How does it work?

CAES, or Compressed Air Energy Storage, is a highly flexible large-scale energy storage technology. The technology is reliable and has been working safely since 1978 in Germany and 1991 in the US. To implement CAES, we use underground storage caverns created in geological salt deposits via a salt extraction process. These caverns are more commonly known as salt caverns.

“Air is an essential part of the energy transition. How simple can it be?”

What’s going to happen?

To achieve a properly functioning and safe, large-scale, underground energy storage with compressed air, there are several steps that must be followed.

The Engineering – the design

It all starts with designing the installation and the salt cavern where compressed air will be stored. Following this, permit applications must be made and the design elaborated down to the smallest detail. When the necessary permits have been granted, the actual construction begins.

CAES Explained ENG


The construction can roughly be divided into two parts: the underground salt caverns and the above ground associated installation. The salt caverns (large, solid cavities in the salt layers in the soil) are made by dissolving salt.

The salt caverns must then be prepared for compressed air storage. Once the salt caverns and the associated above ground installation / buildings are ready, tests will be conducted to ensure that everything is working properly. Only when the relevant licenses have been granted will the entire installation be put into operation.

More about the technique

In the case of the above-ground CAES installation, 220 MW of compression capacity is involved at the entrance. We will divide this capacity over four compressors of 55 MW each, retaining as much flexibility as possible. During the air compression process, a lot of heat is released. To cool this air before it enters the cavern, we use hybrid cooling towers, resulting in an application of both air and water cooling. As a result, the air temperature in the cavern is around 50 degrees Celsius. This is an ideal temperature to guarantee the stability and safety of the cavern.

During the operation of the CAES facility, in the storage phase, electricity is used to force air into the storage cavern. In the generation phase, the compressed air is released and heated to drive turbines, which produce electricity when needed. When supplying power back to the electricity network, we use two Turbine Expanders with a total capacity of 320 MW. As the air expands, it cools down; therefore, we must warm up the air again, ideally using hydrogen. As a result of this, we are one of the first to be able to apply hydrogen on a large scale and drive the hydrogen economy.

Compressed Air Energy Storage (CAES) made simple

Storage phase

  • Compressors compress outside air into compressed air and use (excess) electricity for this purpose.
  • The compressed air is cooled (to max. 45⁰C) and stored in caverns

Production phase

  • The compressed air is released from the caverns
  • The compressed air heated with H2 (or gas) which drives a modified turbine.
  • The turbine drives a generator that produces electricity

Facts & Numbers

Households in the Netherlands contribute about 20% to the emission of CO2 and other greenhouse gases. In the Netherlands, we use 58% natural gas, 26% coal and 13% other forms of energy to generate electricity. Only 8% of our energy comes from renewable energy sources. Our goal is to increase this.

By making it possible to store renewable energy, we ensure more energy is available to generate electricity.

Our technology makes it possible to store 4 gigawatt hours of energy. You can compare this with the electricity needs of about 158,000 households.