The HYDROCK concept - seasonal storage of heat and cold

S.Å. Larsson
Gothenburg University, SE

Keywords: storage, heat, cold, hydraulic fracturing, seasonal

Summary:

The HYDROCK concept HYDROCK is a low-cost system for enery storage in hard rock. It makes use of artificially created fissures as heat exchange surfaces in order to store heat or cold in the bedrock. The simple principle is to use the stress situation in the shallow part of the crust (down to a depth of 200 to 300 m) to create new cracks or enhance existing fractures by hydraulic fracturing. In situ stress measurements from shield regions normally indicate a linear relationship between stress magnitude and depth. As the vertical stress is on average almost equal to the weight of the overlying strata this is normally the least principal stress at these depths and the fractures will propagate more or less horizontally when formed. The fractures can be kept open by sand injection during the process of hydrofracturing. Water will be circulated through the fractures and heat exchange will take place at the water/bedrock interface in the fractures. As the heat exchange surfaces can be made relatively large and the spacing between discrete fractures can be designed, the HYDROCK store can be used for both seasonal and short-term storage of energy