Volume 43, Issue 7 - July 2008
Turning to the Sun
Over the years glass manufacturers and fabricators have been focused on providing products that meet a number of high demands—it keeps out the heat, but lets in the light; resists bullets, blasts and hurricanes; and now often includes a decorative element to boot. Now with the goal of reducing energy usage gaining ground at the forefront of today’s building design and construction (see March 2008 USGlass, page 46) it may soon be expected that buildings not only save energy but also generate it.
Photovoltaic (PV) modules—the solar cells that use sunlight to generate electricity—have been in existence for decades. But today these modules are being integrated into some interesting places—including sunshades and spandrels and even, in some cases, façade and curtainwall vision areas.
Teaching Old Glass New Tricks
Pilkington’s Solar Group has been producing glass for PV panels for about eight years, says account manager Tim McKittrick. He explains that the biggest difference between glass used for traditional versus an active BIPV façade is that the latter requires low-iron, tempered glass with very high light transmission.
Most PV solar cells—the technology beneath the glass that converts sunlight into energy—makes use of crystalline silicone technology (see sidebar on page 44 for more on solar cell technology). “That’s the biggest part of the market for PV at the moment,” McKittrick says.
However, the use of thin film technology is beginning to grow and demand new requirements. “The requirement for that [thin film] is slightly different,” McKittrick says. “You require a conducting coating, and you also need high light transmission.”
“For PV, [you need] low-iron glass with solar transmittance greater than 91 percent and AR coatings to reduce reflection of sunlight,” elaborates Deep Bhattacharya, vice president of development and technology for Oldcastle Glass in Santa Monica, Calif. “For BIPV, transparent-conductive oxide-coated glass has begun to be used.”
Claus Carlsen, head of Finland-based Glaston Corp.’s new solar energy business, explains that low-iron glass naturally provides higher light transmission, which is why low-iron products are the focus for glass companies expanding into solar. “Traditional architectural float is normal soda lime glass, either clear or colored,” Carlsen says. “Low-iron glass is used due to its higher/better light transmission. That way the solar panel has a higher efficiency than if normal soda lime float was used.”
When it comes to PV glass, low iron means high in efficiency.
“The PV panel manufacturer normally specifies heat-treated low-iron glass that is either uncoated, textured or coated, although heat-treated clear is also used in some cases, including as a panel stiffener,” adds Michael Ondrus, director of Perrysburg, Ohio-based Glasstech Inc.’s solar energy systems.
According to Ondrus, there’s another key difference important for PV: careful attention to flatness.
“The solar industry normally needs strengthened glass with tighter tolerances in many areas but especially in dimensional tolerances and flatness,” he says.
“PV glass is laminated and the panel has a lifetime of 25 years,” Carlsen adds. “During this time there should be no de-lamination. To avoid de-lamination it is absolutely crucial that the glass is very flat. This means the tempering process needs to deliver glass where the typical problem zones of tempered glass (edge-kink and rollerwave distortion) need to be eliminated, or almost eliminated.”
Carlsen adds, “As you know from normal laminated applications, a lifespan of up to 10 years without any de-lamination is rare.”
To meet such high tolerances, some companies are providing lines dedicated to solar-geared products—although fabricators say no new equipment is required.
“The emphasis is on equipment that can provide tight tolerances, repeatability, high volume fabrication and low operating cost,” says Ondrus of these solar-dedicated glass lines.
“PV glass manufacturing lends itself well to a high degree of automation and integrated manufacturing facilities,” Carlsen adds. “Although the key processes such as cutting, edge treatment, coating, drilling and tempering are very similar, the scale of the plant is typically much larger and the level of integration much closer to something like automotive OEM.”
When Arch Aluminum and Glass Co. Inc. began producing glass for the solar industry earlier this year, they opted to invest in equipment geared toward this type of production.
“We built all-custom equipment to be able to produce this material in a more efficient and high quality manner. It took a ton of time, effort and resources but in the end it’s working and we are thrilled,” says Max Perilstein, vice president of marketing for Arch.
Once the glass has been produced, it can be fabricated in much the same way as a regular lite.
