Georgia Institute of Technology March 24, 1997
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.
"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.
So far, the system has operated close to its expected
efficiency, although actual energy production has been lower than
"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
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.
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
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-
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
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