Patent Publication Number: US-10790671-B2

Title: Modular inverter system and charging system for off-grid power generation

Description:
BACKGROUND 
     Modern society requires a large amount of electrical power generated from a variety of sources. Such power may often be generated on macro levels at facilities such as hydroelectric dams, coal and natural gas-driven generators, and nuclear power plants. As technology improves in other areas, solar-powered generators and wind-powered generators are also becoming a more prevalent source of power generation in society. Generating electrical power has conventionally been accomplished by large enterprises on massive scales, such as utility companies and power companies that produce energy on the order of megawatts and tie directly to a national electrical grid. However, some newer technologies, such as solar and wind, may be well suited to produce energy on micro levels such that individual home owners and businesses may own solar- and wind-driven power generators that may supply power to a local house or even produce small amounts of energy to be fed back to the electrical grid. 
     As a result, a local power sink (e.g., a home), may sometimes draw power from the national electrical grid or from a local micro-generator (or both). Thus, the connection point for the local micro-generator may use a switch controller to facilitate the connections to and from the home and to and from the electrical grid. This may typically involve an inverter/charger because the local micro-generator may produce electrical energy at a voltage that is incongruent with a typical AC voltage of 120/240 volts and 60 Hz. Therefore, local switching circuitry that includes control logic, a proper number and size of inverters/chargers, and a battery for storing electrical energy are all components of a local system needed to properly generate, use and store electrical energy from a local micro-generator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the subject matter disclosed herein in accordance with the present disclosure will be described with reference to the drawings, in which: 
         FIG. 1  is a block diagram of an electrical system at a micro level that includes a modular inverter system according to an embodiment of the subject matter disclosed herein; 
         FIG. 2  is a diagram of the modular inverter system of  FIG. 1  according to an embodiment of the subject matter disclosed herein; 
         FIG. 3  is a diagram of one inverter/charger module of  FIG. 2  according to an embodiment of the subject matter disclosed herein; 
         FIG. 4  is a diagram of the modular inverter system of  FIG. 1  having some inverter/charger modules removed according to an embodiment of the subject matter disclosed herein; and 
         FIG. 5  is a flow chart of a method for handling power routing within the modular inverter system of  FIG. 1  according to an embodiment of the subject matter disclosed herein. 
     
    
    
     Note that the same numbers are used throughout the disclosure and figures to reference like components and features. 
     DETAILED DESCRIPTION 
     The subject matter of embodiments disclosed herein is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described. 
     Embodiments will be described more fully hereinafter with reference to the accompanying drawings, which form a part hereof, and which show, by way of illustration, exemplary embodiments by which the systems and methods described herein may be practiced. This systems and methods may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy the statutory requirements and convey the scope of the subject matter to those skilled in the art. 
     By way of overview, the systems and methods discussed herein may be directed to a modular inverter system having a single device enclosure with a plurality of module receptacles capable of receiving one or more modules having tailored functionality. Such modules work in conjunction with each other to handle control of various power sources and power sinks in a mixed use power generation and consumption system. In various embodiments, these swappable modules include a charge controller module configured to control charging a battery, an inverter/charger module configured to convert an AC voltage to a DC voltage for charging the battery and configured to invert a DC voltage to and AC voltage for supplying AC power, a controller module configured to control the plurality of inverter/charger modules and the charge controller module; and a backplane disposed in the enclosure such that each module receptacle facilitates engaging a respective module with the backplane. 
     The modular inverter system, as described, provides a number of advantages over conventional non-modular solutions. First, as a local power requirement grows, one can easily add additional functionality to the modular inverter system by simply inserting an additional module. For example, as the AC draw from a battery may grow because a home has added new circuits, one may add an additional inverter/charger module to supply inverted AC power from a local battery stack. Second, a modular inverter system allows for swapping and maintenance while the system remains under load. That is, the modules in the modular inverter system are hot-swappable. Third, the modular inverter system provides a simple and manageable solution for an inverter-grid tie-in such that local power generation system (e.g., wind, solar, and the like) may be continuously in use even if a battery stack is fully charged. That is, the local power that is generated may be sold back to the power company. These and other advantages will become more apparent with the discussion below in conjunction with  FIGS. 1-5 . 
