Malta and Duke Energy to Study Converting Coal Units into Energy Storage Facilities

A U.S. Department of Energy grant is funding the year-long study of the emerging technology.

Malta is developing a pumped heat energy storage system that leverages well-understood subsystems, components and thermodynamics in a novel energy storage application. By leveraging existing subsystems from well-established industries, the system relies on decades of performance data to ensure safe, resilient operations.

The system stores electricity either directly from a power plant or from the grid by converting electricity into thermal energy (heat and cold). Heat is stored in molten salt, a decades-old and proven method of storing thermal energy. Cold is stored in an antifreeze-like solution with components and subsystems widely used in the liquefied natural gas industry.

The system operates like a conventional power plant. When electricity is needed, the thermal energy powers a heat engine to produce clean, reliable energy.

“Malta is excited to work with Duke Energy to identify cost-effective, common-sense paths forward for fossil assets that consider all stakeholders,” said Ramya Swaminathan, Malta’s CEO. “For utilities like Duke Energy to meet their net-zero carbon emissions goals, major advancements in technology are needed. The Malta system could be part of the solution by providing zero-emissions, load-following technology that provides reliable, resilient and around-the-clock power.”

Though the study will focus on the energy industry’s current need for 10-12 hours of energy storage, the Malta system can be configured to store up to 200 hours of energy storage.

“Duke Energy is investing in innovation as part of our clean energy transformation plan to achieve net-zero carbon emissions by 2050,” said Regis Repko, senior vice president of Duke Energy’s Generation and Transmission Strategy organization. “For years, Duke Energy has actively evaluated emerging technologies, and the Malta study marks the first time we will evaluate long-duration thermal energy storage. We expect the results to influence the future of energy and apply to our larger generation fleet.”

The study’s deliverables include an engineering conceptual study, a technology maturation plan and a socioeconomic report on potential benefits, including:

• Job retention. Incumbent workforces could transition from operating coal-fired plants to operating the mechanically similar Malta system.
   
• Local economic impacts. An operating clean energy storage system could preserve some jobs and a portion of the local property tax base, offsetting some impacts from closing coal plants.
   
• Environmental benefits. Adding more utility-scale, long-duration storage could allow the company to integrate more renewables like solar, particularly when the sun isn’t shining.
   
• Operational benefits. Long-duration energy storage could increase flexibility, reducing wear on generation assets by decreasing the number of times a unit needs to turn on and off.

The Department of Energy announced the grant in March, and the team is identifying which of Duke Energy’s six coal plants in North Carolina is best suited to serve as the test site.