METHOD FOR OPERATING STORAGE BATTERY SYSTEM

A plurality of storage batteries are divided into a plurality of storage battery blocks. A useful life of each of the storage batteries is shorter than the project life. Total capacity of the plurality of storage batteries is equal to or greater than the product of capacity required for a project and a ratio of the project life to the useful life. The project life is divided into a plurality of periods. For each of the plurality of periods, a rest storage battery block is selected from the plurality of storage battery blocks in rotation, the rest storage battery block is rested, and an operational storage battery block is operated. The sum of actual operating time of each of the storage battery blocks and equivalent operating time of each of the storage battery blocks is prevented from exceeding the useful life during the project life.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for operating a storage battery system.

Description of the Background Art

Conventionally, storage batteries had been required to each have a performance warranty of approximately two years. With improvement in performance of the storage batteries, however, the storage battery system has recently been required to be used over a project life having a long period of 25 years to 30 years.

In a case where useful lives of the storage batteries are shorter than the project life of the storage battery system, a use of storage batteries over the project life is enabled by replacing all the storage batteries before the end of those useful lives.

On the other hand, extension of the useful lives of the storage batteries has also been contemplated.

In technology disclosed in Japanese Utility Model Registration No. 3093649, for example, a cycle battery output is performed. Stored electric energy of a previous set of batteries is used up before switching to a next set of batteries. A function to secure used lives of batteries can thereby be achieved.

In technology disclosed in Japanese Patent Application Laid-Open No. 2017-120685, a battery pack having a temperature higher than an average temperature of battery packs during charge or discharge is detected as a rest target battery pack. The rest target battery pack is electrically separated from a load and a power source, and then control is performed so that the temperature of the rest target battery pack is within a predetermined temperature range. A life of the battery pack can thereby be prolonged.

In technology disclosed in Japanese Patent Application Laid-Open No. 2017-127169, a particular group of assembled batteries is selected from n groups of assembled batteries in rotation, and is discharged to reach 100% in DOD once every n cycles. This leads to long lives of storage batteries.

In a case where the useful lives of the storage batteries are significantly shorter than the project life of the storage battery system, it is only necessary to replace all the storage batteries every time the end of the useful lives of the storage batteries arrives, and even when doing so, removal of storage batteries having long remaining lives can be avoided. For example, in a case where the project life is 20 years, and the useful lives of the storage batteries are five years, it is only necessary to replace all the storage batteries every five years, and even when doing so, removal of storage batteries having remaining lives can be avoided.

On the other hand, also in a case where the useful lives of the storage batteries are shorter than the project life of the storage battery system, but are close to the project life, it is necessary to replace all the storage batteries before the end of those useful lives, but in this case, storage batteries having long remaining lives are forced to be removed. For example, in a case where the project life is 25 years, and the useful lives of the storage batteries are 20 years, it is necessary to replace all the storage batteries every 12.5 years, so that storage batteries having remaining lives of 7.5 years are forced to be removed.

However, there is no choice but to dispose of the removed storage batteries having long remaining lives unless an environment to recycle the removed storage batteries as used storage batteries is created. Disposal of the storage batteries having long remaining lives is waste of resources, and adversely affects the environment. In terms of economics, disposal of the storage batteries having long remaining lives causes an increase in cost, and causes an increase in disposal cost. Disposal of the storage batteries having long remaining lives thus makes establishment of a project difficult.

SUMMARY

The present invention relates to a method for operating a storage battery system.

