Moving body and power transmission method

Abstract

The present invention is a moving body in a power transmission system which charges a battery mounted on the moving body with power generated by a power generation facility and feeds the power to a power reception facility from the battery transferred to the moving body. This moving body is provided with a battery control device which causes the battery to be charged with the supply of power due to a voltage value that does not become the maximum voltage value of DC power while the DC power reaches the power reception facility from the power generation facility.

Description

Mobile units, power transmission methods

[0001] The present invention relates to a mobile object in a power transmission system and a power transmission method for the power transmission system.

[0002] Conventionally, offshore wind power generation systems have been known to have a configuration in which a power transmission cable is laid on the seabed or underwater, and electricity generated by offshore power generation equipment is transmitted to an onshore power grid via the undersea power transmission cable.

[0003] In recent years, the development of offshore wind power generation facilities has been increasing not only in areas close to shore, but also in areas over 50 km from shore. The longer the distance from shore, the greater the need to reduce power loss due to long-distance transmission. For this reason, it has become common to use high-voltage DC cables as undersea power transmission cables.

[0004] Patent Document 1 listed below discloses a system for transmitting power generated by a wind turbine generator through a high-voltage DC cable.

[0005] Patent Publication No. 2018-107980

[0006] When transmitting DC power using high-voltage DC cables, it is necessary to install high-voltage output transformers at power collection stations and offshore substations to boost the voltage in order to reduce transmission losses. This requires that the electrical equipment within the transmission system meet high-voltage specifications. In addition to expensive DC submarine transmission cables, AC / DC converters that can handle high voltages and DC circuit breakers that ensure high reliability are required at the transmitting and receiving ends. These measures increase the complexity of the transmission system configuration and the associated cost increases.

[0007] Therefore, the present disclosure proposes a technology that can facilitate simplification of the configuration and cost reduction in a power transmission system.

[0008] A mobile body according to the present invention is a mobile body in a power transmission system in which a storage battery mounted on the mobile body is charged with power generated by a power generation facility and the storage battery transported by the mobile body supplies power to a power receiving facility. The mobile body is equipped with a battery control device that charges the storage battery with power supplied at a voltage that does not become the maximum voltage value of DC power from the power generation facility to the power receiving facility. In other words, the charging voltage for the storage battery mounted on the mobile body is a predetermined voltage that is lower than the maximum voltage value of power from the power generation facility to the power receiving facility.

[0009] According to the present invention, by replacing power transmission via DC submarine cables with power transmission via mobile bodies equipped with storage batteries, it is possible to eliminate the need for voltage boosting to suppress power transmission losses. At the same time, high-voltage compatible equipment is also no longer required. These factors enable a significant simplification of the power transmission system configuration and cost reduction.

[0010] It is an explanatory diagram of the power transmission system of the embodiment of the present invention. It is an explanatory diagram of the charge and discharge configuration for the storage battery of the electric carrier of the embodiment. It is an explanatory diagram of the power transmission system using the high voltage DC cable as a comparative example. It is an explanatory diagram of the transition of the voltage level of the power transmission system of the embodiment.

[0011] Hereinafter, the embodiments will be described in the following order: <1. Configuration of a power transmission system according to the embodiments> <2. Power transmission system using a high-voltage DC cable as a comparative example> <3. Voltage transition of a power transmission system according to the embodiments> <4. Effects and modifications of the embodiments>

[0012] 1 shows an overview of a power transmission system 1 according to an embodiment. The figure shows the main components of the power transmission system 1: a wind power generation facility 2, an array cable 3, an offshore converter station 4, an onshore substation 5, a cable 6, a power grid 7, connector cables 8 and 9, and an electricity carrier 10.

[0013] The wind power generation facility 2 is installed offshore. There are no particular restrictions on the sea area, but in the case of this power transmission system 1, the wind power generation facility 2 is also suitable for installation in sea areas where the distance from the shore is, for example, more than 50 km.

[0014] For example, one or more wind power generation facilities 2 are installed as floating structures, and an offshore converter station 4 is provided for one or more wind power generation facilities 2. The AC power generated by each wind power generation facility 2 is converted into DC power as described below. The power is then transmitted to the offshore converter station 4 via an array cable 3 serving as a DC cable.

[0015] The offshore converter station 4 functions as an offshore substation having equipment for supplying the electric power generated by the wind power generation facility 2 to an electric carrier 10, which is a mobile body.

