By integrating the solar-electric array into the structure itself, building-integrated photovoltaics blur the aesthetic division between where the home stops and the PV system begins.
Until recently, most residential solar-electric arrays consisted of rigid modules attached to a roof-mounted rack. There’s no mistaking this type of system—most of them are quite visible and easily identifiable. But while some folks view a standout system as a chance to educate and enlighten, others don’t like the looks or just want the system to inconspicuously blend in, generating clean energy without standing out. If you fall into this latter group, a building integrated photovoltaic (BIPV) system might just be what you’ve been looking for. For roof retrofits, expect to pay a little more, but if it’s for new construction, the costs of BIPV can be very similar to a typical framed PV array.
The most common home-scale BIPV application is in new home construction. Due to the ever-growing demand for energy-efficient, “green” homes, many homebuilders have begun to offer some sort of BIPV product as an option or as part of a planned green-housing development.
Another opportunity to incorporate BIPV into an existing home comes during reroofing, when the roof’s structure is exposed. The PV mounting hardware is installed first, and the roofing is placed around it, resulting in more trustworthy weatherproofing.
Solar roofing PV modules integrate seamlessly with the roofing material. They are attractive, not only because the modules blend in aesthetically but also because they serve a second purpose as the roofing material.
Atlantis Energy Systems, BP Solar, GE Energy, Sharp, SunPower, Suntech, and Uni-Solar all offer ready-to-install roofing tiles. Some of these products are not directly available to end users or installers, and several products are only available to roofing companies and new home builders/developers. Lumeta also has BIPV roofing products that are currently undergoing the Underwriters Laboratories’ certification process and are to be released later this year.
Atlantis Energy Systems’ Sunslate is a PV shingle made of six single-crystalline cells on a fiber-cement backing. Sunslates can be incorporated into a concrete tile, composition, wood shake, metal, or slate roof. These modules are mounted using a traditional roofing method, with an underlayment of standard 30# felt tar paper. The roof deck is prepared with vertical 2 by 2s fastened through the deck and into the rafters. One-by-fours are nailed horizontally to the 2 by 2s to create a raised batten framework. The Sunslates hang on supplied hooks nailed to the 1 by 4s. The spacing behind the slates allows airflow to help reduce PV cell temperature and associated power loss.
Sunslates are typically connected in series strings of 24 slates, using a proprietary connector system (designed to hold a bypass diode for each tile). Failure of a single slate presents a challenge for replacement, for a section of the slates will need to be removed to gain access to the failed slate. Installations typically require multiple strings, with all strings grouped together and entering into a single penetration into the attic. This product comes with a limited 20-year power warranty.
GE Energy’s PV Roof Integrated Modules are designed to integrate with flat concrete-tile roofs. Each module contains 18 multicrystalline cells and one bypass diode. Modules are wired together with Solarlok connectors. To install, brackets are screwed down to unraised battens. Modules are secured to the roof with clips into the brackets. This product comes with a 20-year limited power warranty.
Sharp manufactures a roof-integrated module that is designed to replace five standard, flat cement tiles. The modules are comprised of 18 multicrystalline cells with one bypass diode per module and are wired together with Onamba C3 quick connects. These modules are secured to standard unraised battens with gasketed screws. The limited power warranty is 25 years.
Uni-Solar manufactures a thin-film laminate for standing-seam metal roofs. An adhesive seals the modules to the metal, avoiding roof penetrations. Laminates are wired together via MC connectors, with the connections routed through the roof’s ridge cap. Bypass diodes are wired across every cell in Uni-Solar products, which makes the modules more shade-tolerant than PV products that protect multiple cells with a single bypass diode.
Manufactured with triple-junction thin-film amorphous silicon, these modules offer better low-light and high-temperature performance. The primary disadvantage is the lower efficiency of amorphous thin-film products (see “Efficiency vs. Roofing Space” sidebar). This product comes with a limited 20-year power warranty.
BP Solar’s Energy Tile is a solar roofing product designed to integrate with flat concrete roof tiles. With 18 multicrystalline cells, each tile uses one bypass diode. Tiles are wired together via MC connectors and secured to the roof via standard, unraised battens. The limited power warranty is 25 years.
SunPower’s SunTile is another product for S- or flat concrete tile roofs. SunTiles have 22 monocrystalline cells per tile, with all of the cells’ electrical contacts on the back. Without gridlines on the cell fronts, more sun gets through, which means higher efficiency (the manufacturer claims up to 22%). The tiles each have one bypass diode and include MC connectors. SunPower does not require a raised batten system, as the SunTile design allows for continuous airflow beneath the array. Mounting clips are integrated, and the tiles attach to the roof with gasketed screws. The power warranty is 25 years. SunTiles are only available for new housing developments of 25 or more homes.
