Researchers release findings on energy storage

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Eric Hittinger and Inez Azevedo

Adding energy storage to the U.S. electricity grid results in increases in greenhouse gas emissions and local pollution from power plants, even if storage is charged from renewable energy, according to a team of researchers from Rochester Institute of Technology and Carnegie Mellon University.

Their findings, published in this week’s issue of Environmental Science and Technology, report that an operating storage plant, such as the pumped hydro and compressed air plants already operating in the U.S., causes an average of 260 kilograms of carbon dioxide pollution for every megawatt-hour of electricity it provides. Storage plants also increase the amount of nitrogen oxide and sulfur dioxide pollution emitted in the U.S.

“We did the analysis over two years at 20 different locations around the U.S., and the results were pretty consistent,” said Eric Hittinger, assistant professor from RIT’s Department of Public Policy, who conducted the research with Inês Azevedo, associate professor at Carnegie Mellon and co-director of the Carnegie Mellon’s Center for Climate and Energy Decision Making.

“People need to be aware of this,” Hittinger said. “We need to pay more attention to energy storage and its possible complications.”

The emissions are due to two effects: First, storage generally charges up at night from dirtier coal power and discharges during the afternoon when a cleaner natural gas generator would be operating. Second, a storage plant has an efficiency of around 75 percent, so the storage plant needs extra coal-generated electricity to meet the daytime demand.

These results can hold true even if the storage is only charged with renewable energy, such as wind power, because of the effect on other electricity generators.

“For energy storage, the economic and environmental effects are opposed,” said Azevedo. “If you want to maximize revenue, you increase system emissions. If you tried to minimize emissions, your storage plant would lose money.”

“Grid energy storage is a valuable technology and we should use more of it,” Hittinger said. “However, it is not a green technology. People talk about energy storage being the ‘holy grail’ of renewable energy, but adding a lot of batteries or pumped hydro to our current grid would actually make more pollution.”

Their research was made possible with grants from the National Science Foundation.

See the March 3, 2015, issue of Environmental Science and Technology or the journal’s website for the complete report.