[0016] The electricity carrier 10 is a ship equipped with a storage battery 14. The offshore converter station 4 has equipment for connecting a connector cable 8 to the electricity carrier 10. This allows the offshore converter station 4 to supply power for charging the storage battery 14 of the electricity carrier 10 based on the power generated by the wind power generation facility 2.

[0017] That is, when the electricity carrier 10 arrives near the offshore converter station 4, the offshore converter station 4 and the electricity carrier 10 are electrically connected by a connector cable 8, and the electricity collected from the wind power generation facility 2 at the offshore converter station 4 is supplied to the electricity carrier 10 via the charging connector cable 8. The electricity carrier 10 uses this electricity to charge the storage battery 14.

[0018] After charging the storage battery 14, the electricity carrier 10 sails toward the onshore substation 5, which is a power receiving facility. The onshore substation 5 has a facility for connecting a connector cable 9 to the electricity carrier 10. This allows the onshore substation 5 to receive the discharge current from the storage battery 14.

[0019] That is, when the electricity carrier 10 arrives near the onshore substation 5, the onshore substation 5 and the electricity carrier 10 are electrically connected by a connector cable 9, and DC power is transmitted from the storage battery 14 to the onshore substation 5 via the connector cable 9. The onshore substation 5 converts the transmitted DC power into AC power and transmits it to the power grid 7 via a cable 6.

[0020] As described above, in the power transmission system 1 of this embodiment, electrical energy is transported from the offshore wind power generation facility 2 to the onshore substation 5 by the electricity carrier 10 equipped with the storage battery 14. In other words, the electricity transmission system 1 transmits power from the offshore wind power generation facility 2 to the power grid 7 via an intervening stage of transporting the storage battery 14. Although it depends on the power source of the electricity carrier 10, even a motor-type electricity carrier 10 powered by electricity can travel approximately 300 to 500 km on the ocean without charging. For this reason, the distance from the offshore wind power generation facility 2 to the onshore substation 5 may be approximately 300 to 500 km.

[0021] FIG. 2 shows components related to the storage battery 14 in the electric carrier 10. Here, the electric carrier 10 is assumed to be a motor-type ship powered by electricity. However, the electric carrier 10 may also be an internal combustion engine-type ship powered by fossil fuel, or a hybrid ship that uses both a motor and an internal combustion engine. Furthermore, the electric carrier 10 may also be a ship powered by hydrogen. For example, when using hydrogen as a power source, the electric carrier 10 may be a fuel cell-type ship that drives a motor with electricity generated by a fuel cell, or a hydrogen engine-type ship that obtains power by burning hydrogen in an internal combustion engine.

[0022] The electric carrier 10 has components directly related to the storage battery 14, such as a charge / discharge port 11, a DC / DC converter 12, and a battery control device 13. The storage battery 14 is composed of a plurality of battery cells 14a.

[0023] The charging / discharging port 11 is an interface for charging and discharging each battery cell 14a, and the connector cables 8 and 9 are detachable for charging and discharging. The DC / DC converter 12 receives the DC voltage supplied from the charging / discharging port 11 and performs voltage conversion.

[0024] The battery control device 13 is connected to each battery cell 14a and includes a circuit for charging and discharging each battery cell 14a, as well as a control circuit for controlling the charge amount, discharge amount, charge rate, and discharge rate. Specifically, the battery control device 13 includes a charge / discharge circuit for each battery cell 14a, a microprocessor, a memory for storing a control program, a communication circuit for communicating with external devices, and a sensor for detecting the charge state of the battery cell 14a.

[0025] When the electricity carrier 10 is connected to the connector cable 8 of the offshore converter station 4, the battery control device 13 charges the battery cells 14a based on the DC voltage converted by the DC / DC converter 12. When the electricity carrier 10 is connected to the connector cable 9 of the onshore substation 5, the battery control device 13 controls the discharge of the battery cells 14a. The discharged DC voltage is converted by the DC / DC converter 12 and sent to the onshore substation 5 through the connector cable 9.

[0026] The above-described charging / discharging port 11, DC / DC converter 12, battery control device 13, and storage battery 14 may be provided in a container that is detachable from the hull. This allows, for example, the container to be removed from the hull and transported to the offshore converter station 4 to charge the storage battery 14. Also, for example, the container can be removed from the hull and transported to the onshore substation 5 to discharge the storage battery 14 (transmit power to the onshore substation 5).

