Abstract:
Embodiments herein disclose an apparatus for a modular PV system. The apparatus may include a wire box coupled to an alternating current (AC) system through an AC bus and to both a first direct current (DC) power source and a second DC power source through a conduit; a first inverter having a first chassis attached to the wire box and being coupled to the first DC power source through the wire box, the first inverter comprising a first pass-through channel and a second pass-through channel; and a second inverter having a second chassis attached to the first chassis and being coupled to the second DC power source through the first pass-through channel and the wire box, wherein the first chassis and the second chassis are separate chassis.

Description:
BACKGROUND 
     In recent years, climate change concerns, reductions in costs, governmental initiatives, and other factors have driven a rapid rise in the installation of renewable energy generation (EG) systems (i.e., systems that generate energy using renewable resources such as solar, wind, hydropower, etc.) at residential and non-residential sites. Solar photovoltaic (PV) systems, in particular, have been very popular EG systems. 
     PV systems include PV modules that generate direct current (DC) power from photons emitted from the sun. When strung together in series, the string of PV modules will have a high DC voltage equal to the sum of the PV module DC voltage. In systems that utilize centralized or so-called string inverters, the combined DC power output of a group of serially connected modules is converted into alternating current (AC) power by the inverter for use by a load, such as a residential appliance, commercial tool, the utility grid and the like. String and central inverters can take one or more PV module strings as input in order to increase the amount of available DC power to converter into AC power. The inverter must be matched to the DC and AC power in order to maximize inversion efficiency. However, manufacturing costs prevent string inverters from being able to be precisely matched to the power out of a particular array. They often come in integer sizes such as 5 kW, 10 kW, etc., where that number represents the maximum capacity of the inverter. As a result, the particular string inverter used on any particular job may have quite a bit of excess capacity for which a return on investment is never achieved. Therefore, the one size fits all or relatively small numbers of sizes fits all approach to string inverters results in unnecessarily high hardware costs. One solution to overcome this limitation is through the use of micro inverters instead of string and central inverters. These micro inverters convert the DC power output of one to four modules into AC power within the string. This eliminates the sizing issue from above, but leads to increased equipment costs, maintenance complexity, and redundancy. Therefore, there exists a need for an inverter system that combines the lower cost of a string inverter with the efficient inverter to PV module sizing of the micro inverter. 
     BRIEF SUMMARY 
     Embodiments herein disclose an apparatus for a modular PV system. In embodiments, the apparatus may include a wire box coupled to an alternating current (AC) system through an AC bus and to both a first direct current (DC) power source and a second DC power source through a conduit; a first inverter having a first chassis attached to the wire box and being coupled to the first DC power source through the wire box, the first inverter comprising a first pass-through channel and a second pass-through channel electrically isolated from the first pass-through channel, wherein the first inverter is configured to convert DC power generated from the first DC power source into AC power that is outputted into the AC bus; and a second inverter having a second chassis attached to the first chassis and being coupled to the second DC power source through the first pass-through channel and the wire box, the second inverter comprising a third pass-through channel configured to allow a third inverter to be coupled to the wire box through the third pass-through channel and the second pass-through channel, wherein the second inverter is configured to convert DC power generated from the second DC power source into AC power that is outputted into the AC bus, and wherein the first chassis and the second chassis are separate chassis. 
     The second and third pass-through channels may form a single pass-through channel. In embodiments, the first, second, and third pass-through channels are formed of conductive lines on a PCB having contacts disposed at opposite ends of each conductive lines. The conductive lines may comprise a positive and a negative conductive line. In certain embodiments, the first, second, and third pass-through channels may be formed of separate, electrically-insulated conductive wires having contacts disposed at opposite ends of each conductive wire. The second pass-through channel may be formed of a conductive wire that runs through corresponding holes in the first chassis. In embodiments, the apparatus may further include an adapter disposed between the first chassis and the second chassis, the adapter may be configured to route DC power from the second-pass-through channel to the third pass-through channel and/or to the second inverter via connection to the first pass-through channel. In other words, if the third pass through channel is utilized, the second inverter must also be utilized so the adapter must allow at least one pass through connection from the previous chassis to connect directly to the second inverter. 
