Patent Publication Number: US-2013234520-A1

Title: Modular energy portal with ac architecture for harvesting energy from electrical power sources

Description:
BACKGROUND 
     The present invention relates to energy harvesting from multiple power sources. 
     Conventionally, electrical power is generated at a utility company and transmitted over a power grid to homes, factories, and other facilities. These facilities pay the electrical utility for the amount of electrical power that they consume. Electrical power distribution systems having this type of configuration have existed for many decades. 
     SUMMARY 
     Although centralized electrical power generation and distribution systems have functioned well, more recently there is a desire to produce energy locally at homes and factories. Various issues arise when attempting to interface locally produced energy with power provided from a utility company over a grid. Specific complications are presented when energy is generated by solar panels and when power is generated by multiple local power sources, such as solar panels and internal combustion engine generators. Embodiments of the invention are directed to an energy harvesting system and method for use with local power sources, particularly solar panels. Since such power sources are not centralized, they can also be referred to as distributed power sources. 
     An energy harvesting system of the invention may include a modular energy harvesting portal comprising a housing with a bay, a plurality of inverters, a controller, and an AC bus. The plurality of inverters including a first inverter and a second inverter. The first inverter has a first DC input, a first AC output, and a first power rating. The first inverter converts DC power received at the first DC input to AC power and outputs AC power at the first AC output. The second inverter has a second DC input, a second AC output, and a second power rating. The second inverter converts DC power received at the second DC input to AC power and outputs AC power at the second AC output. The plurality of inverters are positioned in the bay. The controller is configured to communicate with each of the plurality of inverters. The AC bus connects the first AC output and the second AC output. The controller selectively controls a switch to couple the AC bus to an AC grid. The modular energy harvesting portal system has a power rating dependent on the number of inverters in the portal and the power rating of each of the inverters of the plurality of inverters. 
     A method of harvesting energy using a modular energy harvesting portal in accordance with the invention may include receiving a first type of power from a first power source, converting the first type of power to AC power using a first inverter, and providing the first inverted AC power to an AC bus. The method also includes receiving a second type of power from a second power source, converting the second type of power to AC power using a second inverter, and providing the second inverted AC power to the AC bus. The method further comprises outputting the AC power from the AC bus to grid connection switches controlled by a controller and controlling the grid connection switches to connect the AC power from the AC bus to one of an AC grid and a local load. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a system architecture known to exist prior to the existence of embodiments of the present invention. 
         FIG. 2   a  depicts an energy harvesting system according to one embodiment of the invention. 
         FIG. 2   b  depicts an energy harvesting system according to another embodiment of the invention. 
         FIG. 3  is an end view of an energy portal (having three inverters) of the energy harvesting system. 
         FIG. 4  illustrates one inverter of the energy portal of the energy harvesting system. 
         FIG. 5   a  is a perspective view of the energy portal where a lid or cover of the portal housing has been removed and the inverters are stacked in a horizontal configuration. 
         FIG. 5   b  is a perspective view of the energy portal where a lid or cover of the portal has been removed and the inverters are stacked in a vertical configuration. 
         FIG. 6  is a perspective view of the housing of the energy portal and illustrates air flow through the housing. 
         FIG. 7  is a flowchart depicting the method of harvesting energy using the energy harvesting system. 
         FIG. 8  is a flowchart depicting the method of replacing an inverter with a new inverter. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
       FIG. 1  depicts an energy harvesting system  75  having a DC power bus configuration or architecture. The energy harvesting system of  FIG. 1  is the subject of U.S. patent application Ser. No. 12/953,985, which is commonly owned with the present application. The system  75  includes separate preconditioner modules  80 , one for each power source  82 , and a shared DC bus  85 . One or more inverters  90  are coupled to the shared DC bus  85  to receive the combined DC output from the various preconditioners  80 . The inverters  90  invert the received DC power to AC power, which is output to various local loads and an AC utility grid. While the DC-bus configuration has certain advantages, the system  75  is, at least compared to some AC-bus configurations, more costly and complex due in part to the use of separate preconditioner modules  80  (one for each power source  82 ). In some distributed power system scenarios, the advantages of the DC architecture may not merit the increased costs and complexity. Additionally, in some instances, a DC architecture has reduced efficiency relative to the AC architectures described herein. 