In a method for operating a storage battery system, a storage battery system including a plurality of storage batteries is prepared. The plurality of storage batteries are divided into a plurality of storage battery blocks. A useful life of each of the plurality of storage batteries is shorter than a project life. Total capacity of the plurality of storage batteries is equal to or greater than the product of capacity required for a project and a ratio of the project life to the useful life. The project life is divided into a plurality of periods. For each of the plurality of periods, a rest storage battery block is selected from the plurality of storage battery blocks in rotation, the rest storage battery block is rested, and an operational storage battery block of the plurality of storage battery blocks other than the rest storage battery block is operated. The sum of actual operating time, which indicates time each of the plurality of storage battery blocks has been operated, and equivalent operating time, which indicates time needed to cause, through the real operation of each of the plurality of storage battery blocks, the equivalent degradation to degradation caused to each of the plurality of storage battery blocks during the resting, is prevented from exceeding the useful life during the project life.

According to the present invention, the storage battery system can be used over the project life of the storage battery system, even in the case that the storage batteries has shorter useful lives than the project life. Furthermore, removal of the storage batteries having long remaining lives from the storage battery system can be suppressed.

It is therefore an object of the present invention to be able to use a storage battery system over a project life of the storage battery system even in the case that storage batteries has shorter useful lives than the project life, and to suppress removal of storage batteries having long remaining lives.

The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

1 Storage Battery System

FIG. 1is a block diagram schematically showing a storage battery system.FIG. 2is a diagram for describing a rest storage battery block and operational storage battery blocks of the storage battery system.

A storage battery system1shown inFIG. 1includes five storage battery blocks11a,11b,11c,11d, and11e, five switches12a,12b,12c,12d, and12e, a bi-directional converter (PCS)13, and a transformer14. The five storage battery blocks11a,11b,11c,11d, and11emay be replaced with four or less or six or more storage battery blocks. The five switches12a,12b,12c,12d, and12emay be replaced with four or less or six or more switches.

The five storage battery blocks11a,11b,11c,11d, and11e(hereinafter also simply referred to as storage battery blocks11) each include 10 storage batteries101a,101b,101c, . . . , and101jas shown inFIG. 1. The storage battery system1thus includes 50 storage batteries101a,101b,101c, . . . , and101j. The 10 storage batteries101a,101b,101c, . . . , and101jof each of the storage battery blocks11may be replaced with nine or less or 11 or more storage batteries. The 50 storage batteries101a,101b,101c, . . . , and101jof the storage battery system1may thus be replaced with 49 or less or 51 or more storage batteries.

The storage batteries101a,101b,101c, . . . , and101j(hereinafter also simply referred to as storage batteries101) are also referred to as module batteries. The storage batteries101each include an assembled battery111as shown inFIG. 1.

The storage battery blocks11a,11b,11c,11d, and11erespectively correspond to the switches12a,12b,12c,12d, and12e. The storage battery blocks11a,11b,11c,11d, and11eare electrically connected, via the respective switches12a,12b,12c,12d, and12e, to a DC side of the PCS13. An AC side of the PCS13is electrically connected to a system19via the transformer14.

As shown inFIG. 2, the storage battery blocks11a,11b,11c,11d, and11einclude a rest storage battery block11pand operational storage battery blocks11q.

The rest storage battery block11pis selected from the storage battery blocks11a,11b,11c,11d, and11e. The operational storage battery blocks11qare storage battery blocks of the storage battery blocks11a,11b,11c,11d, and11eother than the rest storage battery block11p.

A switch corresponding to the rest storage battery block11pis opened. Switches corresponding to the operational storage battery blocks11qare closed.

When the storage battery system1outputs AC power to the system19, the operational storage battery blocks11qoutput DC power. The PCS13converts a DC voltage as output into an AC voltage. The transformer14steps up the AC power, and outputs the AC voltage as stepped up to the system19. The rest storage battery block11p, however, does not output the DC power. When the AC power is input into the storage battery system1from the system19, the AC power is input into the transformer14. The transformer14steps down the AC power as input. The PCS13converts the AC power as stepped down into the DC power. The DC power is input into the operational storage battery blocks11q. The DC power, however, is not input into the rest storage battery block11p.

