Patent Publication Number: US-2011054707-A1

Title: System and method for controlling power usage

Description:
BACKGROUND 
     The present disclosure relates generally to the field of building electrical systems and more specifically to building generation systems including utility power sources and standby power sources. Standby power systems are generally configured to provide backup power to electrical loads having the highest priority in the event of a utility source failure. The cost of electricity provided by utility sources can vary by the day, hour, or minute depending on the cost of the fuel source and the amount of power being consumed. 
     SUMMARY 
     One exemplary embodiment relates to a control system for a home generator. The control system includes circuitry configured to determine a first cost of electricity provided by an off-site provider, determine a second cost of electricity produced by the home generator, compare the first cost with the second cost, and provide the result of the comparison as an output. 
     Another exemplary embodiment relates to a method of controlling a home generator. The method includes determining a first cost of electricity provided by an off-site provider, determining a second cost of electricity produced on-site, comparing the first cost of electricity to the second cost of electricity, and using the result of the comparison to decide whether to operate the home generator to produce electricity instead of using the electricity provided by the off-site provider. 
     Another exemplary embodiment relates to a home electricity system. The home electricity system includes a circuit breaker panel coupled to a number of electrical loads, a transfer switch coupled to the circuit breaker panel, a power line coupled to the transfer switch and configured to provide electricity from a utility provider, an engine-generator-set coupled to the transfer switch, and a control system. The control system is configured to determine a first cost of electricity provided by the utility provider, determine a second cost of electricity produced on-site, and compare the first cost with the second cost and provide the result of the comparison as an output. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below. 
         FIG. 1  is a schematic diagram illustrating a building electrical system, according to an exemplary embodiment. 
         FIG. 2  is a more detailed diagram of the main transfer switch of  FIG. 1 , according to an exemplary embodiment. 
         FIG. 3  is a more detailed diagram of the distribution panel of  FIG. 1 , according to an exemplary embodiment. 
         FIG. 4  is a more detailed diagram of the secondary transfer switch of  FIG. 1 , according to an exemplary embodiment. 
         FIG. 5  is a more detailed diagram of the subpanel of  FIG. 1 , according to an exemplary embodiment. 
         FIG. 6  is a flow chart illustrating a method for selecting a power source for an electrical system, according to an exemplary embodiment. 
         FIG. 7  is a flow chart illustrating a method for selecting a power source for an electrical system, according to another exemplary embodiment. 
         FIG. 8  is a flow chart illustrating a method for selecting a power source for an electrical system, according to still another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     According to various exemplary embodiments, the standby generator of a building may be used to supplement or replace an off-site utility power source and allow for the consumer to power appliances for a lower cost than the utility power provider. A cost per kWh (e.g., real time cost, cost as a function of time of day, cost as a function of usage, etc) can be provided to the consumer so they know which appliances are more cost effective to operate under standby power rather than prime or utility power. The consumer can decrease energy costs by running electrical loads (e.g., appliances) off of a secondary source of power (e.g., a generator), rather than the primary off-site utility source when it would be more cost effective to do so. This approach puts consumers in more control of the overall cost of electricity. 
       FIG. 1  illustrates an electrical system  100  for a building (e.g., a residential electrical system) according to an exemplary embodiment. Electrical system  100  includes an electric utility meter  102  electrically coupled to an off-site utility power source (not shown) and configured to provide power from the off-site utility source to a distribution panel  104 . Distribution panel  104  (e.g., a circuit breaker box, a fuse box, etc.) is configured to route electrical power to electrical loads  106  (not specifically shown in  FIG. 1 ) in the building. Electrical system  100  also includes a generator  108  (e.g. a home standby generator) for providing electrical power to distribution panel  104  instead of or in addition to the power provided at meter  102 . Generator  108  may be configured to provide power to distribution panel  104  in the event of a utility power failure. A transfer switch  110  is configured to transfer the source of electrical power provided to distribution panel  104  and may transfer the power source automatically or manually via a user operated lever. For example, in the event of a utility power failure, transfer switch  110  may automatically sense the loss of power and route power from generator  108  to distribution panel  104  instead of from the utility source at meter  102 . 
