Hydrostor’s Compressed Energy Storage Technology Requires Caverns Built in Igneous or Metamorphic Rock, A Closed-Loop Water Reservoir, and Both Air and Water Shafts

      Company Hydrostor has patented its compressed air energy storage (CAES) technology, which utilizes constructed caverns in igneous or metamorphic rock. The company builds its caverns in a ‘room-and-pillar’ fashion, similar to underground mines. The system uses air pressure provided by large compressors and water pressure provided by water pumped in and out from a surface reservoir.

     Building the system in igneous and metamorphic rock severely limits where it can be deployed, but those rocks have low porosity and permeability, so that air and water do not leak out, which would make the system less effective. When the air is injected into the cavern, the water is pushed out to the surface reservoir.

“To increase the energy density of the cavern and improve the operating efficiency, the cavern is flooded with water and connected to a water reservoir on the ground surface – referred to as hydrostatic compensation.”

     Below, it is shown how the caverns are constructed.

     Below is the company’s Willow Rock Energy Storage project in Kern County, California, which is at an advanced stage of development. The company also has active projects in Australia, Ontario, Canada, and near Phoenix, Arizona.

     The technology is basically emissions-free when it is running, but things like cavern construction and rock analysis through drilling cores are generally emissions-intensive. There is no information about costs, which are likely to be high, especially for the cavern and shaft building. The rock removed needs to be stored or moved for disposal. Moving rock is energy-intensive, and storing it may have environmental impacts. I have not seen anything about the economics of these projects, but they are likely to be very high, as most long- duration energy storage (LDES) projects are. This limits their applicability. Thus, issues like cost and the lack of availability of suitable rocks will limit where such facilities can be built. However, LDES projects can provide important benefits to places where intermittent renewables are saturating power grids by storing excess generation and limiting the need for backup power that is often provided by natural gas.

   

 

References:

 

What Lies Beneath: Unearthing Advanced Compressed Air Energy Storage. Hydrostor. 2026. What Lies Beneath – Unearthing Advanced Compressed Air Energy Storage - Hydrostor