       FIG. 1  is a block diagram of an electrical system  100  at a micro level that includes a modular inverter system  110  according to an embodiment of the subject matter disclosed herein. The electrical system  100  may typically be a power sink (e.g., a home, a building, and the like) with various capabilities for receiving electrical power from an electrical grid  130  or for generating local electrical power from one or more power generation sources. In this example, the power sink is a residential home  135  having a local electrical distribution panel  137  that may include a typical array of electrical devices that consumer power, such as electric heaters, lights, kitchen appliances and the like. Of course, the power sink may be any other facility, building, complex, or standalone device that uses electrical power for operation. As is common, one source for electrical power for the home  135  is the national electrical grid  130  or simply grid  130 , hereinafter. In the United States, the national electrical grid comprises a power source with a nearly constant voltage of 120/240 VAC with a nearly constant frequency of 60 Hz. Industrial and commercial scenarios may further involve 3-phase connections at 208 VAC. In other countries, the grid may vary to include voltages up to 240 V and frequencies down to 50 Hz. For this example, the grid will comprise a nearly constant voltage of 120/240 VAC with a nearly constant frequency of 60 Hz. 
     The grid  130  may be coupled to the home through the modular inverter system  110  in this example. Further, these electrical connections may include respective circuit breakers/disconnect switches (switch  131  associated with the grid  130  and switch  136  associated with the home  135 ) that may be part of the modular inverter system  110  and controlled by the modular inverter system  110 . Each of the switches shown in  FIG. 1  may be circuit breakers and may also be part of the modular inverter system  110  in order to comply with NEC rules and code for providing circuit protection for each of the various electrical connections throughout the system of  FIG. 1 . As such, these switches, throughout this disclosure may be referred to as disconnect switches or circuit breakers without limitation on underlying function. The specific parameters of control are discussed further below. For now, attention is turned to alternative sources for electrical power associated with the system  100  of  FIG. 1 . 
     A first local power source (other than the grid  130 ) may be an electrical generator  140  coupled to the modular inverter system  110  though an associated disconnect switch  141 . The electrical generator  140  may be a gasoline-fired generator, a natural gas-fired generator, a propane-fired generator or any other generator that is capable of generating electrical power at a nearly constant voltage of 120/240 VAC with a nearly constant frequency of 60 Hz. Such a local electrical generator  140  may be used at the home  135  to supply electrical power in lieu of the electrical grid  130  in grid power outages. Since the electrical generator  140  generates electrical power with the same parameters as the grid  130 , the modular inverter system  110  simply provides the capabilities of a transfer switch. Such a transfer switch is discussed further below with respect to  FIG. 2 , but for now, it is sufficient to understand that the transfer switch prevents the grid  130  and the generator  140  from being simultaneously coupled to the home  135  (via mutually exclusive control of switches  141  and  131 ). 
     Aside from the power sources that supply power at a nearly constant voltage of 120/240 VAC with a nearly constant frequency of 60 Hz (generator  140  and grid  130 ), additional local power sources may be used in conjunction with a local battery array  120 . A first example of a local power source may be a solar panel array  115  configured to convert solar energy into electrical energy. This converted electrical energy may be used to provide charge to the battery array  120  and may be isolated from the battery array via disconnect switch  118 . A typical solar array  115  will generate electrical power at approximately 600 VDC with individual panels generating about 10-20 VDC each. Similarly, a second example of a local power source may be a wind turbine  118  configured to convert wind energy into electrical energy. Other local power sources contemplated but not shown include fuel cells and hydro-electric generators that may include commercial applications up to 1000 VDC. This converted electrical energy may be used to provide charge to the battery array  120  and may be isolated from the battery array via disconnect switch  119 . A typical wind turbine will generate electrical power at approximately 600 VDC. 