[0027] The electric carrier 10 has a configuration similar to that of a typical motor-driven ship powered by electricity, for example. That is, the electric carrier 10 includes a drive battery 17, an inverter 15, a motor 16, etc. The drive battery 17 stores electricity consumed as a power source for the electric carrier 10 and its internal equipment.

[0028] The inverter 15 controls or converts the electricity output from the drive battery 17 and supplies it to the motor 16. The motor 16 converts the electricity received from the inverter 15 into power. For example, the motor 16 obtains propulsion power for the electric carrier 10 by rotating a screw propeller through a shaft (not shown).

[0029] As described above, the electric carrier 10 has a drive battery 17 in addition to the storage battery 14 that stores electricity for transportation, and therefore can navigate without consuming the electricity in the storage battery 14 (battery cell 14a). However, in the illustrated example, the drive battery 17 is electrically connected to the battery cell 14a via the battery control device 13. Therefore, in an emergency, the electricity in the battery cell 14a can be supplied to the drive battery 17. In other words, the electric carrier 10 can also navigate using the electricity in the battery cell 14a as a power source.

[0030] <2. Comparative Example of Power Transmission System Using High-Voltage DC Cable> As described above, the power transmission system 1 of the present embodiment transmits power via the electricity carrier ship 10. Before describing the voltage transition in the power transmission system 1, a power transmission system 201 using a high-voltage DC cable will be described for comparison.

[0031] FIG. 3 shows a configuration relating to voltage conversion in a power transmission system 201 using a high-voltage DC cable, and a transition of the voltage level.

[0032] In this power transmission system 201, power generated by offshore wind power generation facilities 202 is collected at an offshore AC power collection station 204, and then further boosted and converted to DC at an offshore AC / DC converter station 206. The power is then transmitted via a high-voltage DC submarine cable 207. The transmitted power is sent from a landing point 208 to an onshore substation 209, and then transmitted to the power grid 7.

[0033] In this power transmission system 201, in the wind power generation facility 202, AC power of about 300 V is extracted by a generator 221. This is then converted to DC by an AC / DC converter 222. After being further converted to AC by a DC / AC converter 223, the voltage is boosted to about 3 kV by a transformer 224 and sent to the array cable 203, which is an AC cable.

[0034] In this wind power generation facility 202, the AC / DC converter 222 and DC / AC converter 223 convert the power to direct current and then convert it back to alternating current in order to allow variable speed operation (output adjustment) of the wind turbine. In the case of the power transmission system 201, the generator 221 to the power grid 7 is always connected. For this reason, output adjustment is required in accordance with the power demand and other conditions on the power grid 7 side, and this adjustment is performed by controlling the DC stage. In addition, the transformer 224 is provided to obtain boosted AC for transmission through the array cable 3. Furthermore, the boost by the transformer 224, in conjunction with the subsequent transformers 241 and 261, also serves the purpose of gradually boosting the voltage up to the high-voltage DC submarine cable 207.

[0035] The AC power sent to the offshore AC power collection station 204 via the array cable 203 is further boosted to about 200 kV by a transformer 241 and transmitted to the offshore AC / DC converter station 206 via a cable 205. In the offshore AC / DC converter station 206, the voltage is boosted to 500 kV or more by a transformer 261, and then converted to DC by an AC / DC converter 262, and transmitted via a high-voltage DC submarine cable 207.

[0036] In the onshore substation 209, the DC power transmitted through the high-voltage DC submarine cable 207 is converted into AC power by a DC / AC converter 291, and the voltage is stepped down to, for example, 66 kV by a transformer 292. This 66 kV AC power is sent to the power grid 7.

[0037] In this power transmission system 201, the voltage level changes during the power transmission process as shown in the lower part of the figure. In particular, the transmission stage via the high-voltage DC submarine cable 207 requires an extremely high voltage of 500 kV or more. The reason for using a high voltage is to reduce power loss, especially during long-distance transmission via cable. However, this increase in voltage requires a multi-stage transformer configuration, high-voltage devices, components, cable structures, etc.

[0038] As mentioned above, the wind power generation facility 202 has a complex configuration because it first converts the power to direct current using the AC / DC converter 222 and the DC / AC converter 223 before sending it to the array cable 203, and then converts it back to alternating current to adjust the output.