According to Vince Van Son, commercial manager of Sustainable Solutions for Alcoa Building and Construction Systems, parent company of Kawneer in Norcross, Ga., “The amount of tempering varies with the application.” He notes that PV laminates also can be integrated with insulating glass units, and low-E coatings may be applied if the glass/PV/glass laminate is part of an insulating glass unit.
“The module … is about the thickness and has the characteristics of a piece of laminated glass so anything you can do with a piece of laminated glass you can do with a solar module,” says Steve Fronek, vice president of Wausau Window and Wall Systems in Wausau, Wis. “You can use it as one lite of an insulating glass unit (IGU), you can structurally glaze it, you can put it into a sunshade. But remember, this solar module has wires coming off it, and if it’s going to be used in a vision area for solar control or for view, those wires ideally should come off of the edge. So when you make the IGU out of it you have to make sure you don’t wreck those wires.”
Ah yes, those wires, which provide a new challenge for installers.
However others are getting their feet wet—and glaziers with experience installing electric hardware (see February 2008 USGlass, page 38) may not be intimidated in the least when it comes to these wires. Some experts even say that glass for BIPV can be installed in the same way as traditional architectural glass.
“Wherever glass can be used, a PV panel can be used. It would only be limited by the PV manufacturer’s size limitations, which generally would be coordinated by the architect during the design phase of the project,” says Eric Enloe, marketing product manager of EFCO in Monett, Mo.
That doesn’t mean there aren’t some challenges to placing these panels.
“You have all of the concerns of glazing and glass, things like weatherability and proper support and protection of the edge, but then there’s a whole other list of concerns,” Fronek says.
According to Fronek, many of those concerns revolve around the framing rather than the glass, as it’s through the framing that the wiring runs. For instance, how will the frame be grounded? How will the wiring exit the module or the glazing pocket, and without causing a leak? And, most importantly, how many modules will be hooked together to make a string and how many strings will be hooked together to make an array?
“It’s simple in concept, however, as the size of PV modules changes, so does its electrical characteristics, its amperage, voltage and wattage,” Fronek says. “So that electrical applications engineering can get quite involved if not complicated.”
Fronek recommends involving a systems integrator (SI) early on to coordinate the installation of the wiring with the glazing subcontractor. “The role of the SI is to bring all of these separate components together. That firm would be the primary communication link between the curtainwall fabricator, the module manufacturer, the subcontractor and the utility building inspector and the electrical contracting firm on the project.”
An SI can be valuable in coordinating the two trades that come together of necessity in BIPV.
“Typically it’s desirable that the glaziers and the electrical workers on the project share staging and scaffolding and are properly sequenced so there’s not expensive duplication of efforts,” Fronek adds. “Those trade issues, the sooner they’re coordinated the better. You don’t want a trade dispute late in the job. It’s best if the contract documents address how the trades will work together.”
While a SI may be helpful, the first step should be to seek manufacturers who already have some experience in this area—since now there are more of those out there.
“Contract glaziers should look to learn how this stuff works because it is the future,” says Perilstein. “Contractors should work with people who have had significant experience in the installation side and with manufacturers who have the resources and technical savvy to support these projects long-term.”
V is for View
“Reduced visibility and aesthetics are certainly going to be a challenge with architects and owners,” Bhattacharya says.
“Some designers are just sickened when they see it. [It’s hard for them to] look past the benefits because they see it as having zero curb appeal,” says Perilstein.
Others do embrace the appearance. “Some architects seek to include PV cells in vision areas as an architectural design element and/or to highlight technology and differentiate the building,” says Van Son.
Such was the case for a project supplied by Wausau Window and Wall Systems.
“In our first demonstration project, now more than ten years ago, crystalline cells were used because it was obvious from even a fair distance away that there was something special going on, that there was a statement being made about being high-tech and sustainable and not relying on fossil fuels,” Fronek says. “It made that statement very clearly.”
However, many architects are only now beginning to focus on the aesthetic possibilities offered by a wide array of glass products available today and may not want to make that particular visual “statement.”
“As we have progressed through the last ten years we find more and more architects interested in thin film modules, which appear to be just brown or black glass,” Fronek continues. “They look like conventional glazing and maybe don’t make such a visible statement that there are solar panels on this building.”
Bhattacharya adds, “Creative use of the PV glass, and advanced thin-film solar cells/materials could minimize visibility concerns.”
