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A new solution for solar

by Stephanie Shimada
solar panels
Photo: Stephen Cronin and his team are exploring a new technology that allows the storage of solar energy for use when the sun is not shining.

As winter approaches, days will get shorter and nights longer, requiring more electricity to light and heat homes.

While solar power has the potential to provide ample electricity during the day, cities lack the technology to store solar energy for use when it is needed most — during darkness.

At the present time, solar panels can only produce electricity when hit by sunlight, and that electricity must be used instantaneously. Since the energy cannot be stored, people frequently find themselves in an energy shortage after sunset.

But what if there was a technology that allowed the storage of solar energy for use when the sun is not shining?

Stephen Cronin, associate professor of electrical engineering and electrophysics at the USC Viterbi School of Engineering, is thinking about that.

Since 2009, he and his team of 10 PhD students have worked on solar-to-chemical energy conversion through plasmonic catalysis. The process uses chemical compounds such as carbon dioxide to transform solar energy into chemical energy, specifically methane and methanol, which can later be burned to produce electricity.

Though carbon dioxide is known as a greenhouse gas, Cronin has found a way to conduct this solar-to-chemical conversion process as a carbon neutral cycle, similar to how plants reduce carbon dioxide using chlorophyll.

Cronin envisions that his technology will be installed in gigawatt solar power plants — the standard size for a power plant where solar energy could be stored for future use. The energy could later be converted into usable fuel, such as methane and methanol, which would then be burned to produce electricity and heat buildings. A gigawatt of energy could produce enough electricity to power 770,000 homes.

“I wanted to do research that crossed some boundaries between applied science and technology,” Cronin said. “[Through this research], we are doing fundamental science that will eventually become a technology that is commercially viable.”

In addition to solar energy, Cronin’s plasmonic processes can be used in a  variety of commercial applications, including water remediation and purification.

Plasmonic catalysis involves shining solar light onto titanium dioxide (TiO2), an inorganic compound used in sunscreen, among other products. When illuminated, TiO2 converts water and carbon dioxide to create methanol or methane. These hydrocarbons can subsequently be burned to produce electricity in a carbon neutral process: When the methanol is later burned, carbon dioxide is released back into the atmosphere, leaving us with the same amount with which we started.

Plasmonic catalysis can also help lead to innovations in existing products produced by industrial chemistry. Alexander Benderskii, a Cronin research collaborator and an associate professor of chemistry at USC Viterbi, said that using compounds such as gallium phosphide and indium phosphide can help the chemical industry innovate by allowing new chemical transformations of materials and producing new types of plastics.

“These new types of catalysts are potentially very useful in the chemical industry,” Benderskii said. “This will allow industrial processes to use efficient, more selective [compounds], ones that can give you one product preferentially over another.”

The current efficiency of plasmonic catalysis processes is years away from commercial viability. However, Jing Qiu, a PhD student in Cronin’s lab, said the processes can have a substantive effect once the efficiencies are improved.

“If we can get the efficiency of these conversions to 10 percent, we can provide the total energy we need for our society,” Qiu said.

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