     As these local power sources (solar panel  115  and wind turbine  118 ) typically do not generate power at that which is typically used at a home  135  (a nearly constant voltage of 120/240 VAC with a nearly constant frequency of 60 Hz), the battery array  120  may be used to store electrical charge generated from the local VDC sources. Further, any battery array  120  will only provide a direct current (DC) voltage (typically 48 VDC) and most power sinks require alternating current (AC) voltage (Typically 120/240 VAC). Thus, the modular inverter system  110  may be used to invert DC voltage from the battery array  120  into AC voltage for use at the home  135 . Therefore, the battery array may be electrically isolated at times from the modular inverter system  110  via disconnect switch  121 . 
     Each of the disconnect switches in  FIG. 1  ( 116 ,  119 ,  121 ,  131 ,  136 , and  141 ) may be housed within and controlled by the modular inverter system  110  at various times according to what power source may be providing electrical power to the home  135 . The modular inverter system  110  therefore performs several functions in a singular interconnected control system. These functions may include modules for providing one or more automatic transfers between power sources, one or more inverters, one or more battery chargers, one or more charge controllers, one or more electrical panels, electrical surge protection, and electrical circuit breaker protection. Further, each of these functions may be provided with dedicated modules that may be swapped in and out (during operation—referred to as “hot swapping”) of a system housing having common backplanes (e.g., a 120/240 VAC backplane and a 48 VDC backplane). Therefore, the overall inverter system  110  is modular, configurable and flexible to meet the needs to almost any configuration of equipment. These modules and associated features are discussed next with respect to  FIG. 2 . 
       FIG. 2  is a diagram of the modular inverter system of  FIG. 1  according to an embodiment of the subject matter disclosed herein. As discussed above with respect to  FIG. 1 , the modular inverter system  100  includes a number of modules for facilitating various interconnection between power sources and power sinks. Such interconnections are managed in a manner that will convert power signals from any power source to a suitable power condition (e.g., electrical power at a nearly constant voltage of 120/240 VAC with a nearly constant frequency of 60 Hz) for use at the power sink—in the case of  FIG. 1 , a residential home  135 . Several different modules are shown in  FIG. 2 , but a skilled artisan understands that the configuration shown in  FIG. 2  is but one example. In the example of  FIG. 2 , the modules include an electrical panel module  210 , a set of four inverter/charger modules  205 - 208 , a charge controller module  210 , a system controller module  230 , and an electrical interconnection panel module  220 A/B. The modular inverter system  110  may further include one or more handles  250 . Each of these modules may be configured to be inserted into a rack-style housing  201 , wherein at least some of these modules may be pulled out or inserted while other modules remain functional and in use. Prior to discussing the inter-related functionality of the modules within the modular inverter system  110 , each of the modules is described next with respect to individual underlying functionality. 
     The first module to be discussed is one of the set of four inverter/charger modules  205 - 208 ; for the sake of selecting one module for the purpose of exemplary discussion, inverter/charger module  205  will be used. The inverter/charger module  205  comprises two portions: an inverter portion and a charger portion. The inverter portion, sometimes called a power inverter, is an electronic device having circuitry that changes direct current (DC) to alternating current (AC). The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry. Thus, one function of the inverter portion is to convert a 48 VDC signal from a battery array ( 120  of  FIG. 1 ) to a 120/240 VAC signal at 60 Hz for use at a power sink, such as a residential home ( 135  of  FIG. 1 ). Inverters are often rated in terms of power (e.g., watts) that the circuitry can handle. In one embodiment, each modular inverter  205  can handle approximately 2 kW or power, however, other sizes are possible and each inverter in the set of five inverter/charger modules need not be matched. Further, not all five spaces need be filled with an inverter/charger module. 
