Eric Hittinger and Inês Azevedo recently published a piece in ES&T titled: “Bulk Energy Storage Increases United States Electricity System Emissions”

“Bulk energy storage is generally considered an important contributor for the transition toward a more flexible and sustainable electricity system. Although economically valuable, storage is not fundamentally a “green” technology. Hittinger and Azevedo model the economic and emissions effects of bulk energy storage providing an energy arbitrage service. They find that net system CO2 emissions resulting from storage operation are nontrivial when compared to the emissions from electricity generation.”