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Flexible and artistic – they're not words commonly applied to solar panels. But thin-film technology delivers a more aesthetically pleasing and flexible architectural element than traditional PV panels. Pair them with a lower price tag and it's easy to see why thin films are the fastest growing segment of the solar market.
Thin films are defined by the thickness of the cell and the substrate. While traditional PV panels use crystalline silicon (monocrystalline), thin films are powered with amorphous silicon (noncrystalline), silicon nanocrystals, transition metals, or organic compounds. "The materials and properties differ between these two solar technologies, but the concept is the same," explains Dan Bailey, an energy consultant for Sieben Energy Associates.
While PV panels require racks and penetrations, thin films are laminated to a surface. Their level profile reduces drag, load, and visibility. "Thin films typically come in rolls, are about a quarter of an inch thick, and can be installed flush with the surface," says Scott Shell, principal architect for EHDD Architecture. "This allows them to integrate seamlessly into the architecture."
Thin films have also spawned building integrated photovoltaics (BIPVs), solar cells that are glazed into a laminated glass sandwich. "BIPVs use thin-film technology and apply it to materials that are already used in a building envelope – roofing, glazing, awnings, windows and skylights, or facades," says Bailey.
Because BIPVs are physically a part of your building, they can be integrated into materials that would not typically withstand the weight of a traditional PV panel. For example, a glass atrium would be a great area to add BIPVs. Not only will the glass continue to perform as intended, but you'll have the added benefits of solar power.
"When placed in glass, BIPVs give you dual performance from both daylighting and electricity," says Shell. "The density of cells can be spaced apart to let various light levels through." While the concentration of cells will affect the power density of the panel, the lightweight and streamlined design of BIPVs offers greater placement flexibility.
Traditional PV panels are immediately recognizable – they're large, square, and blue. While their appearance makes a strong statement, it's also a limited one. Thin films have a wider range of applications and can be designed as an eye-catching showpiece or a camouflaged architectural element.
Thin-film panels are particularly attractive for visible roofing applications. "Some people object to the appearance of the standard crystalline panels mounted on racks. Thin film is flush with the roofing material and doesn't have any geometry associated with it," explains Shell. You can also select a roofing color that minimizes any color disparities.
Your roof load, available space, and warranty are also important considerations. Not all roofs have the load capacity to accommodate a PV array. Some owners may also be uncomfortable with the idea of extra penetrations from PV racks. Because thin films are directly applied to the roofing material, penetrations only occur where wiring is needed.
While thin-film membranes may go unnoticed on a roof, BIPVs are ideal as show stoppers. They are often used as a signature design element, explains Shell. High-traffic areas, such as entrances, overhangs, and skylights, are a great way to get people's attention.
"BIPVs are becoming more popular simply because they're a new way of doing it. They're changing the notion of what a solar cell is," says Bailey. "BIPVs are showing that a solar cell doesn't have to look like a utilitarian engineering project – it can have beauty. It doesn't just have to produce power."
BIPVs Aid in Net-Zero
When Integrated Design Associates (IDeAs) purchased a 1960s windowless bank for an office renovation, owner and partner David Kaneda wanted to create a green laboratory. Located in San Jose, CA, the IDeAs Z Squared Design Facility is closing in on net-zero thanks to two sets of BIPVs. When combined, they total a 30kW system that cost $8.50 per watt. The system produces approximately 6.79 kWh per square foot annually.
The large rooftop installation is directly laminated to a single-ply cool roof membrane. Positioned between skylights, the roof BIPVs have no racks or penetrations. Another set of BIPVs was integrated into a shade canopy on the building's south face. Not only does the feature supply electricity, but it provides shade and precipitation protection like a regular glass overhang.
"We wanted to make our building an innovative showcase," says Kaneda. "Everyone's familiar with an array stuck up on a roof. We wanted to find innovative ways to use photovoltaics so people would consider using them in more creative ways."
The 50% Rule
While any type of solar can offset a portion of your electricity load, a silicon PV panel output has a 2-1 advantage over thin films. Thin films generally cost 50% less than monocrystalline PV panels, but they also have half as many watts per square foot. This means that where a thin film array could produce 5 peak watts per square foot, a PV panel will generate 10 peak watts.
With a significantly lower cost than PV panels, thin films bring an affordable option to owners who may pass up solar otherwise. "Anyone considering solar must consider the tradeoff between cost and efficiency," says Bailey. "An inexpensive system might be acceptable if it is highly efficient and lasts a long time. Conversely, an inefficient system may be attractive if it is very cheap."
Funding opportunities for PV panels and thin films are generally the same. As with any type of incentive or rebate program, they are dependent on your area's regulations. It may also be more difficult to acquire a power purchase agreement (PPA) with thin films because of ownership issues. The solar provider typically owns the PV array under a PPA. If your solar is integrated into your building, it complicates the provider's ability to take back the system at the end of the contract.
A Word to the Wise
Although thin-film technology is established, thin films are not standard manufactured products. The variety of materials they can be glazed or laminated into also brings an added level of complexity. This means using thin films, particularly BIPVs, thoughtfully and deliberately. "While they do integrate beautifully into a building, we tend to use thin films more selectively than if we're trying to meet a very large energy load," explains Shell.
A quickly changing market and the lack of mass production can also affect the strength of your warranty. Like other solar panels, thin films have a rated life of 20-30 years. You may have purchased a new and exciting product, but what happens if the company is gone in 5 years? Kaneda experienced this very situation. While IDeAs' solar company helped iron out some bugs in the original installation, shortly thereafter, it went out of business.
"You have to be careful and remember that these technologies are proprietary," warns Kaneda. "If your solar company goes bankrupt, that 20-year warranty is now worthless. There's no support or replacement available."
With all new green technologies, there is always a higher risk level associated with products that don't have established track records, says Kaneda. "You need to go in with your eyes open. As you go through the thought process, make sure to identify a substitute product or company if something doesn't work out in the future."
Thin-film solar applications represent a new wave in green building design. Tucked away on a roof, thin films reduce drag and uplift to minimize your roof load. Placed in glass or a curtain wall, BIPVs can visually represent your company's commitment to sustainability. "Thin films take solar cells out of the engineering realm and place them into a design context," says Bailey.
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Jennie Morton (firstname.lastname@example.org) is assistant editor of BUILDINGS.