     The second portion of the inverter/charger module  205  comprises a battery charger portion. A battery charger, or simply charger, is a device used to inject energy into a one or more cells of a rechargeable battery by coupling an electric current from a power source (e.g., the battery  120 , the grid  130 , the generator  140  and the like as shown in  FIG. 1 ). The charging procedure depends on the size and type of the battery being charged. Some battery types have high tolerance for overcharging and can be recharged by connection to a constant voltage source or a constant current source. Once charged (determined via common battery charge level monitoring), the charger may be disconnected from the battery at the end of the charge cycle, or may have a timer to cut off charging current at a fixed time. 
     Thus, the inverter/charger module  205  may function as an inverter when the power source for supplying power to the home  135  is the battery  120  (e.g., off-grid and not on generator power). In such a mode, the modular inverter system  110  may also invoke the charger portion of each inverter/charger module  205 - 209  to continue providing a charge signal from an off-grid power source (e.g., the solar panel  115  or wind turbine  118 ). In a reciprocal manner, the inverter/charger module  205  may function as a charger when the power source for supplying power to the home  135  is the grid  130  or the generator  140  such that power is drawn from the grid  130  or generator  140  to charge the battery  120 . 
     When one or more inverter/charger modules  205 - 208  are used to provide charge to the battery  120 , a charge controller module  210  may be also used to monitor and facilitate a more efficient transfer of electrical energy from one of the various power sources to the battery array  120 . A charge controller, (sometimes called a charge regulator or battery regulator) may be used to limit the rate at which electric current is fed to or drawn from the battery array  120 . The charge controller module  210  may be further controlled by the system controller module  230  such that overcharging may be prevented to protect against overvoltage, which can reduce battery  120  performance or lifespan, and may pose a safety risk. In conjunction with the system controller module  230 , the charge controller module  210  may also prevent completely draining (“deep discharging”) the battery array  120 , or perform controlled discharges, depending on the battery technology, to protect battery life. Upper and lower limits of battery voltage may be set by the system controller module  230  for the purposes of engaging the charge controller module  210 . 
     If the charge controller  210  is to be used to facilitate efficient charging of the battery array  120  from power derived from an off-grid power source (e.g., the solar panel  115  or the wind turbine  118 ), the charge controller module  210  may be used to maximize the efficiency of power transfer. This may be accomplished with a charge controller module  210  that includes a Maximum Power Point Tracking (MPPT) feature such that the voltage generated from the off-grid power source may be tracked to determine an optimal current to be used to charge the battery array  120 . MPPT is a technique used commonly with wind turbines and photovoltaic (PV) solar systems to maximize power extraction under all conditions. A particular problem addressed by MPPT is that the efficiency of power transfer from the solar cell or wind turbine depends on both the amount of sunlight falling on the solar panels or wind speed and the electrical characteristics of the load. As the amount of sunlight or wind varies, the load characteristic that gives the highest power transfer efficiency changes, so that the efficiency of the system is optimized when the load characteristic changes to keep the power transfer at highest efficiency. This load characteristic is called the maximum power point and MPPT is the process of finding this point and keeping the load characteristic there. Electrical circuits can be designed to present arbitrary loads to the photovoltaic cells and then convert the voltage, current, or frequency to suit other devices or systems, and MPPT solves the problem of choosing the best load to be presented to the cells in order to get the most usable power out. 
     Embodiments of the charge controller module  210  may include inputs for 200 VDC and 600 VDC. The 200 VDC embodiment is capable of handling 120-160 amps making such charge controller modules  210  among the largest in the market. The 600 VDC embodiment is capable of handling 100 amps making such charge controller modules  210  the largest in the present-day market. Further, in the modular inverter system  110  can be configured to have a mix of charge controller modules  210  including different versions (e.g., a 200 VDC version next to a 600 VDC version) such that different sets of solar panels and/or wind turbines may be accommodated. 
