Thermal energy storage system

Abstract

A thermal energy storage system in which at least one vertically extending cavity is formed within ground constituted by geologically stable consolidated rock, and at least one cylindrical steel vessel having a diametral dimension smaller than its longitudinal dimension is positioned within the cavity and surrounded peripherally by a containment material. Conduits are provided for directing pressurised water in vapour and/or liquid phase into the vessel and for conveying steam from an upper region of the vessel. The vessel has a peripheral wall acting as a liner for the containment material and internal pressure-induced forces are transferred from the vessel to the containment material via the peripheral wall. The containment material in one embodiment of the invention includes the surrounding rock. In a further embodiment the containment material includes a filler material and the internal pressure induced forces are transferred from the vessel to the surrounding rock via the filler material.

1 . A thermal energy storage system comprising at least one vertically extending cavity formed within ground that is constituted by geologically stable consolidated rock, at least one cylindrical steel vessel having a diametral dimension smaller than its longitudinal dimension positioned within the at least one cavity and surrounded peripherally by a containment material, conduits provided for directing pressurised water (in vapour and/or liquid phase) into the vessel and for conveying steam from an upper region of the vessel, the vessel having a peripheral wall that functions as a liner for the containment material whereby, in operation of the system, internal pressure-induced forces are transferred from the vessel to the containment material by way of the peripheral wall. 
     
     
         2 . A thermal energy storage system comprising at least one vertically extending cylindrical cavity formed within ground that is constituted by geologically stable consolidated rock, the cavity having a diametral dimension that is substantially smaller than the cavity's longitudinal depth, a cylindrical steel vessel positioned within the cavity and conduits provided for directing pressurised water (in vapour and/or liquid phase) into the vessel and for conveying steam from an upper region of the vessel, the vessel being dimensioned to function as a liner for the cavity and, in operation of the system, to transfer internal pressure-induced forces to the surrounding rock. 
     
     
         3 . A thermal energy storage system comprising a vertically extending cavity formed within ground that is constituted by geologically stable consolidated rock, at least one cylindrical steel vessel positioned vertically within the cavity, conduits provided for directing pressurised water (in vapour and/or liquid phase) into the vessel and for conveying steam from an upper region of the vessel, a thermally stable filler material located between the vessel and a surrounding wall of the cavity, the vessel having a diametral dimension that is substantially smaller than the vessel's longitudinal length and the wall of the vessel functioning as a liner for the filler material whereby, in operation of the system, internal pressure induced forces are transferred from the vessel to the surrounding rock by way of the filler material. 
     
     
         4 . The thermal energy storage system as claimed in  claim 3  wherein the thermally stable filler material comprises a material that maintains its physical and chemical properties when exposed to operating temperatures of the storage system. 
     
     
         5 . The thermal energy storage system as claimed in  claim 3  wherein the filler material is selected from a material that has the capacity to accommodate thermal expansion of the vessel. 
     
     
         6 . The thermal energy storage system as claimed in any one of  claims 1  to  3  wherein the steel vessel has circular cross-section and a diameter within the range of about 1.0 m to about 3.0 m. 
     
     
         7 . The thermal energy storage system as claimed in any one of  claims 1  to  3  wherein the steel vessel has a peripheral wall thickness within the range of about 6 mm to about 18 mm. 
     
     
         8 . The thermal energy storage system as claimed in any one of  claims 1  to  3  wherein the steel vessel has a lower end wall of convex form and thickness within the range of about 6 mm to about 18 mm. 
     
     
         9 . The thermal energy storage system as claimed in  claim 8  wherein the lower end of the cavity is formed as a concavity that complements the convex form of the lower end of the vessel. 
     
     
         10 . The thermal energy storage system as claimed in any one of  claims 1  to  3  wherein the steel vessel has an upper end wall of convex form and a thickness of at least 20 mm. 
     
     
         11 . The thermal energy storage system as claimed in any one of  claims 1  to  3  wherein the upper end of the vessel is anchored to surrounding rock strata by rock bolts. 
     
     
         12 . The thermal energy storage system as claimed in  claim 3  wherein the filler material is selected as one having a coefficient of thermal expansion approximately equal to that of the steel from which the vessel is formed. 
     
     
         13 . The thermal energy storage system as claimed in  claim 3  wherein the filler material is selected as one having a resiliency permitting compression and expansion with thermally induced changes in the dimensions of the vessel. 
     
     
         14 . The thermal energy storage system as claimed in  claim 3  wherein the filler material comprises a mineral material that solidifies in situ. 
     
     
         15 . The thermal energy storage system as claimed in  claim 3  wherein the filler material comprises a mineral material in particulate form. 
     
     
         16 . The thermal energy storage system as claimed in any one of  claims 1  to  3  and comprising a plurality of the vessels, with each vessel being located within its own cavity. 
     
     
         17 . The thermal energy storage system as claimed in  claim 3  wherein a plurality of the vessels is located in a matrix of the filler material. 
     
     
         18 . The thermal energy storage system as claimed in  claim 16  wherein each vessel has a diameter of approximately 1.5 m and the vessels are separated by approximately 3.0 m. 
     
     
         19 . The thermal energy storage system as claimed in  claim 16  wherein the vessels are clustered in closely-spaced relationship. 
     
     
         20 . The thermal energy storage system as claimed in  claim 17  wherein the vessels have a circular cross-section. 
     
     
         21 . The thermal energy storage system as claimed in  claim 17  wherein the vessels have a polygonal cross-section. 
     
     
         22 . The thermal energy storage system as claimed in any one of  claims 1  to  3  incorporated in a power generating plant having a solar energy collector system and a steam turbine connected in circuit with the thermal energy storage system. 
     
     
         23 . The thermal energy storage system as claimed in  claim 22  wherein the solar energy collector system comprises a field of arrayed ground-mounted pivotal reflectors that in use are driven to track the sun and reflect incident solar radiation to at least one elevated receiver system. 
     
     
         24 . A method of storing thermal energy wherein water at a high temperature is maintained under pressure within a cylindrical steel vessel which is positioned within a cavity which is formed within ground that is constituted by geologically stable consolidated rock, wherein the vessel is surrounded peripherally by a containment material and wherein the vessel has a peripheral wall that functions as a liner for the containment material and internal pressure-induced forces are transferred from the vessel to the containment material by way of the peripheral wall. 
     
     
         25 . (canceled) 
     
     
         26 . (canceled)