Many green architects and builders envision a day when the majority of buildings support, rather than damage, ecosystems even as they serve their occupants and intended purposes. Buildings that emit clean water and improve habitat for native animals and plants. Buildings that produce clean power rather than siphon energy from power plants that burn fossil fuels.

In an age of global warming, the ability to generate clean energy is high on that wish list, and no technology currently produces cleaner power than photovoltaics – solar cells made from semiconductors like silicon that transform sunlight into electricity. Photovoltaics, or PVs, produce 20 times more energy in their lifetime than needed to make them, and produce that energy without emitting a wisp of greenhouse gas or radioactive byproduct.

But getting PVs on buildings has been a difficult task. Since the 1960s, when solar cells cost $1,000 per peak Watt (dollars per peak Watt is the common way of pricing photovoltaics), PVs have been associated with high costs and, as one architect put it, “Darth Vader landing craft”-like mounting structures.

Things are changing. First, prices for the PVs themselves have been continuously dropping from that initial $1,000 per Watt to an installed cost of $6 to $7 per Watt today – a price that is already cost-competitive in off-grid applications – and will continue to drop in the coming years. And costs are reduced further by government incentives and programs such as “net-metering,” a program now operational in 23 states that obliges utility companies to buy power from consumers who produce a surplus through their solar arrays. Secondly, a new breed of PV’s have been integrated into the same materials architects are used to working with such as curtainwalls and architectural standing seam roofing modules, thereby replacing regular materials and their related costs while taking on a sleek new look.

These new building-integrated photovoltaics, or BIPVs, are a key part to creating buildings that provide clean, high-quality power at the point of use.

The Cost Problem

In a small New York University classroom last Earth Day in New York City, solar energy expert Steve Strong was stretching his words out for emphasis as he addressed architects and designers interested in BIPVs. “How cost effective is your marble lobby, your granite facade, your elaborate landscaping?” he asked. “None of these things are put to the cost return investment test. They are included by design teams because they are a part of the building’s character.” He flipped to a slide showing a building glistening with BIPVs that have been integrated into the glass facade. “It should be the same with photovoltaics.”

According to Strong, president of Solar Design Associates, a Harvard, MA-based architecture and consulting firm that has extensive experience working with photovoltaics, architects who are designing buildings for clients interested in an environmental image should view photovoltaics as they do equally expensive materials such as marble – something that adds to a building’s character. “Architects that want to be with the current trend in green design often get into photovoltaics for the wrong reasons and find they get caught in the chasm of return on investment. They are taking the wrong approach.”

Looking for a fast payback on a photovoltaic system is, at least for now, the wrong approach. As some curtainwall systems can cost over $100 per square foot, BIPVs more often than not have payback periods that stretch past two decades. Although some projects are earning far better ROIs, they are usually in areas that have high utility rates and are blessed with high amounts of solar irradiation. In general, electricity generated by PVs costs around $0.30 per kW, compared to the average $0.08 or $0.10 per kW of sources derived from fossil fuels. For this reason, experts like Strong urge architects to first make their buildings energy and resource efficient before looking at PVs as a way to become more environmentally sensitive.

But there are some compelling reasons why architects and builders should be working with the new technology now. “Innovative architects are beginning to make PVs integral to their design, to use them as signature elements,” explained Strong, citing as an example Four Times Square, a new office tower in New York designed by Fox & Fowle Architects that contains photovoltaic spandrel panels. (Kiss + Cathcart, a New York-based architectural firm and a well-known BIPV expert, was brought in to assist on the project.) “These firms are integrating PVs because it is a highly visible statement of the architect’s and the client’s commitment to the environment,” said Strong.

As PV prices come down to competitive levels, as they are projected to do over the next five years, these forward-thinking architects will be ready to handle the projected increase in clients interested in PVs. In fact, the Solar Energy Industries Association (SEIA), a national trade organization for solar energy companies, reports that the BIPV market is growing 30% per year.

BIPVs also displace conventional building materials, “And that gives you a credit for the material you don’t have to purchase,” explained Strong. “You also get a credit for the labor to install those same materials.”

Protecting, or Even Replacing, Roofs

PV systems laid out on top of roofs can provide extra protection and insulation as they generate green power or can directly replace roofing structures and even open up daylighting opportunities.

