WO2014022445A1

WO2014022445A1 - Modular energy storage system

Info

Publication number: WO2014022445A1
Application number: PCT/US2013/052801
Authority: WO
Inventors: Stephen Alford; Phillip Andrew STEWART; Bruce James SILK; Daryl Leo CAMPBELL
Original assignee: Enerdel, Inc.
Priority date: 2012-08-01
Filing date: 2013-07-31
Publication date: 2014-02-06

Abstract

Battery assemblies are disclosed which may include a plurality of battery cells positioned in trays which are stacked. The battery cells of each tray may be electrically connected together. The battery assemblies may be supported by a modular battery frame.

Description

MODULAR ENERGY STORAGE SYSTEM

RELATED APPLICATIONS

[0001] This application claims the benefit of US Provisional Application Serial No.

61/678,258, filed August 1, 2012, titled MODULAR ENERGY STORAGE SYSTEM, docket ENERD-P 12-005 -01 -US, the disclosure of which is expressly incorporated by reference herein in its entirety.

[0002] The disclosure of PCT Application Serial No. PCT/US 12/40776, titled ENERGY

STORAGE SYSTEM, filed June 4, 2012, is expressly incorporated by reference herein in its entirety. The disclosure of PCT Application No. PCT/USl 1/52169, filed September 19, 2011, titled ENERGY STORAGE SYSTEM, is expressly incorporated by reference herein in its entirety.

BACKGROUND

[0003] Modular battery assemblies are known. Exemplary known modular battery assemblies may be used for providing power to a power grid, providing power to computing devices in data centers, and providing power to an electric vehicle or a hybrid vehicle.

SUMMARY

[0004] In one embodiment of the present disclosure, a modular battery assembly is provided. The modular battery assembly comprises: a first frame including a lower portion and an upper portion removably coupled to the lower portion, the first frame defining a plurality of guide slots extending between the lower portion and the upper portion; and a first plurality of battery assemblies received within respective guide slots of the first frame, wherein each of the first plurality of battery assemblies includes a plurality of battery cells supported on a plurality of battery trays.

[0005] In one example thereof, the modular battery assembly further comprises a second frame including a lower portion and an upper portion removably coupled to the lower portion, the second frame defining a plurality of guide slots extending between the lower portion and the upper portion; and a second plurality of battery assemblies received within respective guide slots of the second frame, wherein each of the second plurality of battery assemblies includes a plurality of battery cells supported on a plurality of battery trays, the second frame being

52516575 1 supported by the first frame and the second frame being removably coupled to the first frame. In In a variation thereof, the first frame and the second frame are covered with a plurality of panels to form a generally enclosed cabinet. In another variation thereof, the first frame and the second frame serve as a shipping dunnage for the respective plurality of battery assemblies.

[0006] In another example thereof, the upper portion of the first frame is spaced apart from the lower portion of the first frame by a plurality of posts. In a further example thereof, the plurality of guide slots of the first frame are oriented in a non-overlapping arrangement. In still a further example thereof, the first plurality of battery assemblies are electrically coupled together through connections made proximate a front side of the first frame. In yet still a further example thereof, the first frame serve as a shipping dunnage for the respective plurality of battery assemblies. In still another example thereof, the lower portion of the first frame includes a plurality of lower guide members and the upper portion of the first frame includes a plurality of upper guide members, the plurality of lower guide members and upper guide members bounding the plurality of guide slots. In still a further example thereof, the first frame includes a plurality of longitudinal frame members extending generally along a longitudinal direction of the plurality of guide slots and a plurality of transverse frame members extending generally transverse to the longitudinal direction of the plurality of guide slots. In a further example thereof, the modular battery assembly further comprises a first and a second terminal coupled to the plurality of battery cells. In an additional example thereof, the modular battery assembly further comprises a sensor monitoring a characteristic of the plurality of battery cells and a controller receiving a value associated with the monitored characteristic.

