Engineering Challenges

A new StoreAge


Gravity Storage requires suitable geological conditions but no elevation difference.


Gravity Storage plants should be located in areas with solid bedrock. The most favorable sites have stable, little-faulted rock such as granite or compact layers of otherwise solid rock material. The geological conditions must first be assessed in detail by a team of geologists. Heindl Energy provides all services required to evaluate potential sites.

In order to estimate how widespread suitable geological conditions for Gravity Storage might be, Heindl Energy has conducted a study analyzing different types of magmatic, metamorphic and sedimentary rock. A total of 117 globally distributed sites where analyzed, and a classification performed based on the internationally recognized Rock Mass Rating (RMR) system. The suitability of the geological conditions for construction of a Gravity Storage plant was found to be “very good” (RMR I) at 3% of the evaluated sites, and “good” (RMR II) at 43%. The remaining sites would require extensive, expensive rock stabilization measures, or would be suitable only for a relatively small Gravity Storage plant.

Geological suitability of evaluated sites for construction of a Gravity Storage plant (corresponding number of sites in brackets).

In addition, a large volume of water (depending on the size of the Gravity Storage – e.g. around 6 million cubic meters for a piston with a diameter of 250 m) must be available. This water is constantly re-used, and thus must only be provided once.


Sealing the surfaces

The Gravity Storage is cut out of surrounding rocks. Because rocks nearly always have crevasses and fine cracks through which water can flow, it is necessary to completely seal the piston and the surrounding piston cylinder against the surrounding area.

For this purpose, all freely exposed surfaces are sealed with a geomembrane and concrete.

Sealing the pressurized water


The solution to the key challenge of sealing the gap between the piston and the cylinder, retaining the highly pressurized water below, is a “rolling membrane” which is securely connected to both piston and cylinder. The rolling membrane is assembled in situ from individual membrane elements that connect radially from the piston to the cylinder. The membrane elements, similar to conveyor belts as used in the mining industry, consist of vulcanized rubber reinforced with steel cables or aramid fibers.
Features and design requirements:

  • Typical pressure at rolling membrane: 50 to 60 bar
  • High resistance to abrasion
  • Adaptable to the piston’s fluctuating position
  • Self-centering
  • Full access possible for maintenance