     The charge controller module  210  may also include indicator lights  231  showing the state of the charge controller (e.g., currently charging battery at a first indicator light, currently discharging the battery at a second indictor light, and battery disconnected at a third indicator light). Further, the charge controller  210  may include a current meter  232  showing current flow to or from the battery and may be set manually to monitor specific currents. 
     The modular inverter system  110  may also include an electrical panel  220 A/B that may be coupled to various loads or power sinks via circuit breakers/disconnects. The electrical panel  220 A/B provides circuit breakers  211  for each circuit load to be fed. In  FIG. 1 , the electrical panel  220 A/B is shown as a first module (“A”) and a second module (“B”) though these modules need not be separate and can be one single large module (“A/B”). These circuit breakers may correspond to the disconnect switches  116 ,  119 ,  121 ,  131 ,  136 , and  141  depicted in  FIG. 1 . The circuit breakers may typically range in size from 15 amps to 200 amps and may be configured to directly receive circuit wires through a rear-panel harness (not shown). The electrical panel  220 A/B may include spaces for additional circuit breakers that have yet to be installed. The entire electrical panel module  220 A/B itself is modular in that the electrical panel module  220 A/B may be inserted and removed from the housing such that the module interfaces with a backplane voltage bar (not shown in  FIG. 2 ). 
     The electrical panel module  220 A/B may include an AC bypass switch  221  that is configured to couple one or more AC inputs directly to one or more AC output nodes and to decouple the AC bus that is part of the backplane of the modular inverter system  110 . In this manner, one can bypass the modular inverter system  110  for the purposes of maintenance and troubleshooting without risk of electric shock from components coupled to the AC bus. The electrical panel module  220 A/B may feature the circuit breaker/disconnect switches (e.g.,  116 ,  119 ,  121 ,  131 ,  136 , and  141  of  FIG. 1 ), in reachable positions such that an operator may manually connect or disconnect any switch at any time. However, the modular inverter system  110  may provide hardware-based or software-based safety provisions that do not allow certain circuit breakers/disconnect switches to be simultaneously connected. Further, the electrical panel module  220 A/B may include a number of meters  222  for monitoring current flow to and from various power sources and power sinks. 
     The modular inverter system  110  may also include one or more surge protection devices  240 . A surge protection device (sometimes called, surge protector, surge suppressor, surge diverter, or lightning arrestor) is an appliance or device designed to protect electrical devices from voltage spikes. The surge protection device  240  attempts to limit the voltage supplied to an electric device by either blocking or shorting to ground any unwanted voltages above a safe threshold. Lastly, the modular inverter system  110  may also include a simple handle module  250  for handling the overall housing. This handle module  250  may be replaced with a number of other more useful electrical-based modules. 
     The modular inverter system  110  when equipped with the modules as shown provides a number of advantages when used within the system  100  of  FIG. 1 . One advantage is that the modular inverter system  110  is, in fact, modular. This allows any of the modules to be hot swapped while any power source remains engaged and providing power to any connected load. In this embodiment, there are five “power” module spaces shown that are currently filled with inverter/charger modules  205 - 208 . In other embodiments, there may be only three power modules (differentiated from module spaces reserved for control features, such as modules  210 ,  220 A/B, and  230 ). In still further embodiments, there may more than five modules or a second housing (not shown) with additional power module spaces electrically coupled to a first housing  201 . Further yet, not all power module spaces need be filled (as is shown in  FIG. 4  and discussed below). 
     The modules may be easily swapped in and out using simple securing mechanisms such as thumbscrews  255 . Such thumbscrews typically do not require any tool to operate and actuate. Further, the housing may include wing brackets  260  for mounting to a wall using conventional screws or other fastener. The weight of the modular inverter system  110  is small enough to not require triangle bracing or other form of support from below. Additional features of the modular inverter system  110  are discussed further below in the context of  FIGS. 3-5 . 