     The first chassis may have a first direct current (DC) inlet, a first DC outlet, a first AC inlet and a first AC outlet, and the second chassis has a second DC inlet, a second DC outlet, a second AC inlet, and a second AC outlet. The first pass-through channel may be coupled to the first DC inlet and the first DC outlet. In embodiments, DC power may flow into the first chassis from the first DC power source through the first DC inlet, and AC power may flow out of the first chassis from the first AC outlet. In some embodiments, DC power may flow into the second chassis from the second DC power source through the second DC inlet, and AC power may flow out of the second chassis from the second AC outlet. The first and second chassis may include a switch for coupling first and second inverters to first and second DC power sources, respectively. The switch may be a manual switch or a computer-controlled switch. In embodiments, the first and second chassis are field configurable. In embodiments, the AC system includes a main panel, load center, substation, and/or a transformer. In certain embodiments, the first and second inverters include single-stage inverters. The first and second inverters may include multi-stage inverters. In other embodiments, the first and second inverters may include single-stage and multi-stage inverters. 
     In embodiments, a photovoltaic (PV) power generation system may include a PV array having an electrical output divided into first direct current (DC) power source and a second DC power source; and a modular inverter system. The modular inverter system may include a wire box coupled to an alternating current (AC) system through an AC bus and to both the first DC power source and the second DC power source; a first inverter having a first chassis attached to the wire box and being coupled to the first DC power source through the wire box, the first inverter comprising a first pass-through channel and a second pass-through channel separate from the first pass-through channel, wherein the first inverter is configured to convert DC power generated from the first DC power source into AC power that is outputted into the AC bus; and a second inverter having a second chassis attached to the first chassis and being coupled to the second DC power source through the first pass-through channel and the wire box, the second inverter comprising a third pass-through channel configured to allow a third inverter to be coupled to the wire box through the third pass-through channel and the second pass-through channel, wherein the second inverter is configured to convert DC power generated from the second DC power source into AC power that is outputted into the AC bus, and wherein the first chassis and the second chassis are separate chassis. 
     The first, second, and third pass-through channels may be formed of conductive lines on a PCB having contacts disposed at opposite ends of each conductive lines. In embodiments, the system may further include an energy storage device. In some embodiments, the first, second, and third pass-through channels are formed of separate, electrically-insulated conductive wires having contacts disposed at opposite ends of each conductive wire. The system may further include an adapter disposed between the first chassis and the second chassis, the adapter configured to route DC power from the second-pass-through channel to the third pass-through channel as well as from the first pass-through channel to the second inverter. 
     In embodiments, a method for converting power for an energy generation system includes receiving, at a wire box, first and second DC power inputs; performing maximum power point tracking (MPPT) with respective first and second MPPT circuits on the first and second power inputs; connecting an output of the first MPPT circuit to a first DC inlet of a first inverter chassis; inverting the output of the first MPPT circuit with a first inverter in the first inverter chassis; connecting an output of the second MPPT circuit to a first pass-through circuit of the first inverter chassis; receiving, at a second DC inlet of a second inverter chassis, the DC power from the first pass-through channel in the first inverter chassis; inverting the output of the second MPPT circuit with a second inverter in the second inverter channel; and routing the DC power through at least a portion of a second pass-through channel in the second inverter chassis to an inverter in the second inverter chassis. 
     The method may further include combining the output of the first and second inverters onto a common AC bus that is also connected to a terminal in the wire box. 
     A better understanding of the nature and advantages of embodiments of the present invention may be gained with reference to the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a simplified block diagram illustrating a PV system including an inverter and a plurality of DC power sources. 
         FIG. 1B  is a simplified block diagram illustrating a PV system including a plurality of inverters and a plurality of DC power sources. 
         FIG. 2  is a simplified block diagram illustrating a PV system including a plurality of inverters housed in a single inverter enclosure. 
         FIG. 3  is a simplified block diagram illustrating a PV system including a modular inverter system, according to embodiments of the present invention. 
         FIG. 4  is a simplified block diagram illustrating an inverter chassis of a modular inverter, according to embodiments of the present invention. 
         FIG. 5  is a simplified block diagram illustrating a modular inverter stack where inverters are coupled to pass-through channels by design, according to embodiments of the present invention. 
         FIG. 6  is a simplified block diagram illustrating a modular inverter stack where inverters are coupled to respective pass-through channels through an adapter, according to embodiments of the present invention. 
         FIG. 7  is a simplified block diagram illustrating a modular inverter stack where inverters are coupled to respective pass-through channels through a manual switch, according to embodiments of the present invention. 
         FIG. 8  is a simplified block diagram illustrating a modular inverter stack where inverters are coupled to respective pass-through channels through a computer-operable switch, according to embodiments of the present invention. 
