Patent Publication Number: US-2023155409-A1

Title: Mobile charging system achieved by transportation of secondary batteries

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application No. PCT/JP2021/019317, filed on May 21, 2021, which claims priority to and the benefit of Japanese Patent Application No. 2020-122205, filed on Jul. 16, 2020. The contents of these applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF INVENTION 
     1. Field 
     The present invention relates to electrical energy supply, and in particular, to a technology for supplying electrical energy by transportation of secondary batteries. 
     2. Description of Related Art 
     There is a growing interest in a “sustainable society” against a backdrop of population growth accompanied by rapid increase in energy consumption. A sustainable society can be defined as a society capable of preserving the global environment, passing the preserved global environment to the next generation, and also satisfying the needs of the current generation. 
     In order to achieve a sustainable society, there have been needs for active use of natural energy such as photovoltaic power generation, wind power generation, and geothermal power generation. A future town has been currently planned in which a best mix of a variety of power sources including natural energy based on regional characteristics is pursued and energy is supplied as much as possible by local production for local consumption. 
     RELATED ART LIST 
     Patent Literature 1: JP 5360157 B 
     In addition, many of advanced countries face the problem of crumbling infrastructure including power grids. For remodeling a town, reconstruction of power grids is also necessary. Overhead power lines spoils the landscape of a town. If power lines are laid underground (to remove utility poles), however, the construction costs become higher. In a country like Japan that is prone to natural disasters such as earthquakes and typhoons, the risk that a power grid is torn has to be considered. 
     SUMMARY OF INVENTION 
     The present invention has been achieved on the basis of recognition of the aforementioned problems, and a chief object thereof is to provide a novel method for supplying energy. 
     A mobile charging system according to an aspect of the present invention includes: a home to which power is to be supplied from a first secondary battery; a mobile object including a second secondary battery and being autonomously movable; and a server connected with the home and the mobile object via a communication network. 
     The home includes: a battery managing unit to measure a battery charge level of the first secondary battery; and a communication unit to transmit battery information including the battery charge level to the server. 
     The server includes: a receiving unit to receive the battery information from the home; and a transmitting unit to transmit a start instruction to the mobile object in a standby state when the battery charge level in the battery information is lower than a first threshold. 
     The mobile object includes: a drive mechanism to move the mobile object; a receiving unit to receive the start instruction; a movement control unit to set the home as a goal point and instruct the drive mechanism to move upon receiving the start instruction, and a battery managing unit to supply power to the first secondary battery from the second secondary battery when the mobile object has reached the home. 
     A mobile object according to an aspect of the present invention includes: a second secondary battery; a drive mechanism to move the mobile object by the second secondary battery as a power source; a receiving unit to receive a start instruction specifying a home from a server; a path calculating unit to refer to map information and calculate a path from a current position to the home upon receiving the start instruction; a movement control unit to control the drive mechanism in accordance with the calculated path; and a battery managing unit to supply power to a first secondary battery installed at the home from the second secondary battery upon reaching the home, wherein 
     The movement control unit controls the drive mechanism to return to a predetermined return position from the home after power supply to the first secondary battery. 
     A server according to an aspect of the present invention is connected, via a communication network, with a home to which power is to be supplied from a first secondary battery and a mobile object including a second secondary battery and being autonomously movable. 
     The server includes: a receiving unit to receive battery information including a battery charge level of the first secondary battery from the home; and a transmitting unit to transmit a start instruction specifying the home as a goal point to the mobile object in a standby state when the battery charge level indicated in the battery information is lower than a first threshold. 
     A mobile charging system according to another aspect of the present invention includes: a plurality of homes to each of which power is supplied from a first secondary battery; a plurality of mobile objects each including a second secondary battery and each being autonomously movable; and a server connected with the homes and the mobile objects via a communication network. 
     The homes each include: a battery managing unit to measure a battery charge level of the first secondary battery; and a communication unit to transmit first battery information including the battery charge level together with a home ID to the server. 
     The server includes: a first receiving unit to receive the first battery information from each of the homes; a second receiving unit to receive second battery information including a battery charge level of a second secondary battery from each of the mobile objects; a first determining unit to determine whether or not one or more homes with a battery charge level indicated in the first battery information being lower than a first threshold are present; a second determining unit to determine whether or not one or more mobile objects with a battery charge level indicated in the second battery information being equal to or higher than a fourth threshold are present; and a transmitting unit to transmit a start instruction when a home with the battery charge level in the first secondary battery being lower than the first threshold is present, the start instruction specifying the home, the transmitting unit transmitting the start instruction to any one of mobile objects in a standby state and with the battery charge level of the second secondary battery being equal to or higher than the fourth threshold. 
     The mobile objects each include: a drive mechanism to move the mobile object; a receiving unit to receive the start instruction; a path calculating unit to refer to map information and calculate a path from a current position to the home specified by the start instruction upon receiving the start instruction; a movement control unit to control the drive mechanism in accordance with the calculated path; and a battery managing unit to supply power to the first secondary battery installed at the specified home from the second secondary battery of the mobile object upon reaching the specified home. 
     The movement control unit of each of the mobile objects controls the drive mechanism to return from the home to a predetermined return position after power supply to the first secondary battery. 
     The present invention enables supply of energy by a delivery system. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a conceptual diagram of a mobile charging system; 
         FIG.  2    is a schematic diagram for explaining a method for supplying power by using electricity delivery vehicles; 
         FIG.  3    is a functional block diagram of an electricity delivery vehicle; 
         FIG.  4    is a functional block diagram of a home; 
         FIG.  5    is a functional block diagram of a server; 
         FIG.  6    is a data structure table of home power consumption information; 
         FIG.  7    is a data structure table of home estimation information; 
         FIG.  8    is a data structure table of vehicle information; 
         FIG.  9    is a flowchart illustrating processes performed by the server to determine whether or not an electricity delivery vehicle is to start moving; 
         FIG.  10    is a flowchart illustrating processes performed by an electricity delivery vehicle in receipt of a start instruction; 
         FIG.  11    is a flowchart illustrating processes performed by an electricity delivery vehicle after finishing power supply; 
         FIG.  12    is a data structure table of home adjustment information; 
         FIG.  13    is a data structure table of town adjustment information; and 
         FIG.  14    is a data structure table of weather adjustment information. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    is a conceptual diagram of a mobile charging system  100 . 
     In the present embodiment, assume that the mobile charging system  100  is operated in a town of several hundred to several thousand people. In this town, local production for local consumption of energy, or in particular, electrical energy is set as a goal. 
     The mobile charging system  100  includes a power supply system  104  and a power consumption system  106 . The power supply system  104  corresponds to a producer of electrical energy. The power consumption system  106  includes a plurality of homes  400 . The homes  400  correspond to consumers of electrical energy. A secondary battery (first secondary battery) of a relatively large size (hereinafter also referred to as a “fixed battery”) is installed in each home  400 . In each home  400 , the fixed battery covers necessary electrical energy at home. 
     The power supply system  104  includes a power station  102 , a server  300 , and a plurality of electricity delivery vehicles  200 . The power station  102  is a collection of one or more power production sources. The power station  102  includes power production sources using natural energy such as photovoltaic power generation, geothermal power generation, biomass power generation, and wind power generation. The power production sources included in the power station  102  need not be concentrated in one place, and may be distributed over the whole town. In addition, the power station  102  may include existing power stations such as a thermal power station, a hydraulic power station, and a nuclear power station in addition to power generation using natural energy. 
