JP7518630B2 - How to operate the storage battery - Google Patents

Description

The present invention relates to a method for operating a storage battery that is installed in parallel with a renewable energy source for the purpose of smoothing the power generated by the renewable energy source.

Power generation systems that use renewable energy, such as solar power generation systems and wind power generation systems, vary in power generation depending on the amount of sunlight in the case of solar power generation and the amount of wind in the case of wind power generation. Therefore, it is known that a storage battery is provided as a power storage means, and when the output power of the renewable energy is insufficient, it is supplemented from the storage battery, and when there is a surplus, the storage battery is charged, thereby smoothing out the output power (Patent Document 1).

JP 2008-295208 A

The capacity of storage batteries installed for the purpose of smoothing the power generated by renewable energy varies depending on the amount of power generated, which varies with the amount of sunlight in the case of solar power generation and the amount of wind in the case of wind power generation. On the other hand, storage batteries used are generally set with an expected lifespan and expected number of cycles. The expected lifespan may be expressed as the number of years obtained by dividing the expected number of cycles by the number of days of operation per year. Since the expected number of cycles is the number of cycles obtained from the results of repeated evaluation of certain charging and discharging conditions, when used for smoothing the power generated by renewable energy that involves irregular charging and discharging, there will be a large variation in the charging and discharging capacity during the certain period. Furthermore, if the charging and discharging capacity during a certain period becomes extremely large, the deterioration of the storage battery will be accelerated, and the expected lifespan of the storage battery may not be met.

The present invention solves these problems, and provides a method for operating a storage battery that is installed in parallel with a renewable energy source for the purpose of smoothing the power generated by the renewable energy source, comprising the steps of:
Set the total discharge capacity in advance,
Assuming that the discharge capacity and the charge capacity of the charge/discharge performed per day are equal, a discharge capacity is set assuming that one cycle of discharging the storage battery from a first state of charge to a second state of charge lower than the first state of charge and then charging the storage battery back to the first state of charge can be performed once per day;
Calculating an expected life span by dividing the total discharge capacity set in advance by the discharge capacity set in advance ;
Calculate the maximum total discharge capacity that can be used during the certain period by dividing the expected life period by a value obtained by dividing the expected life period by a certain period that is equal to or less than half of the expected life period, and then divide the total discharge capacity set in advance by the value obtained by dividing the expected life period by a certain period that is equal to or less than half of the expected life period.
The method for operating a storage battery is characterized in that the storage battery is operated within the range of the maximum total discharge capacity during the certain period .
Furthermore , the method for operating a storage battery of the present invention reduces the maximum total discharge capacity used during a certain period before half of the expected life period has elapsed.

In this way, by determining the maximum total discharge capacity of the storage battery during a certain period and operating within this range, it is possible to suppress variation in the storage battery's capacity usage and to suppress significant deterioration of the storage battery, so that the expected lifespan can be satisfied through gentle deterioration. Furthermore, by gradually reducing the total discharge capacity used during a certain period as operation progresses, a longer lifespan can be provided. Storage batteries deteriorate gently as they are operated, and the discharge capacity that can be taken out of the storage battery also gradually decreases. Therefore, if a storage battery is operated with the same discharge capacity from the beginning to the end of operation, the load on the storage battery will be relatively large at the end of operation, making it more prone to deterioration. By reducing the total discharge capacity used during a certain period as operation progresses, it is possible to suppress deterioration of the storage battery even during the middle to end stages of operation, and provide an even longer lifespan.

According to the present invention, in a method for operating a storage battery installed in parallel for the purpose of smoothing the output power of renewable energy, the maximum total discharge capacity used during a certain period is determined, and the total discharge capacity during the certain period is operated within that range, thereby making it possible to suppress the decrease in the capacity of the storage battery over the long term and to achieve the expected lifespan of the storage battery.

Furthermore, by gradually reducing the total discharge capacity during the certain period as operation progresses, an even longer life can be achieved.

