• One of the lowest CAPEX per kWh of any storage technology
  • Zero-emission (no fossil fuel burning)
  • Use of proprietary thermal energy storage technology (TES)
  • Enabling large-scale electricity storage
  • Low environmental footprint
  • > 72% round-trip efficiency
  • < 5 minutes ramping time




The increasing share of intermittent renewables in the electricity mix creates the need for efficient and viable electricity storage solutions to stabilize the grid. In the ALACAES storage technology, excess electricity from the grid is used to compress air using adiabatic compressors. During the compression, the air is naturally heated up to 550 °C . The hot stream of compressed air is then cooled down in a thermal energy storage (TES) before being stored in the pressure chamber. When needed, the direction of the flow is reversed to convert the compressed air back to electricity using turbines.

The distinctive feature of the ALACAES technology is that the thermal energy storage is placed inside a much larger pressure chamber, usually a mountain or underground cavern. Therefore, the TES, being in the pressure zone itself, does not have to bear any pressure. This dramatically reduces the cost and complexity of the TES unit, giving the ALACAES technology a major economic advantage over alternative storage technologies.

Thermal Energy Storage

The key component of the technology is the proprietary thermal energy storage system (TES), that has been improved and optimized through more than ten years of fundamental research and practical experience. ALACAES has designed, built, and tested several pilot and industrial scale TES systems, refining and optimizing it with each step for costs and performance. Each TES system is engineered using the in-house design tool that gathers all of the know-how obtained throughout the years. The storage medium is tested in the lab and selected for best performance. The proprietary high temperature building material of the TES tank is optimized for high mechanical stability vs. low thermal losses. By optimizing each aspect, the thermal energy storage system achieves near-perfect round-trip efficiency and stable performance for many years of operation.