It seems like yesterday that the cool, sparkling racing pool of the Georgia Tech Aquatic Center was immersed in the cheers of crowds gathered for the 1996 Olympic Games in Atlanta. One would never guess, however, that the most spectacular record set at the facility was not a diving score or a blazing time for the 100-meter backstroke. It takes a trip up a precarious set of utility ladders to the roof of the building to view the real record setter: a solar power array that became the largest roof-mounted system in the world when the facility was completed in 1996.

Although it has since been relegated to the status of largest in the U.S. (a competitor building from Germany now takes the honors), the sight is still impressive. Installed on the roof’s gently curving surface, 150 feet above the ground at its crest, are 2,856 photovoltaic modules silently gathering energy from the sun. The multicrystalline modules, made by Solarex of Frederick, MD, can produce up to 120 watts of electrical current each, with the entire installation rated at 342 kilowatts (kW) DC. The system is estimated to save 440,141 kW of utility electricity use per year, which, when compared to the use of fossil fuel sources, amounts to a savings of 9,900 tons of carbon dioxide, 100 tons of sulfur dioxide and 36 tons of nitrogen oxide over an estimated 30-year life span.

The $5.2 million project was sponsored by the U.S. Department of Energy (DOE), Georgia Tech and Georgia Power, a utility company. Daniel H. Nall, AIA, PE, and John R. Hardesty, PE, both of whom at the time of the project were employed by the Atlanta-based engineering firm Roger Preston and Partners, designed and installed the system together with Georgia Tech’s University Center for Excellence in Photovoltaics (UCEP) and Solarex. Dr. Ajeet Rohatgi and Dr. Miroslav M. Begovic of UCEP were the project leaders for the installation.

Although most of Solarex’s business remains in supplying panels for jobs where their product is more cost-effective, the company was quick to participate in the project because of the awareness it was going to generate for photovoltaics. “The project showed the architectural and building trade community that photovoltaics are not science fair projects anymore,” said Bill Rever, marketing manager for Solarex. “These modules can be installed in large scale projects by architects and engineers without much difficulty. It’s not rocket science.”

Because the project was unprecedented, however, there was still a substantial amount of troubleshooting. According to Hardesty, one of the main difficulties of installing an array of this size on the standing seam roof was maximizing the number of panels while still allowing for access to each unit. “There was an awful lot of troubleshooting involved in these things, and we had to be able to walk around in there . . . but we still wanted to cram as many solar panels on the roof as we could,” said Hardesty. Another concern was the hardware that was available for the job: to keep prices down and to make replacements easier, the engineers tried to use off-the-shelf parts. This limited, however, the amount of power they could safely generate. “The configuration had to suit what we could buy,” said Hardesty. The engineers also “compartmentalized” the modules so that a failure in any area wouldn’t significantly disrupt power generation.

The electricity produced by the array is collected and “inverted” into AC current by the center’s power conditioning system, made by Trace Technologies of Livermore, CA, and rated at 315 kW DC continuous. The roof-mounted array, plus a small array above the facility’s entrance, produce a third of the aquatic center’s annual electric needs. From June 1996 to July 1997, the installation produced 333.3 megawatt-hours. Because the array is connected to the local utility grid, an “anti-islanding” safety feature was used to prevent solar-generated electricity from entering the grid should there be a utility power failure. A protective relay was also installed for added safety.

The team from UCEP has been monitoring the array with data acquisition systems by Southwest Technology Development Institute of Las Cruces, NM, and Advanced Energy Systems of Wilton, NH. Using a combination of hardware and software, these systems check the “vital signs” of the array every ten seconds, including DC voltage, DC current, AC power, array temperature, and solar irradiance. “With the diagnostics system, it’s really easy to turn off and test certain panels. We could even see the effects of trees growing leaves near the PV panels above our entrance area,” explained Ph.D. candidate Michael Ropp, who is responsible for the day-to-day operation and monitoring of the system.

The UCEP team has been using a number of modeling programs with the system in order to test the ability of the programs to match actual conditions. PVFORM Version 3.3 from Sandia National Labs is one of the most used programs at the center.

Although the array is rated at 342 kW, the highest it has reached is 270 kW — a discrepancy Ropp attributes mainly to a less than ideal set-up. The slope of the roof, which in the best of cases would be tilted at 30% to face the sun, has only a 13% tilt on the south side, and even tilts away from the sun 10% on the north side.

Although the installation is far from economical — the electric power produced by the grid over its lifetime is estimated to cost 35 cents per kilowatt-hour — the main purpose of the center was to facilitate research and development of solar technology so that in the future it can become a cost-effective alternative to traditional power sources.

For more information on the Georgia Tech Aquatic Center, visit Michael Ropp’s Web page: http://www.ece.gatech.edu/users/2648/natatorium.html