     Generator  108  and distribution panel  104  are also coupled to a transfer switch  112  (e.g., a cost comparison transfer switch) and a distributional subpanel  114  (e.g., a cost comparison subpanel). Distribution panel  104  may route power for some loads  116  through transfer switch  112  and subpanel  1   14 . Transfer switch  112  is configured to determine the most cost effective power source between the generator  108  and the utility source provided via meter  102 . If the cost to power loads  116  would be less if the power were provided by generator  108 , then transfer switch  112  may route power for loads  116  through subpanel  114  from generator  108  rather than from meter  102 . Alternatively, if the cost to power loads  116  would be less if the power were provided from meter  102 , then transfer switch  112  may route power for loads  116  from meter  102  rather than from generator  108 . 
     Transfer switch  112  may receive signals representing cost data for comparison purposes from various sources. According to one exemplary embodiment, transfer switch  112  may receive a signal representing utility cost data (e.g., electricity, natural gas for generator  108 , etc.) over the utility line using power line carrier (PLC) technology. According to another exemplary embodiments, transfer switch  112  may receive a signal representing utility cost data from a wireless network of the utility, for example a cellular network or wireless transmitters/transceivers installed on meter  102 , on power line poles, on power line transformers, on power line crossovers, or on other utility locations. According to still other exemplary embodiments, transfer switch  112  may retrieve a signal representing utility cost data from a computer (e.g., a personal computer) via the Internet, from a database stored in transfer switch  112  or stored in a coupled computer, from an electronic bill, or from user entered data. 
     Transfer switch  112  may compare the costs of providing power from meter  102  or from generator  108  by calculating a difference in therm ratio. The signals representing cost data received by transfer switch may include the price per therm or price per British thermal unit (BTU) for the power source. Transfer switch  112  may also receive a signal representing data about loads  116  coupled to transfer switch  112  and subpanel  114  (e.g., from a database, from user entry, from loads  116 ), for example, the therm or BTU usage of the load per kilowatt-hour (kWh). From these signals (e.g., representing cost data and power usage), transfer switch  112  may calculate the price per kWh that loads  116  would use at a particular time for the power source. Thus for any given time period or over preprogrammed time intervals, transfer switch  112  may compare whether it would cost less to provide power to loads  116  from meter  102  or from generator  108 . For example, transfer switch  112  may compare costs about every hour, about every 30 minutes, about every ten minutes, about every 5 minutes, about every minute, etc. 
     For example, a 15 kW generator at half load may use 126,000 BTU/hr of natural gas. The utility company may charge $0.5161 per therm of natural gas in a given month and charge $0.22 per kWh at peak time for electricity. Transfer switch  112  receives a signal representing each of these costs. Given that one therm is about equal to 100,000 BTUs of natural gas, transfer switch  112  determines that a resident running at 7.5 kWh would pay: 
     
       
         
           
             
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     Transfer switch  112  may compare these prices per hour usage to determine a difference of about $1.00 per hour usage of the 7.5 kW load  116  by operating generator  108  with natural gas instead of off-site electric power loads  116 . Transfer switch  112  may then operate generator  108  to power load  116  and disconnect power from the off-site source for load  116 . 
     According to various exemplary embodiments, generator  108  may be a home standby generator, a portable generator, or a generator capable of being used by another type of building. According to some exemplary embodiments generator  108  may be powered by natural gas or propane, while according to other exemplary embodiments, generator  108  may be powered by another fuel source such as gasoline. It is noted that while the illustrated exemplary embodiment shows the use of a generator in combination with a utility power source, different configurations are possible. According to some exemplary embodiments, generator  108  may be substituted by a solar, wind, geothermal, or other non-utility or standby power sources. According to other exemplary embodiments, electrical system  100  may include additional standby power sources (e.g., generator, solar, geothermal, etc.) or an additional utility power source that may be used to provide power instead of or in addition to the power provided by generator  108  and meter  102  depending on the cost comparison performed by subpanel  114 . 
     Meter  102 , generator  108 , and transfer switch  110  are all shown as being mounted exterior of a building (e.g., on the exterior wall or on the ground) while distribution panel  104 , transfer switch  112 , and subpanel  114  are shown mounted on the interior of the building (e.g., on a basement wall). It is noted that according to other exemplary embodiments, meter  102  and transfer switch  110  may be mounted in the interior of the building or one or more of distribution panel  104 , transfer switch  112 , and subpanel  114  may be mounted exterior to the building. 