When the operational storage battery blocks11qoutput the DC power, the storage batteries101a,101b,101c, . . . , and101jof the operational storage battery blocks11qdischarge the DC power. When the DC power is input into the operational storage battery blocks11q, the storage batteries101a,101b,101c, . . . , and101jof the operational storage battery blocks11qare charged with the DC power.

When each of the storage batteries101is discharged, the assembled battery111of the storage battery101is discharged. When each of the storage batteries101is charged, the assembled battery111of the storage battery101is charged.

The storage batteries101each include a heating mechanism112and a cooling mechanism113as shown inFIG. 1.

The heating mechanism112of each of the storage batteries101heats cells163, which will be described below, of the storage battery101. The heating mechanism112is exemplified by an electrothermal heater and a heat pump. The cooling mechanism113of each of the storage batteries101cools the cells163, which will be described below, of the storage battery101. The cooling mechanism113is exemplified by a cooling fan and a heat pump.

The storage battery system1includes a measurement system15and an electrical connection16as shown inFIG. 1.

The measurement system15measures a voltage of each of the storage batteries101, a current flowing through each of the storage batteries101, and the like. The electrical connection16electrically connects each of the storage batteries101and the measurement system15. The electrical connection16directly connects a measurement sensor mounted to each of the storage batteries101and the measurement system15or transmits a signal indicating a result of measurement performed by the measurement sensor from each of the storage batteries101to the measurement system15.

FIG. 3is a circuit diagram schematically showing the assembled battery of the storage battery system in the first embodiment.

The assembled battery111includes four cell blocks161a,161b,161c, and161das shown inFIG. 3. The four cell blocks161a,161b,161c, and161dmay be replaced with three or less or five or more cell blocks.

A cell string162as each of the cell strings162a,162b,162c, . . . , and1621includes eight cells163a,163b,163c, . . . , and163g. The eight cells163a,163b,163c, and163gmay be replaced with seven or less or nine or more cells.

The cell blocks161a,161b,161c, and161dare electrically connected in series. In the cell block161, the cell strings162a,162b,162c, . . . , and1621are electrically connected in parallel. In the cell string162, the cells163a,163b,163c, . . . , and163gare electrically connected in series.

The electrical connection164electrically connects the 384 cells.

The cells163a,163b,163c, . . . , and163g(hereinafter also simply referred to as the cells163) are each a high temperature operating secondary battery. The high temperature operating secondary battery is a secondary battery required to have a temperature higher than a room temperature to be charged or discharged. For example, the high temperature operating secondary battery is a secondary battery operating in a temperature range of 200° C. or more and 360° C. or less. The high temperature operating secondary battery is exemplified by a sodium-sulfur battery and the ZEBRA battery. The ZEBRA battery is exemplified by a sodium-nickel-chloride battery. The cells163may each be a secondary battery other than the high temperature operating secondary battery. For example, the cells163may each be a lithium-ion battery, a nickel metal hydride battery, a nickel-cadmium battery, a lead-acid battery, or the like.

3 Relationship Between Useful Lives of Storage Batteries and Project Life of Storage Battery System and Relationship Between Capacity of Storage Batteries and Capacity Required for Project

A project life of the storage battery system1indicates the length of a project. The project life of the storage battery system1is the length of a period during which the storage battery system1can be used while maintaining performance meeting a specification of the storage battery system1. The project life of the storage battery system1is also the length of a service contract period during which maintenance of performance meeting the specification of the storage battery system1is warranted. Maintenance of performance meeting the specification of the storage battery system1is warranted over an entire operational period of the storage battery system1in the project. The project life of the storage battery system1is typically disclosed to a customer of the storage battery system1.

Capacity required for the project is input/output capacity required for the storage battery system1in a case where the storage battery system1is operated based on an operational condition of the storage battery system1in the project. The input/output capacity is represented by electric energy (Wh) and the like. The input/output capacity may vary from year to year of the operational period of the storage battery system1in the project in view of degradation of the storage battery system1. In this case, the capacity of the storage battery system1when the project life has ended is used as the capacity required for the project. The capacity required for the project is typically disclosed to the customer of the storage battery system1.