[0007] In one embodiment of the present disclosure, a modular battery assembly is provided. The modular battery assembly comprises: a first frame assembly including a lower portion and an upper portion removably coupled to the lower portion, the first frame defining a plurality of guide slots extending between the lower portion and the upper portion and configured to receive a first plurality of battery assemblies within respective guide slots of the first frame, wherein each of the first plurality of battery assemblies includes a plurality of battery cells supported on a plurality of battery trays; a second frame assembly including a lower portion and an upper portion removably coupled to the lower portion, the second frame defining a plurality of guide slots extending between the lower portion and the upper portion and configured to receive a second plurality of battery assemblies received within respective guide slots of the second frame, wherein each of the second plurality of battery assemblies includes a plurality of battery cells supported on a plurality of battery trays; and a plurality of bridge members coupling the first frame to the second frame.

[0008] In one example thereof, the modular battery assembly further comprises a plurality of connectors, the plurality of connectors combining a communication from each plurality of battery assemblies into a wire harness back to a remote controller associated with the assembly. In another example thereof, electrical access to the plurality of battery cells is provided through a front side of the assembly.

[0009] In one embodiment of the present disclosure, a method of assembling a battery assembly is provided. The method comprises the steps of receiving a plurality of frame components at least partially disassembled; constructing a first frame from the plurality of frame components by removably coupling at least a first portion of the plurality of frame components together, the first frame including a lower portion and an upper portion removably coupled to the lower portion, the first frame defining a plurality of guide slots extending between the lower portion and the upper portion; receiving a plurality of battery assemblies, each of the plurality of battery assemblies including a plurality of battery cells supported on a plurality of battery trays; and from a first side of the first frame, locating a first portion plurality of battery assemblies in respective guide slots of the first frame.

[0010] In one example thereof, the method further comprises the steps of constructing a second frame from the plurality of frame components by removably coupling at least a second portion of the plurality of frame components together, the second frame including a lower portion and an upper portion removably coupled to the lower portion, the second frame defining a plurality of guide slots extending between the lower portion and the upper portion; and from a second side of the second frame, locating a second portion plurality of battery assemblies in respective guide slots of the second frame.

[0011] In another example thereof, the method further comprises the steps of supporting the second frame on top of the first frame; removably coupling the second frame to the first frame.

[0012] In still another example thereof, the lower portion of the first frame includes a plurality of lower guide members and the upper portion of the first frame includes a plurality of upper guide members, the plurality of lower guide members and upper guide members bounding the plurality of guide slots.

[0013] In yet another example thereof, said constructing a first frame includes removably coupling a plurality of longitudinal frame members extending generally along a longitudinal direction of the plurality of guide to a plurality of transverse frame members extending generally transverse to the longitudinal direction of the plurality of guide slots.

[0014] The above and other features of the present disclosure, which alone or in any combination may comprise patentable subject matter, will become apparent from the following description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above-mentioned and other features and advantages of this disclosure, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0016] FIG. 1 illustrates a plurality of spaced apart exemplary battery assemblies, each including a plurality of battery cells supported on a battery support;

[0017] FIG. 2 illustrates a plurality of battery assemblies operatively coupled to a remote controller;

[0018] FIG. 3 illustrates an exemplary stack of battery assemblies of FIG. 1, and a housing containing a remote controller;

[0019] FIG. 4 illustrates another exemplary stack of battery assemblies of FIG. 1, and a housing containing a remote controller;

[0020] FIG. 5 illustrates an assembled, front, perspective view of a frame assembly for holding a plurality battery assemblies;

[0021] FIG. 6 illustrates a partial, exploded view of the frame assembly of FIG. 5;

[0022] FIG. 7 illustrates the frame assembly of FIG. 5 supporting a plurality of battery assemblies of FIG. 1;

[0023] FIG. 8 illustrates a second frame assembly supporting a second plurality of battery assemblies, the second frame being supported by the first frame;

[0024] FIG. 9 illustrates an exemplary battery assembly including a plurality of frames of

FIG. 5 and a plurality of battery assemblies of FIG. 1; [0025] FIG. 10 illustrates another exemplary battery assembly including a plurality of frames of FIG. 5 and a plurality of battery assemblies of FIG. 1;

[0026] FIG. 11 illustrates yet another exemplary battery assembly including a plurality of frames of FIG. 5 and a plurality of battery assemblies of FIG. 1; and

[0027] FIG. 12 illustrates still another exemplary battery assembly including a plurality of frames of FIG. 5, a plurality of battery assemblies of FIG. 1, and a plurality of panels cooperating with the plurality of frames to form a generally enclosed structure;

[0028] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate exemplary embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE DRAWINGS

[0029] The embodiments disclosed herein are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may utilize their teachings.