On the sun-drenched roof of the Mauna Lani Bay Hotel and Bungalows in Hawaii, 10,000 square feet of photovoltaic panels are fitted snugly together, gathering up to 100 kW of power from the sun. The installation is five times larger than any other rooftop project on the island to date and is the largest hotel PV systems in the world. What’s most notable about the installation, though, is not its size but rather that it takes solar power one step beyond a simple roof-mounted installation and into the realm of BIPVs.

The product on the Mauna Lani Bay Hotel is the PowerGuard system, a lightweight, patented roof tile assembly manufactured by Berkeley-based PowerLight Corp. that combines PV modules with insulating foam. When the individual, 4- pounds-per-square-foot PowerGuard modules are interlocked to cover a designated surface area (no roof penetrations are necessary), they serve double duty by providing extra insulation where buildings need it most – the roof.

“We’re adding value to the roof,” said Daniel Shugar, PE, executive vice president of PowerLight. “We’re doing good things for the membrane as well as providing PVs. The insulation not only keeps the building cooler but also protects the roof membrane from thermal shock and ultraviolet degradation.” According to Shugar, roof membranes that usually tire out after 10-12 years can be preserved twice to three times that length with PowerGuard.

According to Shugar, by providing R-10 insulation and membrane protection as well as solar power, PowerLight is targeting those that want to use BIPVs but want it to be cost effective. “We have come up with a pre-engineered system where the engineering costs and detailing are very minimal, while our lead time can be as low as two to eight months,” explained Shugar. “And because there’s more sunlight on roofs of buildings, you increase harvest and reduce problems with shadowing and exposure, while keeping the system in an easy to maintain area.” And architects approve of the system, he added, because of its sleek profile and compatibility with conventional construction materials.

For the Mauna Lani resort in Hawaii, where electricity rates and cooling loads are high, the system was a natural choice. It is estimated that hotel will receive a 23% ROI for the turnkey project. PowerLight often works with different manufacturers of solar cells to get the best performance for the specific project; in this case, the company used PVs from ASE Americas Inc., a manufacturer in Billerica, MA.

Other projects have replaced the entire roof with BIPV material. For instance, a building on Riker’s Island, NY, designed for the NYC Department of Sanitation by Solar Building Systems of Cape Charles, VA, features 216 translucent PV modules that replace a standing seam roof. The modules, supplied by Atlantis Energy Inc. of Colfax, CA, allow 17% light transmittance into the building while generating electricity that directly offsets power produced by a diesel generator.

Some projects have even integrated heat-recovery systems into BIPV arrays. An Applebee’s Restaurant in Charlotte, NC, features a 1.7 kW BIPV array that replaces part of the roof above the seating area. Designed by Innovative Design, also based in Charlotte, the installation has been integrated with a heat-recovery system that uses waste heat from the array to preheat water.

According to Gary Bailey, principal at Innovative Design, the system did not cost significantly more than regular roofing and produced a favorable payback by virtue of the electricity and hot water produced. The project earned a 0.1 year payback with state tax credits, even without which it would have earned a 4 to 7 year payback. To insure that the client would continue to incorporate the BIPVs into new projects, his firm designed the system to be easily replicable: “In these kinds of buildings that are built more or less the same, every component is already thought out,” said Bailey. “So we designed this system so that the costs and installation were always the same, so you wouldn’t have to re-engineer it every time and re-educate the contractor. This kind of repeatable design is going to get BIPVs into buildings.” As evidence of this, McDonald’s has already contacted the firm to find out more about the project

Other BIPV products are being introduced by some of the largest architectural building material suppliers: Kawneer Co. Inc. of Atlanta, one of the world’s largest manufacturers of aluminum building products, has teamed up with Solarex, a manufacturer of PV modules, to produce the 1600 PowerWall, a BIPV product that substitutes directly for spandrel panels, glass, or other materials in vertical curtainwalls or sloped glazing systems. In the new Center for Environmental Sciences and Technology Management (CESTM) at SUNY Buffalo, designed by Cannon & Associates of Long Island and completed last year, Kawneer’s 1600 PowerWall system was used to fit 100 Solarex MSX120 modules into the building as sunshades. It was also used to frame a canopy at the entrance to the Georgia Tech Aquatic Center (see the March/April issue of ED&C to learn more about the larger PV array on the roof of the Center).