     The electricity delivery vehicles  200  are unmanned autonomous vehicles; The electricity delivery vehicles  200  each include a built-in secondary battery (second secondary battery) of a relatively small size (hereinafter also referred to as a “mobile battery”). The electricity delivery vehicles  200  each have a height of about 0.5 to 1.2 meters and travel at low speeds of about 3 to 10 kilometers per hour, for example. In addition, the electricity delivery vehicles  200  each have an imaging function using a camera, a position detecting function using a global positioning system (GPS), and a communication function. The electricity delivery vehicles  200  are connected with the power station  102  via power supply lines  108  to charge the built-in mobile batteries. Power may be supplied to the power supply lines  108  not only from the power station  102  in the town but also a power station outside the town as a reserve power supply. Hereinafter, a place at which the electricity delivery vehicles  200  receive power supply through the power supply lines  108  is referred to as a “standby area”. 
     The server  300  periodically receives first battery information including the remaining battery level (battery charge level or state of charge) of the fixed battery from each home  400  via a wired or wireless communication network. The first battery information indicates a home ID for identifying the home  400 , the capacity of the fixed battery, the remaining battery level of the fixed battery, and the usage of electrical energy at the home  400  such as power consumption (the amount of decrease per unit period of the remaining battery level) at the home  400 . The server  300  instructs an electricity delivery vehicle  200  in the standby area to start moving for a home  400  in which the remaining battery level is low. 
     The electricity delivery vehicle  200  in receipt of the start instruction autonomously moves toward the specified home  400 . When the electricity delivery vehicle  200  reaches the home  400 , the built-in mobile battery is connected to the fixed battery of the home  400 , and power is supplied from the mobile battery to the fixed battery. After power supply, the electricity delivery vehicle  200  automatically returns to the standby area. Alternatively, the power supply from the mobile battery to the fixed battery may be known wireless power transfer such as a magnetic field resonance method. 
     Hereinafter, “a power consumption of X[%] of a fixed battery at a home  400  in a certain time slot W (for example, 10:00-11:00 on Friday)” means that the remaining battery level of the fixed battery has lowered by X[%] in this time slot. Note that, however, when the fixed battery is charged by the mobile battery in the time slot W, the power consumption of the home in the time slot W is treated as “not available (N/A)”. The home  400  notifies the server  300  of the time during which the fixed battery is charged as part of the first battery information. 
       FIG.  2    is a schematic diagram for explaining a method for supplying power by using electricity delivery vehicles  200 . 
     The server  300  selects electricity delivery vehicles  200  with the remaining battery level of the mobile batteries being equal to or larger than a threshold (hereinafter referred to as a “moving threshold”) as candidates for a vehicle to be sent (dispatched) from the electricity delivery vehicles  200  in the standby area. Hereinafter, the electricity delivery vehicles  200  that are candidates for a vehicle to be sent will be referred to as “S vehicles (standby vehicles)”. Herein, assume that the moving threshold (fourth threshold) is 90[%]. 
     The server  300  selects homes  400  with the battery charge levels (states of charge: SOCs) of the fixed batteries being smaller than a threshold (hereinafter referred to as a “power supply threshold”) as candidates for power supply from the homes  400 . Hereinafter, the homes  400  that are candidates for power supply will be referred to as “R homes (requesting homes)”. Assume that the basic setting of the power supply threshold (first threshold) is 30[%]. The power supply threshold may be variable, details of which will be described later. 
     The server  300  transmits the home IDs of R homes (homes  400  with the remaining battery levels of the fixed batteries being smaller than the first threshold (power supply threshold)) to S vehicles (electricity delivery vehicles  200  with the remaining battery levels of the mobile batteries being equal to or larger than the fourth threshold (moving threshold)). The S vehicles have stored therein map information of the town and address information of the homes  400 . The server  300  periodically transmits (multicasts) latest map information and address information to all the electricity delivery vehicles  200  to update data in the electricity delivery vehicles  200 . Each electricity delivery vehicle  200  (S vehicle) calculates a travel path to an R home on the basis of the home ID, the map information, and the address information, and starts moving toward the R home. FIG.  2  illustrates travel paths of an electricity delivery vehicle  200   a  (S vehicle) setting a home  400   j  (R home) as a goal point and an electricity delivery vehicle  200   b  (S vehicle) setting a home  400   k  (R home) as a goal point. 
     Because the electricity delivery vehicles  200  are small and travel at low speeds, the electricity delivery vehicles  200  are capable of traveling on pedestrian lanes. Each electricity delivery vehicle  200  includes a camera mounted thereon, and decelerates or stops when an obstacle such as a person is present within a predetermined range from itself. Upon reaching an intersection, an electricity delivery vehicle  200  images a pedestrian traffic signal, checks the signal, and crosses a pedestrian crossing on a green light. 
     Alternatively, special lanes for electricity delivery vehicles  200  may be provided. Still alternatively, guiding lines such as white lines may be marked on the ground, and the electricity delivery vehicles  200  may move along the guiding lines. 
     A plurality of beacons may be placed in the ground, and the electricity delivery vehicles  200  may travel in accordance with guiding signals from the beacons. Each electricity delivery vehicle  200  may receive a guiding signal including a beacon ID from a beacon, and compare the beacon ID with map information in which the positions associated with individual beacon IDs are registered in advance to recognize its current position. 
     The electricity delivery vehicles  200  in the present embodiment are assumed to move distances of up to 1.6 kilometers each way, that is, within 3.2 kilometers per round trip by autonomous driving. 
       FIG.  3    is a functional block diagram of an electricity delivery vehicle  200 . 
     Respective components of the electricity delivery vehicle  200  are implemented by hardware including arithmetic units such as central processing units (CPUs) and various co-processors, storage devices such as memories and storages, and wire or wireless communication lines connecting the components, and software, stored in the storage devices, for supplying processing instructions to the arithmetic units. Computer programs may be constituted by device drivers, an Operating System, various application programs on upper layers thereof, and libraries providing common functions to the programs. The electricity delivery vehicle  200  further includes a hardware mechanism for electromotive drive, such as a drive mechanism  206  and a secondary battery  208  (mobile battery). 
     The blocks described below are not in units of hardware but are in units of functions. 
     The same is applicable to functional block diagrams of a home  400  ( FIG.  4   ) and the server  300  ( FIG.  5   ). 
     The electricity delivery vehicle  200  includes a communication unit  202 , a data processing unit  204 , the drive mechanism  206 , the secondary battery  208  (mobile battery), a camera  210 , and a data storage unit  212 . 
     The communication unit  202  performs processing for communication with the server  300  and the like via a wired or wireless communication network. The data storage unit  212  stores various data. The camera  210  serves as an “eye” of the electricity delivery vehicle  200  by imaging the outside. In addition, the electricity delivery vehicle  200  may include other sensors such as a distance measuring sensor. The data processing unit  204  performs various processes on the basis of data acquired by the communication unit  202 , the camera  210 , and the like and data stored in the data storage unit  212 . The drive mechanism  206  is a mechanism for driving of the electricity delivery vehicle  200 . The secondary battery  208  (mobile battery) is connectable with a fixed battery and a power supply line  108  via a charge and discharge connection port  214 . The secondary battery  208  (mobile battery) is charged by supply of electrical energy from a power supply line  108  via the charge and discharge connection port  214 . In addition, the secondary battery  208  (mobile battery) supplies electrical energy to a fixed battery via the charge and discharge connection port  214 . The secondary battery  208  (mobile battery) also functions as a power supply of the drive mechanism  206  and others. The data processing unit  204  also functions as an interface of the communication unit  202 , the camera  210 , the data storage unit  212 , the drive mechanism  206 , and the secondary battery  208  (mobile battery). 
     The communication unit  202  includes a transmitting unit  216  for transmitting data to external devices such as the server  300 , and a receiving unit  218  for receiving data from external devices. The transmitting unit  216  periodically transmits second battery information to the server  300 . The second battery information includes a vehicle ID for identifying the electricity delivery vehicle  200 , and information indicating the usage of electrical energy in the electricity delivery vehicle  200  such as the remaining battery level (battery charge level) of the secondary battery  208  (mobile battery). The transmitting unit  216  transmits vehicle state information of the electricity delivery vehicle  200 , as necessary. The vehicle state information includes the current position, the moving speed, the operation state, and the like of the electricity delivery vehicle  200 . 
