Power transmission methods

Abstract

To provide efficient operational methods for transport ships. [Solution] The power transmission method uses a plurality of small transport ships 10, each comprising at least a first transport ship 11, a second transport ship 12, and a third transport ship 13. The power transmission method involves discharging power from a first energy storage device 21 installed on the first transport ship 11 to a power grid 50 on land L or a demand facility 60 on land L. While the first energy storage device 21 is discharging power to the power grid 50 on land L or the demand facility 60 on land L, the second transport ship 12, with its second energy storage device 22 installed on the second transport ship 12 charged by the offshore power generation facility 40, sails toward land L, and the third energy storage device 23 installed on the third transport ship 13 is also charged by the offshore power generation facility 40.

Description

Technical Field

[0001] The present invention relates to a power transmission method.

Background Art

[0002] In recent years, the expansion of offshore wind power generation has been desired. As a technology for transporting energy sources such as electricity generated by offshore power generation facilities to onshore receiving facilities, an energy transport system by ship described in International Publication No. 2022 / 239733 (Patent Document 1 below) is known. According to this system, an energy source can be transported from a power generation facility to a receiving facility without using a power transmission cable.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above system, electric energy is transported from an offshore power generation facility to an onshore receiving facility by a transport ship equipped with a storage battery. The transport ship has a container, and this container has a large-capacity storage battery composed of a plurality of battery cells. Therefore, it takes a lot of time to charge the storage battery.

[0005] One aspect of the present invention provides an efficient operation method for a transport ship.

Means for Solving the Problems

[0006] A power transmission method according to one aspect of the present invention is a power transmission method using a plurality of small transport ships, each comprising at least a first transport ship, a second transport ship, and a third transport ship, wherein power is discharged from a first energy storage facility mounted on the first transport ship to a land power grid or land demand facility, and while the first energy storage facility is discharging to the land power grid or land demand facility, the second transport ship, which is in a state where its second energy storage facility mounted on the second transport ship is being charged by an offshore power generation facility, is sailed toward land, and the third energy storage facility mounted on the third transport ship is being charged by the offshore power generation facility. Here, "offshore power generation equipment" may refer to floating offshore wind power generation equipment, fixed-bottom offshore wind power generation equipment, or a distributed energy system installed on a remote island. [Effects of the Invention]

[0007] According to the above embodiment, an efficient method for operating transport ships can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram illustrates the power transmission method of Embodiment 1, showing the second transport ship sailing toward land. [Figure 2] This diagram illustrates the power transmission method of Embodiment 1, showing a second transport ship anchored near the first transport ship. [Figure 3] This diagram illustrates the power transmission method of Embodiment 1, showing the first discharge cable connected to the second transport ship. [Figure 4] This diagram illustrates the power transmission method of Embodiment 1, showing the first transport ship sailing toward an offshore power generation facility. [Figure 5] This diagram illustrates the power transmission method of Embodiment 2, showing the second transport ship sailing toward land. [Figure 6] This diagram illustrates the power transmission method of Embodiment 2, showing the second discharge cable connected to the second transport ship. [Figure 7]This diagram illustrates the power transmission method of Embodiment 2, showing the first transport ship sailing toward an offshore power generation facility. [Modes for carrying out the invention]

[0009] When transporting electricity using large transport ships equipped with containers containing large-capacity batteries, charging these batteries takes a considerable amount of time. As an example of a battery, consider a lithium-ion battery that is charged using constant current constant voltage (CCCV). A lithium-ion battery can be charged at its maximum charge rate (C rate) up to about 60% of its capacity. For example, in the case of a lithium-ion battery with a maximum charge rate of 1C, it takes 45 minutes from the start of charging to charge to about 60% of the battery capacity with a constant current at a charge rate of 1C, and then after the battery voltage reaches the CV voltage, it takes 2 to 4 hours of CV charging to reach a fully charged state.

[0010] To shorten charging time, it is conceivable to perform only CC charging (charging only up to about 60% of the battery capacity) and not CV charging. In that case, a battery capacity of 400 MWh would be required to store 240 MWh of energy, which would increase the size and cost of the battery, and thus the construction and operating costs of the transport ship.

[0011] As an alternative to shortening charging (and discharging) times, one could consider using batteries capable of high-rate charging and discharging. However, such batteries are expensive, which would increase the construction cost of the transport ship.

