USF professor Yogi Goswami captures solar energy using salt balls

Yogi Goswami has developed a solar energy storage system that could cost less and use far less space than systems currently in use.
Yogi Goswami has developed a solar energy storage system that could cost less and use far less space than systems currently in use.
Published Nov. 9, 2013

To Florida's big utilities, the Sunshine State isn't as bright as its nickname indicates.

Too cloudy. Too hazy. Too much darkness. It just doesn't have the pounding rays of, say, Arizona or parts of California.

As such, the reasoning goes, the Sort of Sunny State isn't great for solar energy — unless someone develops storage technology to overcome those limitations.

Enter Yogi Goswami, an internationally renowned mechanical engineer at the University of South Florida.

His solution: salt-filled ceramic balls that can turn water into steam for hours after the sun disappears. The steam powers turbines that produce electricity, in much the same way as burning coal.

Goswami, 65, isn't the only researcher to develop a solar thermal storage technology for renewable energies. And he's not the only one to use salt as a main component.

But he has devised a way to concentrate the energy storage into golf ball-size capsules that even at high volumes take up little space, reduce costs and last longer than other technologies so far.

"We think that this has a bright future," Goswami says. "For solar, in my view, (storage) is essential."

• • •

In the renewable energy world, building a cost-effective, utility-scale system that can store solar power for hours at a time is a Holy Grail of sorts.

"That will be a game changer," Duke Energy Florida president R. Alexander "Alex" Glenn told state lawmakers last spring. "Storage is going to be critical."

A race is on to develop the best technology. A few systems are already in use or being tested.

Duke Energy for instance operates one of the nation's largest storage technologies at its Notrees Battery Storage Project that uses lead-acid battery blocks at a wind farm in Texas.

Arizona's Solana Generating Station already uses a salt-based storage system that powers two 140-megawatt turbines that generate electricity for as long as six hours after sunset. The system produces enough power for 70,000 Arizona Public Service customers.

Goswami's system is similar to Solana's, but instead of large tanks full of salt, his system employs small balls.

Goswami began with encasing salt in nickel and zinc. To increase efficiency, he moved to ceramic casings, with help from a partnership with electronics and ceramic maker Kyocera Corp., based in Kyoto, Japan.

During the day, solar thermal panels heat the balls to extremely high temperatures. The salt in the balls, which can be reused for years, melts to a liquid. The molten material keeps the balls hot enough in an insulated tank to turn water into steam for as long as 12 hours. The salt then turns back to a solid when it cools, and the process can start all over when the sun shines again.

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The steam could power turbines on demand during cloudy days or throughout the night.

The footprint for a 100-megawatt storage system, which could power about 36,000 homes, would be about 40 feet by 40 feet.

The size of Goswami's storage is one of its advantages. By using the small balls, it takes less time to melt the salt, and the heat in the balls is projected to last hours longer than the system in Arizona, which also uses a lot more salt.

Goswami thinks he can drive costs down to $2,000 per kilowatt for the solar thermal system and $15 per kilowatt hour for the storage. Other solar systems and storage have been costing $3,000 per kilowatt for the system and $40 per kilowatt hour for the storage.

The hitch: No one has yet agreed to build one for commercial use.

Haresh Kamath, program manager for energy storage at the Electric Power Research Institute, an organization largely funded by the utility industry, says Goswami's system "has some promise and should be investigated."

Goswami's pricing would make the system financially competitive, said Kamath, and the size of the storage is "a pretty small amount of space."

"It's something that needs significant testing before it's ready for deployment," Kamath said.

The Solana solar power plant in Arizona shows that the technology can work, he added.

"It's not only under consideration, it is actually being used," Kamath said. "Not this particular technology, but similar technology."

Randy Wheeless, a Duke Energy spokesman, said the company would need to see Goswami's technology used with a utility-scale power plant.

"We haven't really been looking at that technology," Wheeless said. "Thermal salt storage isn't that ground-breaking.

"Obviously, it needs to be a certain scale," he said. "How do you get this to scale?"

Goswami's confident response: Test it. It's ready.

• • •

Goswami began developing the system in the 1990s while at the University of Florida.

His initial financial backing came from the U.S. Department of Energy, Florida Power & Light and Florida Power (now Duke Energy). UF, FPL and Florida Power each owned a third of the patent at the time. USF currently owns the entire patent.

Goswami said the power companies abandoned the project when they returned their focus to more traditional forms of generating power. With no companies licensing the technology, the university did not renew the patent.

But Goswami powered on.

The University of South Florida hired him away from the University of Florida, and Goswami became the John and Naida Ramil Distinguished Professor and the co-director of the university's Clean Energy Research Center.

John Ramil, president and chief executive officer of TECO Energy, the state's third largest investor-owned utility, said Goswami's stature in Florida and the world warrants serious consideration of his work.

"We are fortunate to have Dr. Goswami at USF," Ramil said. "He's an internationally recognized researcher and leader in the energy field.

"Dr. Goswami's work to expand the usefulness of solar energy — to match customer consumption patterns — is valuable research that could have a lasting effect on the energy industry."

• • •

When it comes to solar, Florida remains a laggard, trailing not-so-sunny places likes New Jersey and Massachusetts.

In his testimony to state lawmakers last spring, Glenn, the head of Duke's Florida operations, said solar simply isn't ready for prime time.

"Florida is not the greatest renewable state," Glenn said. "We are the Sunshine State, but we're also the partly cloudy state. What we have to do is develop a storage technology."

To Goswami, it's more a matter of Duke and other utilities embracing what is already available.

The sun is "the only inexhaustible (fuel) source," Goswami said. "I'm not a purist who would say only use solar. Solar is intermittent. You can't ignore that. You have to have your diversity of sources."

But he said all fuel sources need to be managed.

"You use diversity of fuel sources, but in a sustainable way," Goswami said. "You use fossil fuels, but in a sustainable way."

Another reason solar has failed to blossom in Florida: It made little financial sense, thanks to electric rates that are much lower here than up North.

But the electricity rates in Florida are starting to rise. Meanwhile, the cost of solar continues to fall and expectations are that it will soon be on par with what residential customers pay the utility for electricity.

Goswami sees his system lowering costs even more.

He is working to reduce the size of the balls used for his system to make them even more efficient, much like computer servers evolved from filling a warehouse in the 1960s to a desktop today.

It's these kinds of advancements that he thinks the utility companies ignore at their own peril.

"Innovation knows no limits," Goswami said. "The utility companies have to recognize that or they will be left behind."

Ivan Penn can be reached at or (727) 892-2332.