Enel, Energy Vault build 18 MW/36 MWh of US gravity storage

Enel Green Power, the renewable energy unit of Italian utility Enel, and UK-based gravity storage specialist Energy Vault have jointly announced plans to build a large-scale gravity storage facility in the United States.

The system will operate in the ERCOT market. It will also serve the Solutions Excellence Center in Texas, a research facility for innovative storage technologies that is currently under construction.

“The plant is one of the first of its kind in the world and the first in the West,” Enel Green Power said in a statement. “The validation of the technology, which has been tested on the US market, will provide our group with the basis for future projects that could employ gravitational technology for long-term storage applications.”

In March, Energy Vault completed a 25 MW/100 MWh gravity-based storage facility in China.

EVx, the Energy Vault system, demonstrated round-trip efficiency of about 75% in a pilot project installed in Switzerland in 2020. The company said it expects that to be improved to about 80%, placing it in a similar range as pumped hydro storage and even grid-scale batteries.

Energy Vault’s storage device lifts composite blocks with an electric (solar-powered) motor. The lifted blocks are stacked, which creates potential energy. As the blocks are lowered, the energy is harvested and dispatched for use.

It said the tower’s design is based on the physics of pumped hydroelectric energy storage. However, as a solid “mobile mass,” the composite blocks do not lose storage capacity over time. The composite blocks can be made cheaply, said the company, using excavated soil from the construction site, waste materials like mine tailings and coal ash, and even fiberglass from decommissioned wind turbines.

The tower is controlled by computer systems and machine vision software that orchestrate the charging and discharging cycles. A range of storage durations from two to 12 hours or longer is achievable, said the company.