new and renovated EU buildings can alone save up to 7 million tonnes of CO2 annually.”
OLIVIER DEMEIJER (MANAGING DIRECTOR OF ISSOL, A BELGIAN BIPV COMPANY)
During the conversation, Commissioner Simson took the time to look at the BIPV samples available in the AGC Glass Shuttle while discussing the importance of the energy transition as well as the transition of the built environment and the important role BIPV can play in this regard.
“We need new innovative solutions like BIPV. To achieve the European Green Deal goals our policies must include different types of solar technologies.”
