Ottana CO2 Battery

Executive Overview

The Ottana CO₂ Battery is a 20 MW / 200 MWh long-duration energy storage facility developed by Energy Dome in Ottana, Sardinia, which began commercial operations in July 2025. It is the world's first full-scale CO₂ battery, preceded by a 2.5 MW / 4 MWh pilot that was inaugurated at the same site in December 2022. ENGIE holds the offtake agreement under Energy Dome's Energy Storage as a Service model. The project received funding through the EU-Catalyst programme, backed by Breakthrough Energy Catalyst, the European Commission, and the European Investment Bank — the first European project to receive EU-Catalyst support. Google announced a strategic investment and global commercial partnership with Energy Dome in July 2025, its first investment in the long-duration energy storage space, with plans to deploy CO₂ batteries across its data centre locations in Europe, the United States, and Asia-Pacific.

How It Works & Differentiation

The CO₂ battery stores energy by using surplus electricity to compress and liquefy ambient CO₂, which is stored in pressure vessels. During discharge, the liquid CO₂ is expanded through a turbine and generator to produce electricity, operating in a fully sealed thermodynamic cycle with no atmospheric emissions. The Ottana facility holds approximately 2,000 tonnes of CO₂, occupies 5 hectares, and achieves a round-trip efficiency of 75% or greater AC-to-AC. The standard 20 MW / 200 MWh configuration discharges at 18 MW for 10 hours and charges at 24 MW over 10 hours. The system uses only off-the-shelf components drawn from the oil and gas industry, requires no rare metals such as lithium, and can be constructed in under two years. It also provides inertia services to the grid through rotating turbomachinery — a service not available from battery-based storage.

Commercialization & Traction

ENGIE's offtake represents Energy Dome's first commercial contract and the first deployment of the Energy Storage as a Service business model, in which the customer pays no upfront capital and receives a fixed, predictable payment schedule. Energy Dome simultaneously has a supply contract with Alliant Energy for a 20 MW / 200 MWh project in Columbia County, Wisconsin (with regulatory approval secured and construction beginning 2026), and a 20 MW / 160 MWh project with NTPC Limited in Kudgi, Karnataka, India (expected completion 2026). The company was the inaugural winner of the LDES Company of the Year award at the 2024 Energy Storage Awards. No total capital investment figure for the Ottana project has been publicly disclosed.

Scalability & Strategic Context

The Ottana facility provides Energy Dome's first operational proof point at full commercial scale, following the 2022 pilot, validating both the technology and the business model for replication across multiple geographies. The 10-hour discharge duration places the CO₂ battery in the daily balancing segment between short-duration lithium-ion and multi-day iron-air storage, addressing a distinct grid need. Google's commitment to deploy across all key data centre regions is the most significant commercial signal yet for the platform's scalability, and the Alliant Energy and NTPC agreements establish a multi-continent commercial pipeline heading into 2026. Energy Dome's use of commodity components and a modular design is intended to allow rapid capacity additions without supply chain constraints that affect battery-based competitors.