[0012] Furthermore, to shorten charging and discharging times, it is conceivable to use high-capacity charging and discharging equipment capable of supplying large currents. Such charging and discharging equipment is large and expensive. Large-diameter, heavy, and costly cables are required for charging and discharging. This expensive charging and discharging equipment is left unused while the transport ship is sailing between port and offshore.

[0013] When using high-capacity discharge equipment to shorten discharge time, there is a possibility that the amount of electricity discharged from the transport ship will exceed the current electricity demand. Therefore, land-based receiving facilities need to be equipped with energy storage facilities to adjust demand.

[0014] To solve the above problems, the inventors came up with the following configuration. (1) The power transmission method uses a plurality of small transport ships, each comprising at least a first transport ship, a second transport ship, and a third transport ship. The power transmission method involves discharging power from a first energy storage facility installed on the first transport ship to a land power grid or land demand facility, and while the first energy storage facility is discharging power to the land power grid or land demand facility, the second transport ship sails toward land with its second energy storage facility, which is charged by the offshore power generation facility, and the third energy storage facility, which is installed on the third transport ship, is charged by the offshore power generation facility.

[0015] The inventors of this invention have conceived of a way to efficiently transport electricity by operating multiple small transport ships in parallel, instead of the large transport ships that have been proposed in the past. A "small transport ship" refers to a transport ship equipped with energy storage equipment smaller than the 200-6000 MWh energy storage equipment that has been proposed in the past, preferably a transport ship equipped with energy storage equipment of less than 200 MWh, and more preferably a transport ship equipped with energy storage equipment of less than 100 MWh. Let's consider a case where, for example, three transport ships are used, each equipped with 80 MWh of energy storage equipment. The first energy storage equipment on the first transport ship can be discharged from the first energy storage equipment to the land power grid or land-based demand equipment over a period of 8 hours according to the electricity demand. During that time, the second transport ship, which has finished charging its second energy storage equipment at the offshore power generation facility, can sail towards land over a period of 8 hours, and the third energy storage equipment of the third transport ship, which has arrived at the offshore power generation facility, can be charged at the offshore power generation facility over the same 8 hours.

[0016] While the second and third transport ships are sailing and charging in parallel, the first transport ship can discharge from the first power storage facility according to the power demand without haste over a long period of time (such as 8 hours). Since it can take a long time to discharge, it can discharge at a relatively low rate. Therefore, the cost of the first power storage facility of the first transport ship can be reduced. As the first discharge cable, a cable with a relatively small diameter, light weight, and easy handling can be used.

[0017] Since the third transport ship can be charged at a relatively low rate because it takes a long time (such as 8 hours) to discharge from the first power storage facility, the costs of the third power storage facility and the offshore power generation facility can be reduced. As the charging cable connecting the offshore power generation facility and the third power storage facility, a cable with a relatively small diameter and easy handling can be used.

[0018] (2) In the power transmission method described in (1) above, before ending the discharge from the first power storage facility, the second transport ship may be parked near the first transport ship.

[0019] According to the above configuration, it is possible to avoid the situation where power is not supplied for a long time and continuously supply power.

[0020] (3) In the power transmission method described in (2) above, while discharging from the first discharge cable connected to the first power storage facility to the onshore power grid or the onshore demand facilities, a second discharge cable is connected to the second power storage facility. After discharging from the first power storage facility to the onshore power grid or the onshore demand facilities, it may be discharged from the second power storage facility to the onshore power grid or the onshore demand facilities via the second discharge cable.

[0021] According to the above configuration, it becomes possible to supply power without interruption as much as possible, and a plurality of small transport ships can function as power storage stations.

[0022] (4) In the power transmission method described in any of (1) to (3) above, the fourth transport ship equipped with the fourth energy storage facility may be moored near the third transport ship before the charging of the third energy storage facility is completed.

