Energy Vault Holdings, a grid-scale energy storage solution provider, and by the Autonomous Region of Sardinia-owned coal mining company Carbosulcis are set to develop a 100MW Hybrid Gravity Energy Storage System. This solution, designed by Energy Vault for underground mines, combines their modular gravity storage technology with batteries.
The system will be deployed within 500m-deep mine shafts and will utilise the VaultOS proprietary energy management software. This project is crucial for the Sardinia Government’s initiative to transform the coal mine into a Carbon Free Technology Hub, aiming to attract new industrial and technological activities with the provision of low/zero emissions energy.
The Hybrid Energy Storage solution integrates Energy Vault’s EV0 gravity technology with a novel water-based, modular pumped hydro application. This system merges traditional pumped hydro energy storage technology with Energy Vault’s cutting-edge gravity energy storage technology, enabling the partners to repurpose the unique underground features of the retired coal mine.
The solution is specifically designed to optimise and fully exploit the topology of the site, particularly the 500m-deep mine shafts, demonstrating Energy Vault’s capability as a comprehensive and diversified provider of customised energy storage solutions. A land lease agreement has been recently executed, with the installation of the first modular gravity components scheduled to begin in September 2024. Testing of the underground component of the Hybrid Energy Storage System is expected to be completed in 2025.
The Nuraxi Figus site of Carbosulcis, situated on the island of Sardinia in Italy, is scheduled for retirement by the end of 2026. The Sardinia Regional Government plans to convert this site into a Technology Hub with minimal environmental impact, facilitating the industrial and economic reconversion of an area significantly affected by the cessation of coal production.
Additionally, the Hybrid Energy Storage System will play a vital role in stabilising the island’s power grid. Plans include dispatching renewable energy to meet high demand during peak load hours, promoting further local use of renewable generation in Sardinia. The proposed site will be wholly owned and operated by Energy Vault, highlighting the Company’s commitment to being a long-term partner in the region.
EV0, part of Energy Vault’s G-VAULT Gravity Energy Storage System (GESS) portfolio, was announced in May 2024 alongside other new gravity storage system products. This novel design, termed ‘modular pumped hydro’, utilises a water and vessel-based approach to specifically address applications for underground deep mine shafts. The current project involves a 500m-deep shaft at one of Italy’s largest coal mines, which is now being closed.
The mine, which once held reserves of 2.5 billion tonnes of sub-bituminous coal, was among the largest of its kind in Europe and the world. This marks the second deployment of a hybrid energy storage system by Energy Vault, following the Calistoga PG&E project in northern California. The Calistoga project, the largest green microgrid globally, integrates green hydrogen with lithium-ion batteries.
Carbosulcis CEO (Amministratore Unico) Francesco Lippi said: “We are very excited about the innovative energy storage combined solution proposed by Energy Vault, including underground gravity energy storage technology, that we are testing together and that can become one of the solutions to support our project to convert our mine into a new Technology Hub.
“This project will maximise the local use of renewable energy, and at the same time provide services that will improve the stability of the power grid in Sardinia.”