Suntech’s SolarSave roofing tiles are sized to integrate with flat concrete tile or S-tile roofs. With 14 multicrystalline PV cells, each tile has one bypass diode. Tiles are wired together with MC connectors. Suntech recommends installing tiles on raised battens to increase airflow and reduce power loss from high temperatures. The tiles are secured to the batten structure either with nails or deck screws, and can be installed with wind clips to increase wind-load ratings. The limited power warranty is 25 years.
Lumeta’s Solar S and Solar Flat tiles are for profiled and flat concrete or clay tile roofs. Each tile has 12 monocrystalline cells, with one bypass diode per tile. Tiles are wired together using locking connectors.
Each solar S- or flat-tile is designed to replace three standard cement or clay tiles. Depending on the roof pitch, battens may be required. The tiles are attached to the roof with stainless steel screws. This product comes with a 25-year power warranty.
Designing BIPV into a home creates significantly different challenges than installing a standard PV system, since the successful integration of the system often relies on the home’s design. If the home is using solar tiles or shingles, roofing design and collaboration with the roofing contractor become essential, since the tiles are installed along with the roofing and can affect the roof structure. Solar tiles usually require a manufacturer-designated mounting method. The roofer can help with mounting the BIPV, sealing roof penetrations, and dealing with any roofing issues that may arise.
The electrical characteristics of BIPV products also differ from standard PV modules. A BIPV roof tile is usually smaller than a PV module, containing fewer cells. That means lower output voltage, requiring many more BIPV roof tiles connected in series to attain the input voltage of a modern residential grid-tied inverter. It’s common to have more than 30 solar tiles in series to reach the operating voltage of the inverter. Requirements for series fusing or combiner boxes may not apply with only one or two strings.
Troubleshooting BIPV systems also can be difficult. When BIPV systems are fully integrated into the building, gaining access to the modules and connections can become an issue, unlike a conventional rooftop-mounted PV array. For example, troubleshooting an individual solar tile may involve removing others to gain access to the malfunctioning one. Plus, just figuring out which tile has failed can be a daunting task: You will first need to isolate each individual string, then each solar tile will need to be tested until the malfunctioning one is found.
Retrofitting an existing home with BIPV products can be more expensive than buying traditional PV modules and racking. However, comparing costs between these two types of installations and even between new home construction projects can be tricky. First, BIPV products generally blend two functions (roofing and electricity generation) into one product, which can help offset their higher cost. Second, BIPV roofing tiles are usually sold to large-scale homebuilders, who are given pricing based on the size of the projects. Complicating the issue further is that many BIPV roof-tile companies do not sell direct to the end user. For new home developments, grid-tied BIPV systems cost about the same as standard, non-BIPV ones: about $7 to $8 per rated watt.
Another consideration is that incentive programs aimed at new homes may boost the BIPV market, eventually lowering costs. For example, the California Energy Commission’s New Solar Homes Partnership gives state rebates and tax credits for PV systems included with new homes. New homes and newly constructed affordable housing projects have their own incentives set aside, highlighting California’s goal of spurring PV design from a project’s inception.
In general, the BIPV market is still relatively a niche market, so these products have not been exposed to the trend of cost reduction that the industry has seen with traditional PV modules.
BIPV installations are increasing every year. Architects and designers are developing new, creative ways to utilize these products and developers are incorporating them into green housing tracts, while manufacturers continue to create new products to meet this market niche. Some companies, such as Sanyo, Schott Solar, Sharp, and Suntech, are working on new BIPV products for facades, skylights, and windows. As the PV market develops and continues to grow at a record pace, keep a close eye on this exciting and creative way to integrate PV technology into the home.
Paul Mync has been installing, designing, troubleshooting and maintaining PV, solar hot water, and radiant heating systems since 2002. He has worked around the world on PV systems ranging from 100 watts to 18 megawatts. Paul also is an instructor for Solar Energy International.
BIPV Product Manufacturers:
Atlantis Energy Systems • www.atlantisenergy.org
BP Solar • www.bpsolar.com
GE Energy • www.gepower.com/solar
Lumeta • www.lumetasolar.com
Sanyo • www.sanyo.com
Schott Solar • www.us.schott.com
Sharp • www.solar.sharpusa.com
SunPower • www.sunpowercorp.com
Suntech • www.suntech-power.com
Uni-Solar • www.uni-solar.com