     The drive mechanism  206  includes a motor  228  and wheels  230 . The motor  228  rotates the wheels  230  with the electrical energy supplied from the secondary battery  208  (mobile battery). The motor  228  controls the rotating speed and direction of the wheels  230  in accordance with instructions from a movement control unit  222 . 
     The data processing unit  204  includes a path calculating unit  220 , the movement control unit  222 , and a battery managing unit  224 . 
     The path calculating unit  220  refers to the map information stored in the data storage unit  212 , and calculates a travel path from the current position to a goal point. The movement control unit  222  controls traveling of the electricity delivery vehicle  200  by transmitting control signals to the drive mechanism  206  in accordance with the travel path. When the camera  210  has detected an obstacle within a predetermined distance, the movement control unit  222  adjusts the moving speed and the moving direction of the electricity delivery vehicle  200  to avoid collision. The battery managing unit  224  periodically measures the remaining battery level of the secondary battery  208  (mobile battery). When the secondary battery  208  (mobile battery) is connected with the fixed battery of a home  400 , the battery managing unit  224  controls charging of the fixed battery with the secondary battery  208  (mobile battery). 
       FIG.  4    is a functional block diagram of a home  400 . 
     The home  400  includes a secondary battery  404  (fixed battery), a charging control device  406 , a panel board  402 , a charge and discharge connection port  414 , and a plurality of electric appliances  408 . The electric appliances  408  are various power consuming entities such as a refrigerator, a washing machine, and a dishwasher. The electric appliances  408  are connected with the secondary battery  404  (fixed battery) via the panel board  402 . The panel board  402  is connected to the charge and discharge connection port  414 . The secondary battery  404  (fixed battery) is connectable with the secondary battery  208  (mobile battery) of an electricity delivery vehicle  200  via the panel board  402  and the charge and discharge connection port  414 . The secondary battery  404  (fixed battery) is charged by supply of electrical energy from the secondary battery  208  (mobile battery) of an electricity delivery vehicle  200  via the charge and discharge connection port  414  and the panel board  402 . In addition, the secondary battery  404  (fixed battery) supplies electrical energy to the respective electric appliances  408  via the panel board  402 . 
     The charging control device  406  includes a communication unit  410  and a battery managing unit  412 . 
     The communication unit  410  performs processing for communication with the server  300  and the like via a wired or wireless communication network. The communication unit  410  includes a transmitting unit  416  for transmitting data to external devices such as the server  300 , and a receiving unit  418  for receiving data from external devices. The transmitting unit  416  periodically transmits the first battery information (described above) to the server  300 . The battery managing unit  412  controls charge and discharge of the secondary battery  404  (fixed battery), and periodically measures the remaining battery level of the secondary battery  404  (fixed battery). 
       FIG.  5    is a functional block diagram of the server  300 . 
     The server  300  includes a communication unit  302 , a data processing unit  304 , and a data storage unit  306 . 
     The communication unit  302  performs processing for communication with the electricity delivery vehicles  200  and the like via a wired or wireless communication network. The data storage unit  306  stores various data. The data processing unit  304  performs various processes on the basis of data acquired by the communication unit  302  and data stored in the data storage unit  306 . The data processing unit  304  also functions as an interface of the communication unit  302  and the data storage unit  306 . 
     The communication unit  302  includes a transmitting unit  308  for transmitting data to external devices such as the electricity delivery vehicles  200 , and a receiving unit  310  for receiving data from external devices. The transmitting unit  308  transmits a start instruction, which will be described later, to an electricity delivery vehicle  200  in accordance with an instruction from a dispatch determination unit  312 . 
     The receiving unit  310  includes a first receiving unit  318 , a second receiving unit  320 , and a weather acquiring unit  322 . 
     The first receiving unit  318  receives the first battery information from the homes  400 . The second receiving unit  320  receives the second battery information from the electricity delivery vehicles  200 . The weather acquiring unit  322  obtains weather information from an external website of weather information via the Internet. Assume that weather information in the present embodiment is a probability of frozen precipitation (chance of snow) provided by the meteorological bureau. 
     The data processing unit  304  includes the dispatch determination unit  312 , a tendency analyzing unit  314 , and a consumption estimating unit  316 . 
     The dispatch determination unit  312  determines whether or not an electricity delivery vehicle  200  is to be sent. The dispatch determination unit  312  includes a first determination unit  324  and a second determination unit  326 . The first determination unit  324  determines whether or not an R home that needs charging with an electricity delivery vehicle  200  is present. The second determination unit  326  determines whether or not an S vehicle that can be sent to an R home is present. Details of methods for identifying an R home and an S vehicle will be described later. The tendency analyzing unit  314  analyzes the power consumption tendency of each home  400 . The power consumption tendency of a home  400  is information (individual consumption information) indicating power consumption (decrease in remaining battery level) of each home  400  in each time slot. Details of power consumption tendencies of homes  400  will be described later with reference to  FIGS.  6  and  7   . The tendency analyzing unit  314  analyzes the power consumption tendencies of the homes  400  or, in other words, the power consumption tendency of the whole town. The power consumption tendency of the whole town is also information (general consumption information) indicating power consumption (decrease in remaining battery level) of the whole town in each time slot. Details thereof will be described later with reference to  FIG.  13   . The consumption estimating unit  316  estimates a future remaining power amount on the basis of past data relating to the power consumption tendency, that is, power consumption. 
       FIG.  6    is a data structure table of home power consumption information  170 . 
     The home power consumption information  170  is stored in the data storage unit  306  of the server  300 . As described above, each home  400  is identified by a home ID. The transmitting unit  416  of each home  400  periodically (every hour, for example) transmits the first battery information to the server  300 . The tendency analyzing unit  314  of the server  300  refers to the first battery information and records the current remaining battery level of the secondary battery  404  (fixed battery) of each home  400 . In addition, the tendency analyzing unit  314  aggregates the power consumption (decrease in remaining battery level) of each home  400  for each predetermined time (in each time slot, for example). 
     The home power consumption information  170  of  FIG.  6    indicates the power consumption tendency of each home on Friday. For example, assume that, according to the first battery information collected from a home  400  with a home ID=H01 (hereinafter expressed as a “home  400  (H01)”), the power consumption of “15:00-16:00 on Friday, June 12th” was 15[%], the power consumption of “15:00-16:00 on Friday, June 19th” was 10[%], and the power consumption of “15:00-16:00 on Friday, June 26th” was 5[%]. The tendency analyzing unit  314  obtains an average power consumption on the basis of data on several recent Fridays. In a case where data of the aforementioned three days are used, the tendency analyzing unit  314  calculates the power consumption (individual power consumption tendency) of the home  400  (H01) in “16:00-17:00 on Friday” to be 10[%]. 
     When the power consumption in the same time slot on Friday, June 19th was “N/A”, the power consumption on Friday, June 5th, which is a week before Friday, June 12, is further included and the average is obtained from the data on recent three Fridays (5th, 12th, and 26th). Each time the tendency analyzing unit  314  calculates the latest power consumption of the home  400  (H01) in “15:00-16:00 on Friday”, the tendency analyzing unit  314  updates the corresponding field of the home power consumption information  170 . The same is applicable to the other days of the week, the other time slots, and the other homes. According to such a control method, an average power consumption of each home  400  in each time slot on each day of the week is registered in the home power consumption information  170 . The home power consumption information  170  shows when and how much power each home  400  tends to consume. The consumption estimating unit  316  estimates a future remaining battery level of each home  400  on the basis of the home power consumption information  170  (which will be described later). 
     According to the home power consumption information  170 , the average power consumption of the secondary battery  404  (fixed battery) of the home  400  (H01) in “15:00-16:00 on Friday” is 10[%]. In contrast, the average power consumption of the home  400  (H02) in the same time slot is 30[%]. This shows that a person or persons in the home  400  (H02) have a lifestyle consuming more power in “15:00-16:00 on Friday” than those in the home  400  (H01). 