       FIG. 2   a  depicts an energy harvesting system  100  with an AC bus configuration. The energy harvesting system  100  converts DC power from power sources  104  to AC power, which is provided to an AC grid (grid)  105 , used by local loads, or both. In some instances, a utility company provides compensation for the power received at the grid  105  from the energy harvesting system  100 . The power sources  104  for the energy harvesting system  100  include power sources  104   a ,  104   b , and  104   c , which may be renewable or nonrenewable. A renewable power source  104  can be photovoltaic cells, photovoltaic arrays, a wind generator, or other types of renewable power sources. Some embodiments receive DC power from renewable power sources  104  whose outputs may vary with environmental conditions. For example, the output of solar cells varies with the amount of solar radiation to which the cells are exposed. The output of wind generators or turbines varies with the amount of wind to which the turbines are exposed. The DC output of each renewable power source  104   a ,  104   b , and  104   c  (referred to collectively as renewable power sources  104 ) is coupled to power source inputs (DC inputs)  106   a ,  106   b , and  106   c  (referred to collectively as DC inputs  106 ) of a modular energy harvesting portal (energy portal)  107 . The DC inputs  106  receive the DC power signal (DC power) from the renewable power sources  104 . The DC power is then sent to the DC inputs  108   a ,  108   b , and  108   c  of the inverters  110   a ,  110   b , and  110   c  (referred to collectively as inverters  110 ). The inverters  110  are located within a bay  112   a  of a housing  112  of the energy portal  107 . The inverter  110   a ,  110   b , and  110   c  are controlled by a controller  113  via a communication bus  114 . 
     The inverters  110  invert the DC power from the renewable power sources  104  to AC power. An AC output  115   a ,  115   b , and  115   c  of each inverter  110   a ,  110   b , and  110   c  is coupled to an AC bus  116 . AC power output by the inverters  110  is transmitted along the AC bus  116  to an AC output  117 . The AC output  117  of the energy portal  107  is connected to auxiliary panel  120 . The auxiliary panel  120  is similar to a conventional circuit breaker panel used in a home or factory that couples an AC power source (e.g., grid  105  and/or energy portal  107 ) to local loads (e.g., auxiliary load  124 ). Additionally, the auxiliary panel  120  provides a connection that enables AC power output by the energy portal  107  to be fed into the grid  105  (via an automatic transfer switch (“ATS”)  130 ). The controller  113 , via the communications bus  114 , is connected to and communicates with the ATS  130 . The ATS  130  couples the AC bus  116  to the AC grid  105 . Although referred to as “auxiliary,” the loads on the auxiliary circuits provided by the auxiliary panel  120  are often loads for which it is important to provide an uninterrupted supply of power. For example, furnaces, hot water heaters, refrigerators, security systems, and fire alarm and suppression systems may be connected to the auxiliary panel  120  so that power from the energy portal  107  is provided to the auxiliary loads  124  in the event that power from the grid  105  is lost (for example, due to grid failure). 
     The grid  105  is an AC power grid with a system of transmission lines and other devices by which electrical power generated by an electric utility company is transmitted to customers. The grid  105  is coupled to a main breaker panel  135 . The main breaker panel  135  is a delivery point of the power from the grid  105  to other local loads (e.g., standard loads  140 ) of a customer. The main breaker panel  135  is a conventional circuit breaker unit that is coupled to the grid  105 . The main breaker panel  135  is operable to break the connection between the grid  105  and the standard loads  140  when current passing through the main breaker panel  135  exceeds a predetermined threshold. For instance, if the standard loads  140  draw excessive current, the main breaker panel  135  breaks the connection between the standard loads  140  and the grid  105 . The auxiliary panel  120  performs a similar protection function for the auxiliary loads  124  as the main breaker panel  135  does for the standard loads  140 . 
     In operation, the energy harvesting system  100  is either grid-tied or off-grid, depending on the particular situation. When the grid  105  is operating normally, the energy harvesting system  100  is generally grid-tied. When grid-tied, the energy harvesting system  100  provides power from the energy portal  107  to the grid  105  and it is intended that such power be purchased by the local electric utility company from the power producer. In the grid-tied mode, AC power from the grid  105 , which includes AC power from the energy portal  107 , powers the auxiliary loads  124  as well as the standard loads  140 . When the grid  105  is operating abnormally (e.g., during a black out or brown out), the ATS  130  disconnects the normal circuit connected to the grid  105  and switches to an emergency position, thus disconnecting the energy harvesting system  100  from the grid  105 . In the off-grid mode, the energy portal  107 , but not the grid  105 , provides power to the auxiliary loads  124  through the auxiliary panel  120 . Also in the off-grid mode, the standard loads  140  are not powered. 