The following describes an embodiment of the present invention. A number of unformed positive and negative plates, which were produced by a known method for producing lead-acid batteries, were stacked alternately through a glass mat made of non-woven glass fiber cloth, and the plates of the same polarity were welded together by strap welding using a burner method on the ears of the plates of the same polarity to produce a plate group. Next, this plate group was placed in a box-shaped polypropylene battery case with an opening, and a lid was welded to the opening by heat sealing. An electrolyte was poured through the inlet of the lid in an amount of about 100% of the saturated electrolyte amount of the plate group, and then charging and discharging were repeated to form the battery case, and if necessary, replenish the electrolyte or charge the battery to produce a 2V-200Ah valve-regulated lead-acid battery.

The manufactured valve-regulated lead-acid batteries were then subjected to accelerated cycle life tests under actual operating conditions. For each test level, one valve-regulated lead-acid battery was connected to the test equipment and evaluated.

The life test conditions were pulse cycle tests simulating wind power generation from wind power generation and solar power generation from solar power generation. In this pulse cycle test, the state of charge (SOC) of the storage battery under the operating conditions was 90%, the depth of discharge was 50%, and the range of SOC of the storage battery was 90% to 40%, and when the battery was discharged from a 90% charged state to a 40% charged state, charging it back to a 90% charged state was counted as one cycle. Charging and discharging are performed at intervals of seconds. When discharging a 90% charged valve-regulated lead-acid battery to a 40% charged state, a current of 1.0C ₁₀ A or less, which is the condition for actual operation, is used, and the battery is discharged at 0.6C ₁₀ A for 1 second and charged at 0.1C ₁₀ A for 1 second is repeated until the state of charge of the valve-regulated lead-acid battery reaches 40%. Then, to return the battery to a 90% charged state, the battery is charged at 0.6C ₁₀ A for 1 second and discharged at 0.1C ₁₀ A for 1 second is repeated. This one cycle took 4 hours. Therefore, up to 6 cycles can be performed in one day. This one cycle was defined as one day's worth. In the case of the valve-regulated lead-acid battery of this embodiment, 1C ₁₀ A is 200A.

The total discharge capacity that can be extracted when the pulse cycle test is repeated is a value obtained from a previous evaluation, and the value was 511 kAh. In this embodiment, the discharge capacity of a 200 Ah lead-acid battery in one cycle of the pulse cycle test is 140 Ah (the discharge amount in two hours until the state of charge of the valve-regulated lead-acid battery is 40% by discharging at 0.6 C ₁₀ A for one second and charging at 0.1 C ₁₀ A for one second is 120 Ah, and the discharge amount in two hours until the state of charge of the valve-regulated lead-acid battery is 90% by charging at 0.6 C ₁₀ A for one second and discharging at 0.1 C ₁₀ A is 20 Ah, totaling 140 Ah), and 511 kAh divided by 140 Ah is 3650, which corresponds to 10 years if charging and discharging once a day, and this is the expected lifespan. This total discharge capacity divided by the expected lifespan of 10 years by the fixed period of 1 year is 10, so dividing the total discharge capacity by this gives 511 kAh ÷ 10 = 51.1 kAh. This value is the maximum total discharge capacity that can be used in one year, and in use over a period equivalent to one year (365 days), the battery was discharged at 0.6 C ₁₀ A for 1 second to achieve this maximum total discharge capacity of 51.1 kAh (100%), and charged at 0.1 C ₁₀ A for 1 second, repeating this for 2 hours until the state of charge of the valve-regulated lead-acid battery reached 40%, and then charged at 0.6 C ₁₀ A for 1 second, discharged at 0.1 C ₁₀ A for 1 second, repeating this for 2 hours until the state of charge of the valve-regulated lead-acid battery reached 90%, forming one day's worth of testing, and a test equivalent to 10 years was conducted assuming one year is 365 days. Since the discharge capacity and charge capacity in the pulse cycle test are equal, the state of charge (SOC) drops slightly as the cycle test continues due to the effects of charge/discharge efficiency and the self-discharge amount of the storage battery itself, and the storage battery voltage reaches the lower limit voltage of 1.8V. If the voltage of the storage battery drops to 1.8V during the test, the storage battery is fully charged once, and then the state of charge (SOC) is adjusted to 90% and the test is resumed. The storage battery that has been in the storage battery for one year was put into the capacity test. In the capacity test, the storage battery voltage was discharged to 1.8V, and the capacity was taken as the discharge capacity. This was divided by the rated capacity to obtain the ratio to the rated capacity, and if the value fell below 70%, it was determined that the storage battery had reached the end of its life. If it was greater than this, the cycle test was continued. As a result of the test, as shown in Test 1 of the Test Lead-Acid Battery in Table 1, the discharge capacity of the valve-regulated lead-acid battery after the expected age of 10 years was 78% of the rated discharge capacity. This result satisfied the expected life.