Pilkington Solar Interna-tional, a subsidiary of Pilkington plc, one of the largest suppliers of architectural glass in the world, has supplied over 100 projects around the world with its BIPV facade product named OPTISOL. In Berne, Germany, for instance, the company is supplying over 100,000 square feet of BIPV glass for a large skylight, and will soon supply Sun Microsystems with BIPVs for a clock tower facade on a new building scheduled to be built soon in the U.S.

The curtainwall products, like most BIPVs, are not overly difficult to install. “All it takes is a little up front coordination with the electrical contractor,” said Richard Stokes of Custom Walls and Windows Inc., a curtainwall and window installer in Jessup, MD. Stokes helped put together a BIPV curtainwall by Pilkington at the GreenTech demonstration building at the National Marketplace for the Environment (NMFE) conference in Washington last year. “It’s no more difficult than when you hook up automatic doors. You just have to coordinate everything up front, instead of waiting to see what happens in the field.”

Architects interested in using photovoltaics do have to sort through the advantages and disadvantages of each type of PV, as competing companies use different techniques to manufacture the individual cells: the two main types available are crystalline cells, which have a blue, iridescent sheen, and amorphous silicon, which has a dark, flat color. Some manufacturers, such as British Petroleum subsidiary BP Solar, have even begun to color their cells (although this does produce a small drop in efficiency).

Many manufacturers are looking to the amerphous “thin-film” photovoltaics to make BIPVs even more attractive to architects and designers. Thin-film photovoltaics are made in a process very similar to that used for tinted glass: photovoltaic material is deposited on glass or metal, and can be then etched to allow light to pass through for glass curtainwall and skylight applications. The end result is a panel that looks very similar to tinted glass. The Four Times Square project, for example, will feature thin-film-based panels supplied by Energy Photovoltaics Inc. (EPV) of Princeton, NJ. EPV offers four standard PV plates laminated onto a single substrate up to a maximum size of 4 x 8 feet.

BP Solar markets its own line of high-tech thin film under the “APOLLO” trademark, and is actively targeting BIPV installations. And Solarex has recently introduced its Millennia line of thin-film modules that can be configured with architectural-grade bronze-anodized extruded aluminum framing, double-glass frameless laminate, or in single glass plates. The modules have a 10-year warranty and meet UL and CEC requirements.

Solar Cells Inc. of Toledo, OH, also produces a thin-film module for architectural application. And PV industry heavyweight Siemens Solar Industries of Camarillo, CA, is set to release a new thin-film product this month.

Many manufacturers view thin-film as an ideal product for building integration: “There’s a definite aesthetic advantage to thin film, so it gives us another tool to go to BIPV market.” said Clay Aldrich, manager of marketing and communications for Siemens. “Of course, we still have to make economics work, which is why we’re investing so heavily in the new technology. It will give us an advantage down the road.” Although thin-film is less efficient than crystalline cells (sometimes by as much as half), it is also cheaper, with prices around 1/3 less than the other more material-intensive methods of production.

BIPVs in Residential Roofs

Interesting developments in BIPVs on residential rooftops are taking placing in Sacramento, CA. For the last five years, local utility Sacramento Municipal Utility District (SMUD), has been conducting one of the world’s most innovative programs to get photovoltaics on consumers roofs. Over 420 systems have been installed on the roofs of utility customers who have been paying an extra “green fee” (approximately $4 more a month on their utility bills) to have SMUD install the system on their roofs and supply them with solar energy. SMUD thereby gains a distributed power system, and consumers get the ultimate in green power at reasonable rates.

The program is progressing, however, in two ways: it is now helping customers to actually buy the systems through subsidies, and it is beginning to use more BIPVs in the rooftop installations. Atlantis Energy Inc., for example, has recently agreed to supply the SMUD program with a unique product called Sunslate, a concrete/fiber slate base tile with a PV unit laminated on top. The tiles, which install just like regular roofing tiles (using galvanized nails and 1- x 2-inch battens), has gas-tight connectors that wire each tile to its neighbor, creating one large PV array. Connection to the grid – which involves wiring the tiles to an inverter and the inverter to the main house panel – can be performed by the same electrical contractor wiring the rest of the house.