       FIG. 2   b  depicts another embodiment of the energy harvesting system  100 , which includes a standby power sub-system  145 . The standby power sub-system  145  includes a standby power source  150  that can include a generator  155 , a battery (or battery pack)  160 , a battery charging circuit  161 , or all three. In some embodiments, the generator  155  is a DC generator. The generator  155  includes a source of the mechanical energy, such as a turbine, an internal combustion engine, etc. The generator  155  converts the mechanical energy into DC power and outputs the DC power to the battery charging circuit  161 . The battery charging circuit  161  charges the battery  160  by outputting DC power to the battery  160  while monitoring the charge of the battery  160 . Once the battery  160  is fully charged, the battery charging circuit  161  discontinues outputting DC power to the battery  160 . The battery charging circuit  161  of the standby power source  150  is coupled to a bidirectional DC/DC converter  165  of the standby power sub-system  145 . The bidirectional DC/DC converter  165  converts low-voltage DC power to high-voltage DC power, or high-level DC power to low-level DC power, depending on its mode of operation. The bidirectional DC/DC converter  165  is electrically coupled to the bidirectional DC/AC inverter  170 . In one mode, the bidirectional DC/AC inverter  170  inverts DC power received from the bidirectional DC/DC converter  165  to AC power for output to the ATS  130 . In another mode, the bidirectional DC/AC inverter  170  rectifies AC power from ATS  130  to DC power for output to the bidirectional DC/DC converter  165 . The bidirectional DC/AC inverter  170  is electrically coupled to the auxiliary panel  115  and the grid  105  through the ATS  130 . 
     When grid-tied, the energy harvesting system  100  provides power from the energy portal  107  to the grid  105  similar to the embodiment shown in  FIG. 2   a . In grid-tied mode, AC power from the grid  105 , which includes AC power from the energy portal  107 , powers the auxiliary loads  124  as well as the standard loads  140 . In grid-tied mode, the AC power from the grid  105  may also used to charge the battery  160  of the standby power source  150 . When charging the battery  160  in grid-tied mode, the standby power sub-system  145  receives AC power from the grid  105  via the ATS  130 , while the generator  155  remains off. The AC power is rectified to high level DC power by the bidirectional DC/AC inverter  170 . The high level DC power is then converted to low level DC power by the bidirectional DC/DC converter  165 . The low level DC power is then output to the battery charging circuit  161 . The battery charging circuit  161  then charges the battery  160  until the battery  160  is fully charged. 
     When the grid  105  is operating abnormally, the ATS  130  disconnects the normal circuit connected to the grid  105 , and switches to the emergency position, thus disconnecting the energy harvesting system  100  from the grid  105 . When off-grid, the auxiliary loads  124  can receive AC power from the energy portal  107 , the standby power sub-system  145 , or both. When powering the auxiliary loads  124  in off-grid operation, the standby power sub-system  145  receives low level DC power from the standby power source  150 . The low level DC power is then converted to high level DC power by the bidirectional DC/DC converter  165 . The high level DC power is then inverted to AC power by the bidirectional DC/AC inverter  170 . The AC power is then sent to the auxiliary loads  124  through the auxiliary panel  120 . 
     During off-grid operation, the ATS  130  requests the standby power source  150  to provide low-level DC power from one or both of the generator  155  and battery  160 . For instance the standby power source  150  provides DC power from the battery  160  until the voltage of the battery pack  160  becomes low. When the voltage of the battery pack  160  becomes low, the generator  155  begins outputting DC power to the battery charging circuit  161  to charge the battery  160  while the standby power source  150  continues to provide DC power to the standby power sub-system  145 . Once the grid  105  is operating normally, the ATS  130  communicates with the standby power source  150  to cease outputting power. The ATS  130  reconnects the energy harvesting system  100  to the grid  105 . 
     In some embodiments, the standby power source  150  includes a generator  155 , but no battery  160  nor battery charging circuit  161 . During off-grid operation, the ATS  130  disconnects the normal circuit connected to the grid  105  and communicates with the generator  155  to turn on. Once on, the generator  155  indicates (or the ATS  130  detects) that the generator  155  is operational and providing power with acceptable characteristics. The ATS  130  then enables AC power from the standby power sub-system  145  to power the auxiliary loads  124  through the auxiliary panel  120 . Once the grid  105  is operating normally, the ATS  130  communicates with the generator  155  to turn the generator  155  off. The ATS  130  reconnects the energy harvesting system  100  to the grid  105 . 
     In some embodiments, the standby power source  150  includes a battery  160  and battery charging circuit  161 , but no generator  155 . During off-grid operation, the standby power sub-system  145  converts the DC power from the battery  160  to AC power until the battery  160  is discharged or the energy harvesting system  100  returns to grid-tied operation. Once the battery  160  is discharged of DC power, the standby power sub-system  145  stops providing AC power to the auxiliary loads  124  through the auxiliary panel  120 . Once the grid  105  is operating normally, the ATS  130  reconnects the energy harvesting system  100  to the grid  105 . The battery charging circuit  161  then charges the battery  160  using power from the grid  105  as explained above. 
     In some embodiments, the main breaker panel  135  is not provided. Rather, both the standards loads  140  and aux loads  124  are coupled to the auxiliary panel  120 . 
