Patent Publication Number: US-RE49532-E

Title: Method and apparatus for storing energy

Description:
The invention relates to a method and apparatus for storing energy. 
     It is a common concern to all providers of electrical energy to match the demand for electricity with their ability to provide electricity. In the course of, for instance, a day, demand typically rises to a high level during certain peak times and falls to lower levels during off-peak times. To meet the peak time demand and make use of any surplus electricity which may be available during off-peak times, electricity providers aim to store surplus energy produced during off-peak times in order to supply this surplus energy during peak times. The source of energy can be either a power plant generating electricity at a more or less constant level or some form of intermittent energy source, such as a solar powered energy source or a wind powered energy source. 
     An example of such a system is discussed in U.S. Pat. No. 5,873,249. Therein, a system is provided for generating energy using the difference in elevation between a relatively high elevation and a relatively low elevation, the system comprising a weight; a lifting device for lifting the weight from the relatively low elevation to the relatively high elevation and for enabling lowering of the weight from the relatively high elevation to the relatively low elevation; a generator for producing electrical energy for consumption; means for converting energy produced by said lifting device during lowering of said weight into drive energy for driving said generator; an electric motor for driving said lifting device to provide lifting of said weight and for driving said generator; and an intermittently operating energy source for supplying electrical energy to the electric motor during operation of the energy source to drive the generator and to enable lifting of the weight by the lifting device whereby the weight can be lifted during operation of the energy source to provide potential energy for the system. 
     Thus, the source of potential energy provided by the weight in the raised position assists in evening out or making more uniform the overall energy that can be supplied. Said system, however, only refers to a single weight, which is being raised and lowered. This limits the flexibility and versatility of the system known in the prior art. While U.S. Pat. No. 5,873,249 also mentions the possibility to have more than one lifting device capable of lifting a respective weight, those embodiments show a high degree of redundancy in that e.g. with every lifting device separate conversion means and a separate generator are associated. 
     It is therefore an object of the present invention to provide a method and a system for storing energy showing improved flexibility and versatility and reduced redundancy. 
     An energy storing system according to the present invention comprises an energy storing system, comprising a plurality of weights, a first storing unit and a second storing unit, wherein the first storing unit is arranged below (i.e. at a lower elevation than) the second storing unit and each of the storing units comprises a guiding track on which weights can be placed and along which weights can be moved, wherein each of said guiding tracks comprises a first portion and a second portion, wherein each second portion is arranged below (i.e. at a lower elevation than) its corresponding first portion; and a loading unit configured to lift at least one weight from the first storing unit to the second storing unit during a first period thereby converting electrical energy to potential energy, said loading unit further configured to lower said at least one weight from the second storing unit to the first storing unit during a second period, thereby converting potential energy to electrical energy, wherein the loading unit is configured to collect a weight from the second portion of the first storing unit and to place said weight on the first portion of the second storing unit during the first period and to collect a weight from the second portion of the second storing unit and to place said weight on the first portion of the first storing unit during the second period. 
     The energy storing system according to the present invention provides for a flexible and scalable system due to the possibility to use a plurality of weights and to operate in a cyclical manner. 
     To allow each weight to move freely along the guiding track on which it is placed, each weight preferably comprises wheels. Those wheels are configured to allow said weight to move from the first, higher portion of said guiding track to the second, lower portion of said guiding track preferably by the action of gravity alone. Thus, a weight which was placed on the first portion of the second storing unit during the first period will move to the second portion of the second storing unit and be ready for collection at the beginning of the second period. 
     In a preferred embodiment, the loading mechanism comprises a loading stage having a guiding track configured to cooperate with the respective guiding track of any of the storing units to facilitate direct transfer of the weight between the loading stage and the respective guiding track. 
     In another preferred embodiment said energy storing system comprises a multitude of storing units arranged at different heights, whereby an even higher degree of versatility is possible. 
     In a preferred embodiment of the present invention, the number of weights transferred during both the first and the second period is equal, whereas the duration of the second period is different from the duration of the first period. Thus, it is possible to generate a higher/lower power level during the lowering of a particular total weight compared to the power level used during lifting of said total weight, wherein power is defined as converted energy per unit of time. 
     The invention also provides a method of producing electrical energy as described below. 
     A method according to the present invention comprises the steps of providing a plurality of weights; providing a first and a second storing unit, wherein the first storing unit is arranged below the second storing unit; lifting at least one weight from the lower storing unit to the upper storing unit during a first period thereby converting electrical energy to potential energy; and lowering said at least one weight from the upper storing unit to the lower storing unit during a second period, wherein the duration of the second period is different from the duration of the first period, thereby converting potential energy to electrical energy. 
     Preferably the second period is either shorter or longer than the first period so as to be able to provide a higher/lower power level during the second period in comparison to the power level used during the first period. 
     In a preferred embodiment, the first period is an off-peak electricity period whereas the second period is a peak electricity period. 
    
    
     
       Further details of the present invention will become clear from the detailed description and the accompanying figures, wherein: 
         FIG.  1    schematically shows an energy storing system according to the present invention; 
         FIG.  2    shows a storing unit to be used in an energy storing system according to the present invention; 
         FIG.  3    shows details of the loading units to be used in the energy storing system according to the present invention; and 
         FIG.  4    shows two upper storing units to be used in an energy storing system according to the present invention. 
     