Next, the battery was operated at the maximum total discharge amount mentioned above until the fourth year, then at 90% of the maximum total discharge amount from the fifth to seventh years, and then at 80% of the maximum total discharge amount from the eighth to tenth years. As a result, the discharge capacity of the valve-regulated lead-acid battery after the test was 93% of the rated discharge capacity, as shown in Test 2 of the test lead-acid battery in Table 1. This is a result that satisfies the expected lifespan, and is also a result that suggests that the battery will have an even longer lifespan. Note that the operation at 90% of the maximum total discharge amount means that after the start of the fifth year, the discharge was stopped when the total discharge capacity reached 90%, or 45.9 kAh, and the valve-regulated lead-acid battery was returned to a charged state of SOC 90% to end the fifth year. After full charging and capacity testing, the state of charge (SOC) was adjusted to 90% and the test was resumed. Operation at 80% of the maximum total discharge amount means that from the start of the eighth year onwards, when the total discharge capacity reached 80%, operation was stopped as described above, and thereafter testing was carried out in the same manner as described above.

On the other hand, when the battery was operated at 76.6 kAh (150%), which is 1.5 times the maximum total discharge capacity, during use for a period equivalent to one year, and a test equivalent to 10 years was also conducted, the discharge capacity of the valve-regulated lead-acid battery was 65% of the rated discharge capacity at the end of the sixth year, as shown in Test 3 of the test lead-acid battery in Table 1, and the expected life was not satisfied. In this case, the battery was discharged at 0.8 _C10 A for one second and charged at 0.3 _C10 A for one second, which was repeated for two hours to bring the state of charge of the valve-regulated lead-acid battery to 40%, and then charged at 0.75 _C10 A for one second and discharged at 0.25 _C10 A for one second to return the battery to a state of charge of 90%, which was repeated for two hours to make one day's charge, and this was repeated for a period equivalent to six years.

Furthermore, in the case of operation alternately at 150% and 50% of the maximum total discharge amount every year, the discharge capacity of the valve-regulated lead-acid battery after the test was 67% of the rated discharge capacity, which also failed to satisfy the expected lifespan, as shown in Test 4 of the test lead-acid battery in Table 1. In this case, the total discharge capacity was the same as in Test 1, but it is believed that the variation in discharge capacity caused the maximum total discharge capacity to exceed 100% for a certain period of time, accelerating deterioration. In this case, the 150% operation was the same as above, and the 50% operation was repeated for 2 hours, discharging at 0.6 _C10 A for 1 second and charging at 0.1 _C10 A for 1 second, until the state of charge of the valve-regulated lead-acid battery reached 40%, and then, to return to a 90% state of charge, charging at _{0.6 C10} A for 1 second and discharging at 0.1 C10 A for 1 second was repeated for 2 hours, and when the total discharge capacity reached 25.5 kAh, which is 50%, the discharge was stopped and the valve-regulated lead-acid battery was returned to a 90% state of charge again, completing the one-year operation.

