Compressed-air energy storage (CAES) is a way to store energy for later use using compressed air. At a utility-scale, energy generated during periods of low demand can be released during peak load periods.

The first utility-scale CAES project has been built in Huntorf, Germany in 1978, and is still operational. The Huntorf plant was initially developed as a load balancer for fossil fuel-generated electricity, the global shift towards renewable energy renewed interest in CAES systems, to help highly intermittent energy sources like photovoltaic and wind satisfy fluctuating electricity demands.

Huntorf’s CAES has 290MW capacity with around 40% of efficiency. The plant includes one 290 MW turbine, a 60 MW compressor, and two reservoirs which are called caverns. The CAES has significant merits including a practical solution for large/small scale, low-cost, and long lifetime.

The two caverns have been placed at around 240 meters depth under the ground and the pipelines are used to send and releasing air from close to 198-meter depth. These two caverns have an approximate volume of 310,000 m3.

The plant runs on a daily cycle with 8 hours of compressed air charging and 2 hours of operation at a rated power of 290 MW. This plant provides black-start power to nuclear power plants, backup to local power systems, and extra electrical power to fill the gap between electricity generation and demand.

According to Wikipedia