         FIG. 9  is a simplified block diagram illustrating a modular inverter stack including a wire box, according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments for modular inverters in PV systems are described. The modular inverters are constructed to each have an individual chassis that can attach to other inverter chassis to form an inverter stack, which may be implemented in a PV system. Each inverter may have pass-through channels that allow power to be routed through its chassis to be received by another inverter in the inverter stack. The inverter stack is field-configurable, meaning inverters may be added to, or removed from, the stack at the installation site, i.e., after the inverters have been manufactured and during/after installation of the PV system, to specifically tailor the inverter stack to support PV modules in a PV system. Also, common wiring functions and MPPT are separate out of the inverter and supplied in a separate interface box shared by all modular inverters. In order to appreciate the aspects of modular inverters, a broad overview of PV systems in general is briefly discussed. 
     I. Photovoltaic Energy Generation System 
       FIG. 1A  is a simplified diagram illustrating a generic PV system  100  including inverter  104  and plurality of DC power sources  102 A- 102 C. DC power sources  102 A- 102 C may be devices for providing DC power to inverter  104  such as PV modules, batteries, fuel cells, and the like. DC power is received by inverter  104  and then converted into AC power for use by a load  106 , inputted back into the utility grid, or inputted into a battery through AC coupling. Some exemplary loads include typical household appliances, consumer electronic devices, commercial machinery, and any other electronic device that consumes power. 
     In PV systems where DC sources output a substantially high amount of power, such as PV module arrays for large residential or commercial applications, one inverter may not be enough to support the total power outputted by the DC sources. As a result, several inverters may be implemented to ensure successful operation of such PV systems. This may exacerbate the problem of excess capacity.  FIG. 1B  illustrates an exemplary PV system  101  where DC power sources  102 A- 102 C output an amount of DC power that requires three inverters  108 A- 108 C. Each inverter  108 A- 108 C may be configured to convert DC power generated by a respective DC source  102 A- 102 C (e.g., one string of PV modules) into AC power. Converted AC power may then be combined into an AC bus and outputted to specific loads and/or to the grid  106 . Typically, inverters  108 A- 108 C are disposed within a single housing to protect them from the environment when installed at a site, as shown in  FIG. 2 . However, in some cases, individual discrete inverter enclosures may be used. 
       FIG. 2  illustrates an exemplary installation configuration  200  where inverters  208 A- 208 C are housed in single inverter enclosure  210 , which may be formed of a single chassis containing an inlet  212  and an outlet  214 . Outputs of DC sources  202 A- 202 C may combine into a DC bus  216  and be inputted into inverter enclosure  210  through inlet  212 . Inlet  212  may be an opening through which a cable for DC bus  216  may insert to allow coupling between DC sources  202 A- 202 C and inverters  208 A- 208 C. Once inverters  208 A- 208 C convert DC power from DC bus  216  into AC power, each respective output of AC power may be combined into AC bus  218  and then outputted through outlet  214  to provide AC power to load/grid  206 . 
     Because inverters  208 A- 208 C are housed within single inverter enclosure  210 , the overall size of inverter enclosure  210  must be substantially large. Often, such inverter enclosures are too large to be mounted on a side of a building containing the PV system, and as a result, such inverter enclosures are mounted on the ground beside or near the building. Additionally, such inverter enclosures are typically built according to a predetermined specification and thus cannot be reconfigured to house more or less inverters once it has been manufactured and installed. Moreover, the large size results in higher installation and material costs. 
     Embodiments herein avoid these shortcomings with the use of modular inverters having separate chassis that are stackable. When stacked, the modular inverters form a modular inverter system that is field configurable even after manufacturing at a client site. 
     II. Modular Solar Inverter System 
       FIG. 3  illustrates an exemplary modular inverter system  300  according to embodiments of the present invention. As shown, DC sources  302 A- 302 C provide DC power to respective inverters  304 A- 304 C that are configured to convert the DC power into AC power and output the AC power onto an AC bus  314  for use by load/grid  306  via an AC system, which may include a main panel, load center, transformer, substation, or any other suitable electrical component for supplying/receiving AC power. DC sources  302 A- 302 C may include PV arrays and/or energy storage devices, such as batteries or fuel cells. 