[0023] With the above configuration, each energy storage facility can be charged at a relatively low rate without interruption. An example of operation of (4) above will be explained below using ships 1 to 4. <First point in time> Ship 1 connects to the discharge cable on land and starts discharging the energy storage equipment. Ship 2 completes its discharge on land and begins sailing towards the offshore power generation facility. Ship 3 connects the charging cable to the offshore power generation equipment and begins charging the energy storage equipment. Ship 4 completes its charging at the offshore power plant and begins sailing towards land. <Second point in time> Ship 1 has almost finished discharging electricity over land. Ship 2 arrives at the offshore power generation facility and gets on standby so that it can start charging as soon as Ship 3 finishes charging. Ship 3 has almost finished charging at the offshore power generation facility. Ship 4 arrives on land and stands by to discharge immediately after Ship 1 finishes its discharge. <Third point in time> Ship 1 completes its discharge on land and begins sailing towards the offshore power generation facility. Ship 2 connects the charging cable to the offshore power generation equipment and begins charging the energy storage equipment. Ship 3 completes its charging at the offshore power plant and begins sailing towards land. Ship 4 connects to the discharge cable on land and begins discharging the energy storage equipment.

[0024] The power transmission methods described above can also be applied when transporting electricity to land areas such as remote islands (hereinafter referred to as "first land areas"). (5) The power transmission method uses a plurality of small transport ships, each comprising at least a first transport ship, a second transport ship, and a third transport ship. The power transmission method involves discharging power from a first energy storage facility mounted on the first transport ship to a first land power grid or demand facility, and while the first energy storage facility is discharging power to the first land power grid or demand facility, the second transport ship, with its second energy storage facility mounted on the second transport ship charged by a second land power generation facility, sails toward the first land, while the third energy storage facility mounted on the third transport ship is charged by the second land power generation facility.

[0025] According to the above configuration, it is possible to deliver electricity to land areas such as remote islands that lack power generation facilities, while keeping initial investment and operating costs down. Furthermore, the following procedures may also be applied. (6) In the power transmission method described in (5) above, the second transport ship may be anchored near the first transport ship before the discharge from the first energy storage facility is terminated. (7) In the power transmission method described in (6) above, the first discharge cable connected to the first power storage facility may be used to discharge power to the first land power system or demand facility, while the second discharge cable is connected to the second power storage facility, and after the first power storage facility has discharged power to the first land power system or demand facility, the second power storage facility may be used to discharge power to the first land power system or demand facility via the second discharge cable. (8) In the power transmission method described in any of (5) to (7) above, the fourth transport ship carrying the fourth energy storage equipment may be moored near the third transport ship before the charging of the third energy storage equipment is completed.

[0026] <Embodiment 1> The embodiments for carrying out the present invention will be described below with reference to Figures 1 to 4. The present invention is not limited to the embodiments described below, but includes modifications made to the embodiments described below as being obvious to those skilled in the art.

[0027] Figure 1 shows the power transmission method of Embodiment 1. This power transmission method uses a plurality of small transport ships 10, each comprising a first transport ship 11, a second transport ship 12, and a third transport ship 13, and transmits electricity by sea from offshore power generation facilities 40 to land-based power grids 50 or land-based demand facilities 60.

[0028] As shown in Figure 1, the offshore power generation facility 40 comprises one or more floating wind power generation facilities 41 and a charging cable 42. For example, the alternating current electricity generated by the wind power generation facility 41 is converted to direct current by a substation (not shown).

[0029] When the transport ship 10 arrives near the offshore power generation facility 40, the DC electricity converted by the substation is supplied to the energy storage facility 20 on the transport ship 10 via the charging cable 42. Thus, it is preferable to supply electricity to the transport ship 10 at sea via the charging cable 42. After the energy storage facility 20 has been charged, the transport ship 10 sails by sea toward the demand facility 60 on land L. The demand facility 60 on land L includes, for example, a substation 61 and a power transmission cable 62.

[0030] When the transport ship 10 arrives near the demand facility 60 on land L, the DC electricity held by the energy storage facility 20 is supplied to the substation 61 via the discharge cable 30. At the substation 61, the electricity is converted from DC to AC and transmitted to the power system 50 on land L, including substations. In Embodiment 1, the first discharge cable 31 is exemplified as the discharge cable 30.

[0031] In this way, the transport ship 10 equipped with the energy storage equipment 20 transports electrical energy from the offshore power generation facility 40 to the demand facility 60 on land L, and ultimately to the power grid 50 (transmission network) on land L. Depending on the power source of the transport ship 10, even a motor-powered transport ship 10 powered by electricity can travel approximately 300 to 500 km on the open sea without recharging. Therefore, the distance from the offshore power generation facility 40 to the demand facility 60 on land L can be set at approximately 300 to 500 km.

