Pumped heat energy storage seeks to demonstrate commercial readiness

In a key milestone for its pumped-heat energy storage (PHES) technology, Malta Inc., a startup spun out of Google X, has announced that Southwest Research Institute (SwRI) has completed assembly and commissioning of a first-of-a-kind PHES demonstration facility.

Malta’s system stores electricity either directly from a power plant or from the grid. It does this by converting electricity into thermal energy (heat and cold). The heat is stored in molten salt, a proven method of storing thermal energy, and the cold is stored in an antifreeze-like solution with components and subsystems derived from the liquefied natural gas industry.

“The full-scale PHES system offers high potential system performance up to 60% round-trip efficiency and can store energy for more than 10 hours,” said SwRI Group Leader Dr. Natalie Smith, the project’s lead investigator. “PHES is a promising, versatile technology that can be applied to many different energy sources without geological or geographical restrictions.”

Under US Department of Energy (DoE) funding, SwRI has successfully commissioned the small-scale demonstration system that uses simple recuperated cycles for both modes of operation with air as the main working fluid. The facility is intended to demonstrate operation, verify system control strategies, and validate data.

While the SwRI pilot is laboratory-scale, a full-size Malta PHES system will be able to store more than 100 MW of power for eight hours to eight days or longer (1,000+ MWh). One such system is being developed in partnership with Siemens. As announced last year, the two companies are designing turbomachinery components that will support long-duration energy storage systems that could scale over time to the gigawatt range as well as a range of services that the PHES will be able to provide to grid operators, including synchronous inertia, reactive power, and fast ramping. 

In another project using a DoE grant, Malta has partnered with Duke Energy to assess the socio-economic, environmental, and operational issues behind converting retiring coal units into long-duration, zero-emissions energy storage systems.

The two companies said last year they would  look at integrating Malta’s 100 MW, 10-hour pumped heat energy storage system into existing infrastructure at a Duke Energy coal plant in North Carolina.

Malta has also garnered investment from physical commodities trader Trafigura and teamed up with engineering and construction company Bechtel to speed the rollout of long-duration energy storage.