The 1996 Summer Olympics ended seven months ago, but one legacy of the Games is giving researchers unique experience and new information that could help make solar energy a more viable source of electrical power.
Built to host swimming and diving events, the Georgia Institute of Technology's Aquatic Center features the country's largest rooftop, solar-powered energy system connected to a utility power grid.
The 342-kilowatt photovoltaic system converts sunlight into electricity, serving as both a research model and a supplementary power source. It went online in July 1996, and researchers are pleased with its performance and the lessons they're learning about solar power.
Project Goals Are Modeling and Research
"The goal is to get a better understanding of how these systems work -- their performance, their reliability and our modeling capability to predict their performance," said Dr. Ajeet Rohatgi, a professor in Georgia Tech's School of Electrical and Computer Engineering. "Even though some of these things are being done elsewhere, very few people have this kind of depth in terms of modeling and experimentation. By combining these two, we think we can provide some new and useful information that is valuable to utility companies."
Funding for the $5.2 million photovoltaic system came from Georgia Tech, Georgia Power Co. and the U.S. Department of Energy. The international attention received during the 1996 Summer Olympic and Paralympic Games gave researchers a unique opportunity to showcase this clean and sustainable energy source.
Performance is Close to Expectations
So far, the system has operated close to its expected efficiency, although actual energy production has been lower than predicted.
"The system has performed very well," said Mike Ropp, a doctoral student in the School of Electrical and Computer Engineering. "We have quantified that by looking at the system's efficiency instead of just the output."
For the seven-month period from July 1996 through January 1997, the system produced 162.2 megawatt hours of electricity. For a full year, researchers had predicted 409 megawatt hours, which is enough to power about 35 average Georgia homes.
Several factors have affected energy output, including fuses blown when lightning struck the Aquatic Center roof in July and a water main break that flooded the electrical control room and forced a 10-day shutdown in October. Also, sunlight levels were lower than expected and extremely high temperatures in August decreased the efficiency of the system, which operates better in cooler temperatures.
Ongoing experiments to compare performance-model equations to the real operating data brought further shutdowns, but will help take the guesswork out of solar energy production.
"If you talk to laymen, the biggest concern they have is that the sunlight changes all the time," Rohatgi said. "You have cloudy days. Somehow they don't realize we can take that into account in our calculations. So it is not a mystery anymore."
In the future, Ropp plans to study "islanding," where the main power source shuts down but the photovoltaic system continues to function. This creates a safety hazard for workers doing maintenance or repairs, especially if they're not aware of the secondary power source.
Solar Array Occupies 3/4 of an Acre
The Georgia Tech system includes a solar array that covers about three-quarters of an acre atop the barrel-vaulted roof of the 95-foot-high Aquatic Center. It's made up of 2,856 photovoltaic modules, each with 72 multicrystalline silicon solar cells connected in series.
A power conditioning system, or "inverter," converts the array's direct current (DC) power to utility-compatible alternating current (AC) power, which then feeds into the Aquatic Center's main power system. The inverter also controls and monitors the overall photovoltaic system.
A data acquisition system samples all "vital signs" every 10 seconds, then averages and stores them every 10 minutes. Incoming data includes meteorological parameters such as ambient air temperature, wind velocity and array temperature, and performance parameters such as AC power, DC voltage and DC current.
The Aquatic Center also features a separate solar thermal system that heats the pool water by circulating it through a different set of rooftop solar panels. It is not part of the research.
Although the photovoltaic system is operating as expected, researchers continue to seek ways to improve solar energy production. At 10 percent to 15 percent efficiency, photovoltaic systems are below traditional ones like coal, natural gas or nuclear power, which have efficiency ratings that fall somewhere between 30 and 60 percent. But their fuel source -- the sun -- is free and unlimited, and its operation is silent and non- polluting.
Aquatic Center is Investment in Future of Photovoltaics
The U.S. Department of Energy (DOE) supports much of Georgia Tech's work in this area through the University Center of Excellence for Photovoltaic Research and Education (UCEP). Established in 1992, it is one of only two such centers in the country; the second is at the University of Delaware in Newark.
"There's money to be made in solar technology for those far- sighted enough to make the investment," said Christine Ervin, assistant secretary of the DOE's Office of Energy Efficiency and Renewable Energy. "The work we're supporting at Georgia Tech is at the cutting edge of this technology. What we learn from projects like the Aquatic Center increases the confidence of those potential investors in photovoltaics products and sets the foundation for our industry's growth and profitability."
The Aquatic Center's photovoltaic system was designed by Rohatgi and Dr. Miroslav M. Begovic, also a professor in the School of Electrical and Computer Engineering, along with Richard Long, project support manager in Georgia Tech's Office of Facilities. Rohatgi also is director of the UCEP.
Although the system was the largest of its kind in the world when it was built, a bigger one has since been constructed in Bonn, Germany.
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WRITER: Amanda Crowell