While the use of the color in the thin films is one such creative approach, other designs call for BIPV in non-vision areas where it can be equally effective.
“To date, the projects we have been involved with, the architect has taken advantage of spandrel areas and roof mechanical areas for PV applications, so the loss of vision area has not been affected,” Enloe says. “Generally speaking, vision area is just as valuable to sustainable design as green power is. If vision areas are going to be compromised too much, an alternate location, like a roof application, would be a better plan, in lieu of a facade application.”
“BIPV systems do not require the architect and building owner to give up or compromise other desired building features,” adds Van Son. “In overhead glazing systems, special PV laminates that still permit light transmission but also lower heat gain can be used in place of conventional glass.”
Yet, in those instances where they are used within the facades, the patterns created by crystalline cells can, in fact, be similar to some of the artistic demands of architects.
“Silkscreened glass and louvered sunshades are very popular design features and they [crystalline cells] create the same interesting interplay of light and shadow,” Fronek says.
While those patterns might in some instances be welcome—there’s a slim chance visible wiring will be appreciated for its “trendy” look.
“When used in vision areas, solar modules have to have acceptable appearance from both sides,” Fronek says. “And many solar modules designed for power generation give no consideration to appearance from the inside … The way the power is exited from the module—standard solar modules would exit from the back and in a vision application that is going to be visible, accessible and perhaps objectionable. And edge exiting modules that are UL-tested are fairly rare in the marketplace.”
How Long Until BIPV is All We See?
“With rising energy costs and greater attention being paid to significant environmental issues (e.g. CO2), increased use of PV glass in the United States is almost certain. Unlike petroleum, solar energy is a renewable source of energy, and is environmentally friendly,” Bhattacharya says.
It’s a benefit that can’t be overlooked with the building industry’s growing emphasis on sustainability.
Enloe adds, “With the growing use of the U.S. Green Building Council’s LEED certification program, I anticipate the integration of PV becoming more prevalent.”
Certainly projects with this technology do already exist, if still in limited numbers.
“Most of the national curtainwall manufacturers have done demonstration projects and are familiar with the design and the applications engineering involved,” Fronek says. “We’ve all incorporated solar panels into our products and some of us have even UL-tested our framing systems.”
The technology is poised and ready to take off, and these experts believe it won’t be long before it does. In other areas of the world, PV is already experiencing a growth spurt.
“Europe was and is still way ahead of the U.S. on the low-E side and they’ll be the same on solar,” Perilstein adds. “But we’re now living in times that we haven’t really experienced before. High gas and energy costs are one thing, but we also have so many people committed to living a more ‘green’ lifestyle. They understand the situations better and are more educated. That will really help grow this trend.”
According to Van Son, “The global annual growth rate of PV is more than 40 percent. In 2007 the number of megawatts (MW) of PV installed in the United States was approximately 230 MW (according to a study by Paula Mints, principal analyst of Navigant Consulting PV Services Program). In contrast, Germany installed over 1,200 MW, even though solar radiation in Germany is roughly equal to that of Seattle.”
Germany has been a leader in PV installation, with 45 percent of the global installed base of PV panels generating power, Carlsen reports. “Other European countries are following the German example and are ‘kick-starting’ the growth through the EU and local subsidy programs,” he says.
“According to recent published information about 70 percent of the market in 2007 was in Europe, mainly Germany and Spain. In part, [this is] due to the feed-in tariff structures making it attractive to install panels,” adds Ondrus.
Of course, growth may be high—but the number of actual completed installations is low overall. “Currently less than 1-percent of Europe’s power is generated using solar systems, so I think it is fair to believe that growth will be very high,” Carlsen says. He says that the PV industry has grown five-fold during the last five years, and predicts it will continue at the same rate.
And while the EU is embracing this technology, projects aren’t unheard of in the United States. “For sure, it’s a very large growth area in the U.S.,” McKittrick says.
“The United States accounts for less than 10-percent currently, though it grew substantially in 2007,” Ondrus adds. “With the rising cost of energy and state solar programs being developed, there is considerable growth potential in the U.S.”
“I believe the United States will experience rapid growth,” Carlsen says. “This growth will be based on PV becoming competitive commercially against coal, oil and gas-generated power without subsidies. The solar power industry believes and plans to reach this within two to three years.”