       FIG. 3  illustrates the energy portal  107  of the energy harvesting system  100 . The energy portal  107  has DC inputs  106   a ,  106   b , and  106   c  (collectively, “DC inputs  106 ”). The DC inputs  106   a ,  106   b , and  106   c  are coupled to the DC inputs  108   a ,  108   b , and  108   c  of each inverter  110   a ,  110   b , and  110   c , respectively. The inverters  110   a ,  110   b , and  110   c  slide into the housing  112  of the energy portal  107 . Each inverter  110  receives DC power from its respective DC input  108 , inverts the DC power to AC power, and outputs the AC power to the AC bus  116 . The inverters can be placed on shelves SHF  1 - 3  ( FIGS. 5   a - 6 ), on tracks, or on other platforms and fixed in place via fasteners or other mechanisms. 
       FIG. 4  is a sectional view of one inverter  110 . The inverter  110  has a DC input  108  for receiving DC power from one of the power sources  104 . The DC power is then filtered through the input common mode filter  405 . The bus balancing controller  410  regulates the DC bus voltages. In some embodiments, the inverter  110  includes a 3 or 4 kW boost  415 . When the received DC power is below a desired voltage level for proper or optimized operation of the inverter  110 , the 3/4 kW boost  415  boosts (or increases) the voltage of the received DC power to the desired level. When the received DC power is at a desirable level, the DC power bypasses the 3/4 kW boost  415 . In some embodiments, the 3/4 kW boost  415  is not included in the inverter  110 . For example, if the power source  105  coupled to the inverter  110  consistently outputs DC power at a desired level, the 3/4 kW boost  415  is not included, reducing the cost of the inverter  110 . 
     The main control circuitry  420  controls the inverter  110  and its components. The main control circuitry  420  can be a digital signal processor with a processor and memory for storing instructions executed by the processor, or similar device. The analog feedback circuit  430  monitors the voltage, temperature, and current of the inverter  110 . The inverter power stage  435  includes power switching elements (e.g., MOSFETs) controlled by the main control circuit  420  to invert the received DC power to AC power. After the DC power is inverted to AC power, the filter inductors  440  and output common mode filter  445  filter the AC power. The filtered AC power is output to the AC bus  116  via an AC output  115 . The logic power supply  451  supplies voltage to the main control circuitry  420  as well as the other circuitry within the inverter  110 . The logic power supply  451  provides one or more regulated DC voltages to power the components. The inverter  110  further includes a fan  455  and heatsink  460  to help maintain the inverter  110  at an appropriate or desired operating temperature. The inverter  110  may also include UL CRD circuitry  463 , designed to conform with certain UL requirements, when compliance with such requirements is desired. The inverter  110  also includes bus capacitors  465 . 
     The inverter  110  can have a power rating of three kilowatts or four kilowatts. A three kilowatt inverter outputs three kilowatts of AC power during normal operation. A four kilowatt inverter outputs four kilowatts of AC power during normal operation. The three kilowatt version of the inverter  110  contains some different components (e.g., lower rated capacitors, etc.) than the four kilowatt version of the inverter  110 . However, the basic architecture of the inverter  110  remains essentially the same regardless of whether a three or four kilowatt configuration is implemented. The configuration of the inverter  110  may be selected based on its associated power source  104 . For instances, a three kilowatt configuration may be optimal for one type of power source  104 , and a four kilowatt configuration may be optimal for another type of power source  104  (e.g., a higher output power source  104 ). 
     The modular architecture of the energy harvesting system  100  is designed such that one, two, or three inverters (inverters  110   a ,  110   b , and  110   c ) can be installed within the housing  112  (e.g., within the bay  112   a ) of the energy portal  107 . Each installed inverter  110  may have either a three kilowatt or four kilowatt configuration. The modular architecture allows for nine configurations of renewable power sources  104  and inverters  110  of the energy harvesting system  100 . The power rating of the energy harvesting system  100  is dependent on the number of inverters  110  and the power ratings of each inverter  110 . The energy harvesting system  100  can, therefore, have a total power rating of three kilowatts (i.e., one three-kilowatt inverter  110  in one slot), four kilowatts, six kilowatts, seven kilowatts, eight kilowatts, nine kilowatts, ten kilowatts, eleven kilowatts, or twelve kilowatts (i.e., four-kilowatt inverters  110  in all three slots). This modularity allows the energy harvesting system  100  to be scalable to the changing needs of the user. For instances, a user may start with a single power source  104  and inverter  110 , then later, purchase and install additional power sources  104  and inverters  110 . Table 1 lists a number of different configurations of inverters  110  in the portal  107  and the resulting power ratings of the portal  100 . In some embodiments, multiple energy portals  107  can be used where AC buses of each energy portal output to the grid. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Total Power Rating 
                 First Inverter 
                 Second Inverter 
                 Third Inverter 
               