[0032] In Embodiment 1, the transport ships 10 are exemplified as a first transport ship 11, a second transport ship 12, and a third transport ship 13, and the energy storage equipment 20 is exemplified as a first energy storage equipment 21, a second energy storage equipment 22, and a third energy storage equipment 23. The first transport ship 11 is equipped with the first energy storage equipment 21, the second transport ship 12 is equipped with the second energy storage equipment 22, and the third transport ship 13 is equipped with the third energy storage equipment 23. Each energy storage equipment 21, 22, and 23 is equipped with a connection part for connecting each cable 31, 32, and 42.

[0033] Although the transport vessel 10 is exemplified as a motor-driven vessel powered by electricity, it may also be an internal combustion engine-driven vessel powered by fossil fuels, or a hybrid vessel that uses both a motor and an internal combustion engine. Furthermore, the transport vessel 10 may be powered by hydrogen. For example, when using hydrogen as a power source, the transport vessel 10 may be a fuel cell-driven vessel that uses electricity generated by a fuel cell to drive the motor, or a hydrogen engine-driven vessel that obtains power by burning hydrogen in an internal combustion engine.

[0034] The energy storage device 20 is a battery, and its storage capacity can be adjusted according to the number of cells installed. For example, depending on the size of the transport ship 10, the energy storage device 20 can preferably secure an electrical capacity of less than 200 MWh, and more preferably less than 100 MWh. The energy storage device 20 is equipped with a control device, which controls the amount of electricity charged to each cell, the amount of electricity discharged, the charge rate, and the discharge rate. The control device is equipped with a CPU, a memory storing a control program, communication equipment for an external server device, and sensor equipment for detecting the charge status of the cells, etc., on a circuit board.

[0035] Figure 1 shows the first transport ship 11 anchored at a demand facility 60 on land L, the second transport ship 12 sailing toward land L, and the third transport ship 13 anchored at an offshore power generation facility 40. The first discharge cable 31 is connected to the first energy storage equipment 21 installed on the first transport ship 11. Discharge is carried out from the first energy storage equipment 21 on the first transport ship 11 to the power grid 50 on land L or to the demand facility 60 on land L via the first discharge cable 31.

[0036] The second energy storage unit 22, mounted on the second transport ship 12, is charged by the offshore power generation equipment 40. The second energy storage unit 22 may be fully charged, or it may be charged to about 60% of its total capacity. A charging cable 42 is connected to the third energy storage unit 23, mounted on the third transport ship 13. The charging cable 42 is used to charge the third energy storage unit 23 from the wind power generation equipment 41. By using multiple small transport ships 10 in this way, charging, discharging, and navigation can be performed simultaneously, providing an efficient method of operating the transport ships 10.

[0037] Figure 2 shows the second transport ship 12 arriving at and anchoring at the demand facility 60 on land L. At this point, the first discharge cable 31 is connected to the first energy storage facility 21. However, once the discharge from the first energy storage facility 21 is complete, as shown in Figure 3, the first discharge cable 31 is disconnected from the first energy storage facility 21 and connected to the second energy storage facility 22. Thus, the first discharge cable 31 initiates discharge from the second energy storage facility 22 of the second transport ship 12 to the power grid 50 on land L or to the demand facility 60 on land L. Subsequently, as shown in Figure 4, the first transport ship 11 begins sailing from the demand facility 60 on land L towards the offshore power generation facility 40. This prevents prolonged power outages and ensures a continuous power supply.

[0038] <Embodiment 2> The embodiments for carrying out the present invention will be described below with reference to Figures 5 to 7. The present invention is not limited to the embodiments described below, but includes modifications made to the embodiments described below as being obvious to those skilled in the art.

[0039] In Embodiment 2, the discharge cable 30 is exemplified as a first discharge cable 31 and a second discharge cable 32. Figure 5 shows the first transport ship 11 anchored at a demand facility 60 on land L, the second transport ship 12 sailing toward land L, and the third transport ship 13 anchored at an offshore power generation facility 40. The first discharge cable 31 is connected to the first energy storage facility 21 installed on the first transport ship 11, but the second discharge cable 32 is not connected to any of the energy storage facilities 20.