The useful life of each of the storage batteries101is the length of a period until the capacity of each of the storage batteries101is reduced to capacity to be determined to be at the end of life, which has been set in the project, or to capacity to be determined to be at the end of life of each of the storage batteries101based on deterioration characteristics of each of the storage batteries101, in a case where charge and discharge cycle operation of the storage battery system1is continued based on the operational condition of the storage battery system1. The capacity to be determined to be at the end of life is typically 80% of initial capacity.

The project life of the storage battery system1is 10 years or more. The useful life of each of the storage batteries101is five years or more. The useful life of each of the storage batteries101is shorter than the project life of the storage battery system1. For example, the useful life of each of the storage batteries101is 20 years, and the project life of the storage battery system1is 25 years.

Total capacity of the 50 storage batteries101of the storage battery system1is equal to or greater than the product of the capacity required for the project and a ratio of the project life of the storage battery system1to the useful life of each of the storage batteries101. The total capacity of the 50 storage batteries101is only required to be equal to or greater than the product before the end of the useful lives of the 50 storage batteries101arrives.

The 50 storage batteries101of the storage battery system1are divided into the five storage battery blocks11a,11b,11c,11d, and11e. In a case where one rest storage battery block11pof the five storage battery blocks11a,11b,11c,11d, and11eis rested, and four operational storage battery blocks11qother than the one rest storage battery block11pare operated in the storage battery system1, total capacity of 40 storage batteries101belonging to the four operational storage battery blocks11qis equal to or greater than the capacity required for the project. The capacity required for the project can thus be provided by operating the four operational storage battery blocks11qeven in a case where the one rest storage battery block11pis rested.

4 Method for Operating Storage Battery System

FIG. 4is a diagram for describing a method for operating the storage battery system in the first embodiment.

When the storage battery system1is operated, the storage battery system1is prepared.

When the storage battery system1is operated, a project life171of the storage battery system1is divided into a plurality of periods172a,172b,172c,172d, and172eas shown inFIG. 4.

The plurality of periods172a,172b,172c,172d, and172e(hereinafter also simply referred to as periods172) each have the length of one year or more.

When the storage battery system1is operated, the rest storage battery block11pis selected, for each of the periods172, from the storage battery blocks11a,11b,11c,11d, and11ein rotation. The rest storage battery block11pis rested during each of the periods172. The operational storage battery blocks11qare operated during each of the periods172. For example, the storage battery block11eis rested as the rest storage battery block11pduring the first period172a. The storage battery blocks11a,11b,11e, and11dare operated as the operational storage battery blocks11qduring the first period172a. The storage battery block11dis rested as the rest storage battery block11pduring the second period172b. The storage battery blocks11a,11b,11c, and11eare operated as the operational storage battery blocks11qduring the second period172b. The storage battery block11cis rested as the rest storage battery block11pduring the third period172c. The storage battery blocks11a,11b,11d, and11eare operated as the operational storage battery blocks11qduring the third period172c. The storage battery block11bis rested as the rest storage battery block11pduring the fourth period172d. The storage battery blocks11a,11c,11d, and11eare operated as the operational storage battery blocks11qduring the fourth period172d. The storage battery block11ais rested as the rest storage battery block11pduring the fifth period172e. The storage battery blocks11b,11c,11d, and11eare operated as the operational storage battery blocks11qduring the fifth period172e. The rest storage battery block11pis thus selected from the storage battery blocks11a,11b,11c,11d, and11ein rotation, and is rested. The rest storage battery block11prested during each of the periods172may include two or more storage battery blocks.

