Energy Features - Building Integrated Photovoltaics

Energy Features

Mary Ann Cofrin Hall, the new University of Wisconsin-Green Bay classroom building integrates two Building Integrated Photovoltaic (BIPV) sections with separate photovoltaic (PV) technologies, allowing it to put the power of the sun to work to make its own electricity. One section uses a commercially available roofing product, used commonly throughout Wisconsin, known as Standing Seam Metal roofing.

Mary Ann Cofrin Hall showcases the viability of this product, while also encouraging builders to install small Standing Seam Metal BIPV systems on their new buildings.

The other section incorporates a thin-film BIPV vision glass product. The vision glass product is the first installation of its kind in the United States. Hopefully its use in Mary Ann Cofrin Hall inspires other builders to install similar systems, giving their buildings a visible "green building" feature. In total, about 4,300 square feet of BIPV material were installed, which will generate approximately 27,500 kWh annually.

Daylighting, energy-efficient lighting, and SolarWall technology are three additional energy features that add to the uniqueness of Mary Ann Cofrin Hall. While more common to current construction practices, the artistic manner in which these features were incorporated into the building's design is noteworthy.

Power conversion systems and utility interconnections are other devices that function behind-the-scenes to ensure that BIPV and PV technologies are running accurately, efficiently, and safely. In addition, a variety of other equipment is needed for a complete photovoltaic power system. Equipment needs range from simple wires and mounting hardware to fuses and junction boxes. When compared to the sophisticated PV modules and inverters, this equipment may seem relatively minor, but it is vital to the building's overall construction.

Standing Seam Metal Roofing

Standing Seam Metal (SSM) roofing is a traditional roofing material that uses long, vertically sloped metal trays with raised edges. The trays are snapped together along the long axis to build the roof. Thin-film, amorphous-silicon, triple-junction photovoltaic (PV) modules can be glued or laminated to the tray surface. The material, manufactured by United Solar Systems Corporation, produces electricity as well as performs its traditional weather-sealing function.

Mary Ann Cofrin Hall displays 100 of the 128-watt laminated modules (model SSR-120) on its south-facing wing. This system spans 2,300 square feet and generates approximately 15,000 kWh annually. Standing Seam Metal (SSM) Roofing

Vision Glass

Photovoltaic (PV) vision glass substitutes a thin-film, semi-transparent photovoltaic panel for the exterior glass panel in an otherwise traditional double-pane glass window or skylight. Electric wires extend from the sides of each glass unit and are connected to wires from other windows, building up the entire system. The technology, while available in Europe, is currently being developed as part of a United States Department of Energy PV-BONUS project.

On the University of Wisconsin-Green Bay campus, the system, rated at about 11 kW, substitutes Building Integrated Photovoltaic vision glass for traditional windows in the Wintergarden of Mary Ann Cofrin Hall.

This system spans 2,000 square feet and generates about 12,500 kWh annually. The "PV Glass" unit was manufactured by Viracon, Inc. using BP Solar MST-43LV 43-watt, thin-film photovoltaic modules and was installed in a standard Kawneer Company 1600 PowerWall (TM). In this application, BP Solar laser-etched their photovoltaic modules to create a desired transmittance for the Wintergarden.
Sunspace

Artist's rendering of Wintergarden.

A total of 252 modules were installed. Each vision glass surface has 13 layers of thin film, altogether thinner than one piece of paper, sandwiched between two protective layers of glass.

Daylighting

Five different types of glazings, with transmittancies ranging from 15% to 25%, were incorporated into the structure of Mary Ann Cofrin Hall.

The design includes skylights, clerestories, borrowed light, daylight diffusers, and direct sunlight. Glazings were selected based on their abilities to reduce solar gain, provide insulation, ensure meeting performance goals, and permit a "looking in on learning" atmosphere. Photosensors and mechanical shading devices were also utilized.

Diagram of daylighting possibilities

Artists rendering of daylighting benefits

Photo of skylight use in the new classroom building

Daylighting

Photo of clerestores in the new classroom building

Photo of shared daylighting in the new classroom building

SolarWall Technology

The fairly ordinary-looking black wall along the South side of Mary Ann Cofrin Hall is actually a 2,256 square foot "transpired" solar collector. This unglazed porous collector, or SolarWall, absorbs the sun's energy and uses it to heat the air that is pulled through the collector surface and into the air distribution path connected to the mechanical system of the building. The system is shut down during the summer months so that air heated by the SolarWall does not have to be cooled prior to its release into the building, causing unnecessary energy use.

Solar Wall Technology

Photo of SolarWall technology on new classroom building

Solar Wall Technology

Artists rendering of
SolarWall technology performance

Solar Wall Technology

SolarWall technology installation on new classroom building

Solar Wall Technology

Close-up photo of SolarWall technology

Power Conversion System

Power conversion systems are relied upon to change the make up of a specific power source. Since most photovoltaic (PV) modules generate direct current (DC) and most devices that use electricity require alternating current (AC), a solid-state electronics device called an inverter is installed to achieve the DC to AC power conversion. This device is usually installed in an interior equipment or mechanical room. It collects the energy produced by the PV system, does the power conversion, and injects the power into the building's electrical distribution system through a nearby electrical junction box. Typical inverters include safety features that prevent the flow of electricity to a building when utility power is not present. Two Trace Technologies inverters were used in Mary Ann Cofrin Hall.
Power Conversion System

Photo courtesy of Trace Technologies.

Utility Interconnection

Most photovoltaic (PV) system inverters, or power conversion systems, incorporate utility interconnection safety features to serve as checks and balances for the system. A PV system produces electricity and, if not installed correctly, can cause harm to building occupants, workers, and utility line personnel. The inverter monitors the utility power voltage and frequency. If either of these measurements fall outside a set range, the inverter automatically disconnects itself and the PV system from the building. This action prevents the accidental electrocution of utility line workers who, as a rule, do not expect power to flow out from a building. Most utilities have very detailed interconnection guidelines to insure the safe operations of the electrical distribution system and the safety of their workers. PV system owners must contact their local utility to discuss these guidelines prior to installing any on-site electricity-generating systems.