       FIG. 3  is a diagram of one inverter/charger module  205  of  FIG. 2  according to an embodiment of the subject matter disclosed herein. The inverter/charger module  205  is shown disengaged from any modular inverter system  110  so that additional features may be seen. Specifically, two different internal protrusions  350  and  351  are shown. These protrusions  350  and  351  may be printed circuit boards (PCB) having electronic components configured to be coupled the inverter/charger module  205  to one or more internal busses in a modular inverter system  110 . Thus, a first PCB protrusion  350  may be a circuit configured to engage a 48 VDC bus such that the inverter/charge module may draw power from the battery ( 120  of  FIG. 1 —also coupled to the 48 VDC bus) to be inverted into a voltage signal at nearly 120/240 VAC and nearly 60 Hz. The inverted 120/240 VAC signal is routed to the second PCB protrusion  351  to be coupled to a second bus that is for 120/240 VAC and coupled to the home  135  and/or grid  130 . Thus, when the inverter/charger module  205  is being used as an inverter, a 48 VDC signal is drawn from the battery and inverted to a 120/240 VAC signal for use at the load. 
     Likewise, the second PCB protrusion  351  may be a circuit configured to engage a 120/240 VAC bus such that the inverter/charge module  205  may draw power from the grid ( 130  of  FIG. 1 —also coupled to the 120/240 VAC bus) to be converted into a voltage signal at nearly 48 VDC. The converted 48 VDC signal is routed to the first PCB protrusion  350  to be coupled to a first bus that is for 48 VDC and coupled to the battery  120 . Thus, when the inverter/charger module  205  is being used as a charger, a 120/240 VAC signal is drawn from the grid  130  (or generator  140 ) and converted to a 48 VDC signal for charging the battery  120 . 
     In an embodiment, inverter/charger module  205  is rated to provide approximately 2000 watts of continuous power inverted from a coupled battery  120  wherein the battery  120  is coupled to a 48 VDC nominal input. When used as a charger, the inverter/charger module  205  includes circuitry to provide power factor correction depending on the current charge state of the coupled battery  120 . Each inverter/charger module includes indicator lights for various states of operation. In one embodiment, these indicator lights include inverter engaged  310  (e.g., power on), input voltage present  311  and a scale light  312  indicative of the what a local meter is measuring. Further, the inverter/charger module  205  includes a meter  315  for current flow (either to the battery  120  when charging or to the home  135  when inverting). Further yet, inverter/charger module  205  includes a fan port  330  for providing an airflow path through the inverter/charger module  205  for cooling the inverter/charger module  205 . 
     In this embodiment, the inverter/charger module  205  is hot swappable. Thus, an operator may use a front-panel mounted handle  320  to pull the inverter/charger module from the housing (assuming the thumb screws have been disengaged). This pulling motion will disengage connectors on each PCB board  350  and  351  and may result in a current arc (e.g., current spike). Such current spikes may cause voltage fluctuations. However, built-in circuitry in each PCB board  350  and  351  provides a current path such that all voltage above 30V are dissipated within 0.5 seconds after backplane connectors disengage. Further, each inverter/charge module  205  includes on-board fuses for AC input/output and for DC input. Thus, a defective module  205  blows local fuses rather than taking down the entire modular inverter system  110  by blowing a battery breaker. Further yet, the indicator lights  310 - 312  may be powered separately from a local 9V battery so that the indicator lights  310 - 312  continue to function even when the inverter/charger module  205  fails. Additionally, the inverter/charger module includes a safety door engagement protrusion  335  that will be discussed in greater detail below with respect to  FIG. 4 . 
