The Glass Electric
Even as the world gets greener, global power demand is growing, pushing renewable forms like solar energy into the mainstream. Meanwhile, buildings continue to top the list of power guzzlers, consuming 40 percent of world demand. As architecture moves forward, it will become increasingly important to not only use less energy, but to produce it. Aaron Seward investigates the promise and pitfalls of building-integrated photovoltaics, and the hurdles that remain in the way of architecture’s future.
When the global glass industry convened in Tampere, Finland in June, the top item on the agenda was the coming wave of solar power—glassy arrays spanning the desert and crowning rooftops. But architects in the audience took note of one prophet in particular: Lèon Glessen, the CEO of Scheuten, a leading electric glass producer based in Germany. Office buildings, he pointed out, are notoriously wasteful, being occupied only five days in a week, and just eight hours a day. Factor in lunch breaks, sick time, and vacation, and they’re used about 12 percent of the time. These are primarily glass-clad structures, often 800 feet tall or higher, standing vacant most of the time: a vast opportunity, in other words, to generate solar power.
Over the past decade, the architectural glass industry has made huge strides in improving the material’s thermal and sun-control performance. Its next step is the grail that Glessen went on to promote: energy production. Up until this point, creating buildings with energy-producing solar cells integral to the design—known as building-integrated photovoltaics (BIPV)—has remained something of a chimera. On paper, BIPVs open the way to elegant, carbon-neutral architecture. In practice, however, they never seem to generate much power, usually only a fraction of a building’s overall demand. And aesthetically, today’s clunky panel systems leave much to be desired. “One limitation of many of the solar products is that they come in only standard sizes,” explained Michael Ludvik of facade consultant Dewhurst MacFarlane & Partners, “which can make paneling an actual facade tough.”
The game is slowly changing, however, thanks to advances in solar technology. BIPVs come in two basic forms: crystalline and thin film. The crystalline variety is composed of silicon, a semiconducting material, which is typically fabricated in five-inch squares that are .012 inches thick. These squares are then wired together and laminated to glass to create modules that can then be used in architectural applications. The thin-film variety involves spraying a fine layer of semiconducting material to a substrate of glass, though stainless steel and plastic can also be used. Both technologies have their pros and cons. Crystalline cells—by far the most commonly used—can be combined more flexibly to create a wider variety of panel dimensions. They are also more efficient electricity producers than their thin-film counterparts. On the other hand, crystalline cells are more expensive to produce and wasteful of material—electrical current is only produced on the surface of the semiconductor; the rest of the .012-inch thickness is only needed for structural support during manufacturing. Thin film, which is gaining market share, offers the benefit of a sleeker look. The material can also be etched away from its substrate with lasers to allow light and views to pass through.
The majority of BIPV projects completed to date are in Europe and Japan, where lavish government incentives and strong public support have made fertile ground for such systems to be developed and implemented. Noteworthy examples include the Solon Headquarters in Germany, designed by Schulte-Frohlinde Architekten. Solon, a solar-panel manufacturer, outfitted its 300,000-square-foot facility with a BIPV canopy and array that has an output of 210 kWh, producing 15 percent of the electricity needed for its administrative functions. The company made the canopy’s 1,000 panels out of crystalline wafers laminated to glass. They ring the sloping grass roof and provide sun shading as well as power generation.
A second notable project with a BIPV canopy is the Kanazawa Municipal Bus Terminal in Japan, designed by Taiyo Architects. As opposed to a crystalline system, here the architects specified a thin-film product from Suntech called See Thru, which is five percent transparent and resembles tinted glass. With 3,000 panels covering 32,000 square feet, Kanazawa’s array produces 112 kWh, saving the terminal 86,465 kilowatt hours annually.
BIPVs have made less of an inroad in the United States. This is ironic, considering that the practice got its start here in the 1970s, when solar electric and hot-water panels began sprouting on south-facing roofs. While there are many reasons that the U.S. has fallen behind, experts seem to agree that the principal culprit is code requirements. In the U.S., as in Japan and Europe, BIPV hardware must be tested by a publicly registered laboratory. In Europe and Japan, however, once that piece of hardware is certified, the manufacturer can make minor changes without having to go back for more testing. Not so in the U.S. And, until very recently, there has been only one venue for testing: Underwriters Laboratories (UL).