Next, assuming a fixed period of one month, dividing the expected life of 10 years by one month gives 120, which gives 4.2 kAh when dividing the total discharge capacity by this. This is set as the maximum total discharge capacity for one month, and a test equivalent to 10 years was conducted with the monthly discharge capacity set to this maximum total discharge capacity (100%). As a result, the discharge capacity of the valve regulated lead-acid battery after the test was 86% of the rated discharge capacity, as shown in Test 5 of the Test Lead-Acid Battery in Table 1. This is a result that satisfies the expected life. In this case, the operation was to discharge at _0.6C10A for 1 second and charge at _0.1C10A for 1 second for 2 hours to bring the state of charge of the valve-regulated lead-acid battery to 40%, then charge at _0.6C10A for 1 second and discharge at _0.1C10A for 1 second for 2 hours to return it to a 90% state of charge, and charge and discharge were performed for the number of days equivalent to the number of days in a month according to the calendar, and if the total discharge capacity reached 4.2kAh before the corresponding number of days in each month was reached, the charge and discharge was stopped at that point and the valve-regulated lead-acid battery was returned to a 90% state of charge again to complete the month. The charge and discharge conditions of the test were the same as those of Test 1, but the number of recovery charges to restore the state of charge to 100% is thought to be the reason why the discharge capacity in the 10th year was larger than that of Test 1. Generally, when a lead-acid battery is operated in a PSOC (partial charge) state, lead sulfate, a discharge product, accumulates in the active material, which then coarsens. This deterioration factor, called sulfation, is not eliminated even when the battery is charged, and the capacity of the battery decreases, eventually reaching the end of its life. In order to prevent this, it is important to periodically perform a recovery charge to refresh the active material by fully charging the battery from the PSOC state. If the fixed period is one month, the number of recovery charges performed immediately before the capacity test is greater than the fixed period of one year, which is why we believe that sulfation was suppressed.

Assuming the fixed period is 5 years, dividing the expected lifespan of 10 years by 5 years gives a value of 2, and dividing the total discharge capacity by this gives a value of 255.5 kAh, which is the maximum total discharge amount over 5 years. A test equivalent to 10 years was conducted with the discharge capacity every 5 years set to this maximum total discharge amount (100%). As a result, the discharge capacity of the valve regulated lead-acid battery after the test was 71% of the rated discharge capacity, as shown in Test 6 of the test lead-acid battery in Table 1. This is a result that satisfies the expected lifespan. In this case, the operation is as follows: for the period corresponding to the first year of the five years, discharge at 0.8 _C10A for 1 second and charge at 0.3 _C10A for 1 second, and repeat this for two hours to bring the state of charge of the valve-regulated lead-acid battery to 40%, then charge at 0.75 _C10A for 1 second and discharge at 0.25 _C10A for 1 second to bring it back to a 90% state of charge, repeating this for two hours to make up for one day's worth of charge, and repeating this for a period corresponding to one year; for the period corresponding to the second year, discharge at 0.25 _C10A for 1 second and charge at _{0.1 C10A} for 1 second, and repeating this for two hours to make up for one day's worth of charge, _and This was repeated for two hours to make up one day's worth of charge, and this was repeated for a period equivalent to one year. For the period equivalent to the third year, the same operations were performed as for the first year, for the period equivalent to the fourth year, the same operations as for the second year, _and for the period equivalent to the fifth year, a cycle of discharging at _0.6C10A for one second and charging _{at 0.1C10A} for one second was repeated for two hours to make up one day's worth of charge, and this cycle was repeated for a period equivalent to one year.

If the fixed period is set to 6 years, and the expected lifespan of 10 years is divided by 6 years, the value is 1.6, and dividing the total discharge capacity by this gives 319.3 kAh, which is the maximum total discharge amount over 6 years. A test equivalent to 10 years was conducted with the total discharge capacity every 6 years being this maximum total discharge capacity (100%), and as a result, the discharge capacity of the lead-acid battery after the test was 68% of the rated discharge capacity as shown in Test 7 of the test lead-acid battery in Table 1, and the expected lifespan could not be satisfied. In addition, since there are only 4 years remaining from the 7th year onwards, the maximum total discharge capacity is 67% (4/6).
In this case, the operation is as follows: in the first year, discharge at 0.8 _C10 A for 1 second, charge at 0.3 _C10 A for 1 second, and repeat this for 2 hours to bring the state of charge of the valve-regulated lead-acid battery to 40%, then charge at 0.75 _C10 A for 1 second and discharge at 0.25 _C10 A for 1 second to return it to a 90% state of charge, repeating this for 2 hours for one day, and repeating this for a period equivalent to one year; in the second year, discharge at 0.25 _C10 A for 1 second and charge at 0.1 _C10 A for 1 second, repeating this for 2 hours to bring the state of charge of the valve-regulated lead-acid battery to 75%, then charge at 0.25 C10 A for 1 second and discharge at _{0.1 C10} A for 1 second to return it to a 90% state of charge. This was repeated for a period equivalent to one year, and from the third year onwards, the first and second years were repeated once every year. In all tests, if the battery voltage fell below 1.8V, a recovery charge was performed to fully charge the battery.