What’s Holding Back BIPV Adoption?
“We see a lot of interest early in project design development, not only by early adopters but by design architects in all building segments. Unfortunately many times it’s value-engineered out trying to get projects within budget,” Fronek says, adding,
“but the interest is certainly widespread. As more and more people become familiar with the technology involved, and as more manufacturers in the solar panel business get interested in BIPV applications, making more products available, I think you’ll see it becoming more cost-effective.” According to Van Son, “System costs can vary widely depending on the PV technology selected (thin film or crystalline), the amount of customization involved with the PV laminate and curtainwall, and the power density.” However, he adds that many other cost elements—including electrical design, engineering, interconnection equipment and metering systems—are relatively fixed regardless of system size. But perhaps BIPV is more cost-efficient than one might think, if the end-user is looking at the “big picture.”
“Many people naturally recognize first cost, but not all understand the net cost of a given BIPV system,” he says. For instance, Van Son says that the value of the energy produced and the installed cost of building materials displaced by the system need to be considered when determining the net incremental cost of a BIPV system. In addition, there are financial incentives being offered today to promote the use of PV technology. Among those incentives is an investment tax credit equal to 30 percent of the cost of the system and accelerated depreciation provided by the federal government. Van Son adds that some utilities and state and local governments also provide benefits to system owners.
“These systems are already fairly cost-effective in the subsidized environment that exists in many European countries,” Fronek adds.
With further development of the available technologies, costs are expected to decrease.
“Technology advances should address the cost and size issues over time,” Bhattacharya says.
In addition to cost, design flexibility is still a limit in some areas, although, as McKittrick notes, “It’s a fairly new technology.” Because it’s a new technology, there are still a number of limitations being worked out, and cost is only one of them.
“The largest part of the market is crystalline silicone and that is not transparent. So you’re only looking at a small part of the market that lends itself to BIPV,” McKittrick says.
And although everyone seems to be jumping into this new field, the solar cells themselves are available in limited supply.
“The limiting factor keeping supply lower than demand will most likely be manufacturing capacity, at least in the near future,” Carlsen says. “When PV power reaches the competitive threshold, demand will increase to another much higher level.”
As with any new trend where companies are working to quickly meet demand, businesses appear and disappear with regular rapidity. According to Fronek, “Reliable sources of supply of solar modules and balance of system components have limited market growth.”
In addition, some glass companies have found themselves limited by the size of the solar modules available.
“The limit in the size is from the actual module manufacturers’ equipment,” McKittrick says. “At the moment most manufacturers will have a size of about 4 by 5 feet.”
Bigger sizes are starting to show up on the marketplace, though. McKittrick says he has come across panels as large as 7 by 8 ½ feet.
As far as designs go, the wiring aspect of the systems also can be limiting for the designer tackling his first BIPV system. “Many architects are simply not aware of the design implications associated with the electrical performance characteristics of a PV laminate,” says Van Son. “If an architect wants a certain number of PV laminates then the output of the laminates may need to be customized to meet electrical constraints. In some situations, a few faux cells or laminates may be necessary to resolve both technical requirements and aesthetic design goals.”
If this technology does continue to spread in applications, then the expertise will follow.
“I would say that education is the key to the future of PV application,” Enloe says. “When you have knowledgeable contractors and manufacturers involved in a project, who are willing to coordinate efforts, there is usually nothing to keep the project from being successful.”
Dissecting Solar Cells
According to information from SCHOTT Solar in Roseville, Calif., crystalline solar technology uses roughly 0.3-mm thick wafers made of semiconductor material silicon that are processed to convert sunlight hitting them directly into solar power. To make this power accessible for use, a series of solar cells are connected to make up “series strings.” On the sunward side, a highly transparent solar glass lite protects the cells, while the underside may take the form of an insulating film or a second lite of glass. According to SCHOTT, solar cells are enclosed in these self-contained glass units in order to protect them from the environment.
A connection socket picks up the direct current generated by the cell. Several modules are connected together via cables, which link them to the inverter, the device that converts AC to DC and then feeds the energy into the power grid.
“However,” Fronek adds, “the thin film modules of either morphasilicon or cadmium telluride are becoming much more popular. The crystalline cells are the ones that look like solar panels. The thin films just look like dark glass.”