“The most significant barrier to market penetration in the U.S. is UL testing,” affirmed Steven Strong of Boston-based Solar Design Associates. “UL says if you change anything, you have to come back to us and we’re going to retest your hardware. They have killed more projects than I care to list.”
Another factor that makes BIPV less attractive financially in the U.S. is a lack of what are known as feed-in tariffs, which give developers strong incentives for pursuing the technology by basically offering cash to feed energy back into the grid. “We have one hand tied behind our back,” said Robert Heintges of facade consulting firm R.A. Heintges Associates. “In Europe you can sell the electricity back to the power company at four times the cost.”
As a result, the BIPV projects that do wind up getting built are generally those with long lead times and deep-pocketed, idealistic clients. And considering that BIPVs are generally not as efficient as the plain-vanilla roof systems, since they don’t always wind up in the optimum orientation to the sun, they typically are requested by clients who are looking for a very visible indicator of their dedication to sustainability—a green billboard.
Such was the case at the Lillis Business Center at the University of Oregon in Eugene, completed in 2003. Designed by SRG Partnership, the project features a 65-foot-high, south-facing glass wall outfitted with crystalline wafers. The architects adjusted the density of the wafer grid so that it is more tightly packed at the top, reducing glare on the interior, and more loosely filled toward the bottom, maintaining a good degree of transparency. The wall generates only about 6 kWh, but it is tied to a skylight system of the same make and to standard PV arrays mounted on the mechanical penthouse, for a total of 45 kWh. All told, the project’s PVs make up 10 percent of the building’s energy usage.
Perhaps the highest-profile U.S. project to date is the Renzo Piano– designed California Academy of Sciences in San Francisco. According to Michael Wilson of Stantec Architecture, the architect of record on the project, a photovoltaic canopy was not part of the original concept, as Piano did not think the cells would complement his design. But in 2003, after looking at the quality of the solar glass available, he changed his mind. More than 700 four-by-six-foot glass panels embedded with crystalline photovoltaic cells ring the academy’s 197,000-square-foot roof—the largest such installation in the U.S. The system was expected to generate 213,000 kWh per year, providing up to 10 percent of the academy’s electricity need. During September 2008, its first full month of operation, the canopy generated 850 kWh of energy per day, putting it well on target to meet its annual goal.
BIPV is still kicking in the U.S. residential market as well. The National Association of Home Builders’ 2009 New American Home, its annual showcase of construction technology, features a 10.64 kWh photovoltaic system integrated into a trellis and awning structure that shelters a poolside cabana. The BIPV system features Sanyo solar cells that use a hybrid crystalline/thin film technology to generate electricity from both the front and back of the panel, turning the company’s standard 200-watt panel into a 260-watt panel. It is expected to generate the home’s estimated annual consumption, powering the lights and electrical appliances, and even heating the pool.
The harsh realities of working with BIPVs in the U.S. have not stopped the architecture profession from dreaming big. While current technologies account for only small portions of buildings’ electricity demands, increasing efficiencies in both photovoltaic output and building energy usage is expected to eventually close that gap. Kiss + Cathcart’s design for the hypothetical 2020 Tower gives a glimpse of what this future might resemble. Project engineer Arup found that a tall building in 2020 would consume an average of 60 kWh per square meter per year, significantly less than the 100 kWh that the most efficient buildings of this type use today. Since tall buildings do not have much roof area, the architects had to work with the vertical surfaces. They increased the ratio of facade area to floor area, determining that a 60-foot-deep building could generate all its energy on an annual basis from a BIPV facade independent of orientation.
The consensus is that in most countries solar will reach grid parity—meaning it will cost the same to produce as conventional sources—within five years. But even with the status quo, there is a strong argument for incorporating PVs into buildings. “What I like about BIPV is that if you are already putting up a glass structure, you’ve already paid for much of the hardware that you would need to support a solar cell,” said Paul Stoller of environmental consultant Atelier Ten. One way or another, solar will soon hit the mainstream, and those who have turned their backs on the technology might look rather like the Luddites of industrializing England. Surely architects will know better.
Aaron Seward is an associate editor at AN.
Solar panel manufacturer Solon’s headquarters in Germany, designed by Schulte-Frohlinde Architekten, produces 15 percent of the electricity needed for administrative functions through its BIPV array.