     A notable difference between modular inverter system  300  and installation configuration  200  is that inverters  304 A- 304 C of modular inverter system  300  each have their own respective chassis  308 A- 308 C instead of sharing a single inverter enclosure, e.g. inverter enclosure  210  in  FIG. 2 . Inverter chassis  308 A- 308 C may be stacked one upon another to form an inverter stack  316 , which may be stacked on a common interface box such as wire box  310 . Another notable difference is that, outputs  312 A- 312 C of DC power sources  302 A- 302 C, respectively, are not combined onto a DC bus, but are instead routed to respective inverters  304 A- 304 C through separate connection routes in a conduit, a bussing in the inverter chassis, or any other suitable passageway within the spirit and scope of the present invention. 
     Each inverter chassis is configured to enable inverters to be added to or removed from inverter stack  316  after manufacturing and during/after installation at a customer site. For instance, inverter chassis  308 A is configured to allow an additional inverter to be added to inverter stack  316  by merely coupling the additional inverter with an upper interface of inverter chassis  308 A. Removal of an inverter may be just as simple. As an example, each inverter chassis is configured to removal from inverter stack  316  by simply separating the desired inverter from inverter stack  316 . The ease and simplicity of modifying inverter stack  316  allows modular inverter system  300  to be field configurable. This also enables the installer to utilize only so much inverter capacity as is necessary to deal with the number and size of the strings associated with any given PV system. 
     According to embodiments of the present invention, each inverter chassis may contain pass-through channels for enabling field configurability by allowing outputs  312 A- 312 C to be provided to certain inverters through intermediate inverter chassis. For instance, pass-through channels in inverter chassis  308 C may allow outputs  312 A and  312 B from DC sources  302 A and  302 B, respectively, to be provided to inverters  304 A and  304 B. In this example, inverter chassis  308 C is an intermediate inverter chassis for both inverters  304 A and  304 B, and inverter chassis  304 B is an intermediate inverter chassis for inverter  304 A. 
     Although  FIG. 3  illustrates a modular inverter system  300  having only three inverters  304 A- 304 C for inverter stack  316 , embodiments are not limited to such configurations. Other embodiments may have more or less inverters and inverter chassis depending upon design and/or requirements. For example, modular inverter system  300  may have additional inverters that are added upon inverter stack  316  by connecting them above inverter chassis  308 A, between two inverter chassis, or between inverter chassis  308 C and wire box  310 . This may be particularly useful if the customer decides to increase the size of the system at some point in the future. Alternatively, modular inverter system  300  may have less inverters than shown in  FIG. 3  by removing one or more inverter chassis from inverter stack  316 . The ease and simplicity of adding and subtracting inverters from inverter stack  316  enables field configurability, lowers installation cost, reduces lost power due to a failure, and reduces time required to repair following a fault. In embodiments, each inverter  304 A- 304 C may be a single-stage inverter or a multi-stage inverter. In other embodiments, inverters  304 A- 304 C may include single-stage and multi-stage inverters. It is to be appreciated that any suitable inverter can be implemented in modular inverter system  300  without departing from the spirit and scope of the present invention. 
     A. Modular Inverter 
       FIG. 4  illustrates an exemplary inverter chassis  400  according to embodiments of the present invention. Inverter chassis  400  may include DC inlet  420  for inputting DC power from DC sources, such as DC power sources  302 A- 302 C in  FIG. 3  which may be a PV module, battery, fuel cell, or any other suitable DC power source. For purposes of explanation from the perspective of inverter chassis  400 , DC power entering inverter chassis  400  is hereinafter referred to as inputs, such as DC inputs  402 A- 402 C for different DC power sources. DC inputs  402 A- 402 C may enter through DC inlet  420  and conduct through respective pass-through channels (PTC)  418 A- 418 C configured for route power to DC outlet  422  through inverter chassis  400 . 
     Pass-through channels  418 A- 418 C may be configured to route power from DC inlet  420  to DC outlet  422  through electrically isolated paths. As an example, pass-through channels  418 A- 418 C may be formed of separate conductive lines on a printed circuit board (PCB) that route power from DC inlet  420  to DC outlet  422 . Conductive pads (not shown) disposed at respective positions in DC inlet  420  may provide an avenue through which DC power may conduct into pass-through channels  418 A- 418 C. Likewise, corresponding conductive pads (not shown) disposed at respective positions in DC outlet  422  may provide an avenue through which DC power may conduct out of pass-through channels  418 A- 418 C and into another inverter chassis disposed above inverter chassis  400 , as will be discussed further herein. In embodiments, pass-through channels  418 A- 418 C may each be formed of two separate conductive lines: a positive terminal line and a negative terminal line, for routing power from a DC source. 