Furthermore, when the storage battery system1is operated, the sum of actual operating time, which indicates time each of the storage battery blocks11has been operated, and equivalent operating time, which indicates time needed to cause, through the real operation of each of the storage battery blocks11, the equivalent degradation to degradation caused to each of the storage battery blocks11during the resting, is prevented from exceeding the useful life of each of the storage batteries101during the project life171of the storage battery system1. The equivalent operating period is considered to be 10/50 times a rest period when the length of a period until the capacity of each of the storage battery blocks11is reduced to 80% of the initial capacity is assumed to be 10 years in a case where cycle operation to discharge rated capacity is continued within a range of an environmental condition and a state of charge (SOC) assumed in the project and the length of a period until the capacity of each of the storage battery blocks11is reduced to 80% of the initial capacity is assumed to be 50 years under a particular environmental condition set in the rest period.

The one storage battery block11eis added to the four storage battery blocks11a,11b,11c, and11dthat are the minimum necessary to provide the capacity required for the project, and one of the five storage battery blocks11a,11b,11c,11d, and11eis rested in rotation, so that the storage batteries101each having the useful life shorter than the project life171of the storage battery system1can be used over the project life171of the storage battery system1. Furthermore, removal of the storage batteries having long remaining lives from the storage battery system1can be suppressed. The storage batteries101can thus be used generally until the end of the useful lives of the storage batteries101. The effect is particularly significant in a case where the useful life of each of the storage batteries101is close to the project life171of the storage battery system1, and the project life171of the storage battery system1is shorter than twice the useful life of each of the storage batteries101.

4.1 Rest and Operation of Storage Battery Blocks

The storage batteries101of the rest storage battery block11p(hereinafter, rest block storage batteries) are not charged and discharged even in a case where the AC power is input into the storage battery system1from the system19and in a case where the AC power is output from the storage battery system1to the system19. The storage batteries101of each of the operational storage battery blocks11q(hereinafter, operational block storage batteries) are charged and discharged in a case where the AC power is input into the storage battery system1from the system19and in a case where the AC power is output from the storage battery system1to the system19.

In a case where the cells163are high temperature operating secondary batteries, the cells163a,163b,163c, . . . , and163gof each of the rest block storage batteries (hereinafter, rest block cells) are brought to the room temperature during each of the periods172. Meanwhile, the cells163a,163b,163c, . . . , and163gof each of the operational block storage batteries (hereinafter, operational block cells) are brought to a temperature higher than the room temperature during each of the periods172. The temperature higher than the room temperature is approximately 300° C. Since the heating mechanism112for heating the operational block cells is not stopped and supply of the heat retaining power to the heating mechanism112is not interrupted, the operational block cells are heated by the heating mechanism112. On the other hand, supply of heat retaining power to the heating mechanism112for heating the rest block cells is interrupted, thereby to stop the heating mechanism112, and thus, the rest block cells are not heated by the heating mechanism112. Degradation of members constituting the rest block cells caused by bringing the rest block cells to the temperature higher than the room temperature can thereby be suppressed. In a case where the rest block cells are brought to the room temperature, the rest storage battery block11pis hardly degraded, and the equivalent operating time of the rest storage battery block11pcan be considered to be almost zero.

The state of charge of the rest block storage batteries is caused to fall within a set range at the start of each of the periods172. Supplemental charge to supplement natural discharge of the rest block storage batteries is performed to maintain the state of charge of the rest block storage batteries within the set range during each of the periods172. The set range is a range within which degradation of the storage batteries101can be suppressed. Degradation of the rest block storage batteries can thereby be suppressed. In a case where the cells163are lithium-ion batteries, degradation of the storage batteries101is likely to progress when the storage batteries101are at the end of charge, and thus the set range is preferably 80% or less. In a case where the cells163are lithium-ion batteries, the state of charge of the storage batteries101is reduced by approximately 5% per month due to self-discharge, so that periodic supplemental charge to supplement the self-discharge of the rest block storage batteries is performed approximately once a year when the rest block is rested over a long period. In a case where the cells163are nickel-cadmium batteries or nickel metal hydride batteries, the state of charge of the storage batteries101has little influence on the progress of degradation of the storage batteries101. The state of charge of the storage batteries101, however, is reduced by approximately 25% per month due to self-discharge. Supplemental charge to supplement the self-discharge of the rest block storage batteries is thus performed approximately a few times a year to suppress over-discharge of the storage batteries101.