               
                   
               
             
            
               
                 3 kW 
                 3 kW 
                 NONE 
                 NONE 
               
               
                 4 kW 
                 4 kW 
                 NONE 
                 NONE 
               
               
                 6 kW 
                 3 kW 
                 3 kW 
                 NONE 
               
               
                 7 kW 
                 3 kW 
                 4 kW 
                 NONE 
               
               
                 8 kW 
                 4 kW 
                 4 kW 
                 NONE 
               
               
                 9 kW 
                 3 kW 
                 3 kW 
                 3 kW 
               
               
                 10 kW  
                 3 kW 
                 3 kW 
                 4 kW 
               
               
                 11 kW  
                 3 kW 
                 4 kW 
                 4 kW 
               
               
                 12 kW  
                 4 kW 
                 4 kW 
                 4 kW 
               
               
                   
               
            
           
         
       
     
     Returning to  FIG. 3 , the AC power from the inverters  110   a ,  110   b , and  110   c  is output from the AC outputs  450   a ,  450   b , and  450   c  to the AC bus  116 . The AC bus  116  combines the AC power from the outputs of the inverters  110 . The power on the AC bus  116  is provided to an AC output  117  of the energy portal  107 . 
     The controller  113  is contained within the housing  112 . However, the controller  113  may be located external to the housing  112  of the energy portal  107 . The controller  113  may be a computer, microcontroller, or similar device and, as a consequence, the controller may include a processor (not shown) and memory (not shown). The controller  113  is connected to user interface  335  ( FIG. 3 ). The user interface  335  includes a local display screen  340  and buttons  345 . The controller  113  monitors and controls the inverters  110  by, for example, executing software stored in the memory within the controller. The user interface  335  receives data inputs from the processor and buttons  345  and outputs data to the local display screen  340 . 
     The controller  113  communicates with the ATS  130  when the ATS  130  couples the auxiliary loads  124  to AC power from the grid  105 , from the AC bus  116  of the energy portal  107 , and/or from the standby power sub-system  145 , as described above. The controller  113  may also communicate with the ATS  130  of the standby power sub-system  145  to turn the generator  155  on and off. The controller  113  may also directly communicate with and control the standby power sub-system  145 . 
     The user may communicate with the controller  113  via wired connections (e.g., using the communication ports  355 ) or wirelessly through the antennas  360 . Communications may relate to diagnostic checks, system monitoring, and powering the energy portal  107  on and off, among other things. In some embodiments, the controller  113  includes a web interface  365 . The web interface  365  allows for user communication with the energy harvesting system  100  across the Internet. For instance, the energy harvesting system  100  may communicate to a remote web server hosting a website that is accessible by a user via a web browser. In some instances, the energy harvesting system  100  may host a web site remotely accessible by a user via the web interface  365 . 