[0039] <3. Voltage Transition of Power Transmission System of Embodiment> Based on the above, the voltage transition of the power transmission system 1 of this embodiment will be described. Fig. 4 shows the configuration related to voltage conversion of the power transmission system 1 using the electric carrier 10, and the transition of voltage levels. Note that in the transition of voltage levels at the bottom of Fig. 4, the solid line indicates the voltage transition of the power transmission system 1, and for comparison, the dashed line indicates the voltage transition of the power transmission system 201 in Fig. 3. Note that the voltage values ​​given in the following description are examples for illustrative purposes.

[0040] In the power transmission system 1 of this embodiment, in the wind power generation facility 2, AC power of a rated voltage or lower (for example, about 300 V to 6600 V) is obtained by the generator 21, and this is extracted as DC by the AC / DC converter 22. This is then converted to DC of about 10 kV by the DC / DC converter 23 and sent to the array cable 3 configured as a DC cable. This DC / DC converter 23 is provided for the purpose of increasing the voltage level to a certain extent in order to reduce power transmission loss during power transmission through the array cable 3, which is a submarine cable.

[0041] In this way, in the wind power generation facility 2, after conversion to DC by the AC / DC converter 22, the power is sent out of the facility while remaining in the DC state, simply by boosting the voltage to match transmission through the array cable 3. In the case of the power transmission system 1, the wind power generation facility 2 and the power grid 7 are not connected, so there is no need to adjust the output according to the situation on the power grid 7 side.

[0042] In this disclosure, the wind power generation facility 2 refers to the configuration from the generator 21 to just before the array cable 3 that transmits power to the offshore converter station 4. The area beyond the array cable 3 is outside the wind power generation facility 2. Although the figure shows three wind power generation facilities 2, the number of three is an example for the purpose of explanation. The figure shows an AC / DC converter 22 and a DC / DC converter 23 for one wind power generation facility 2, but the other wind power generation facilities 2 are assumed to have the same configuration.

[0043] The DC power sent to the offshore converter station 4 via the array cable 3 is stepped down to about 1.5 kV by a DC / DC converter 41. Then, based on the stepped-down voltage, a charging current flows from a charging circuit (not shown) to a storage battery 42, which is charged. This storage battery 42 is used to store the power generated by the wind power generation facility 2 while the electric carrier 10 has not yet arrived at the offshore converter station 4.

[0044] When the electricity carrier 10 arrives at the offshore converter station 4 and the connector cable 8 is connected, power is sent (discharged) from the storage battery 42. At this time, the DC voltage at the time of power sending is converted by the DC / DC converter 43 to a voltage set according to the rated voltage of the connector cable 8, the cable transmission efficiency, etc., such as about 10 kV. This is also a voltage increase to reduce power transmission loss due to the connector cable 8.

[0045] In the electric carrier 10, a connector cable 8 is connected to a charge / discharge port 11, and the voltage of the power received from the connector cable 8 is stepped down to, for example, about 1.5 kV by a DC / DC converter 12. Then, based on the stepped-down voltage, a charging current is passed to the storage battery 14 (battery cell 14a) by a charging circuit in a battery control device 13, thereby charging the storage battery 14.

[0046] After charging, the electricity carrier 10 sails toward the onshore substation 209. When the electricity carrier 10 arrives at the onshore substation 209, the connector cable 9 is connected and electricity is sent (discharged) from the storage battery 14. At this time, the DC voltage at the time of electricity sending is converted by the DC / DC converter 12 to a voltage set according to the rated voltage of the connector cable 9, cable transmission efficiency, etc., for example, about 10 kV.

[0047] In the onshore substation 5, the DC power transmitted via the connector cable 9 is converted into AC power by a DC / AC converter 51 and then boosted to, for example, 66 kV by a transformer 52. This 66 kV AC power is sent to the power grid 7.

[0048] In such a power transmission system 1, the transmitted power changes at a low voltage level during the power transmission process as shown in the lower part of the figure, and there is a large voltage difference as shown as voltage difference VD, particularly when compared at the stage of high-voltage DC submarine cable 207 and storage battery 14. Therefore, in the case of power transmission system 1, compared to power transmission system 201, a multi-stage transformer configuration, high-voltage devices, parts, cable structure, etc. are not required.