This summer, over 50 residential homes will have 3 kW Sunslate systems installed, for a cost of $7,000 each after subsidies. That comes out to approximately $2.35/watt, which, when wrapped into a homeowner’s mortgage, costs less than the typical monthly electric bill of a conventional utility hook-up. Although subsidies will decrease over the coming years, SMUD officials estimate that the cost of the photovoltaic products will drop just as quickly, keeping the cost to the end-user at a reasonable two and half dollars per Watt.

According to Steve Coonen, vice president of business development for Atlantis, one of the main reasons Sunslate hopes to be popular among architects and builders is because it looks similar to regular cement tiles, which in California cover the majority of homes. “Builders are a very conservative lot. Their concerns are warranty, system performance, ease of installation, and most importantly, that the product doesn’t change the look, or ‘curb-appeal’ of the building,” he said. “We’ve met all these concerns with Sunslate.”

Another innovative photovoltaic roofing tile is manufactured by United Solar Systems Corp., or Uni-Solar, of Troy, MI. The company encapsulates amorphous cells in weather-resistant polymers and then binds them to asphalt shingles as well as structural or architectural standing seam roof modules.

The shingle product, dubbed PV Shingle, has been recognized by Popular Science and Discover magazines for its innovative design, and even got a boost from President Clinton, who waved one about while announcing a new government initiative for energy-efficient building earlier this year. The PV Shingle is an 86- x 12-inch tile that is used to build 1kW to 4kW arrays on residential and commercial building roofs. The Southface Energy and Environmental Resource Center, a model green home in Atlanta, has a 2 kW grid-connected PV Shingle system on its roof to demonstrate the product’s potential to visitors.

According to Larry Slominski, manager of marketing and business development for Uni-Solar, although a system the size of Southface’s can cost upwards of $20,000, in certain states and with national incentives, that cost can drop below $10,000. “And that cost should be considered in light of the fact that it provides back-up power during outages, not to mention the environmental benefits of using solar power.”

Uni-Solar’s architectural standing seam product has been used in an energy-efficient townhouse built by the National Association of Home Builders as part of the organization’s 21st Century Townhouses project in Bowie, MD. There, the solar cells have been laminated onto 19-foot metal roof panels to form a 1.5 kW array.

“There was a time when it was said that we don’t need computers on everyone’s desk,” said Slominski. “Now everyone’s got them. It’s the same with PVs on roofs. PVs not only provide energy savings at point of use, sustainable backup power, and a demonstrated environmental commitment, but with BIPVs they are now attractive and practical.”

Other areas of the world are actively involved in residential BIPV programs: in Sydney, Australia, 665 homes in the Olympic Village will feature 1 kW, roof-integrated PV systems, most of which will be supplied by BP Solar; in Japan, government funding on PV research and installation programs is driving a boom in residential rooftop installations.

Government Efforts

Getting these kinds of products on roofs should become easier as President Clinton’s Million Solar Roofs program gathers steam. Announced on June 26 of last year, the program plans to coordinate and encourage the installation of one million rooftop PV and solar hot water systems by 2010. The program intends to improve access to financing for solar energy systems, build a network of state-level renewable energy funds, establish a million solar roofs tax credit, obtain commitments from other federal agencies, and support research and demonstration programs. (Although many in the industry are taking a wait-and-see attitude towards the program’s actual funding and commitment.)

According to Dr. Patrina Eiffert Taylor, project leader at National Renewable Energy Labs, many of the architects and engineering firms the government works with will benefit from the government’s own involvement with BIPVs, as Clinton has committed the government to completing 20,000 roofs on its own facilities. “We work with A/E firms through our federal clients, and those firms are going to learn about the technology as they work on government projects,” said Eiffert Taylor . “Then, they will be able to offer that expertise to other clients.”

Eiffert Taylor feels that, although a lot of work has been done by the DOE to help reduce the costs of technologies, work still has to be done on bringing the costs of design and engineering and system standardization down. “I look forward to the day when you can go into Home Depot and get BIPV products,” she said.

More information on the Million Solar Roofs program can be found at www.eren.doe.gov/millionroofs on the Internet.