[0030] While the present disclosure primarily involves storing and providing energy for a stationary energy storage market, it should be understood, that the invention may have application to other devices which receive power from batteries. Exemplary applications for a stationary storage market include providing power to a power grid, providing power as an uninterrupted power supply, and other loads which may utilize a stationary power source. In one embodiment, the systems and methods disclosed herein may be implemented to provide an uninterrupted power supply for computing devices and other equipment in data centers. A controller of the data center or other load may switch from a main power source to an energy storage system of the present disclosure based on one or more characteristics of the power being received from the main power source or a lack of sufficient power from the main power source. In one embodiment, the systems and methods disclosed herein may be implemented to provide power to an electric vehicle or a hybrid vehicle.

[0031] Referring to FIG. 1, an exemplary battery assembly 700 is shown. Battery assembly 700 includes a plurality of battery trays 702 A-H, a battery management tray 706 housing a plurality of controllers 708A-D, and a cover 710. Each of battery tray 702A-H support support a plurality of battery cells 104. Battery trays 702 A-H and battery management tray 706 are held together through a plurality of fasteners 872. Fasteners 872, in one embodiment thread into nuts provided in recesses in a lower side of battery tray 702A.

[0032] Additional details regarding battery assembly 700 and additional exemplary battery assemblies are disclosed in PCT Application Serial No. PCT/US 12/40776, titled

ENERGY STORAGE SYSTEM, filed June 4, 2012, the disclosure of which is expressly incorporated by reference herein in its entirety. As discussed in PCT Application Serial No. PCT/US12/40776, the disclosure of which is expressly incorporated by reference herein, the battery cells 104 supported by the battery trays 702 are electrically coupled together. Battery assembly 700 includes a first terminal 900 and a second terminal 902 which are electrically coupled to the battery cells 104 of battery assembly 700. The terminals 900 and 902 of battery assembly 700 may be coupled to a load to provide power to the load. Further, one or both of terminals 900 and 902 may be coupled to the terminals of additional battery assemblies 700 to form a combined battery assembly which may be coupled to a load to provide power to the load.

[0033] As discussed in PCT Application Serial No. PCT/US 12/40776, the disclosure of which is expressly incorporated by reference herein, battery assembly 700 includes sensors to monitor temperature and electrical characteristics associated with battery cells 104. These monitored values are provided to controllers 708 A-D. Controllers 708 A-D are stringed together with data wire harnesses which are coupled to a connector 718 accessible from an exterior of battery management tray 706 of battery assembly 700. Connector 718 may receive a wire harness to couple controllers 708 A-D to a remote controller 717 (see Fig. 2) which monitors and controls the battery assembly 700. Exemplary remote controllers are disclosed in PCT

Application No. PCT/US 11/52169, filed September 19, 2011, titled ENERGY STORAGE SYSTEM, the disclosure of which is expressly incorporated by reference herein in its entirety. As illustrated in FIG. 2, four battery assemblies 700 are operatively coupled to remote controller 717 through respective wiring harnesses. Fewer or additional battery assemblies 700 may be coupled to remote controller 717 through one or more wiring harnesses. In one embodiment, controllers 708A-D of battery assembly 700 communicate with remote controller 717 over a wireless connection. [0034] In one embodiment, as illustrated in FIGS. 3 and 4, battery assemblies 700 and a housing 910 including controller 717 may be stacked. In one embodiment, battery assemblies 700 and housing 910 include nesting features to permit the stacking of battery assemblies 700.

[0035] In one embodiment, one or more battery assemblies 700 may be supported in a frame assembly 1000 (see FIG. 5). As illustrated in FIG. 5, frame assembly 1000 includes a plurality of battery assembly guide slots 1002A-F which are accessible from a first side 1004 of frame assembly 1000. The plurality of battery assembly guide slots 1002A-F are bounded by upper guide members 1006 and lower guide members 1008.