       FIG. 2  is a more detailed diagram of transfer switch  110 , according to an exemplary embodiment. Transfer switch  110  is coupled to utility meter  102  via a port  202 , to generator  108  via a port  204 , and to distribution panel  104  via port  206 . Transfer switch  110  may be capable of bidirectional communication with utility meter  102 , generator  108 , and distribution panel  104  via ports  202 ,  204 , and  206 , respectively. Transfer switch  110  includes a ground terminal  208  for providing a ground line to generator  108  and distribution panel  104  as well as a neutral terminal  210  secured by a bonding screw  211  for providing a neutral or common line among utility meter  102 , distribution panel  104 , and generator  108  (line N). Power input lines from generator  108  (lines E 1  and E 2 ) are coupled to a generator connection  212 , and control lines from generator  108  (lines F 1  and F 2 ) are coupled to a generator control connection  214  (e.g., a 240V control connection). A transmit/receive (TxRx) connection  216  couples a controller of transfer switch  112  to a controller  218 . According to various exemplary embodiments, controller  218  may be any digital or analog control logic or hardware capable of controlling transfer of power between generator  108  and meter  102  and controlling startup and communication with generator  108 . Controller  218  may also be coupled to current transformers  222  and  224 , which provide signals to controller  218  representing how much power (kW) generator  108  is supplying. Load lines (L 1  and L 2 ) providing power to distribution panel  104  are coupled to transfer switch  110  via a load connection  220 . 
     While transfer switch  110  is illustrated as being separate from distribution panel  104 , it is noted that according to other exemplary embodiments, transfer switch  110  may be integral with distribution panel  104 . Referring also to  FIG. 3 , a more detailed diagram of distribution panel  104  is illustrated, according to an exemplary embodiment. The ground line (G) from transfer switch  110  is coupled to a ground bus  302  and out to transfer switch  112 . The neutral line (N) from transfer switch  110  is coupled to a neutral bus  304  and out to transfer switch  112 . Distribution panel  104  includes a number of circuit breakers  306  configured to route power to loads  106  and break the electrical connection to loads  106  in the case of a power surge to reduce damage to the loads. Distribution panel  104  also includes a breaker  308  (e.g., a two pole breaker) configured to route power for loads  116  to transfer switch  112 . 
       FIG. 4  is a more detailed diagram of transfer switch  112 , according to an exemplary embodiment. Transfer switch  112  is coupled to distribution panel  104  via a port  402 , to generator  108  via a port  404 , and to subpanel  114  via port  406 . Transfer switch  112  may be capable of bidirectional communication with distribution panel  104 , generator  108 , and subpanel  114  via ports  402 ,  404 , and  406 , respectively. Transfer switch  112  includes a ground terminal  408  for providing a ground line to generator  108  and subpanel  114  as well as a neutral terminal  410  for providing a neutral or common line among distribution panel  104 , subpanel  114 , and generator  108  (line N). Power input lines from generator  108  (lines E 1  and E 2 ) are coupled to a generator connection  412 . A generator communication line  416  (TxRx) is coupled to a control system or a controller  418  (e.g., a cost comparison control board) for bidirectional communication with generator  108  while a communication line  420  facilitates bidirectional communication with controller  218  of transfer switch  110 . As such, controller  418  may control operation of controller  218  as well as operation of generator  108 . 
     According to various exemplary embodiments, controller  418  may be any digital or analog control logic or hardware capable of controlling transfer of power between generator  108  and meter  102 , capable of controlling startup and communication with generator  108 , capable of receive signals representing costs of power sources, and capable of comparing cost and load data to determine whether it would be more cost effective to power loads  116  using generator  108  or using off-site electricity via meter  102 . According to some exemplary embodiments, controller  418  could output indicators of cost savings, cost usage of loads  116 , and/or power usage of loads  116  to a display, a computer, an email account, a mobile or cellular phone, etc. While controller  418  is illustrated as being mounted in transfer switch  112 , according to other exemplary embodiments, controller  418  could mounted at other locations, for example on generator  108 , on subpanel  114 , on a remotely located computer, etc. Load lines (L 1  and L 2 ) providing power to subpanel  114  are coupled to transfer switch  112  via a load connection  426 . 