From the results of tests 1 to 4 of the test lead-acid battery in Table 1, it was found that the expected life can be satisfied by operating within the maximum discharge capacity range during a certain period of time, but that the expected life cannot be satisfied if this is exceeded. Furthermore, from the results of test 2, it was found that the life can be extended by gradually reducing the total discharge capacity used during a certain period of time over time. From test 5, it was found that the minimum period of the certain period of time can be one month, rather than one year, without any problem, and the expected life can be satisfied without any problem. From these results, it is easy to imagine that there is no problem with operating the certain period in days.
The results of tests 6 and 7 show that the expected lifespan can be satisfied by setting the certain period to half or less of the expected lifespan, but that the expected lifespan cannot be satisfied if this period is exceeded.

As described above, the method of operating a storage battery installed alongside the battery for the purpose of leveling out the power generated by renewable energy sources is to determine the maximum total discharge capacity to be used during the certain period of time by repeatedly charging and discharging the battery under the conditions in which the battery is operated, and dividing the total discharge capacity that can be extracted during the expected life span by a value obtained by dividing the total discharge capacity by a certain period of time that is equal to or less than half of the expected life span. By operating the battery within the range of the maximum total discharge capacity during the certain period of time, the expected life span of the storage battery can be achieved. Furthermore, by gradually decreasing the total discharge capacity during the certain period of time over time, it is possible to achieve an even longer life span.

In the above embodiment, the case where only one valve-regulated lead-acid battery is used is shown, but the same effect can be obtained when multiple batteries are connected in series and parallel, and further, the same effect can be obtained when so-called liquid-type lead-acid batteries that contain a large amount of electrolyte are used as the batteries. Furthermore, it is believed that the same effect can be obtained when other types of secondary batteries, such as alkaline batteries, are used.

In this way, the method of operating a storage battery installed alongside the battery for the purpose of leveling out the power generated by renewable energy sources is to determine the maximum total discharge capacity to be used during the certain period of time by repeatedly charging and discharging the storage battery during the expected life span, divided by a value obtained by dividing the total discharge capacity by a certain period of time that is less than half of the expected life span, and by operating the battery within the range of the maximum total discharge capacity during the certain period of time, thereby achieving the expected life span of the storage battery. Furthermore, by gradually reducing the total discharge capacity used during the certain period of time as operation progresses, it is possible to extend the life span of the battery.

Claims (3)

In a method of operating a storage battery installed in parallel for the purpose of smoothing the power generated by renewable energy,
Set the total discharge capacity in advance,
Assuming that the charging and discharging performed per day have a discharge capacity equal to the charge capacity, the discharge capacity is set assuming that one cycle of discharging the storage battery from a first state of charge to a second state of charge lower than the first state of charge and then charging the storage battery back to the first state of charge can be performed once per day;
Calculating an expected life span by dividing the total discharge capacity set in advance by the discharge capacity set in advance ;
Calculate the maximum total discharge capacity that can be used during the certain period by dividing the expected life period by a value obtained by dividing the expected life period by a certain period that is equal to or less than half of the expected life period, and then divide the total discharge capacity set in advance by the value obtained by dividing the expected life period by a certain period that is equal to or less than half of the expected life period.
A method for operating a storage battery, the method comprising: operating the storage battery within the range of the maximum total discharge capacity during the certain period. 2. The method for operating a storage battery according to claim 1, further comprising the step of: reducing the maximum total discharge capacity used during a certain period before half of the expected life period has elapsed. 3. The method for operating a storage battery according to claim 1 or 2, wherein the storage battery is a lead-acid battery.