     Hereinafter, a preset time slot like “15:00-16:00 on Friday” registered in the home power consumption information  170  will be referred to as a “preset period”. While the length of a preset period in the present embodiment is one hour, a preset period may be set to any length. 
       FIG.  7    is a data structure table of home estimation information  120 . 
     The home estimation information  120  is stored in the data storage unit  306  of the server  300 . The consumption estimating unit  316  estimates a future remaining battery level on the basis of the home power consumption information  170 . The home estimation information  120  shows estimated values of near-future remaining battery level of each home  400 . 
     Assume that the current time is “14:50 of Friday” and that the current remaining battery level of the home  400  (H01) is 90[%]. According to the home estimation information  120  in  FIG.  7   , the remaining battery level at 15:50, which is one hour later, is estimated to decrease to 80[%] unless the secondary battery  404  (fixed battery) is not newly charged. According to the home power consumption information  170  in  FIG.  6   , the power consumption of the home  400  (H01) in “15:00-16:00 on Friday” is estimated to be about 10[%]. In this case, for estimation of the remaining battery level after one hour, the consumption estimating unit  316  adopts 10[%] in the preset period “15:00-16:00 on Friday” that overlaps the most with a time slot of “14:50 (current time) to 15:50 (one hour later) on Friday”. The consumption estimating unit  316  estimates the remaining battery level after one hour to be 80[%] by subtracting 10[%], which is the estimated power consumption, from 90[%], which is the current remaining battery level. 
     Similarly, for estimation of the remaining battery level of the home  400  (H01) after two hours, 30[%] is adopted for the time slot of “15:50 (one hour later) to 16:50 (two hours later) on Friday” on the basis of the data in a preset period of “16:00-17:00 on Friday” in the home power consumption information  170  in  FIG.  6   . In this case, the remaining battery level of the secondary battery  404  (fixed battery) at 16:50, which is two hours later, is estimated to be 50[%] (=80−30). 
     The tendency analyzing unit  314  aggregates the power consumption of each home  400 . The tendency analyzing unit  314  calculates the average power consumption of each home  400  in each preset period. Data on the aggregated power consumption indicate the power consumption tendency. 
     The first determination unit  324  determines a home  400  with the current remaining battery level being lower than the power supply threshold (30[%]) to be an “R home”. According to  FIG.  7   , the home  400  (H04) is an R home because the remaining battery level is lower than the power supply threshold. In this case, the first determination unit  324  makes an electricity delivery vehicle  200  (S vehicle) start moving toward the home  400  (H04). Similarly, the first determination unit  324  makes an electricity delivery vehicle  200  (S vehicle) start moving toward a home  400  (H05). 
     The remaining battery level of a home  400  (H08) is 40[%], which is higher than the power supply threshold, and therefore the home  400  (H08) is not an R home. In view of the past power consumption tendency, however, the remaining battery level is estimated to significantly decrease from 40[%] to 10[%] one hour later. The home  400  (H08) may therefore be an R home one hour later. 
     The remaining battery level of a home  400  (H03) is 50[%], which is higher than the power supply threshold, and is estimated to be 32[%], which is higher than the power supply threshold, one hour later. In view of the past power consumption tendency, the remaining battery level of the home  400  (H03) is estimated to decrease from 32[%] to 10[%] two hours later. The home  400  (H03) may therefore be an R home two hours later. The power supply threshold may be a fixed value, or may be variable on the basis of the power consumption tendency. Hereinafter, the description will first be on the assumption that the power supply threshold is a fixed value to clarify a basic idea of the present invention. An embodiment in which the power supply threshold is varied will be described with reference to  FIG.  12    and subsequent drawings. 
       FIG.  8    is a data structure table of vehicle information  130 . 
     The vehicle information  130  is stored in the data storage unit  306  of the server  300 . As described above, each electricity delivery vehicle  200  is identified by a vehicle ID. The transmitting unit  216  of each electricity delivery vehicle  200  periodically transmit the second battery information to the server  300 . 
     The second determination unit  326  updates the vehicle information  130  each time the second battery information is received. In addition, each electricity delivery vehicle  200  transmits the vehicle state information indicating the state of the electricity delivery vehicle  200  as necessary during movement from the standby area to a home  400 , at start of power supply upon arrival at a home  400 , or the like. According to the vehicle information  130  in  FIG.  8   , an electricity delivery vehicle  200  (M01) is in a standby state in the standby area, and the remaining battery level of the secondary battery  208  (mobile battery) thereof is 75[%]. 
     There are four states of the electricity delivery vehicles  200 , which are “standby”, “moving”, “power supplying”, and “returning”. The “standby” state means that an electricity delivery vehicle  200  waits in the standby area, is connected with a power supply line  108  for charging of the secondary battery  208  (mobile battery) thereof. The “moving” state means that an electricity delivery vehicle  200  having left the standby area is moving toward a home  400 . The “power supplying” state means that an electricity delivery vehicle  200  having arrived at a home  400  is charging the secondary battery  404  (fixed battery) of the home  400 . The “returning” state means that an electricity delivery vehicle  200  having finished power supply is moving toward the standby area (return position). 
     As described above, the second determination unit  326  determines an electricity delivery vehicle  200  with the remaining battery level of the secondary battery  208  (mobile battery) being equal to or higher than the moving threshold (90[%]) and being in the “standby” state to be an “S vehicle”. According to the vehicle information  130  in  FIG.  8   , an electricity delivery vehicle  200  (M05) and an electricity delivery vehicle  200  (M06) are S vehicles. When an R home is present, the dispatch determination unit  312  instructs the electricity delivery vehicle  200  (M05) or the electricity delivery vehicle  200  (M06) to start moving. 
       FIG.  9    is a flowchart illustrating processes performed by the server  300  to determine whether or not an electricity delivery vehicle  200  is to start moving. 
     The processes illustrated in  FIG.  9    are performed each time the server  300  receives the first battery information from any of the homes  400 . First, each time the first battery information is received from a home  400 , the first determination unit  324  of the server  300  updates the record of the remaining battery level in the home power consumption information  170  (S 10 ). The first battery information includes the current remaining battery level of the secondary battery  404  (fixed battery) of the home  400 . The tendency analyzing unit  314  periodically receives the first battery information to recalculate the amount by which the remaining battery level decreases in each preset period, that is, the power consumption per preset period. Similarly, the tendency analyzing unit  314  also updates data on the power consumption tendency of the whole town. 
     The first determination unit  324  determines whether or not a home  400  with the remaining battery level being lower than the power supply threshold, that is, an R home is present (S 12 ). If no home  400  being checked is an R home (N in S 12 ), the process is terminated. If a home  400  is an R home (Y in S 12 ), the second determination unit  326  determines whether or not any electricity delivery vehicle  200  with the remaining battery level being equal to or higher than the moving threshold and in the “standby” state, that is, any S vehicle is present (S 14 ). The second battery information and the vehicle state information are also periodically transmitted from each electricity delivery vehicle  200 , and the second determination unit  326  updates the vehicle information  130  as appropriate. 
     If no S vehicle is present (N in S 14 ), the process is terminated. If an S vehicle is present (Y in S 14 ), the second determination unit  326  selects the S vehicle (S 16 ). If a plurality of S vehicles are present, the second determination unit  326  selects an S vehicle with the highest remaining battery level. The dispatch determination unit  312  transmits a start instruction including the home ID of a home  400  (R home) that needs charging to the selected S vehicle (S 18 ). The second determination unit  326  also updates the vehicle information  130  by changing the state of the S vehicle that starts moving from “standby” to “moving” (S 20 ). 