Thin-film technology involves fixing an active semiconductor film onto the substrate. According to information provided by SCHOTT, silicon is a natural semiconductor and is most suitable for thin-film technology. Amorphous silicon has no crystalline structure and so can be vaporized in ultra thin films on glass, for example.
Solarbuzz LLC, solar industry consultants in San Francisco, note that crystalline silicon solar cells make up 93 percent of market share, with comparatively newer—and more expensive—thin film technologies making up the remaining 7 percent.
According to Vince Van Son, commercial manager of Sustainable Solutions for Alcoa Building and Construction Systems, parent company of Kawneer in Norcross, Ga., “Thin film technology that is less efficient at converting sunlight into electricity and has roughly half the power density (Watt/unit area) of crystalline cell technology and costs less per square foot—although PV laminates are priced in terms of their capacity (dollars/Watt).”Either of these technologies can be used in façades or curtainwall.
“The solar modules that can be used in vision glass areas … need to be semi-transparent, with either crystalline silicon cells with spaces between them in rows and columns, or thin film solar modules that have a laser-etched degree of transparency to them so you can actually see through the thin film almost like a screen or a mesh appearance,” Fronek says.
The Three Kinks of Solar Energy
“Photovoltaics (PV) is only one segment of the market,” says Michael Ondrus, director of Perrysburg, Ohio-based Glasstech’s solar energy systems.
Solar thermal systems use sunlight to heat water or to provide space heating to buildings. According to the Department of Energy, concentrating solar power (CSP) uses different kinds of mirrors to convert the sun’s energy into high-temperature heat. The heat energy is then used to generate electricity in a steam generator. CSP’s relatively low cost and ability to deliver power during periods of peak demand mean that it can be a major contributor to the nation’s future needs for distributed sources of energy.
“CSP, including parabolic trough technology, is poised for substantial growth in the Southwestern region of the U.S.,” Ondrus says.
Even by narrowing it down to PV, there are still subsets.
“In general when people refer to building integrated (BI) PV there are three subsets within that broad category,” explains Steve Fronek, vice president of Wausau Window and Wall Systems in Wausau, Wis. “There are roof-mounted PV arrays in which the modules are installed into racks that are attached to the roofs or even ballasted into the roofs. There are of course off-grid buildings … that aren’t on the electrical grid that are powered by PV arrays. And then finally there are façade-integrated PV installations which can either be in skylights or slope glazing or in vertical curtainwall and sometimes even in exterior ornamental elements such as sunshades or trellises.”
Tiger Woods Powered by Sun—His Learning Center, Not His Swing
California-based architectural firm Langdon Wilson designed TWLC to be powered by both a rooftop solar array and also a building integrated photovoltaic (BIPV) curtainwall. Culminating a four-year construction effort, achieving TWLC’s desired look and the BIPV system’s proper performance demanded close collaboration between all the building team’s members. Designed by Solar Design Associates (SDA) in Harvard, Mass., and installed by The Carvist Corp. in Placentia, Calif., Wausau Window and Wall Systems in Wausau, Wis., engineered and manufactured TWLC’s energy generating curtainwall system. According to SDA, the BIPV system should produce 3,800 kilowatts of energy per year.
To span the 21-foot-high by 65-foot-wide opening, the building team selected Wausau’s SuperWall system using photovoltaic (PV) modules from SCHOTT North America Inc. The vertical mullions that fully enclose the building’s structural steel were fabricated to integrate the wiring of the PV modules. Wausau research and product development manager Tom Mifflin says that the project’s BIPV curtainwall was tested and certified for safety by Underwriters Laboratories Inc. and also complies with the seismic requirements of California’s building code.
The SuperWall system was carefully sequenced and shipped “knocked-down” in 11 vertical ladder frames for The Carvist Corp. to accurately assemble the UL-listed system on-site. Each framing unit contained five lites and, due to the curtainwall’s sloping and splayed design, each lite varied in size. The lites also varied in opacity and power-generation: the top panels of the PV array produce 72 watts each with an opacity of 5 percent, while the lower panels offer 25 percent opacity and produce 60 watts of energy. The bottom and largest lites in the framing system are clear vision glass.
The 35,000-square-foot, $25 million facility opened in February 2006.