[0036] Referring to FIG. 6, in one embodiment, frame assembly 1000 is comprised of removably coupled frame components. As shown in FIGS. 5 and 6, a lower portion 1011 of frame assembly 1000 includes a plurality of frame members 1010 which extend generally along a longitudinal direction 1003 (see FIG. 5) of battery assembly guide slots 1002 and a plurality of frame members 1012 which extend generally transverse to the longitudinal direction 1003 of battery assembly guide slots 1002. The frame members 1010 and frame members 1012 are held together with fasteners. On the corners, frame members 1010 and frame members 1012 are held together with fasteners through corner brackets 1014. The lower guide members 1008 are coupled to frame members 1012 through fasteners. In the illustrated embodiment, frame members 1010 and frame members 1012 each form a generally U-shaped channel having an upper lip extending inward on the top. The fasteners which couple corner brackets 1014 and lower guide members 1008 to the respective frame members 1010 and frame members 1012 are threaded into components which are captured in the respective channels of frame members 1010 and frame members 1012 and which are held against the respective lips of frame members 1010 and frame members 1012 when the fasteners are tightened.

[0037] As shown in FIGS. 5 and 6, an upper portion 1021 of frame assembly 1000 includes a plurality of frame members 1020 which extend generally along the longitudinal direction 1003 of battery assembly guide slots 1002 and a plurality of frame members 1022 which extend generally transverse to the longitudinal direction 1003 of battery assembly guide slots 1002. The frame members 1020 and frame members 1022 are held together with fasteners. On the corners, frame members 1020 and frame members 1022 are held together with fasteners through corner brackets 1024. The upper guide members 1006 are coupled to frame members 1022 through fasteners. In the illustrated embodiment, frame members 1020 and frame members members 1022 each form a generally inverted U-shaped channel having an upper lip extending inward on the bottom. The fasteners which couple corner brackets 1024 and upper guide members 1006 to the respective frame members 1020 and frame members 1022 are threaded into components which are captured in the respective channels of frame members 1020 and frame members 1022 and which are held against the respective lips of frame members 1020 and frame members 1022 when the fasteners are tightened.

[0038] The lower portion 1011 of frame assembly 1000 and the upper portion 1021 of frame assembly 1000 are coupled together through a plurality of upstanding posts 1030 which are coupled to respective corner brackets 1014 and corner brackets 1024. Along a second side 1040 of frame assembly 1000, a frame member 1042 is provided that limits the movement of battery assembly 700 along longitudinal direction 1003 of frame assembly 1000. Once assembled, frame assembly 1000 receives one or more battery assemblies 700 from side 1004 in battery assembly guide slots 1002 along longitudinal direction 1003.

[0039] In one embodiment, frame assembly 1000 may include additional components coupled thereto to support additional frame assemblies 1000, to support housing 910, anchor points to couple frame assembly 1000 to an environment (as opposed to being freestanding), to aid in the movement of frame assembly 1000 (fork truck tubes proximate the lower portion of frame assembly 1000 and/or pick-up points or eyehooks proximate the upper portion of frame assembly 1000 to assist in the raising of frame assembly 1000). Referring to FIG. 6, a plurality of bridge frame members 1050 are provided which through fasteners serve to couple a first frame assembly 1000 on top of a second frame assembly 1000.

[0040] In one embodiment, frame assembly 1000 may be shipped to an installation site at least partially unassembled. Frame assembly 1000 may then be assembled on site with battery assemblies 700 being received therein. In one embodiment, the assembly of frame assembly 1000 may be performed without any welding requirement. In one embodiment, the installation site has limited access. The ability to assemble frame assembly 1000 onsite permits the positioning of battery assemblies 700 in locations not readily accessible by traditional cabinets. Exemplary installation sites with limited access include ships, submarines, basements, and other sites having limited access.

[0041] Referring to FIG. 7, frame assembly 1000 is shown having six battery assemblies

700 received in respective battery assembly guide slots 1002 of frame assembly 1000. A frame member 1052 is coupled to posts 1030 to hold battery assemblies 700 in place. Frame member 1052 further supports a plurality of connectors 1054 which serve as a switch to combine the individual communications from each module into a wire harness back to the remote controller 717.

