29/10/2026
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Ucu Tech class
Ucu Tech class
29/10/2026 lesson👇
Depth of Discharge (DOD) of Solar Battery.
DOD is a measure of how deeply a solar battery is discharged. It refers to how much capacity will be withdrawn from a battery. Most solar battery (lead acid battery) are design to be discharge between 50-80 percent DOD. When a battery is 100% full, the DOD is 0% Ampere hours removed from a fully charged battery are expressed as a percentage of the rated capacity. If 25Ah is removed from a 100Ah battery, its depth of discharge is 25% and the battery state of charge (SOC) is 75%.
Solar Battery life is directly related to how deep a battery is cycled. For example, if a solar battery DOD is maintained at 40%, that is SOC of 60% daily; it will last twice longer than when maintained at 80% DOD, that is 20% SOC
In many battery types, the full energy stored cannot be withdrawn ie the battery cannot be fully discharged without causing serious and often irreparable damage to the cells of the battery. Lead acid batteries should never be completely discharged, else there will be negative effect on the cells of the battery. Some deep cycle batteries can survive this condition but the voltage will continually decrease. NiCad batteries, on the other hand, can be totally discharged without harming the battery and still hold their voltage. After fully discharging NiCad battery, it may reveres it polarity potentially harming the electrical load he electric
It is important to always check the manufacturers recommended DOD for any battery.
Shallow cycling, that is DOD between 10 to 20 percent is the best way to maintain your solar battery.
There are many advantages attached when a solar battery is shallow cycled:
1. Solar batteries that are shallow cycled will have a longer life span, if a battery is only cycled to 10 percent DOD, it will last about 5 times longer than a solar battery cyded to 50 percent.
2. A reserved Ah capacity is designed into the battery to be use during days of autonomy or worst weather condition
If a battery is shallow cycled for only 25 percent DOD, it will be expected to last at least 4000 cycles. On the other hand, if a battery is cycled for 80 percent DOD, it will last for 1500 cycles. If one battery cycle is equivalent to one day, the battery that is shallow cycled will last approximately 10.95 years whereas the deeply cycled battery would last for 4.12 years.
If discharging is below the DOD given by the manufacturer, it will result in
👉Formation of hard sulfation (Crystalized sulphate): Sulfation is the chemical reaction between sulphuric acid and the lead plates within a battery. It happens when a battery is discharged. Batteries kept in a poor state of charge develop a build-up of lead sulphate crystals, which permanently damages a battery. This is called sulphation. To reduce sulfation, it is important to recharge a battery and return it to a full state of charge as soon as possible. If the lead sulphate crystal harden, a battery takes longer to charge and can never obtain a state of charge of 100%
👉Plate Bucking: Extreme over discharging leads to physical deformation of the grids that contain the active material and this process is called buckling
👉Over discharging also leads to Stratification