    
    
       FIG.  1    is a schematic diagram showing an embodiment of the energy storing system  10  according to the present invention. 
     The energy storing system  10  comprises a plurality of weights  12 , one of which being indicated in  FIG.  1   . The energy storing system  10  further comprises a first storing unit  14  and a second storing unit  16 , wherein the first storing unit  14  is arranged below the second storing unit  16 . Each of the storing units  14 ,  16  comprises a guiding track  18 ,  20  on which weights can be placed and along which weights can be moved. The first, lower guiding track  18  comprises a first portion  22  and a second portion  24 , wherein the second portion  24  is arranged slightly below the first portion  22 . Similarly, the second, upper guiding track  20  comprises a first portion  26  and a second portion  28 , wherein the second portion  28  is arranged slightly below the first portion  26 . 
     The energy storing system further comprises a loading unit  30  comprising a loading stage  32 . As indicated in  FIG.  1   , said loading stage  32  can be moved up and down in between the first and second storing units  14 ,  16  in a predominantly vertical direction. 
     Shown in the left hand part of  FIG.  1    is the transfer of a weight  12  from the lower portion  24  of the lower storing unit  14  on to the loading stage  32  (indicated by an arrow). Said weight  12  on loading stage  32  can then be lifted up to the second storing unit  16 . To this end, the loading stage  32  is raised to and aligned with the first, upper portion  26  of the guiding track  20  of the second storing unit  16 , as shown in the right hand part of  FIG.  1   . Subsequently, said weight  12  is transferred or placed on the guiding track  20 . This latter operation is indicated by the arrow shown in the right hand part of  FIG.  1   . 
     Since the first portion  26  of guiding track  20  is arranged at a higher position/elevation relative to the second portion  28  thereof, weight  12  will move along the guiding track  20  from position “A” in the first portion  26  to position “B” in the second portion  28 , since each weight  12  is fitted with wheels  13  allowing said weight  12  to move freely along each guiding track  18 ,  20 . Once in position “B”, said weight  12  is ready for collection to be transferred back to the first storing unit  14 . More specifically, loading stage  32  can collect weight  12  from the second portion  28  of the upper guiding track  20 , lower said weight  12  to the lower guiding track  18  and offload said weight  12  on to the first portion  22  of lower guiding track  18 . Again, said weight  12  will move from the first, higher portion  22  to the second, lower portion  24  of guiding track  18 . Thus, weight  12  is once more ready for collection to be lifted back up to the upper storing unit  16  and thus to start a new cycle. 
     The system shown in  FIG.  1    can be used to lift weights  12  from the lower storing unit  14  to the upper storing unit  16  during a first peak electricity period and to lower those weights  12  from the upper storing unit  16  back to the lower storing unit  14  during a second, off-peak electricity period. By varying the duration of the second period relative to the duration of the first period, the released power can be controlled. For instance, if a particular weight  12  is lifted within a duration of 60 minutes and lowered within a duration of 30 minutes, twice the power will be available in the course of the second period. 
       FIG.  2    shows an embodiment of the energy system, wherein the upper storing unit  16  is arranged near the top of a hill or mountain  100 . Loading unit  30 , which, in the embodiment shown in  FIG.  2    comprises two lifters  40 ,  42 , lifts weights  12  during a first period from the lower storing unit  14  (not shown in  FIG.  2   ) up to the second storing unit  16 , more particularly, to the first end  26  of guiding track  20  of the second, upper storing unit  16 . From said first end  26  the weights  12  will move towards the second end  28 , which is arranged at the slightly lower level in comparison to the first end  26 . The loading unit  30  can then collect weights  12  from the second end  28  and lower those weights back to the first storing unit  14  during a second period. 
       FIG.  3    shows details of the loading stage  32 . Loading stage  32  comprises a cabin  50  having an opening  52  facing the storing units  14 ,  16  during raising and lowering operations. A stage guiding track  54  is arranged at the bottom and on the inside of cabin  50 . Said stage guiding track forms an extension of the guiding tracks  18 ,  20  of the lower and upper storing units  14 ,  16 , respectively, when said cabin  50  is substantially aligned with either end of a guiding track  18 ,  20 . In this aligned state, weight  12  having wheels  13  can be readily transferred between cabin  50  and the guiding tracks  18 ,  20 . 
       FIG.  4    shows two upper storing units  16 ,  16 ′ at the back of the edge of a mountain, wherein both guiding tracks reach the edge of the mountain  100 . On the lifters there will be to every unit an axis on which in this case the axis of unit  16 ′ will be higher than the axis of unit  16  also by raising the height of the lifters more units can be added on the back of the mountain&#39;s edge. 
     The invention also provides a method of producing electrical energy as described below. 
     A method according to the present invention comprises the steps of providing a plurality of weights; providing a first and a second storing unit, wherein the first storing unit is arranged below the second storing unit; lifting at least one weight from the lower storing unit to the upper storing unit during a first period thereby converting electrical energy to potential energy; and lowering said at least one weight from the upper storing unit to the lower storing unit during a second period, wherein the duration of the second period is different from the duration of the first period, thereby converting potential energy to electrical energy. 
     Preferably the second period is either shorter or longer than the first period so as to be able to provide a higher/lower power level during the second period in comparison to the power level used during the first period. 
     In a preferred embodiment, the first period is an off-peak electricity period whereas the second period is a peak electricity period. 
     Although the present invention has been described in relation to specific exemplary embodiments thereof, it will be understood by those skilled in the art that variations and modifications can be effected in these exemplary embodiments without departing from the scope of the invention.