[0049] Furthermore, in terms of power transmission efficiency, it is desirable for the electric carrier ship 10 to be able to transport as much electric power as possible in one voyage. On the other hand, in consideration of the handling of cables for the electric power charging and discharging system around the storage battery 14 and battery control device 13 on the electric carrier ship 10, it is desirable to use fewer and smaller cables. Taking these factors into consideration, it is preferable to set the voltage to about 1.5 kV via the DC / DC converter 12.

[0050] 4. Effects and Modifications of the Embodiments The power transmission system 1 according to the above-described embodiments provides the following effects.

[0051] The electric carrier 10, which is a mobile body in the power transmission system 1, is equipped with a battery control device 13 that charges the storage battery 14 with power supplied at a voltage that does not reach the maximum voltage of DC power between the wind power generation facility 2 and the onshore substation 209, which is a power-receiving facility. That is, the charging voltage for the storage battery 14 installed on the electric carrier 10 is a predetermined voltage that is lower than the maximum voltage of power between the wind power generation facility 2 and the onshore substation 209. For example, in the example of FIG. 4 , the voltage of the storage battery 14 during charging and discharging is lower than the voltage during transmission via the array cable 3 and the connector cables 8 and 9. That is, in the power transmission system 1, power transmission via a high-voltage DC submarine cable 207 as in the comparative power transmission system 201 is replaced with power transmission via the electric carrier 10, and the system is designed so that the voltage during charging does not reach the maximum voltage. This design is possible because there is no need to boost the voltage to suppress transmission loss in the high-voltage DC submarine cable 207. This eliminates the need for high-voltage compatible equipment around the storage battery 14 of the electric carrier 10. As a result, the power transmission system 1 can achieve a simplified configuration and cost reduction.

[0052] The electric carrier 10 also includes a DC / DC converter 12 as a converter that receives power generated by the wind power generation facility 2 and converted to a first DC voltage (e.g., about 10 kV) and converts the power to a second DC voltage (e.g., about 1.5 kV), which is a lower voltage than the first DC voltage. The battery control device 13 then charges the storage battery 14 with the power supplied at the second DC voltage. In other words, the electric carrier 10 is configured to convert the DC voltage supplied from the offshore converter station 4, which serves as a relay facility, to a voltage lower than that supplied to the storage battery 14 and charge the storage battery 14. This allows the storage battery 14 to be charged at a voltage lower than that transmitted via the connector cable 8. Since high voltage is not required for power storage in the storage battery 14, there is no need to significantly boost the voltage within the system, as in the comparative example of the power transmission system 201 using a high-voltage DC submarine cable 207. In other words, there is no need to increase the voltage of the power transmission medium when transmitting power over long distances. This eliminates the need for high-voltage equipment and cables, improving the efficiency of the overall system configuration and reducing costs.

[0053] In the embodiment, an example has been given in which the power transmission system 1 is configured using a ship shown as an electric carrier ship 10. This makes it suitable for generating electricity not only on land or in coastal areas, but also offshore, relatively far from land. For example, it is possible to construct a power transmission system that realizes the efficiency of the above-mentioned configuration while enjoying the advantages of eliminating the need for long-distance DC submarine cables and eliminating problems such as noise associated with power generation.

[0054] Note that mobile objects to which the power transmission system according to the present disclosure can be applied are not limited to ships, but may also include vehicles and aircraft equipped with storage batteries.

[0055] In the embodiment, the power transmission system 1 of the present disclosure is applied to an offshore wind power generation facility 2. This makes it suitable for power generation not only on land or along the coast, but also offshore at long distances from shore. This makes it possible to build a power transmission system that realizes the efficiency of the above-described configuration while enjoying the benefits of improved power generation efficiency due to stable offshore winds.

[0056] The power generation facility according to the present disclosure is not limited to wind power generation facilities, but may also be a solar power generation facility, a tidal power generation facility, a geothermal power generation facility, a hydroelectric power generation facility, a biomass power generation facility, or the like. The power generation facility according to the present disclosure is not limited to offshore facilities, but may also be onshore facilities. For example, it may be a power transmission system between onshore power generation facilities and onshore power receiving facilities. The present disclosure can also be applied to a power transmission system between offshore power generation facilities and offshore power receiving facilities.

