The depth of discharge has a great influence on the cycle life of the battery. If the battery is discharged deeply, the cycle life will be shortened. Because deep discharge of batteries with the same rated capacity means that they are often charged and discharged with high current, and can not be recharged in time when they are discharged with high current or under-voltage, resulting in large sulfate particles and inadequate utilization of plate active substances. The actual capacity of batteries will gradually decrease over a long period of time, which will affect the normal operation of batteries. Because the solar photovoltaic power generation system is not easy to overcharge, the main reason for the battery failure and life shortening in the solar photovoltaic system is the long-term power deficit.

Two

Discharge rate

It is generally stipulated that the capacity of 20-hour discharge rate is the rated capacity of storage battery. If the discharge rate is lower than the prescribed hour, the battery capacity can be higher than the rated value; if the discharge rate is higher than the prescribed hour, the discharge capacity is smaller than the rated capacity of the battery, and the discharge rate also affects the terminal voltage value of the battery. When the battery discharges, the electrochemical reaction current preferentially distributes on the surface nearest to the main solution, resulting in the formation of lead sulfate on the surface of the electrode and blocking the porous electrode. When the discharge current is high, the above problems become more prominent, so the larger the discharge current, the smaller the capacity of the battery, and the faster the drop of terminal voltage, that is to say, the discharge termination voltage decreases with the increase of discharge current. On the other hand, it is not the lower the discharge rate, the better. Some studies show that long-term too small discharge rate will significantly increase the amount of lead sulfate molecule, resulting in plate bending and active material shedding, and also reduce the life of the battery.

Three

External temperature is too high

The rated capacity of batteries refers to the value of batteries at 25 C. It is generally considered that the working temperature of VRLA batteries is ideal in the range of 20 30 C. When the temperature of the battery is too low, the capacity of the battery decreases, because the electrolyte can not react well with the active material of the plate at low temperature. Reduced capacity will not meet the expected backup time and keep within the prescribed discharge depth, which can easily lead to battery overdischarge. From the external parameters of the battery, the voltage has a great relationship with the temperature. The voltage drop of the single cell battery decreases by 3 mV every time the temperature rises by 1 C. That is to say, the voltage of lead-acid batteries has a negative temperature coefficient, whose value is – 3mV /. In the same way, the increase of ambient temperature is easy to cause battery overdischarge. High temperature will also lead to the loss of water and thermal runaway phenomenon of storage battery. Temperature is a major factor affecting the normal operation of storage battery. In solar photovoltaic system, the controller is generally required to have temperature compensation function.

One

Visually inspect the cleanliness of the outer surface of the battery, the completeness of the shell and cover, the appearance of the battery with or without drum deformation, and the battery with or without overheating marks.

Two

The environmental temperature of the battery system and the average temperature of the system can be recorded at the unified detection point of the battery system every quarter. When the temperature is below or above 25 C, the temperature control system should be adjusted. If the temperature control system is not installed, the floating charge voltage should be adjusted.

Three

Measure and record the total floating charge voltage at the battery end, compare with the display value of the panel meter, and find out the cause of the difference in time to correct it.

Four

Measuring and recording the floating charge voltage of each battery in the system should fluctuate within a certain range under normal conditions. If abnormal is found, the causes should be found and corrected.

Five

To do restorative discharge test, discharge with false load or actual load, i. e. cut off the power supply and supply with battery. If it is found that the capacity of individual batteries is on the low side, the batteries will be charged equally, but the capacity can not be restored after equalized charging, the batteries with too low capacity should be replaced.