       FIGS. 5   a  and  5   b  are perspective views of the housing  112  of the energy portal  107 . In the embodiment shown in  FIGS. 5   a  and  5   b , the housing includes a top cover  505  and a bottom cover  510  (removed from the housing  112 ). The user interface  335  is shown on the top cover  505 , although the user interface  335  is on the bottom cover  510  is some embodiments.  FIG. 5   a  shows the inverters  110   a ,  110   b , and  110   c , positioned in the bay  112   a , in a horizontal, stacked relationship.  FIG. 5   b  shows the inverters  110   a ,  110   b , and  110   c , positioned in the bay  112   a , in a vertical, stacked relationship. When attached to the housing or in place, the top cover  505  covers the bay  112   a  of the housing  112 , and the bottom cover  510  covers a bottom portion  112   b  of the housing  112 . The housing  112  may be wall-mounted or free standing. Preferably, each component of the energy harvesting system  100  weighs less than thirty pounds. For example, each inverter  110  is less than thirty pounds and the housing is constructed to be similarly lightweight. When so constructed, a single individual (installer) may readily lift and carry the components during the installation of an energy harvesting system  100 . For instances, in a residential basement installation, a single installer can unload the components of the energy harvesting system  100  components from a vehicle, carry them down a staircase, and lift them for wall mounting. 
       FIG. 6  is a perspective view of the housing  112  showing the airflow of the energy portal  107 . The airflow is shown by arrows  605 ,  610 , and  615 . The airflow is directed by the fans  455 . Cool air enters into the housing  112  via one or more openings (not shown) in the lower portion of the bottom cover  510  and/or the bottom portion  112   b . The air travels through the housing  112  to help maintain the operating temperature of the energy portal  107  below a level where components could fail or be damaged. The air then exits through one or more openings (not shown) in the upper portion of the top cover  505  and/or the inverter section  112   a.    
       FIG. 7  illustrates a method  700  for harvesting energy using the energy harvesting system  100 . The energy harvesting system  100  receives DC power from the renewable power sources  104   a ,  104   b , and  104   c  (Step  705 ). The DC power from the renewable powers sources  104   a ,  104   b , and  104   c  is then inverted to AC power by the inverters  110   a ,  110   b , and  110   c  (Step  710 ). The AC power from the inverters  110   a ,  110   b , and  110   c  is then output to the AC bus  116  (Step  715 ). The AC power from the AC bus  116  is then output to the grid  105  or to auxiliary load  124  (Step  720 ). 
     The user may alter the total power rating of the energy harvesting system  100  by adding, removing, or replacing one or more of the inverters  110 .  FIG. 8  illustrates a method  800  for replacing one of the inverters  110   a ,  110   b , and  110   c  with another one of the inverters  110  having a different power rating. Method  800  begins with the removal of one of the inverters  110  installed in the energy harvesting system  100  (Step  805 ). The inverter  110  selected for installation (the “new inverter  110 ”) is inserted in the energy portal  107 , for instance, in place of the inverter  110  removed in step  805  (Step  810 ). The new inverter  110  is then connected to the power source  104  (Step  815 ). In some instances, the power source  104  is also new and has a different power output than the power source  104  used with the inverter  110  removed in step  805 . The energy harvesting system  100  receives DC power from the power source  104  connected in step  815  (Step  820 ). The DC power from the power source  104  is then inverted to AC power by the new inverter  110  (Step  825 ). The AC power from the new inverter  110  is then output to the AC bus  116  (Step  830 ). 
     The modular energy harvesting system enables the harvesting or collection of electrical power from various combinations of energy sources (such as solar arrays) and can be easily modified (such as by installing an additional inverter in the bay) to accommodate adding additional energy sources (such as an additional solar array) at the facility where the portal  107  is installed. Thus, the energy harvesting system is applicable in various residential and commercial scenarios. The modular design and selective coupling to the grid and local loads provides an easy-to-use, easy-to-customize, and easy-to-alter energy harvesting system. Various features and advantages of the invention are set forth in the following claims.