     In other embodiments, pass-through channels  418 A- 418 C may each be formed of separate, electrically isolated positive and negative conductive wires with corresponding contacts on either end of the conductive wires for routing power through inverter chassis  400 . In yet other embodiments, pass-through channels  418 A- 418 C may be physical conduit tunnels, or a corresponding pair of openings in inverter chassis  400 , through which positive and negative electrically isolated wires may thread. The isolated wires may run through respective conduit holes disposed at DC inlet  420  and DC outlet  422  to route power from DC inlet  420  to DC outlet  422 . It is to be appreciated that any other method of routing power as a pass-through channel that does not depart from the spirit and scope of the present invention is envisioned herein. 
     The exemplary inverter chassis  400  in  FIG. 4  illustrates an instance where inverter chassis  400  has three inputs, where each input may correspond to a respective DC source. However, embodiments are not limited to inverter chassis with only three pass-through channels. Some embodiments may have inverter chassis with more than three pass-through channels and other embodiments may have inverter chassis with less than three pass-through channels. The number of pass-through channels may be determined by system design. More DC sources may require more pass-through channels, and less DC sources may require less pass-through channels. In some embodiments there may be more pass-through channels than DC sources, which may result in some pass-through channels not being utilized to route power through the inverter chassis. 
     In embodiments, at least one of the pass-through channels may be tapped to route at least some of the DC power out of the pass-through channel and into inverter  404 . For instance, as shown in  FIG. 4 , inverter  404  may tap into pass-through channel  418 C to route DC power provided by DC source as DC input  402 C. Inverter  404  may convert the DC power into AC power through one or more converters. As an example, inverter  404  may include DC-to-DC boost converter  414  and DC-to-AC converter  416 . DC-to-DC boost converter  414  may receive DC power from pass-through channel  418 C and step up the voltage of the DC power to output a greater DC power than what was originally inputted into DC-to-DC boost converter  414 . The stepped up voltage may then be inputted into DC-to-AC converter  416  that is configured to convert the inputted DC power to AC power. 
     Outputted AC power may be outputted into common AC bus  428 , which may provide outputted AC power to a load, into a utility grid, such as load/grid  306  in  FIG. 3 , or into an AC coupled battery system. In some embodiments, common AC bus  428  may also contain outputted AC power from other inverters in an inverter stack, such as inverter stack  316  in  FIG. 3 , in which case the AC power outputted by inverter  404  may be combined with existing AC power in common AC bus  428 . The AC power from other inverters may enter into common AC bus  428  via AC inlet  424  and exit out of common AC bus  428  via AC outlet  426  as AC output  430 . Similar to pass-through channels  418 A- 418 C, common AC bus  428  may be formed of any suitable power routing mechanism, such as a pair of positive and negative conductive lines on a PCB with corresponding contacts at either end of the conductive lines, electrically isolated positive and negative wires with corresponding contacts at either end of the wires, or conduits through which electrically isolated positive and negative wires may be threaded. 
     Although  FIG. 4  illustrates AC bus  428  as being formed of two power lines, embodiments are not limited to such configurations. AC bus  428  may be formed of more than two power lines in other embodiments. For instance, AC bus  428  may be formed of three conductive lines in some embodiments, and AC bus  428  may be formed of four conductive lines in other embodiments. 
     Inverter stack  316  may be configured with an arrangement of inverters suitable to support an outputted power level of DC sources  302 A- 302 C. Each inverter  304 A- 304 C may be configured to support a specific power level. The power level capable of being supported by inverter stack  316  as a whole may be determined by a sum of the power levels of the individual inverters  304 A- 304 C. As an example, if inverter  304 A,  304 B, and  304 C are configured to support power levels of 2.88 kW, 2.88 kW, and 1.91 kW, respectively, inverter stack  316  may be able to support a power level of 7.67 kW (2.88 kW+2.88 kW+1.91 kW). It is to be appreciated that the inverters may be arranged in any other combination suitable to support a power level outputted by the DC sources. 
     In embodiments, the structure and configuration of pass-through channels  418 A- 418 C and common AC bus  428  enable devices coupled to one end of inverter chassis  400  to send and/or receive power from devices coupled to the opposite end of inverter chassis  400 . By enabling this coupling, a wide variety of inverter combinations can be mated with one another in an inverter stack while having an electrical path for coupling to respective DC sources, as will be discussed further herein. 