     For example, assume that the home  400  (H05) is identified as an R home that needs charging, and the electricity delivery vehicle  200  (M06) is selected to start moving. In this case, the transmitting unit  308  transmits a start instruction including a home ID=H05 to the electricity delivery vehicle  200  (M06). The electricity delivery vehicle  200  (M06) has addresses of the homes  400  registered therein. The electricity delivery vehicle  200  (M06) starts moving toward the home  400  (H05) on the basis of the map information. The second receiving unit  320  also receives the vehicle state information from the electricity delivery vehicle  200  (M06) when the electricity delivery vehicle  200  (M06) has reached the home  400  (H05) or when the electricity delivery vehicle  200  (M06) has finished power supply at the home  400  (H05). Each time the second battery information or the vehicle state information is received, the second determination unit  326  updates the vehicle information  130 . 
       FIG.  10    is a flowchart illustrating processes performed by each electricity delivery vehicle  200  in receipt of a start instruction. 
     The processes in  FIG.  10    are performed when an electricity delivery vehicle  200  in a standby state has received a start instruction from the server  300 . The start instruction includes the home ID of an R home set as a goal point. The path calculating unit  220  of the electricity delivery vehicle  200  refers to the address information, and sets the specified R home as the destination. Subsequently, the path calculating unit  220  refers to the map information, and calculates the travel path to the R home (S 30 ). A method for calculating the travel path is a method similar to a technology used in a typical car navigation system. 
     Subsequently, the electricity delivery vehicle  200  calculates the distance from the current position (standby area) to the destination (R home) on the basis of the map information (S 32 ). The battery managing unit  224  sets a “return threshold (second threshold)” depending on the calculated distance (S 34 ). As the distance is longer, the return threshold is set to a higher value. When the remaining battery level of the secondary battery  208  (mobile battery) has become lower than the return threshold during charging at a home  400 , the electricity delivery vehicle  200  starts returning to the standby area even if the secondary battery  404  (fixed battery) is not sufficiently charged, details of which will be described later. As the destination is farther, that is, as the moving distance is longer, more of electrical energy stored in the secondary battery  208  (mobile battery) is consumed as energy for the movement of the electricity delivery vehicle  200 . When the moving distance is long, the return threshold is set to be high, so that the electricity delivery vehicle  200  can keep sufficient electrical energy necessary for returning from the home  400  to the standby area. 
     After setting the return threshold, the electricity delivery vehicle  200  starts automatic movement toward the home  400  (R home) (S 36 ). When the electricity delivery vehicle  200  has reached the home  400 , the charge and discharge connection port  214  of the electricity delivery vehicle  200  is connected with the charge and discharge connection port  414  of the home  400 . The connection mechanism of the charge and discharge connection ports  214  and  414  may be similar to those of known technologies such as plug-in connection. After the connection, the battery managing unit  224  of the electricity delivery vehicle  200  applies electric current from the secondary battery  208  (mobile battery) to the secondary battery  404  (fixed battery) to charge the secondary battery  404  (fixed battery). When the secondary battery  404  (fixed battery) is fully charged, the battery managing unit  412  of the home  400  notifies the electricity delivery vehicle  200  of completion of charging. In addition, as described above, the battery managing unit  224  of the electricity delivery vehicle  200  measures the remaining battery level of the secondary battery  208  (mobile battery). The battery managing unit  224  terminates power supply to the secondary battery  404  (fixed battery) when the secondary battery  404  (fixed battery) is fully charged or when the remaining battery level of the secondary battery  208  (mobile battery) has become lower than the return threshold. 
       FIG.  11    is a flowchart illustrating processes performed by each electricity delivery vehicle  200  after finishing power supply. 
     The processes in  FIG.  11    are performed after completion of power supply. The battery managing unit  224  of the electricity delivery vehicle  200  disconnects the connection between the charge and discharge connection port  414  of the home  400  and the charge and discharge connection port  214  of the electricity delivery vehicle  200  (S 40 ). Subsequently, the path calculating unit  220  searches for a travel path from the current position to the standby area (return position) (S 42 ). The movement control unit  222  causes the electricity delivery vehicle  200  to move automatically along the calculated travel path (S 44 ). At this point, the transmitting unit  216  of the electricity delivery vehicle  200  notifies the server  300  of start of returning as the vehicle state information (S 46 ). Upon being notified of the start of returning, the server  300  changes the state of this electricity delivery vehicle  200  from “power supplying” to “returning”. 
     Thereafter, the electricity delivery vehicle  200  returns to the standby area. After the electricity delivery vehicle  200  has reached the standby area, the battery managing unit  224  connects the charge and discharge connection port  214  with a power supply line  108 . The second determination unit  326  of the server  300  changes the state of the electricity delivery vehicle  200  from “returning” to “standby”. The secondary battery  208  (mobile battery) of the electricity delivery vehicle  200  is charged through the power supply line  108 . 
     [Power Supply Threshold Adjusting Method 1 (Home Adjustment)] 
     The power supply threshold may be a fixed value or a variable value. The first determination unit  324  may adjust power supply threshold depending on homes  400  and depending on time slots on the basis of the power consumption tendencies of the individual homes  400 . Hereinafter, such a method of adjusting a power supply threshold will be referred to as “home adjustment”. 
       FIG.  12    is a data structure table of home adjustment information  140 . 
     The home adjustment information  140  is stored in the data storage unit  306  of the server  300 . In home adjustment, the first determination unit  324  adjusts the power supply threshold depending on the power consumption tendencies of the homes  400 . In other words, the first determination unit  324  adjusts the power supply threshold on the basis of the home power consumption information  170  indicating the power consumption tendencies of the homes  400 . Firstly, assume that the basic value of the power supply threshold is 30[%]. When an average decrease amount of the remaining battery level after one hour or, in other words, an estimated power consumption, which is calculated on the basis of past data, is equal to or higher than 20[%], the first determination unit  324  adds 20[%] as a first correction value to the basic value. Similarly, when an estimated power consumption after two hours is equal to or higher than 20[%], the first determination unit  324  further adds 10[%] as a second correction value. The home adjustment information  140  indicates a power supply threshold obtained by home adjustment for each home  400 . 
     For example, assume that the current time is 15:50. With reference to the home estimation information  120  in FIG.  7 , the power consumption of the home  400  (H01) after one hour is 10[%], and the power consumption thereof after two hours is 30[%]. The first determination unit  324  therefore adjusts the power supply threshold for the home  400  (H01) to 40[%] (=30+0+10). When the current remaining battery level of the home  400  (H01) is 90[%], which is higher than the adjusted power supply threshold (40%), the first determination unit  324  determines the home  400  (H01) as not being an R home. 
     The current remaining battery level of the home  400  (H03) is 50[%], the power consumption thereof after one hour is 18[%], and the power consumption thereof after two hours is 22[%]. The first determination unit  324  adjusts the power supply threshold for the home  400  (H03) to 60[%] (=30+20+10). Because the current remaining battery level 50[%] of the home  400  (H03) is lower than the power supply threshold (60[%]) resulting from home adjustment, the first determination unit  324  determines the home  400  (H03) as being an R home. Although the current remaining battery level of the home  400  (H03) is sufficient, power consumption is estimated to be high after one hour and after two hours, and the first determination unit  324  therefore makes the power supply threshold higher to cause an electricity delivery vehicle  200  to move toward the home  400  (H03) early. 
     Such a control method enables prevention of future power shortage at the homes  400  by sending electricity delivery vehicles  200  to homes  400  that are likely to increase power consumption in the near future even when the current remaining battery level is sufficient. 
     The tendency analyzing unit  314  calculates a power consumption in a preset period on the basis of a difference between the remaining battery level at the start point of the preset period and the remaining battery level at the end point thereof. When the secondary battery  404  (fixed battery) has received power supply from the secondary battery  208  (mobile battery) during the preset period, however, the data in this period is excluded from aggregation (N/A). 
