Compressed-air storage installation
BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawing wherein the single FIGURE schematically illustrates, partially in sectional view, a compressed-air storage installation constructed according to the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Describing now the drawing, an exemplary embodiment of the invention is shown schematically and partially in sectional view in the single FIGURE, wherein reference character 1 denotes two compressors between which there can be located a cooler 2. Between the compressors 1 and one side of a motor-generator 3 and the other side of the motor-generator 3 and a gas turbine 4 there are provided couplings 5 by means of which the gas turbine 4 can be selectively coupled with the motor-generator 3 or the motor-generator 3 can be coupled with the compressors 1, as required. Between the gas turbine 4 and the compressors 1, there are pipes or conduits 6 and 6&#39; which incorporate shutoff elements in the form of stop valves 7 and 7&#39;, respectively. The pipes 6 and 6&#39; are joined to an insulated pipe or conduit 8 which leads into a subterranean heat accumulator 9. 
     Now the subterranean heat accumulator 9 is preferably of such a form that it consists of a cavern, generally indicated by reference character 30, cut out of the naturally occurring rock 32. The insulated pipe or conduit 8 carries heated air coming from the compressors 1 to the center or central region of the heat accumulator 9. The heat accumulator 9 is covered at the top by a cover 10 connected in any appropriate manner with the insulated pipe 8. It is advantageous if the cover 10 is extended further downwards until it encounters a rock wall 11 to which it is anchored, forming a seal in the upward direction. 
     Inside of the subterranean heat accumulator 9 there is a storage medium 12, preferably stones or artificially calcined and hardened stones, between which there are arranged the partition walls or partitions 13. Between the spaced partition walls 13 there are formed air passages 14 through which the hot air flows in a generally outward direction, in other words in the direction of the indicated arrows. The air passages 14 are provided in such a manner that the last passage, here indicated by reference character 14a, is formed between one of the partition walls 13 and the rock wall 11. At places with particularly large temperature differences, for example at the air inlet, i.e., the region where the air travelling through the insulated pipe 8 enters the heat accumulator 9, and at a baffle device 15 closing off the cavern 30 of the heat accumulator 9 from a compressed-air storage cavern 16, the partition walls 13, the cover or cover member 10 and the baffle device 15 are provided with thermal insulation 17. Located at an air outlet 18 from the heat accumulator 9 into the compressed-air storage cavern 16 are heat-loss coolers 19 which absorb any heat losses still present before the inlet 34 into the compressed-air storage cavern 16. 
     Between the insulated pipe 8 carrying air into the heat accumulator 9, and also the cover 10 and the rock wall 11 surrounding the cover 10 and the insulated pipe 8, there is provided a gap or intermediate space 20 where the heat passing through the thermal insulation 17 can be removed to the outside by natural air circulation. Furthermore, a protective cover 21 is located on the insulated pipe 8 and this protective cover 21 prevents rain or snow from entering the gap or intermediate space 20 and hence passing into the heat accumulator 9. 
     The compressed-air storage installation with heat accumulator as contemplated by the present invention functions in the following manner: 
     At times of low load demand, the motor-generator 3 is coupled by way of coupling 5 to the compressors 1 and drives the latter. At the same time, coupling 5 between the motor-generator 3 and the gas turbine 4 is disengaged, and the stop valve 7&#39; in the pipe 6&#39; is closed, and the stop valve 7 in the pipe 6 is open. The air which has been compressed and heated in the compressors 1 passes along the pipe 6 and the open stop valve 7 and through the insulated pipe 8 into the center or central region of the storage medium 12 contained in the subterranean heat accumulator 9. This air is forced between the partition walls or partitions 13 into the air passages 14 and thus flows in a generally outward direction, while giving-up the heat contained in it to the storage medium 12. In the last air passage 14a such air flows downwards between the rock wall 11 and the last partition wall 13a, flows through the heat-loss coolers 19, where it surrenders any remaining heat, and passes through the air outlet 18 and passage 34 into the compressed-air storage cavern 16. 
     At times of peak load with additional demand for energy, the air stored in the subterranean cavern 16 passes upward through the heat accumulator 8, whereupon it must again flow through the air passages 14, but in the opposite direction. In doing so it absorbs heat which has been stored in the storage medium 12 and is led through the insulated pipe 8 and the now open stop valve 7&#39; in the pipe 6&#39; to the gas turbine 4 which now is coupled to the motor-generator 3 by way of the related coupling 5. 
     The compressed-air storage installation with heat accumulator as described above is not restricted to what has been shown in the drawing. For example, there can be provided a pipe system filled with liquid instead of a solid storage medium 12, which may consist of natural stones or of artificially calcined and hardened stones, and so forth. Furthermore, not particularly illustrated non-return valves could be arranged at the heat-loss coolers 19 so that the compressed air flowing into the cavern 16 is passed through the residual heat coolers 19, whereas when the flow is reversed the compressed air from the cavern 16 by-passes the residual heat coolers 19. Non-return valves of this kind would reduce a relatively large drop in pressure of the compressed air. 
     While there are shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims. Accordingly,