Underground thermal energy storage

Abstract

Underground thermal energy storage in a cylindrical or n-gonal prism shape with a vertical axis, comprising an inner volume for holding a liquid, an outer wall, an inner wall around the inner volume, and a filling layer between the inner wall and the outer wall. The inner wall comprises a series of modular wall parts provided with a heat exchanger for exchanging thermal energy with the liquid. The modular wall parts, arranged in rings, contact the inner volume and have an elastic sealing limiting liquid flow between the inner volume and the filling layer and taking up thermal expansion of the modular wall parts. The filling layer comprises an insulating layer designed to keep the outer wall below 30° C. when the inner volume is at least 90° C., and a structural layer for maintaining the insulating layer and the inner wall's modular wall parts in position.

1 .- 13 . (canceled) 
     
     
         14 . A method for constructing an underground thermal energy storage, said method comprising:
 forming an in-situ outer wall in a trench around an inner volume;   excavating said inner volume to provide an inner space surrounded by the outer wall;   forming an inner wall within the inner space using modular wall parts, leaving a gap between the outer wall and the inner wall, and   filling said gap with a filling layer.   
     
     
         15 . The method of  claim 14 , wherein the outer wall is formed in-situ by means of a soil mix cutter. 
     
     
         16 . The method of  claim 14  wherein the inner wall is formed from prefabricated modular wall parts. 
     
     
         17 . The method of  claim 16 , wherein the prefabricated modular wall parts comprise insulating material attached to a surface of the prefabricated modular wall parts designed to be facing the outer wall. 
     
     
         18 . The method of  claim 14 , wherein the modular wall parts are arranged in a ring, and first a lowest ring of the modular wall parts is positioned, aligned and fixed in said inner space. 
     
     
         19 . The method of  claim 18 , wherein first alternating modular wall parts for said lowest ring of modular wall parts are positioned, aligned and fixed, then the remaining modular wall parts that complete the lowest ring are positioned, aligned and fixed. 
     
     
         20 . The method of  claim 19 , wherein said modular wall parts of said lowest ring are positioned above a bottom of the inner space, said modular wall parts are kept at their height position using a temporary provision, and after completion of said positioning, aligning and fixing of said lowest ring, a support structure is provided for each of the lowest modular wall parts, keeping said modular wall parts at their predetermined height position. 
     
     
         21 . The method of  claim 14 , comprising providing an alignment actuator for positioning said modular wall parts, wherein said alignment actuator provides a radial force directed inwards, and wherein said alignment actuator is provided between said inner wall and said outer wall. 
     
     
         22 . The method of  claim 14 , wherein the underground thermal energy storage has a shape selected from cylindrical and an n-gonal prism having an axial direction that in use is vertical, and wherein the outer wall defines the shape. 
     
     
         23 . The method of  claim 14 , wherein the modular wall parts each have opposite radial surfaces that are in use vertical, an inner tangential surface contacting said inner volume, an outer tangential surface directed towards said outer wall, and opposite axial surfaces that are in use horizontal, said modular wall parts comprising an elastic sealing between a joint of adjacent radial surfaces that limits a liquid flow between the inner volume and the filling layer and takes up thermal expansion of the modular wall parts. 
     
     
         24 . The method of  claim 23 , wherein said elastic sealing comprises a vertical expansion joint, compressible in a tangential direction, between the adjacent radial surfaces. 
     
     
         25 . The method of  claim 14 , further comprising providing the underground thermal energy storage with a heat exchanger for exchanging thermal energy with a liquid. 
     
     
         26 . The method of  claim 14 , wherein the filling layer comprises an insulating layer extending over at least part of a height of the underground thermal energy storage, having a thermal resistance R value where R=d/λ [m 2 K/W], in which d is a layer thickness of the insulating layer, and λ the thermal conductivity of said insulating layer, and the thermal resistance R value is configured to keep said outer wall at a temperature of below 30° C. when said inner volume is at a temperature of at least 90° C., and a structural layer that maintains said insulating layer and said inner wall modular wall parts in position. 
     
     
         27 . The method of  claim 26 , wherein said thermal resistance R value at an upper part of said underground thermal energy storage is at least 8 m 2 K/W. 
     
     
         28 . The method of  claim 14 , wherein filling said gap with a filling layer comprises arranging in the gap a composition having a pressure resistance of more than 500 kPa. 
     
     
         29 . The method of  claim 20 , wherein the lowest wall parts are provided with a flexible container that is filled with a setting composition that extends between said lowest wall parts and said bottom for keeping said lowest wall parts further fixed at their position. 
     
     
         30 . The method of  claim 21 , wherein the alignment actuator comprises a series of balloons set at a fluid pressure. 
     
     
         31 . The method of  claim 14 , further comprising stacking an upper ring of the modular wall parts above a lower ring of the modular wall parts. 
     
     
         32 . The method of  claim 31 , further comprising arranging a horizontal thermally insulating layer between adjacent axial surfaces of the modular wall parts of the upper ring and the modular wall parts of the lower ring. 
     
     
         33 . The method of  claim 14 , further comprising providing a bottom layer connected to said inner wall and/or said outer wall, and a lid of the underground thermal energy storage, such that the lid is at, above, or below a ground level.