From Augwind to Airengy: The Quest for Long-Duration Energy Storage in German Salt Caverns

By Investigative Desk | August 2026

The quest to solve the "Dunkelflaute"—the German term for periods of low wind and solar output—has long focused on short-term battery storage and hydrogen. However, a new, ambitious player in the energy storage sector is attempting to revive a forgotten giant: compressed air energy storage (CAES). Following a corporate rebranding, the Israeli-based firm Airengy (formerly Augwind) is currently navigating the complex regulatory and economic landscape of the German energy market, specifically targeting the salt caverns of Lower Saxony.

The Strategic Shift: From Augwind to Airengy

In early 2026, Augwind, an Israeli cleantech firm listed on the Tel Aviv Stock Exchange, completed a strategic rebranding to "Airengy." The shift was more than cosmetic; it signaled a pivot toward becoming an integrated developer and operator of energy infrastructure across Europe and Israel.

Led by CEO Tal Raz and Chairman Yiftah Ron-Tal—the latter a former head of the Israel Electric Corporation—the company aims to deploy its proprietary "AirBattery" technology. Unlike conventional batteries that rely on lithium, cobalt, or rare earth elements, the AirBattery utilizes a hybrid of pumped-hydro and compressed-air technology. By using excess renewable energy to drive hydraulic systems that compress air into underground salt caverns, the company claims it can store energy for months, not just hours. When the grid requires power, the compressed air forces water through turbines to drive generators.

Chronology: The Road to Jemgum

The journey toward a German industrial-scale deployment has been marked by cautious optimism and shifting partnerships:

• Summer 2025: Augwind announces plans to build the world’s first industrial-scale AirBattery in Germany, targeting a 2027–2028 operational window.
• November 2025: A critical milestone is reached when Augwind signs a Memorandum of Understanding (MoU) with SEFE Storage GmbH, a major operator of gas storage facilities in Kassel, Germany.
• Early 2026: Rebranding to Airengy takes place to reflect a broader infrastructure focus.
• August 2026: SEFE spokesperson Stefanie Hallaschka confirms that the collaboration is currently in the assessment phase. The focus is specifically on the salt caverns in Jemgum, Eastern Frisia, which are currently used for natural gas and are slated for hydrogen conversion.

Despite the excitement, no formal construction project has been approved. The current phase is limited to a technical and economic feasibility study conducted by independent consultants.

Technical Nuance: The Isothermal Advantage

The primary challenge with traditional compressed air storage, such as the 1978 Huntorf plant in Germany, is heat loss. When air is compressed, it generates heat; if that heat is not captured or managed, the overall round-trip efficiency of the system plummets.

Airengy’s proprietary system aims for "near-isothermal" compression—compressing the air at a nearly constant temperature. In their Israeli pilot plant, the company reported an efficiency rate of 47%. They aim to push this beyond 60% for commercial-scale European projects.

For the German market, the appeal of the AirBattery lies in its role as a seasonal storage solution. While lithium-ion batteries are excellent for frequency regulation and short-term load balancing, they are economically unviable for multi-day energy storage. Airengy’s proposal for Denmark—a 2.5 GWh system with a relatively low power output of 3–10 MW—illustrates this philosophy. Such a facility could potentially discharge power for 250 to 800 hours, providing a massive buffer during prolonged periods of low renewable generation.

Global Context: China’s Rapid Scaling

While Germany debates the regulatory framework, China is moving at breakneck speed. In early 2026, a 600 MW, 2.4 GWh compressed air plant began operations in Huai’an, Jiangsu province. This represents the third major facility of its kind in China in just a few years. Utilizing advanced heat-storage technology involving molten salt and pressurized water, these Chinese facilities are achieving round-trip efficiencies of 71%—rivaling traditional pumped-hydro plants.

The success of these projects underscores a growing consensus among experts: the technology is mature, but the business case in Europe remains obstructed by market design. Katja Fröhlich of the Austrian Institute of Technology (AIT) notes that compressed air storage is often more "socially acceptable" than other forms of large-scale infrastructure because the primary storage medium is located deep underground, minimizing visual and environmental impact.

The Regulatory and Economic Hurdles

Airengy’s path to deployment in Germany is complicated by several factors:

1. The Legacy of Failed Projects

The German energy sector remains wary of CAES due to previous project failures. The "ADELE" project in Staßfurt, intended to be an adiabatic compressed air storage system, was abandoned by RWE in the mid-2010s. More recently, the Corre Energy project in Ahaus-Alstätte faced significant local opposition from farmers and residents, exacerbated by the financial instability of the parent company, which eventually filed for insolvency. While the project was rescued by the investor Addigen in early 2026, progress has stalled, and no new development timeline has been issued.

2. Market Frameworks

Germany currently lacks a dedicated regulatory framework for long-duration energy storage. The current "Capacity Market" design focuses heavily on new gas-fired power plant tenders, often sidelining storage technologies. Furthermore, the exemption from grid usage fees is currently restricted to storage systems commissioned by 2029—a tight window for complex, multi-year infrastructure projects.

3. Financial Viability

As it stands, storage operators must rely on the "arbitrage" of electricity prices—buying when prices are low (or negative) and selling when they are high. For a multi-day storage system, the frequency of these cycles is lower than for a high-frequency battery, requiring a different financial incentive structure that has yet to be fully realized in German energy law.

Official Responses and Industry Outlook

The partnership between SEFE and Airengy is being watched closely by the energy industry. SEFE, as a state-involved operator, has a mandate to secure Germany’s energy future, particularly as the country moves away from fossil fuels.

"We are currently evaluating technical, economic, and market-related aspects," says Stefanie Hallaschka of SEFE. "The integration of an AirBattery into our existing or planned cavern infrastructure in Jemgum is a complex puzzle. We are not yet at the stage of a formal investment decision."

Despite the silence on specific timelines, the potential is vast. Experts estimate that over 400 salt caverns across Germany are potentially suitable for compressed air storage. If the Jemgum feasibility study yields positive results, it could serve as a "proof of concept" that finally unlocks the potential for large-scale, long-duration energy storage in the heart of Europe.

Conclusion: The Path Forward

The transition from Augwind’s initial vision to the professional, consultative approach of Airengy suggests a maturation of the company’s strategy. By partnering with established players like SEFE in Germany and Nobian in Denmark, Airengy is positioning itself as a technology provider rather than just a developer.

However, the "AirBattery" faces an uphill battle. It must contend with a regulatory environment that still favors traditional gas-based capacity, the skepticism of local communities who have seen previous projects fail, and the need for significant capital investment. As Germany continues its Energiewende, the need for long-duration, non-chemical storage will only increase. Whether the Jemgum caverns become the site of a revolutionary shift or another footnote in the history of German energy innovation remains to be seen. The coming months, as the feasibility studies reach their conclusion, will be decisive for the future of compressed air in the European grid.