     B. Interworking of Mated Modular Inverters 
       FIGS. 5-8  illustrate some exemplary ways modular inverters interact with one another in an inverter stack to enable modularity and field configurability according to embodiments of the present invention. The embodiments illustrated in  FIGS. 5-8  show how only two modular inverters may be coupled together for ease of discussion. However, it is to be understood that embodiments are not limited to modular inverter systems with only two inverters, and that the principles, functions, and features discussed with respect to two-inverter modular inverter systems may be implemented in modular inverter systems having more than two modular inverters. As will be appreciated through the discussion of  FIGS. 5-8 , the existence of pass-through channels and the ease of connectivity between modular inverters in an inverter stack enables more or less inverters to be coupled together after the modular inverters have been manufactured, thereby enabling field configurability. 
     1. Coupling by Design 
       FIG. 5  illustrates an exemplary inverter stack  500  where modular inverters are coupled to respective pass-through channels by design and where inverter chassis are directly mated with one another according to embodiments of the present invention. As shown, inverter chassis  501 A may be directly coupled to inverter chassis  501 B such that pass-through channels  518 A- 518 C in inverter chasses  501 B are coupled to respective pass-through channels  520 A- 520 C in inverter chassis  501 A, and that common AC bus  528 B in inverter chasses  501 B is coupled to common AC bus  528 A in inverter chassis  501 A. Contacts (not shown) positioned at a DC outlet of inverter chassis  501 B may couple to respective contacts (not shown) positioned at a DC inlet of inverter chassis  501 A at DC mating surface  503  to enable DC power to be routed between inverter chassis  501 A and  501 B. Additionally, contacts (not shown) positioned at AC outlet of inverter chassis  501 A may couple to respective contacts (not shown) positioned at AC inlet of inverter chassis  501 B at AC mating surface  505  to enable AC power to be routed between inverter chassis  501 A and  501 B. 
     In embodiments, inverters  504 A and  504 B may each be coupled to a pass-through channel to receive DC power from a DC source. With respect to the example illustrated in  FIG. 5 , inverter  504 B may be coupled to pass-through channel  518 C to receive DC input  502 C, and inverter  504 A may be coupled to pass-through channel  520 B to receive DC input  502 B. Pass-through channel  520 B may be coupled to pass-through channel  518 B such that they act as a single pass-through channel for providing an avenue through which DC power may flow. Although  FIG. 5  shows inverter  504 A coupled to pass-through channel  520 B to receive DC input  502 B, it is to be appreciated that inverter  504 A can be coupled to any of pass-through channels  520 A- 520 C in other embodiments. Similarly, inverter  504 B may be coupled to any of pass-through channels  518 A- 518 C. In some embodiments, inverter  504 A can be coupled to the same pass-through channel as inverter  504 B such that DC input  502 C is received by both inverters  504 A and  504 B. Two inverters may be utilized to convert DC power from a single DC source into AC power if the outputted DC power is too much for a single inverter to handle. 
     Pass-through channels  518 A and  520 A may be coupled to one another to provide a conductive path through which another inverter may couple to a DC source to receive DC input  502 A. As an example, a third inverter (not shown) could be coupled to pass-through channels  520 A and  518 A to receive DC input  502 A from another DC source. The third inverter chassis may attach to inverter chassis  501 A the same way inverter chassis  501 A is attached to inverter chassis  501 B. DC input  502 A may flow through pass-through channels  520 A and  518 A and be outputted by inverter chassis  501 A as DC output  532 A from DC outlet  522  of inverter chassis  501 A. DC output  532 A may be inputted into the third chassis and be converted by a third inverter. More pass-through channels may enable more DC sources to couple with inverters in the inverter stack. 
     Like pass-through channels  518 A- 518 C and  520 A- 520 C, common AC busses  528 A and  528 B may also be coupled to one another in similar fashion to allow power to flow between inverter chassis  501 A and  501 B. In embodiments with a third inverter, the third inverter may be coupled to inverter chassis  501 A and output AC power into common AC buses  528 A and  528 B as AC input  534 . AC input  534  may be combined with AC power outputted by inverters  504 A and  504 B and outputted as a collective whole to a load or a utility grid as AC output  530 . 
     In embodiments, adjacent inverter chassis in an inverter stack may be fastened together to prevent inadvertent separation. For example, a locking mechanism (not shown) positioned at an interface between inverter chassis  501 A and  501 B may attach and fix them together. The locking mechanism may be any suitable mechanical contraption configured to fix two structures together. Exemplary locking mechanisms include clamps, hooks, screws, pins, and the like. One exemplary locking mechanism may be a threaded inlet and outlet for each inverter chassis where each inlet may be threaded to fasten to a respective outlet, and vice versa. Inverter chassis  501 A and  501 B are illustrated as having protruding inlets and recessed outlets; however, it is to be appreciated that such illustrations are for ease of discussion and are not intended to be limiting. Other embodiments may have protruding inlets and outlets, recessed inlets and outlets, or inlets and outlets that neither protrude nor recess from the inverter chassis. 