[0057] The wind power generation facility 2, which is a power generation facility in the power transmission system 1 according to the embodiment, includes a generator 21 and an AC / DC converter (AC / DC converter 22) that converts AC power generated by the generator 21 into DC power. The DC power is then transmitted outside the facility via the array cable 3. In other words, the generated power transmitted to charge the storage battery 14 of the electric carrier ship 10 is converted from AC to DC and then transmitted outside the power generation facility as DC without being converted back to AC. In the case of the power transmission system 1, the wind power generation facility 2 is not constantly connected to the power grid 7 via the electric carrier ship 10, and therefore output adjustment is not required on the wind power generation facility 2 side. This eliminates the need to convert the generated power to DC, adjust the output, and then convert it back to AC within the wind power generation facility 2 for output outside the facility. Furthermore, in the case of the power transmission system 1, the array cable 3 transmits DC power. By incorporating the electric carrier 10 into the offshore wind power transmission system 1, it becomes possible to adopt a DC extraction method from the offshore wind power generation facility 2, and the power converted from AC to DC can be transmitted directly or after the necessary voltage conversion. For these reasons, the wind power generation facility 2 does not require the DC / AC converter 223 or transformer 224, which are required in the wind power generation facility 202 of the comparative example. Furthermore, by using the array cable 3, which is a DC cable, instead of the array cable 203, which is an AC cable, a three-core cable can be replaced with a two-core cable. This significantly reduces the cost required for the array cable 3. These features simplify the configuration of the power generation facility, and can reduce, for example, the installation and operating costs of the wind power generation facility 2.

[0058] The array cable 3 is also assumed to be a DC transmission line to the offshore converter station 4, which is a relay facility that supplies power to the electricity carrier ship 10. The array cable 3 is configured as a DC cable, and transmits DC power to the offshore converter station 4, which is located in a relatively close location. By providing the offshore converter station 4, which is a relay facility, there is no need to provide the wind power generation facility 2 itself with a mechanism for connecting to the electricity carrier ship 10. This can facilitate simplification of the configuration of the wind power generation facilities 2 that are installed in large numbers.

[0059] Furthermore, when transmitting power to the array cable 3, a DC voltage converter (DC / DC converter 23) converts the power to an appropriate voltage value, enabling power transmission with little loss to the offshore converter station 4. Note that, although Fig. 4 shows an example in which the DC / DC converter 23 is used as the DC voltage converter, a transformer may be used instead of the DC / DC converter 23. In particular, when insulation is required at the power transmission stage of the wind power generation facility 2, it is preferable to use a transformer to perform the necessary voltage conversion.

[0060] REFERENCE SIGNS LIST 1 Power transmission system 2 Wind power generation facility 3 Array cable 4 Offshore converter station 5 Onshore substation 6 Cable 7 Power system 8, 9 Connector cable 10 Electric carrier 11 Charging / discharging port 12, 23, 41, 43 DC / DC converter 13 Battery control device 14 Storage battery 14a Battery cell 21 Generator 22 AC / DC converter 42 Storage battery 51 DC / AC converter 52 Transformer

Claims

1. A moving body in a power transmission system that charges a storage battery mounted on a moving body with electric power generated by a power generation facility and supplies power from the storage battery transferred by the moving body to a power receiving facility, comprising a battery control device configured to charge the storage battery by power supply at a voltage value that is not the maximum voltage value of the DC power between the power generation facility and the power receiving facility. Moving body.

2. Comprising a conversion unit that receives the supply of electric power generated by the power generation facility and converted to a first DC voltage and converts it to a second DC voltage that is a voltage value lower than the first DC voltage, wherein the battery control device is configured to charge the storage battery by power supply at the second DC voltage. The moving body according to claim 1.

3. The first DC voltage is a voltage value converted for transmission to the cable in the relay facility when power from the power generation facility is supplied to the cable from a relay facility capable of storing power. The moving body according to claim 2.

4. The moving body is a ship. The moving body according to any one of claims 1 to 3.

5. The power generation facility is an offshore wind power generation facility. The moving body according to any one of claims 1 to 3.

6. A power transmission method for a power transmission system that charges a storage battery mounted on a moving body with electric power generated by a power generation facility and supplies power from the storage battery transferred by the moving body to a power receiving facility, wherein charging of the storage battery is performed by power supply at a voltage value that is not the maximum voltage value of the DC power between the power generation facility and the power receiving facility. Power transmission method.