[0040] When the second transport ship 12 arrives at the demand facility 60 on land L, the second discharge cable 32 is connected to the second energy storage facility 22 mounted on the second transport ship 12. Therefore, as shown in Figure 6, the first discharge cable 31 is connected to the first energy storage facility 21, and the second discharge cable 32 is connected to the second energy storage facility 22. Once the discharge from the first energy storage facility 21 is finished, the discharge from the second energy storage facility 22 can be started immediately, eliminating the time loss required for switching cables.

[0041] Once discharge begins from the second energy storage facility 22, the first discharge cable 31 is disconnected from the first energy storage facility 21, and the first transport ship 11 can sail toward the offshore power generation facility 40 (see Figure 7). At this time, charging, discharging, and sailing can be performed simultaneously on either transport ship 10, enabling more efficient operation of the transport ship 10.

[0042] <Other Embodiments> The present invention is not limited to the embodiments described above and in the drawings, and the following embodiments, for example, are also included in the technical scope of the present invention.

[0043] (1) In the above embodiment, the operation of three transport ships is assumed, and the discharge time is set to 8 hours based on the calculation 24 hours ÷ 3 = 8 hours. However, if it does not take 8 hours to travel, the time to connect to the discharge location can be set to a time longer than 8 hours, for example, 9 hours or 10 hours. Eight hours after the start of discharge, the next transport ship will arrive and connect to the second discharge cable. If the first transport ship still has power remaining, it will continue to discharge preferentially from the first transport ship and will continue to discharge until it is empty (or the planned lower limit of SOC). This ensures that the first transport ship does not carry back any remaining power, and can also respond to increased power demand on the load side when the second transport ship connects to the second discharge cable while the first transport ship is discharging.

[0044] (2) Small-scale power storage facilities, such as those with a capacity of 1 / 10 to 1 / 3 of the storage capacity of three small transport ships, may be installed at the discharge site (e.g., a substation on land). By charging the small-scale power storage facilities at the discharge site with the excess power from the transport ships, fluctuations on the load side can be absorbed without having to bring the excess power back. [Explanation of symbols]

[0045] 10: Transport ship 11: First transport ship 12: Second transport ship 13: Third transport ship 20: Energy storage equipment 21: First energy storage equipment 22: Second energy storage equipment 23: Third energy storage equipment 30: Discharge cable 31: First discharge cable 32: Second discharge cable 40: Offshore power generation equipment 41: Wind power generation equipment 42: Charging cable 50: Power grids on land 60: Land-based demand facilities 61: Substations 62: Transmission cables L:Land

Claims

1. A method of transporting electricity using a plurality of small transport ships, each comprising at least a first transport ship, a second transport ship, and a third transport ship, The first energy storage equipment installed on the first transport ship discharges power to the land power grid or land demand equipment. A power transport method comprising: while the first energy storage facility is discharging power to the land power grid or the land demand facility, the second transport ship sails toward land with the second energy storage facility, which is mounted on the second transport ship, being charged by the offshore power generation facility, and the third energy storage facility, which is mounted on the third transport ship, being charged by the offshore power generation facility.

2. A power transmission method according to claim 1, A method of transporting electricity, wherein the second transport ship is moored near the first transport ship before the discharge from the first energy storage facility is terminated.

3. A power transmission method according to claim 2, While discharging from the first discharge cable connected to the first energy storage facility to the land power grid or the land demand facility, the second discharge cable is connected to the second energy storage facility. A power transmission method comprising discharging from the first power storage facility to the land power grid or land demand facility, and then discharging from the second power storage facility to the land power grid or land demand facility via the second discharge cable.

4. A power transmission method according to claim 1 or claim 2, A method of transporting electricity, wherein before the charging of the third energy storage facility is completed, a fourth transport ship equipped with a fourth energy storage facility is moored near the third transport ship.

5. A method of transporting electricity using a plurality of small transport ships, each comprising at least a first transport ship, a second transport ship, and a third transport ship, Discharge from the first energy storage equipment installed on the first transport ship to the first land-based power grid or demand equipment. A power transport method comprising: discharging from the first energy storage facility to the first land power grid or demand facility; sailing the second transport ship toward the first land with the second energy storage facility, which is mounted on the second transport ship, charged by the second land power generation facility; and charging the third energy storage facility, which is mounted on the third transport ship, by the second land power generation facility.

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