The rest block cells are heated by the heating mechanism112or cooled by the cooling mechanism113during each of the periods172to cause the temperature of the rest block cells163a,163b,163c, . . . , and163gto fall within a set range. The set range is a range within which degradation of the storage batteries101a,101b,101c, . . . , and101jcan be suppressed. In a case where the cells163are lead batteries or lithium-ion batteries, degradation of the storage batteries101a,101b,101c, . . . , and101jprogresses as the temperature of the cells163a,163b,163c, . . . , and163gof each of the storage batteries101a,101b,101c, . . . , and101jincreases, and thus the set range is preferably 20° C. or less. In a case where the cells163are high temperature operating secondary batteries, such as sodium-sulfur batteries, the set range is preferably the room temperature.

The electrical connection164electrically connecting the rest block cells is opened during each of the periods172. Degradation of the cells163a,163b,163c, . . . , and163gcaused by a prolonged flow of a circulating current between circuits electrically connected in parallel, which is caused by a potential difference between the cells163a,163b,163c, . . . , and163gdue to self-discharge of each of the cells163, can thereby be suppressed.

The electrical connection16electrically connecting each of the rest block storage batteries and the measurement system15is opened during each of the periods172. The continuation of micro-discharge of the storage batteries101due to a leakage current flowing from the rest block storage batteries to the measurement system15can thereby be suppressed.

The rest storage battery block11erested during the first period172aof the plurality of periods172a,172b,172c,172d, and172eis installed in the storage battery system1after the start of the first period172a. The rest storage battery block11eis only required to be installed in the storage battery system1before the start of the period172bduring which the rest storage battery block11eis operated. An initial cost of the storage battery system1can thereby be suppressed.

When the rest storage battery block11pis selected, a storage battery block having longer operating time is preferentially selected as the rest storage battery block11p. In a case where the storage battery blocks have substantially the same operating time, a storage battery block including more storage batteries each having a degree of degradation higher than a degree of degradation set for storage batteries is preferentially selected as the rest storage battery block11p. When the degree of degradation of each of the storage batteries is identified, the number of failing cells of each of the storage batteries is also taken into consideration.

A storage battery required to be repaired of the rest storage battery block11pis repaired during each of the periods172. The storage battery required to be repaired is a storage battery determined to be preferably repaired to maintain or improve performance in future operation. The storage battery required to be repaired may be repaired in a state of being installed in the storage battery system1, or may be moved from the storage battery system1to a repair factory to be repaired in the repair factory, and then moved from the repair factory to the storage battery system1. When a certain storage battery is repaired, a cell of the storage battery is replaced with a new cell, for example. The storage battery required to be repaired is moved from the storage battery system1to the repair factory to be repaired in the repair factory, and then moved from the repair factory to the storage battery system1, so that high operating efficiency is enabled in each of the storage battery system1and the repair factory.

At the start of each of the periods172, a first storage battery of each of the operational storage battery blocks11qmay be replaced with a second storage battery of the rest storage battery block11phaving a lower degree of degradation than the first storage battery. The first storage battery is a storage battery having a high degree of degradation. When the degree of degradation of each of the storage batteries is identified, the number of failing cells of each of the storage batteries is also taken into consideration.

An unsound storage battery of each of the operational storage battery blocks11qis replaced with a sound storage battery of the rest storage battery block11p. The unsound storage battery is a storage battery interfering with maintenance of performance of the storage battery system1or having signs of interference with maintenance of performance of the storage battery system1. Performance of the storage battery system1can thereby be maintained and/or improved. Replacement may be temporary or permanent.

While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous unillustrated modifications can be devised without departing from the scope of the invention.