[0042] Referring to FIG. 8, a first frame assembly 1000B is shown supported on top of a second frame assembly 1000A. Each of the first frame assembly 1000B and the second frame assembly 1000A include a plurality of battery assemblies 700 supported therein. Referring to FIG. 9, the arrangement of FIG. 8 is altered. The first frame assembly 1000B is spaced apart from the second frame assembly 1000A through a plurality of upstanding posts 1031 coupled to both the first frame assembly 1000B and the second frame assembly 1000A. In FIG. 9, housing 910 is supported by second frame assembly 1000A in the space provided between the first frame assembly 1000B and the second frame assembly 1000 A.

[0043] Referring to FIG. 10, a third frame assembly lOOOC is supported on top of frame assembly 1000A and frame assembly 1000B. Referring to FIG. 11, a plurality of frame assemblies 1000 are shown both vertically and horizontally arranged. Referring to FIG. 12, the arrangement of FIG. 10 is shown with cabinet panels 1056 added to the sides and top of the assembly and a door 1058 being provided on side 1004.

[0044] In the embodiments disclosed in FIGS. 1-12, both electrical access to the batteries of the respective battery assembly 700 and the control connections for the respective battery assembly 700 are made from a front side, side 1004 of the arrangements.

[0045] In one embodiment, the modular frames and battery assemblies disclosed herein may exhibit one or more of the following features:

Sold as kit (sticks and hardware) for assembly.

• Increased packaging efficiency relative to cabinets.

• Ability to transport and assemble on site in to existing structures with limited access i.e. ships, submarines, basements and the like.

Serve as its own shipping dunnage.

• Panels and doors can be added for higher NEMA enclosure rating.

• Easily re-configured for different battery assembly 700 counts.

• Scalability

• Stackable

• Multi-Configurable Array - Vertical or Horizontal Possible

Optional Pick-up points, eyehooks, fork tubes, and anchor points easily added using the same building blocks.

• Potential for no weldments during assembly. HV bussing - no tools required.

• Easy assembly when in Personal Protection Equipment

Easy disassembly

[0046] The battery arrangements disclosed herein may be coupled together to form battery strings. The processing sequences disclosed in US Provisional Patent Application Serial No. 61/486,151 and PCT Application No. PCT/US11/52169, filed September 19, 2011, titled ENERGY STORAGE SYSTEM may be used to monitor and control the operation of the battery arrangements disclosed herein. The arrangements disclosed herein may replace the racks and drawers in the illustrated embodiment disclosed in US Provisional Patent Application Serial No. 61/486,151 and PCT Application No. PCT/US 11/52169, filed September 19, 2011, titled ENERGY STORAGE SYSTEM to provide the battery power of the energy modules disclosed in US Provisional Patent Application Serial No. 61/486,151 and PCT Application No.

PCT/US 11/52169, filed September 19, 2011, titled ENERGY STORAGE SYSTEM. The disclosure of US Provisional Patent Application Serial No. 61/486,151 and PCT Application No. PCT/US 11/52169, filed September 19, 2011, titled ENERGY STORAGE SYSTEM are expressly incorporated by reference herein in their entirety.

[0047] In one embodiment, the frame members of a frame assembly 1000 and/or multiple frame assemblies may be further coupled together through a permanent coupling. Exemplary permanent couplings include welds, adhesives and other suitable couplings. In one embodiment, the permanent couplings are used at least in part in place of the fasteners used to secure the frame members of a frame assembly 1000 and/or multiple frame assemblies together. In one embodiment, the permanent couplings are used at least in conjunction with the fasteners used to secure the frame members of a frame assembly 1000 and/or multiple frame assemblies together.

[0048] While this invention has been described as having exemplary designs, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.

Claims

CLAIMS We claim:

1. A modular battery assembly comprising:

a first frame including a lower portion and an upper portion removably coupled to the lower portion, the first frame defining a plurality of guide slots extending between the lower portion and the upper portion; and

a first plurality of battery assemblies received within respective guide slots of the first frame, wherein each of the first plurality of battery assemblies includes a plurality of battery cells supported on a plurality of battery trays.

2. The modular battery assembly of claim 1, further comprising

a second frame including a lower portion and an upper portion removably coupled to the lower portion, the second frame defining a plurality of guide slots extending between the lower portion and the upper portion; and

a second plurality of battery assemblies received within respective guide slots of the second frame, wherein each of the second plurality of battery assemblies includes a plurality of battery cells supported on a plurality of battery trays, the second frame being supported by the first frame and the second frame being removably coupled to the first frame.