     [Power Supply Threshold Adjusting Method 2 (Town Adjustment)] 
     The first determination unit  324  may adjust the power supply thresholds for all the homes  400  together depending on the power consumption tendencies of all of a plurality of homes  400  or, in other words, the whole town. Hereinafter, such a method of adjusting power supply thresholds will be referred to as “town adjustment”. 
       FIG.  13    is a data structure table of town adjustment information  150 . 
     The town adjustment information  150  is stored in the data storage unit  306  of the server  300 . In town adjustment, the tendency analyzing unit  314  aggregates the power consumption tendencies of the whole town depending on the days of the week and time slots on the basis of the first battery information obtained from the homes  400 . In town adjustment, the first determination unit  324  adjusts the power supply thresholds for all the homes  400  together depending on the power consumption tendencies of the whole town. 
     The town adjustment information  150  is information indicating a result of aggregation of the power consumption tendencies of the whole town. For example, according to the town adjustment information  150 , in a period of “1:00 to 2:00 a.m. on Sunday”, the remaining battery levels of the secondary batteries  404  (fixed batteries) in the whole town or, in other words, the remaining battery levels of the homes in the same time slot lower by an average of 3[%]. Hereinafter, such an average value of power consumptions per unit time in the whole town will be referred to as “town power consumption”. Each time the first battery information is acquired, the tendency analyzing unit  314  recalculates the town power consumption, and updates the town adjustment information  150 . The tendency analyzing unit  314 , however, excludes the homes  400  that have received power supply during measurement from the calculation. 
     More specifically, when the average power consumptions of the home  400  (H01), the home  400  (H02), and the home  400  (H03) in the same time slot are 5[%], 6[%], and 7[%], respectively, the average power consumption of these three homes  400  is 6[%]. In this manner, the tendency analyzing unit  314  calculates the town power consumption by averaging the power consumptions of the homes  400  in the same time slot. 
     In town adjustment, first assume that the basic value of the power supply threshold is 30[%]. When the town power consumption after one hour is equal to or higher than 20[%] (third threshold), the first determination unit  324  adds 10[%] as a first correction value to the basic value. Similarly, when the town power consumption after two hours is equal to or higher than 20[%], the first determination unit  324  further adds 5[%] as a second correction value. 
     For example, assume that the current time and day is 23:45 on Friday. According to the town adjustment information  150 , the town power consumption in a time slot including “0:45 on Saturday”, which is one hour later, is estimated to be 30[%]. The town power consumption in a time slot including “1:45 on Saturday”, which is two hours later, is estimated to be 15[%]. In this case, the first determination unit  324  adjusts the power supply thresholds for all the homes  400  to 40[%] (=30+10). If the current remaining battery level of the home  400  (H09) is 50[%], the home  400  (H09) is not an R home. If the current remaining battery level of a home  400  (H10) is 35[%], the home  400  (H10) is an R home. 
     Control based on the power consumption tendency in the whole town has been described above. Alternatively, for example, the whole town may be divided into a plurality of blocks, and similar control may be performed in units of blocks. Alternatively, a plurality of homes may be grouped, and similar control may be performed on the group. 
     According to such a control method, the power consumption tendencies in the whole town are referred to, and electricity delivery vehicles  200  can be sent early to homes  400  at which power shortage may occur in the near future. In other words, in a time slot in which the power consumption in the whole town is high, the power supply thresholds are high, and electricity delivery vehicles  200  are therefore sent relatively frequently. 
     Home adjustment and town adjustment may be combined. For example, the power supply threshold for the home  400  (H10) is adjusted by a first correction value and a second correction value based on home adjustment. Subsequently, the first determination unit  324  may further adjust the power supply threshold resulting from home adjustment by a first correction value and a second correction value based on town adjustment. Alternatively, the first determination unit  324  may set, as a new power supply threshold, an average of a power supply threshold calculated by home adjustment and a power supply threshold calculated by town adjustment. 
     [Weather Adjustment of Power Supply Threshold] 
     The first determination unit  324  may adjust a power supply threshold depending on the weather. Hereinafter, such a method of adjusting a power supply threshold will be referred to as “weather adjustment”. 
       FIG.  14    is a data structure table of weather adjustment information  160 . 
     The weather adjustment information  160  is stored in the data storage unit  306  of the server  300 . In weather adjustment, the weather acquiring unit  322  obtains weather information from an external website of weather forecast. Weather information in the present embodiment is a probability of frozen precipitation announced by the meteorological bureau. In the weather adjustment method, the power supply thresholds are adjusted when a probability of frozen precipitation in the near future satisfies a predetermined condition (weather condition). 
     The weather adjustment information  160  defines in advance an adjustment value for a power supply threshold based on a future probability of frozen precipitation. For example, when the probability of frozen precipitation after one hour is lower than 30[%], the adjustment value is “0”. When the probability of frozen precipitation after one hour is equal to or higher than 30[%] and lower than 40[%], the adjustment value is “10”. Assume that the basic value of the power supply threshold is 30[%]. When the probability of frozen precipitation after one hour is 35[%] according to the weather information, the first determination unit  324  sets the power supply threshold to 40[%] (=30+10). 
     For example, assume that the probability of frozen precipitation after one hour is 45[%] and that the probability of frozen precipitation after two hours is 35[%]. According to the weather adjustment information  160  in  FIG.  14   , the adjustment values are “15” and “5”, respectively. In this case, the first determination unit  324  adjusts the power supply threshold to 50% (=30+15+5). 
     When it may snow, the power supply thresholds increase, and electricity delivery vehicles  200  can be sent early. As a result, a risk that electricity delivery vehicles  200  cannot be sent owing to future snowfall can be easily avoided in advance. 
     Home adjustment and weather adjustment may be combined. Similarly, town adjustment and weather adjustment may be combined. Furthermore, home adjustment, town adjustment, and weather adjustment may be combined to adjust the power supply thresholds. Any combination may be applied. 
     [Overview] 
     The mobile charging system  100  has been described above with reference to an embodiment. 
     According to the embodiment, the system of carrying electricity by secondary batteries  208  (mobile batteries) built in the electricity delivery vehicles  200  eliminates the need for power transmission lines. Because the number of electricity delivery vehicles  200  may be adjusted depending on the size and the power demand of a town, the costs necessary for building and improving social infrastructure can be flexibly adjusted. The electricity delivery vehicles  200  are basically assumed to cruise in a “town”, which is a relatively narrow region. Because movement over long distances is not expected, electrical energy consumption of secondary batteries  208  (mobile batteries) due to the movement of the electricity delivery vehicles  200  can be suppressed. 
     Power transmission lines entail transmission loss. In particular, the transmission loss at long-distance power transmission is likely to be high. Overhead power transmission lines impair the landscape in some cases, and there are many cases where power transmission lines are to be eliminated as much as possible in terms of nature conservation. Townscaping measures are important in protection of tourism resources, and the landscape is said to significantly affect the value of real estate. The potential value of using no power transmission lines is therefore very high. When a number of electricity delivery vehicles  200  cruise around a town sluggishly, the residents will gradually be familiar with the electricity delivery vehicles  200  moving around. The electricity delivery vehicles  200  are expected to fit into everyday scenery like buses and trams. Needless to say, a system in which power transmission lines and electricity delivery vehicles  200  coexist may be used instead of a system of delivering electricity only by electricity delivery vehicles  200 . For example, an introducing method increasing the number of electricity delivery vehicles  200  while gradually reducing the number of power transmission lines may be considered. 
     Each electricity delivery vehicle  200  uses the built-in secondary battery  208  (mobile battery) not only for the source of power supply to secondary batteries  404  (fixed batteries) but also for the power source of the electricity delivery vehicle  200  itself. By adjusting the return threshold depending on the moving distance, the electricity delivery vehicle  200  can be controlled so that the electricity delivery vehicle  200  can return to the standby area without fail after terminating power supply to a home  400 . 