     2. Coupling by Adapters 
     Although  FIG. 5  illustrates inverter chassis  501 A and  501 B directly coupled to one another, embodiments are not limited to such configurations.  FIG. 6  illustrates an exemplary inverter stack  600  where inverter chassis  601 A and  601 B are coupled to one another through adapter  642  according to embodiments of the present invention. Adapter  642  may be an intermediary structure that is configured to electrically and physically couple two inverter chassis together. As shown in  FIG. 6 , adapter  642  may include routing channel  644 . Routing channel  644  may change the route of power across different pass-through channels from a route that would have been established without adapter  642 . For instance, without adapter  642 , DC input  602 B would flow through pass-through channels  618 B and  620 B. Incorporating adapter  642  causes routing channel  644  to route DC input  602 B from pass-through channel  618 B to pass-through channel  620 C instead. Thus, inverter  604 A may receive DC input  602 B from pass-through channel  620 C. 
     In addition to routing channel  644 , adapter  642  may include one or more pass-through channels, such as pass-through channel  646 , and common AC bus  648  to enable inverter chassis coupled to one end of adapter  642  to send and/or receive power from devices coupled to the opposite end of adapter  642 . Similar to pass-through channels  618 A- 618 C, pass-through channel  646  and common AC bus  648  may be formed of any suitable power routing mechanism, such as a pair of positive and negative conductive lines on a PCB with corresponding contacts at either end of the conductive lines, electrically isolated positive and negative wires with corresponding contacts at either end of the wires, or conduits through which electrically isolated positive and negative wires may be threaded. 
     Using adapter  642  enables inverter chassis  601 A and  601 B to be interchangeable, meaning inverter chassis  601 A may have the same structure and configuration as inverter chassis  601 B. Having interchangeable inverters greatly simplifies installation of the inverter stack for a PV system. 
     3. Coupling by Manual Switches 
     Other inverter configurations may also simplify the installation process. As an example, inverter configurations incorporated with manual switches may help simplify the installation process. In such configurations, each inverter chassis may include a manual switch for coupling an inverter to any one of a plurality of pass-through channels. As a result, an adapter may not be needed to form a modular inverter stack for a PV system. 
       FIG. 7  illustrates exemplary inverter stack  700  where inverters are coupled to pass-through channels by a manual switch according to embodiments of the present invention. In the exemplary inverter stack  700 , switches  702 A and  702 B may each be a three-position switch that is configured to select between pass-through channels  720 A- 720 C and  718 A- 718 C, respectively. The number of positions for switches  702 A and  702 B may depend upon the number of pass-through channels. In embodiments, the number of positions is at least equal to the number of pass-through channels. With reference to the embodiment shown in  FIG. 7 , switch  702 A may have three positions for coupling to three pass-through channels  720 A- 720 C. 
     Depending on their position, switches  702 A and  702 B may couple inverters  704 A and  704 B to respective pass-through channels. For instance, switch  702 A may be flipped to a second position to couple inverter  704 A to pass-through channel  720 B to receive DC input  702 B, as shown in  FIG. 7 . On the other hand, switch  702 B may be flipped to a first position to couple inverter  704 B to pass-through channel  718 C to receive DC input  702 C. Accordingly, incorporating manual switches in inverter chassis  701 A and  701 B for an inverter stack enables DC sources to be easily coupled to the appropriate inverters. 
     Switches  702 A and  702 B may be any suitable manual switch. As an example, switches  702 A and  702 B may be double pole N-throw switches (where N corresponds with the number of pass-through channels), relays, rotary switches, toggle switches, and any other suitable switch capable of coupling an output with two or more inputs. Such manual switches enable a person, such as an installer of a PV system, to set the position of switches  702 A and  702 B by simply moving a lever, pushing a button, or turning a knob, thereby significantly enhancing the ease and flexibility of installing inverters for PV systems. 
