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In photovoltaic applications the battery will be exposed to a large number of shallow cycles but at different states of charge. The cells or batteries shall therefore comply with the requirements of the test below, which is a simulation of the photovoltaic energy system operation.
The cycle endurance test is an accelerated simulation in extreme conditions of the battery operation in a photovoltaic energy system and shall be conducted by submitting the cells or monobloc batteries to a period of 150 cycles (50 cycles with the phase A and 100 cycles with the phase B).
Test samples shall be set up in accordance with the applicable standards listed in 7.2 after control of the capacity test in 8.1.
Start the test with the battery fully charged. Bring the battery to a temperature of 40 °C ± 3 °C and stabilize for 16 h. Maintain the battery at 40 °C ± 3 °C throughout the test.
8.4.1 Phase A: shallow cycling at low state of charge
l Lead-acid batteries
a) Discharge the battery with a current I10 (A) during 9 h or until 1,75 V/cell is reached.
b) Recharge 3 h with a current 1,03 I10 (A)
c) Discharge 3 h with a current I10 (A).
l Nickel-cadmium batteries
a) Discharge the battery with a current It /10 (A) during 9 h or until 1,00 V/cell is reached.
b) Recharge 3 h with a current 1,03 It /10 (A)
c) Discharge 3 h with a current It /10 (A)
For both battery types, repeat b) and c) 49 times. Recharge the battery to the fully charged condition according to the manufacturer recommendations and continue the phase B. Phase A is summed up in Table 6.
Table 6 – Phase A – Shallow cycling at low state of charge
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Discharging time
h
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Charging time
h
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Lead-acid current
A
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Nickel-cadmium current
A
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a)
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9
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I10 (A)
(or stopping at 1,75 V/cell)
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It /10 (A)
(or stopping at 1,00 V/cell)
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b)
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3
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1,03 I10 (A)
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1,03 It /10 (A)
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c)
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3
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I10 (A)
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It /10 (A)
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Repeat b) to c) 49 times and continue to phase B
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8.4.2 Phase B: shallow cycling at high state of charge
l Lead-acid batteries
a) Discharge the battery for 2 h with a current 1,25 I10 (A)
b) Recharge 6 h with a current I10 (A). The charge voltage shall be limited to 2,40 V/cell, unless otherwise specified by the manufacturer.
l Nickel-cadmium batteries
a) Discharge the battery for 2 h with a current 1,25 It /10 (A)
b) Recharge for 6 h with a current It /10 (A). The charge voltage shall be limited to 1,55 V/cell unless otherwise specified by the manufacturer.
For both batteries, repeat a) and b) 99 times and then perform a capacity determination according to 8.4.3. Phase B is summed up in Table 7.
Table 7 – Phase B – Shallow cycling at high state of charge
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Discharging time
h
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Charging time
h
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Lead-acid current
A
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Nickel-cadmium current
A
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a)
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2
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1,25 I10 (A)
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1,25 It /10 (A)
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b)
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6
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I10 (A)
(charge voltage limited to
2,40 V/cell unless otherwise
specified by the manufacturer)
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It /10 (A)
(charge voltage limited to
1,55 V/cell unless otherwise
specified by the manufacturer )
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Repeat a) to b) 99 times
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8.4.3 Capacity check
After the phase B, the battery is cooled down to the temperature defined in the relevant standard as described in 7.2 and stabilized at this value for 16 h. The capacity test (C10 for lead-acid batteries and C5 for nickel-cadmium batteries) is carried out according to the relevant standard as described in 7.2.
8.4.4 End of test condition
– Capacity is checked after each period of 150 cycles (phases A + B).
– The value of actual capacity determined in 8.4.3 shall be recorded.
– The cycle life shall be expressed in number of 150 cycle (A+B) sequences completed.
The test is finished:
l During the phase A: when the cell voltage measured in discharge is lower than
1,5 V/cell for lead acid batteries and 0,8 V/cell for nickel-cadmium batteries.
l After the phase B: when the checked capacity measured in 8.4.3 is lower than 80 % of the rated capacity.
8.4.5 Water consumption of flooded battery types and cells with partial gas
recombination
During the cycle endurance test, vented type cells or monoblocs may be topped up with water. The amount of water added shall be measured and reported.
8.4.6 Requirements
The number of complete cycle sequences (150 cycles) achieved at the end of the test shall be not less than the value stated by the manufacturer.
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