     The tendency analyzing unit  314  analyzes the power consumption tendencies of the homes  400 . The first determination unit  324  sets a high power supply threshold when power consumption in the near future is estimated to increase. Such a control method (home adjustment) enables pre-emptive measures to meet future power demands by sending electricity delivery vehicles  200  to homes  400  early even when the current remaining battery levels of the homes  400  are sufficient. 
     Similarly, the server  300  may analyze the power consumption tendencies of a plurality of homes  400 , that is, the whole town, and set a high power supply threshold when power demand in the near future is estimated to be high (town adjustment). In addition, a high power supply threshold may also be set when the weather is expected to worsen, such as a case of a predicted snowfall, so that electricity delivery vehicles  200  can be sent early to avoid situations in which electrical energy cannot be delivered when needed. 
     The present invention is not limited to the embodiment described above and modifications thereof, and any component thereof can be modified and embodied without departing from the scope of the invention. Components described in the embodiment and modifications can be combined as appropriate to form various other embodiments. Some components may be omitted from the components presented in the embodiment and modifications. 
     [Modifications] 
     In the description of the present embodiment, the secondary batteries  404  (fixed batteries) of the homes  400  are charged. The power supply from the electricity delivery vehicles  200  is not limited to homes  400 , but may also be to electric vehicles, electric propulsion ships, electric aircrafts, and the like. 
     In the description of the present embodiment, a model in which electricity is delivered by electricity delivery vehicles  200  to individual homes from a power station  102  present in a town is assumed. A plurality of power stations  102  may be dispersedly located, and electricity delivery vehicles  200  may be dispersedly arranged near the power station  102 . For example, in a case where a home  400  (H01) has a solar panel installed on its roof, the home  400  (H01) may be a power supplier. An electricity delivery vehicle  200  (M01) is leased to the home  400  (H01) in advance. The secondary battery  404  (fixed battery) of the home  400  (H01) and the secondary battery  208  (mobile battery) of the electricity delivery vehicle  200  (M01) are charged by the solar panel. When both of the remaining battery levels of the secondary battery  404  (fixed battery) and the secondary battery  208  (mobile battery) have become equal to or larger than respective thresholds, the electricity delivery vehicle  200  (M01) becomes an S vehicle. The server  300  may send this electricity delivery vehicle  200  (M01) to another home  400 , as necessary. 
     Electricity is not limited to be delivered by autonomous vehicles, and may be delivered by drones including built-in secondary batteries  208  (mobile batteries) or robots including built-in secondary batteries  208  (mobile batteries). 
     The server  300  may remotely control electricity delivery vehicles  200 . For example, the server  300  may refer to the map information, indicates a travel path to an electricity delivery vehicle  200 , and remotely control the traveling speed and the moving direction of the electricity delivery vehicle  200 . Beacons may be placed in the ground, and the server  300  may transmit a vehicle ID and a direction indicating signal to each beacon. Upon detecting a direction indicating signal for itself, an electricity delivery vehicle  200  controls the moving direction in accordance with the direction indicating signal. Such a control method enables the server  300  to control each electricity delivery vehicle  200  by using beacons. 
     After completing charging, the electricity delivery vehicles  200  may cruise around the town instead of waiting in the standby area. Each electricity delivery vehicle  200  periodically transmits its current position with its vehicle ID as vehicle state information to the server  300 . Upon detecting an R home, the server  300  may locate an electricity delivery vehicle  200  cruising near the R home, and send the electricity delivery vehicle  200  to the R home. After completion of charging at the R home, the electricity delivery vehicle  200  returns to the standby area and charges the secondary battery  208  (mobile battery) again through the power supply lines  108 . 
     In the present embodiment, a method of recording the power consumption tendencies of the whole town in the town adjustment information  150 , and adjusting the power supply thresholds on the basis of the town adjustment information  150  has been described. In a modification, part of the town, such as several households may constitute a unit section, and the server  300  may analyze the power consumption tendencies of each unit section. When an increase in power consumption in a certain unit section is estimated, the server  300  may adjust the power supply threshold only for the homes  400  belonging to the unit section. 
     For example, assume that a town is divided into unit sections (districts) D 1  to D 5 . Town adjustment information  150  is prepared for each of the unit sections D 1  to D 5 . Upon receiving first battery information from a home  400 , the tendency analyzing unit  314  recalculates an average power consumption of the whole unit section to which the home  400  belongs, and updates the town adjustment information  150 . For example, when the power consumption of the unit section D 1  in a preset period W is estimated to be high, the first determination unit  324  adjusts the power supply threshold for all the homes belonging to the unit section. Such a control method enables determination on whether or not to send an electricity delivery vehicle  200  by estimating power demand in a smaller unit than the whole town. For example, in some unit sections, power consumption may be high in a specific time slot on a specific day of the week because of a held event. Estimation of power demand in a smaller unit than a town facilitates more appropriate control of power supply thresholds. 
     In the present embodiment, calculation of an estimation of a future power consumption is based on an average value of power consumptions. For example, the tendency analyzing unit  314  collects the power consumptions (actual measured values) of a home  400  in a time slot of 12:00 to 13:00, and calculates an average of the collected power consumptions (actual measured values) as an estimated value of power consumption in this time slot. A median may be used instead of an average. In addition, the consumption estimating unit  316  may estimate a future power consumption by multivariate analysis in which a time slot, a day of the week, the number of people in a household, and the like are used as input parameters, or an estimation model such as a neural network. 
     The first determination unit  324  may perform home adjustment and town adjustment in parallel independently of each other. For example, a power supply threshold of the home  400  (H01) is set to T 1 . The first determination unit  324  changes the power supply threshold T 1  of the home  400  (H01) to T 2 A on the basis of home adjustment. In addition, the first determination unit  324  changes the power supply threshold T 1  of the home  400  (H01) to T 2 B on the basis of town adjustment. As a result, the home  400  (H01) has two power supply thresholds T 2 A and T 2 B. The first determination unit  324  may send an electricity delivery vehicle  200  to the home  400  (H01) when the remaining battery level of the home  400  (H01) has become lower than either one of the power supply thresholds T 2 A and T 2 B. Alternatively, the first determination unit  324  may send an electricity delivery vehicle  200  to the home  400  (H01) when the remaining battery level of the home  400  (H01) has become lower than both of the power supply thresholds T 2 A and T 2 B. Still alternatively, the first determination unit  324  may send an electricity delivery vehicle  200  to the home  400  (H01) when the remaining battery level of the home  400  (H01) has become lower than the average of the power supply thresholds T 2 A and T 2 B. 
     When a power consumption in a future time slot (preset period), which is an average based on past records, in a town (or a unit section) is high, the first determination unit  324  may increase the power supply threshold. According to such a control method, electricity delivery vehicles  200  can be proactively sent when power consumption is estimated to increase in the whole town. This facilitates prevention of power shortage at the homes  400 . 
     Conversely, when a power consumption in a future time slot (preset period), which is an average based on past records, in a town (or a unit section) is high, the first determination unit  324  may decrease the power supply threshold. Alternatively, when an increase in power consumption is estimated and the number of S vehicles is a predetermined number or smaller, the first determination unit  324  may decrease the power supply threshold. According to such a control method, priority can be given to charging of the electricity delivery vehicles  200  in anticipation of a high power demand in the future. 
     A past value of a town power consumption in a certain time slot in a town (or a unit section) is represented by P 1 . In addition, a town power consumption in the same time slot is represented by P 2 . When P 1 &lt;P 2 , that is, in other words, when the latest town power consumption is higher as compared with the past power consumption tendencies, the first determination unit  324  may increase the power supply threshold for each home  400 . For example, when a town power consumption P 1  (average) of the past five weeks in a time slot of “12:00 to 13:00 on Friday” is 10[%] and a power consumption P 2  (latest value) of the whole town in the most recent time slot of “12:00 to 13:00 on Friday” is 40[%], the first determination unit  324  increases the power supply threshold for each home  400 . When the town power consumption is high as compared with the past power consumption tendencies, that is, in other words, when the power consumption is higher than estimated, prevention of power shortage at the homes  400  is facilitated by sending electricity delivery vehicles  200  earlier. 