     4. Coupling by Computer Operable Switches 
     Installation and configuration of inverter systems may be further simplified by implementing computer operable switches. In such systems, each inverter chassis may include a computer operable switch for coupling an inverter to any one of a plurality of pass-through channels. The computer operable switch may include a plurality of switches for coupling an inverter to a specific pass-through channel for receiving DC input. A controller may operate the computer operable switch according to an algorithm and/or according to an input to establish a connection between an inverter and a pass-through channel. As a result, a person does not have to manually flip a switch to install a modular inverter stack for a PV system. 
       FIG. 8  illustrates an exemplary inverter stack  800  for an inverter system with computer operable switches  842 A and  842 B according to embodiments of the present invention. Computer operable switches  842 A and  842 B may be disposed between respective inverters  804 A and  804 B and pass-through channels  820 A- 820 C and  818 A- 818 B, and may be formed of a plurality of switches arranged in pairs that correspond to positive and negative terminals for establishing power connections. 
     Each pair of switches may be independently controlled by a controller (e.g., controller  844 A or  844 B) and can be activated to close a switch to route power from any one of pass-through channels  820 A- 820 C and  818 A- 818 C to respective inverters  804 A and  804 B. Each switch of the plurality of switches can be an electrical switch such as a transistor (e.g., MOSFET, BJT, etc.). Controllers  844 A and  844 B may be any suitable electronic device that can be configured to operate switches  842 A and  842 B to couple inverters  804 A and  804 B with a desired pass-through channel. Exemplary electronic devices include, but are not limited to, microcontrollers, application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), programmable logic boards, and the like. 
     In embodiments, controllers  844 A and  844 B can be configured to automatically couple inverters  804 A and  804 B to the correct pass-through channel for receiving DC input from a DC source by communicating with a wire box (not shown, but described in detail further herein). A communication device in the wire box may send a signal to controllers  844 A and  844 B indicating which switch to close. The wire box may know the arrangement of inverters in the inverter stack and the arrangement of DC sources so that it can send signals to respective controllers to couple the correct inverters with the correct pass-through channels. All of this can be performed without user intervention, thereby saving time and cost during installation of a PV system. 
     C. Wire Box 
       FIG. 9  is a simplified diagram illustrating an exemplary modular inverter system  900  with a wire box  902  according to embodiments of the present invention. Wire box  902  may include various electrical components for managing interactions between the DC power sources and the inverter stack, Wire box  902  may be disposed between the inverter stack and the DC sources. 
     In embodiments, wire box  902  may include one or more maximum power point tracking (MPPT) devices  906 A- 906 B for maximizing power output of DC sources. Such devices  906 A- 906 B may comprise circuit boards, integrated circuits or other hardware and software as is known in the art. Typically, MPPT devices are disclosed within inverter chassis; however, according to embodiments herein, MPPT devices may be disposed within wire box  902 . DC power may flow into wire box  902  from the DC power sources through DC inlet  911  and be received by respective MPPTs  906 A- 906 B, which may output maximized power through DC disconnect  904  and into respective pass-through channels  920 A- 920 C to be received by inverters in the inverter stack for the modular inverter system  900  through switches  926 A and  926 B. DC disconnect  904  may be formed of one or more manual switches that can shut off the flow of power between the respective DC power sources and inverters  924 A and  924 B in the inverter stack. 
     Wire box  902  may also include communication module  908  for communicating with controllers  928 A and  928 B in the modular inverter system to control switches  926 A and  926 B. Similar to controllers  928 A and  928 B, communication module  908  may be a microcontroller, an ASIC, a FPGA, a programmable logic board, or the like. Communication module  908  may communicate with controllers  928 A and  928 B by any suitable transmission method, such as radio frequency (RF) transmission, Bluetooth, wireless fidelity (WiFi), AC or DC power line communication (PLC), and the like. AC module  910  may be implemented in wire box  902  to perform AC PLC to controllers  928 A and  928 B. To enable AC PLC, controllers  928 A and  928 B may be coupled to common AC bus  922  by respective communication lines  913 A and  913 B to receive communication signals from AC module  910 . 
     In embodiments, communication module  908  may determine the number of DC sources and the magnitude of their respective power outputs by interacting with MPPTs  906 A- 906 B. Communication module  908  may also determine the arrangement of inverters in the inverter stack by communicating with controllers  928 A and  928 B. Once the DC sources and the available inverters are determined, communication module  908  may determine a connection arrangement between inverters  924 A and  924 B and the DC sources and then cause switches  926 A and  926 B to implement the connection arrangement by altering their switch positions to couple to the correct pass-through channel. The coupling of inverters  924 A and  924 B to corresponding DC sources may be performed automatically without user intervention.