3. The modular battery assembly of claim 2, wherein the first frame and the second frame are covered with a plurality of panels to form a generally enclosed cabinet.

4. The modular battery assembly of claim 2, wherein the first frame and the second frame serve as a shipping dunnage for the respective plurality of battery assemblies.

5. The modular battery assembly of claim 1, wherein the upper portion of the first frame is spaced apart from the lower portion of the first frame by a plurality of posts.

6. The modular battery assembly of claim 1 wherein the plurality of guide slots of the first frame are oriented in a non-overlapping arrangement.

7. The modular battery assembly of claim 1, wherein the first plurality of battery assemblies are electrically coupled together through connections made proximate a front side of the first frame.

8. The modular battery assembly of claim 1, wherein the first frame serve as a shipping dunnage for the respective plurality of battery assemblies.

9. The modular battery assembly of claim 1, wherein the lower portion of the first frame includes a plurality of lower guide members and the upper portion of the first frame includes a plurality of upper guide members, the plurality of lower guide members and upper guide members bounding the plurality of guide slots.

10. The modular battery assembly of claim 1, wherein the first frame includes a plurality of longitudinal frame members extending generally along a longitudinal direction of the plurality of guide slots and a plurality of transverse frame members extending generally transverse to the longitudinal direction of the plurality of guide slots.

11. The modular battery assembly of claim 1 , further comprising a first and a second terminal coupled to the plurality of battery cells.

12. The modular battery assembly of claim 1, further comprising a sensor monitoring a characteristic of the plurality of battery cells and a controller receiving a value associated with the monitored characteristic.

13. A modular battery assembly comprising:

a first frame assembly including a lower portion and an upper portion removably coupled to the lower portion, the first frame defining a plurality of guide slots extending between the lower portion and the upper portion and configured to receive a first plurality of battery assemblies within respective guide slots of the first frame, wherein each of the first plurality of battery assemblies includes a plurality of battery cells supported on a plurality of battery trays; and

a second frame assembly including a lower portion and an upper portion removably coupled to the lower portion, the second frame defining a plurality of guide slots extending between the lower portion and the upper portion and configured to receive a second plurality of battery assemblies received within respective guide slots of the second frame, wherein each of the second plurality of battery assemblies includes a plurality of battery cells supported on a plurality of battery trays; and

a plurality of bridge members coupling the first frame to the second frame.

14. The modular battery assembly of claim 13, further comprising a plurality of connectors, the plurality of connectors combining a communication from each plurality of battery assemblies into a wire harness back to a remote controller associated with the assembly.

15. The modular battery assembly of claim 13, wherein electrical access to the plurality of battery cells is provided through a front side of the assembly.

16. A method of assembling a battery assembly, the method comprising the steps of: receiving a plurality of frame components at least partially disassembled;

constructing a first frame from the plurality of frame components by removably coupling at least a first portion of the plurality of frame components together, the first frame including a lower portion and an upper portion removably coupled to the lower portion, the first frame defining a plurality of guide slots extending between the lower portion and the upper portion; receiving a plurality of battery assemblies, each of the plurality of battery assemblies including a plurality of battery cells supported on a plurality of battery trays;

from a first side of the first frame, locating a first portion plurality of battery assemblies in respective guide slots of the first frame.

17. The method of claim 16, further comprising the steps of:

constructing a second frame from the plurality of frame components by removably coupling at least a second portion of the plurality of frame components together, the second frame including a lower portion and an upper portion removably coupled to the lower portion, the second frame defining a plurality of guide slots extending between the lower portion and the upper portion; and

from a second side of the second frame, locating a second portion plurality of battery assemblies in respective guide slots of the second frame.

18. The method of claim 16, further comprising the steps of:

supporting the second frame on top of the first frame; and

removably coupling the second frame to the first frame.

19. The method of claim 16, wherein the lower portion of the first frame includes a plurality of lower guide members and the upper portion of the first frame includes a plurality of upper guide members, the plurality of lower guide members and upper guide members bounding the plurality of guide slots.

20. The method of claim 16, wherein said constructing a first frame includes removably coupling a plurality of longitudinal frame members extending generally along a longitudinal direction of the plurality of guide to a plurality of transverse frame members extending generally transverse to the longitudinal direction of the plurality of guide slots.