     A past value of a town power consumption in a certain time slot in a town (or a unit section) is represented by P 1 . In addition, the latest town power consumption in the same time slot is represented by P 2 . When P 1 &gt;P 2 , that is, in other words, when the latest town power consumption is lower as compared with the past power consumption tendencies, the first determination unit  324  may decrease the power supply threshold for each home  400 . Alternatively, when the power consumption is lower than that in the past and when the number of S vehicles is a predetermined number or smaller, the first determination unit  324  may decrease the power supply thresholds. According to such a control method, priority can rather be given to charging of the electricity delivery vehicles  200  to address the risk of power shortage in the future. 
     When the amount of power produced by the power station  102  is equal to or larger than a threshold or when the number of S vehicles is equal to or larger than a predetermined number, the first determination unit  324  may increase the power supply thresholds. When there is enough electricity, control may be performed to avoid surplus power by increasing the power supply thresholds and proactively sending electricity delivery vehicles  200 . Conversely, when the amount of power produced by the power station  102  is lower than the threshold or when the number of S vehicles is smaller than the predetermined number, the server  300  may decrease the power supply thresholds. 
     In the description of the present embodiment, the power supply thresholds are adjusted by weather adjustment based on the probability of frozen precipitation. Weather adjustment is not limited to be based on the probability of frozen precipitation, and the server  300  may also adjust the power supply thresholds by weather adjustment based on the probability of rain and a forecast wind force. 
     When worse weather such as snow, rain, strong wind, or the like is anticipated, the first determination unit  324  may increase the power supply thresholds so as to proactively send electricity delivery vehicles  200  before the weather worsens. Conversely, when worse weather is anticipated, the first determination unit  324  may perform control to decrease the power supply thresholds so as to reduce the number of electricity delivery vehicles  200  to be sent for the anticipated bad weather. 
     When better weather such as fine weather is anticipated, the first determination unit  324  may increase the power supply thresholds. In this case, because the amount of power produced by photovoltaic power generation is estimated to increase, the dispatch determination unit  312  may proactively send electricity delivery vehicles  200 . Conversely, when better weather is anticipated, the power supply thresholds may be decreased. In this case, because the amount of produced power is estimated to increase, as many electricity delivery vehicles  200  as possible may be kept on standby to charge many electricity delivery vehicles  200 . 
     In the description of the present embodiment, the balance between dispatch and standby of electricity delivery vehicles  200  is controlled by increasing and decreasing the power supply thresholds. In a modification, instead of adjustment of the power supply thresholds, dispatch of electricity delivery vehicles  200  may be performed or stopped when a predetermined condition is met. For example, when a future power consumption at a home  400  is estimated to be equal to or higher than a predetermined threshold, the dispatch determination unit  312  may send electricity delivery vehicles  200  regardless of the remaining battery levels of the homes  400 . Alternatively, when snow is anticipated, electricity delivery vehicles  200  may be sent regardless of the remaining battery levels of the homes  400 . In a case of bad weather such as snow, the dispatch determination unit  312  may stop dispatch of the electricity delivery vehicles  200 . 
     When the first determination unit  324  has increased the power supply thresholds, more homes  400  are likely to be determined as R homes. In other words, as the power supply thresholds are larger, power supply by the electricity delivery vehicles  200  is more proactively performed. The first determination unit  324  may adjust the moving thresholds instead of the power supply thresholds. When the moving thresholds are decreased, more electricity delivery vehicles  200  are likely to be determined as S vehicles. Thus, as the moving thresholds are decreased, power supply by the electricity delivery vehicles  200  is more proactively performed. The first determination unit  324  may adjust one or both of the power supply thresholds and the moving thresholds to adjust the frequency of starting the electricity delivery vehicles  200 . 
     When an electricity delivery vehicle  200  has been lost, has broken down, or cannot reach a home  400  by a scheduled time, the transmitting unit  216  of the electricity delivery vehicle  200  may transmit an alarm signal. The receiving unit  310  of the server  300  in receipt of the alarm signal may send another electricity delivery vehicle  200  instead toward the home  400  (R home). In addition, upon occurrence of such trouble, an anomaly notifying unit (not illustrated) of the electricity delivery vehicle  200  may turn on a lamp mounted thereon. A person near the electricity delivery vehicle  200  may notify the operator of the server  300  of the presence of the electricity delivery vehicle  200  in trouble. Creating situations in which residents help electricity delivery vehicles  200  may be effective in facilitating coexistence of residents and electricity delivery vehicles  200 . 
     The homes  400  may receive power supply from fuel cells. In this case, the server  300  may cause autonomous vehicles to carry methanol. 
     Carbon dioxide emissions per unit power generation amount of respective types of power supply lines  108  may be set as “carbon metrics”. A higher electricity rate (fee) may be set for a power station with a higher carbon metrics. For example, assume that the carbon metrics of the power station  102 A, the power station  102 B, and the power station  102 C are 2:5:10. When the power generation ratio of the power station  102 A, the power station  102 B, and the power station  102 C in a certain time slot T is 5:3:2, the carbon metrics in the time slot T is 4.5 (=2×0.5+5×0.3+10×0.2). The electricity rate in the time slot T is set to a price proportional to the carbon metrics  4 . 5 . As a result, homes  400  that have received power supply from electricity delivery vehicles  200  pay the electricity rate proportional to the carbon metrics 4.5 when the electrical energy supplied from the electricity delivery vehicles  200  is charged in the time slot T. 
     Such a control method enables reduction in the electricity rate in time slots in which power generation using natural energy is active. This can encourage consumers to change their behaviors to change the usage of electricity depending on the natural environment (power generation environment). This can lead to establishment of lifestyles adapted to the nature. 
     In addition, the electricity rates for homes  400  near the power station  102  are lower because the moving distances of the electricity delivery vehicles  200  are shorter. There is therefore an advantage in living near power stations  102 , which is effective in facilitating disperse arrangement of power stations  102  in a town. Furthermore, there may be a possibility of increasing the values of real estate of lands near power stations  102 . 
     In the description of the present embodiment, the server  300  is assumed to be a computer installed in a stationary manner and configured to transmit commands to a plurality of electricity delivery vehicles  200 . In a modification, one of the electricity delivery vehicles  200  may have the functions of the server  300 . Hereinafter, such an electricity delivery vehicle  200  will be referred to as an “L vehicle (leader vehicle)”. The L vehicle includes a built-in secondary battery  208  (mobile battery) and has the functions of the communication unit  202 , the data processing unit  204 , the drive mechanism  206 , the camera  210 , the data storage unit  212 , the charge and discharge connection port  214 , and the like in a manner similar to the electricity delivery vehicle  200  illustrated in  FIG.  3   . The L vehicle also has the functions as the server  300  illustrated in  FIG.  5    including the communication unit  302 , the data processing unit  304 , and the data storage unit  306 . 
     The L vehicle as the server  300  collects the first battery information from the homes  400 . In addition, the L vehicle collects the second battery information from the other electricity delivery vehicles  200 . When the remaining battery level of a home  400  has become lower than the power supply threshold, the L vehicle selects an electricity delivery vehicle  200  (S vehicle) to be sent to the home  400 . In this case, the L vehicle itself is also included in the candidates for the electricity delivery vehicle  200  to be sent. When an electricity delivery vehicle  200  other than the L vehicle is selected, the L vehicle transmits a start instruction to the selected electricity delivery vehicle  200 . When the L vehicle itself is selected, the L vehicle starts toward the home  400 . The L vehicle is always capable of receiving the first battery information and the second battery information through radio communication in any state regardless of whether the L vehicle is moving, charging or the like. When a new R home is detected during charging at a home  400 , for example, the L vehicle may select an S vehicle and instruct the selected S vehicle to start moving through radio communication.