       FIG. 4  is a diagram of the modular inverter system  110  of  FIG. 1  having some inverter/charger modules removed according to an embodiment of the subject matter disclosed herein. The modular inverter system  110  shown in  FIG. 4  is similar to the modular inverter system  110  of  FIG. 2  except that three particular inverter/charger modules  205 ,  206 , and  207  are removed to show empty spaces  305 ,  306 , and  307 . The empty spaces show inside the housing  201  such that couplings to two backplane busses can be illustrated. The busses are exaggerated here for illustration purposes and a typical module bay may only include an electrical interface such that protruding PCB edges of various module may “stab” into the open interfaces. Other manners of interfacing swappable modules with backplane busses are contemplated but shown for brevity. 
     The first backplane bus in a 48 VDC backplane bus  370  and the second backplane bus shown is a 120/240 VAC backplane bus  372 . The inverter/charger module  208  and the charge controller module  210  may engage these backplane busses with respective stab-in connectors that may be part of respective PCB protrusions  350  and  351  as shown in  FIG. 3 . However, when such modules are removed (e.g., during a hot swap or if such modules are not needed), one can see that the backplane busses  370  and  372  or interfaces to such busses are exposed. Such exposure may be dangerous to operators who may touch said backplane busses accidentally. 
     To prevent accidental shock hazard and to comply with electrical code and electrical standards (e.g., UL listing and the like), each empty space may include a movable safety door  374 . In  FIG. 4 , one safety door  374  is shown at space  305  (space  306  and  307  do not shown any safety door so as to illustrate backplane bus bars  350  and  351 . Safety door  374  may be spring-mounted such that as a module is pulled from housing, the safety door  374  swings down into place. Further, the safety door may include a locking mechanism (not shown in detail) preventing the safety door  374  from swinging back open when any force is applied to the front of the door  374 . The locking mechanism may be released when a safety door engagement protrusion  335  of any module (such as the module  205  depicted in  FIG. 3 ). The safety door  374  may also be opened using a tool (also not shown) designed to disengage the locking mechanism. Providing a closed and locked safety door  374  improves air flow across the backplane bus bars  350  and  351  no module is installed. In other embodiments, air restrictors (e.g., empty modules) may be installed in module bays that are empty so cooling air is not channeled into an empty module bay. In this manner, unique airflow routes for providing cooling air above and below installed modules to get to each module bay is maintained. 
     The busses  370  and  372  may be monitored by the system controller module  230  for voltage level and current flow. Further, each inverter/charger module may also monitor each bus for voltage level and current flow. In this manner, the system controller  230  may then engage of disengage various module functionality as is needed. Thus, the system controller module may be a master controller over other module functionality and embodies logically-based decision circuitry to determine if electric power is to be stored at the battery via a charging procedure or sold back to the grid using an electric grid tie-in procedure. The system controller module  230  may control the flow of electric current on the backplanes via a set of electronic relays (not shown) that may be actuated to couple various circuits to one or both busses. 
     For example, in a home  135  equipped with a generator  140  and the modular inverter system  110 , when an electric grid  130  outage occurs, the system controller module  230  may initiate a startup sequence at the generator  140 . Once the system controller module  230  senses that the generator voltage is sufficiently high enough to provide proper electric power, the system controller module  230  disconnects the electrical grid  130  (via electronic relays) and connects the generator  140  (also via electronic relays to the AC bus. The generator  140  supplies power to the home  135 , but is not connected to the electrical grid  130 . Further, the battery  120  may be charged from power drawn from the now connected generator  140 . It is necessary to isolate the generator  140  from the distribution system to protect the generator from overload in powering loads in the home  135  and for safety, as utility workers expect the electric grid  130  lines to be dead. 
       FIG. 5  is a flow chart  500  of a method for handling power routing within the modular inverter system of  FIG. 1  according to an embodiment of the subject matter disclosed herein. The method steps as depicted in  FIG. 5  may be performed in any order and the order in which the flow chart  500  is arranged and describe is but one embodiments of various method for operating the systems as described in  FIGS. 1-4 . Generally speaking, the method of the flow chart  500  of  FIG. 5  may be initiated at step  502  when monitoring and control of the modular inverter system  110  of  FIG. 1  is undertaken. 