     While transfer switch  112  is illustrated as being separate from subpanel  114 , it is noted that according to other exemplary embodiments, transfer switch  112  may be integral with subpanel  114 . Referring also to  FIG. 5 , a more detailed diagram of subpanel  114  is illustrated, according to an exemplary embodiment. The ground line (G) from transfer switch  112  is coupled to a ground bus  502  while the neutral line (N) from transfer switch  112  is coupled to a neutral bus  504 . Subpanel  114  includes a number of circuit breakers  506  configured to route power to loads  116  and break the electrical connection to loads  116  under certain circumstances (e.g., a power surge) to reduce damage to the loads and protect electrical circuits. While a specific number of breakers and loads are illustrated in the figure, according to other exemplary embodiments, varying numbers of loads may be coupled to subpanel  114 , for example four large loads or loads that are specifically selected. The loads that are coupled to subpanel  114  may be selected based on a variety of criteria. For example, it may be beneficial to couple appliances that run during “peak” utility source times of day to transfer switch  112  to run more cost effectively (e.g., an air conditioner, a refrigerator, a tank water heater, etc.). In another example, it may be beneficial to couple appliances that run more frequently to transfer switch  112  to optimize usage of the cost comparisons made by transfer switch  112  (e.g., a water heater, a furnace, a refrigerator, etc.). 
     It is noted that while  FIGS. 2-5  are schematic diagrams showing certain wire routing and specific components according to one exemplary embodiment, according to other exemplary embodiments, the transfer switches and distribution panels of  FIGS. 2-5  may include various other configurations, components, and wire routing to support the power transfer and cost comparison functionality described herein. 
     Referring to  FIG. 6 , a flow chart illustrates a method  600  for selecting a power or electricity source for an electrical system (e.g., a residential electrical system), according to an exemplary embodiment. Transfer switch  112  (e.g., controller  418 ) determines a cost of electricity or power from a first source (step  602 ). Transfer switch  112  then determines a cost of electricity or power from a second source (step  604 ). Transfer switch  112  compares the costs of electricity or power from the first and second sources (step  606 ). Transfer switch  112  also determines the power source to use based on the comparison made (step  608 ). Thereafter transfer switch  112  can switch to the appropriate power source or remain on the current power source based on the determination, including operating or shutting down generator  108 . 
     Referring to  FIG. 7 , a flow chart illustrates a method  700  for selecting a power or electricity source for an electrical system (e.g., a residential electrical system), according to another exemplary embodiment. Transfer switch  112  (e.g., controller  418 ) determines a cost of electricity or power from an off-site utility source at meter  102  (step  702 ). Transfer switch  112  also determines a cost of electricity or power from standby generator  108  (step  704 ). Transfer switch  112  compares the costs of electricity or power from meter  102  and generator  108  (step  706 ). Transfer switch  112  then determines the power source to use based on the comparison made (step  708 ). Thereafter transfer switch  112  can switch to the appropriate power source or remain on the current power source based on the determination (step  710 ), including operating or shutting down generator  108 . 
     Referring to  FIG. 8 , a flow chart illustrates a method  800  for selecting a power or electricity source for an electrical system (e.g., a residential electrical system), according to another exemplary embodiment. Transfer switch  112  (e.g., controller  418 ) determines a cost of electricity or power from an off-site utility source at meter  102  (step  802 ). Transfer switch  112  also determines a cost of electricity or power from standby generator  108  (step  804 ). Transfer switch  112  also determines a cost and availability of electricity or power from other on-site electrical sources, for example cost and availability of solar (e.g., sufficient sun or stored power available), wind (e.g., enough wind available), or geothermal sources. (step  806 ). Transfer switch  112  compares the costs of available electricity or power from meter  102  and generator  108  and possibly from other on-site sources if power is available (step  808 ). Transfer switch  112  then determines the power source to use based on the comparison made (step  810 ). Thereafter transfer switch  112  can switch to a different power source or remain on the current power source based on the determination (step  812 ), including operating or shutting down generator  108 . 
     While the exemplary embodiments illustrated in the figures and described herein are presently preferred, it should be understood that these embodiments are offered by way of example only. Accordingly, the present application is not limited to a particular embodiment, but extends to various modifications. The order or sequence of any processes or method steps may be varied or re-sequenced according to alternative embodiments. 
     The present application contemplates methods, systems and program products on any machine-readable media for accomplishing its operations. The embodiments of the present application may be implemented using existing computer processors or logic controllers, or by a special purpose computer processor or logic controller for an appropriate system, incorporated for this or another purpose or by a hardwired system. 
     It is important to note that the construction and arrangement of the control system and home electricity system shown in the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter. For example, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present application. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present application. 
     As noted above, embodiments within the scope of the present application include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media which can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions comprise, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions. 
     It should be noted that although the figures herein may show a specific order of method steps, it is understood that the order of these steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. It is understood that all such variations are within the scope of the application. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps.