Solar Roofing: Seamless Integration of Architecture and Engineering
The Jarecki Center of Advanced Learning on the campus of Aquinas College in Grand Rapids, Mich., has been generating solar power for more than four years now—approximately 35,000 kWh of electrical energy per year for the last three years, a savings of roughly $2,500 per year. Photovoltaic systems weren't exactly common in west Michigan when Peter Wege, past president of Steelcase, Inc.
The Jarecki Center of Advanced Learning on the campus of Aquinas College in Grand Rapids, Mich., has been generating solar power for more than four years now—approximately 35,000 kWh of electrical energy per year for the last three years, a savings of roughly $2,500 per year.
Photovoltaic systems weren't exactly common in west Michigan when Peter Wege, past president of Steelcase, Inc., and a benefactor of the College, expressed an interest in alternative energy for the school. But then, Steelcase has been active in the sustainable design movement; its facility in Caledonia, Mich., was awarded a LEED silver certification by the U.S. Green Building Council.
Following Wege's vision, designers at Progressive AE, Grand Rapids, set out to design with energy savings and building integration in mind. A primary goal was to design a power system that combined ease of maintenance with a long use-life.
At the same time, aesthetics were a concern, and Progressive worked with various suppliers and contractors to develop a solar power system that would completely blend with the architecture. The result is a unique building, with a roofing system that is completely integrated with the electrical PV panels.
The PV panels use thin-film amorphous silicon technology on a stainless steel substrate that is covered with a Teflon-based polymer coating. This type of panel has proved efficient under varying lighting levels, conditions and temperatures.
The benefits of this type of roof include reduced materials handling and fewer structural holes and mounting issues. At the same time, it posed challenges for the engineering staff: structural integrity, visual impact, weather tightness, roof and system maintenance, system access, building and electrical code issues, equipment heat rejection, electrical performance and personnel safety.
The building's roof was pitched at a 42ely 4% of the building's total annual requirements.
Power is fed directly into the three-phase electrical system, as no batteries are used in this particular installation. The design called for 100% of the PV-generated power to be consumed within the building itself, offsetting utility- supplied energy. On a cloudless summer day, when the system can generate maximum power for an unoccupied building, net metering is available to sell excess energy back to the utility.
Three horizontal roof sections provide maximum coverage of the south roof using 9.5-ft. runs of PV modules attached to 10.5-ft.-long standing-seam roofing panels. Each PV module generates 3.64 amps at 16.5 volts DC. Eighteen individual modules make up an array.
The Jarecki Center system consists of nine arrays, each providing DC input power to three inverters that are wired on the output side in a three-phase AC power configuration. Each array is connected in series for an operating voltage of 148.5 volts DC between the common center connection point and the positive/negative array lead, with 297 volts DC across positive to negative leads of the total array. A source circuit protector with diodes protects each array, and a fused disconnect switch is installed on the incoming line side of each inverter, allowing for isolation of arrays and phases for maintenance without shutting down the entire system.
The array source circuit protectors are mounted within an accessible attic for weather protection and easy maintenance. The inverters are located within a room designed with proper heat rejection for long-term operation and to limit unauthorized access. All panels, disconnect switches and circuit breakers are carefully labeled with warning signs, voltage levels and component purpose.
From the output of the inverters, the 208/120-volt, three-phase AC is transformed up to 480-volt three-phase power and interconnected to the building's main distribution service panel as required by the National Electrical Code. The PV system has an interconnected data acquisition system to collect incident light levels, ambient outdoor temperatures, solar panel temperatures and wind speed for analysis purposes. The system includes a modem and software that allow for remote access, downloading of collected data and for on-line system monitoring of operational problems.
"I was skeptical at first but we've only had one minor problem with an inverter," said Tom Summers, director of maintenance at Aquinas. "It was easily fixed and the system has worked flawlessly otherwise."
The project is a testament to the fact that it is possible to blend engineering design with architectural features. With close collaboration between engineers and architects, Progressive was able to avoid the typical "add-on look" of exterior PV system components.