     After initiation of control and monitoring at step  502 , a number of sub-methods may be accomplished discretely or simultaneously and in any combination. These three sub-methods may generally be thought of as 1) monitoring for grid connectivity, 2) charging the battery, and 3) maintaining off-grid power generation and consumption. These sub-methods may be in a continuous monitoring state whereby method iterates through three particular queries: 1) is the grid functional  510 , 2) is the battery fully charged  530  and 3) should the overall system shift to off-grid power generation and consumption  550 . 
     Turning the first query  510 —whether the grid is functioning, the method may determine that the grid is, in fact, functioning. If so, the grid disconnect switch ( 131  of  FIG. 1 ) may be automatically engaged (e.g., closed) at step  510  such that the grid is coupled to the home  135 . This may be a steady state such that the state of the grid is continuously monitored at query  510 . If, however, the grid  130  is determined to be not functioning (e.g., the grid is down), the grid disconnect switch  131  may be disengaged (e.g., opened) at step  511  such that the home  135  may no longer be powered from the grid  130 . In such a case, the method may also then power the home from off-grid sources and charge the battery in the second and third sub-methods as alluded to above. 
     In a second sub-method, the system may be monitored and controlled such that charge on the battery  120  is maintained at least at a threshold charge via query  530 . Such a threshold charge may be queried at step  530 . If the charge is sufficient, each of the sub-methods may continue to monitor the status of various parts of the overall system. However, if the battery  120  does not have sufficient charge, one or more power sources may be engaged to provide charge to the less-than-fully charged battery  120 . These battery-charging procedures include charging the battery  120  from the grid  135  at step  532 , charging the battery from the generator  140  at step  534 , charging the battery from the solar panel  115  at step  536 , and charging the battery from the wind turbine  118  at step  538 . 
     In a third sub-method, the system may be monitored and controlled for a decision to go off-grid via query  550 . If no, then the method may loop back to monitor the three sub-methods. If yes, then the electrical grid disconnect switch  131  may be disengaged at step  551  such that the grid does not provide power to or receive power from the overall system. In such a case, the home may be supplied from one or more of the off-grid power sources. Thus, the home  135  may have power supplied from the generator  140  when the generator disconnect switch is engaged at step  554 . Further, the home  135  may have power supplied from the solar panel  115  when the solar panel disconnect switch is engaged at step  556 . Further yet, the home  135  may have power supplied from the wind turbine  118  when the wind turbine disconnect switch is engaged at step  558 . Each of these sources of power supply for the home may also be used to respectively charge the battery  120  as well. 
     It should be understood that the present disclosures as described above can be implemented in the form of control logic using computer software in a modular or integrated manner. Based on the disclosure and teachings provided herein, a person of ordinary skill in the art will know and appreciate other ways and/or methods to implement the present disclosure using hardware and a combination of hardware and software. 
     Any of the software components, processes or functions described in this application may be implemented as software code to be executed by a processor using any suitable computer language such as, for example, Assembly language Java, JavaScript, C, C++ or Perl using, for example, conventional or object-oriented techniques. The software code may be stored as a series of instructions, or commands on a computer readable medium, such as a random access memory (RAM), a read only memory (ROM), a magnetic medium such as a hard-drive or a floppy disk, or an optical medium such as a CD-ROM. Any such computer readable medium may reside on or within a single computational apparatus, and may be present on or within different computational apparatuses within a system or network. 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and/or were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the specification and in the following claims are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “having,” “including,” “containing” and similar referents in the specification and in the following claims are to be construed as open-ended terms (e.g., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely indented to serve as a shorthand method of referring individually to each separate value inclusively falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments and does not pose a limitation to the scope of the disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to each embodiment of the present disclosure. 
     Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and sub-combinations are useful and may be employed without reference to other features and sub-combinations. Embodiments have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present subject matter is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications can be made without departing from the scope of the claims below.