SMA SUNNY ISLAND 8.0H - 9 Battery Management; State of the Battery; Available Battery Capacity; Current State of Charge

9 Battery Management SMA Solar Technology AG
124 SI80H-60H-OffGrid-IA-en-11 Installation Manual
9 Battery Management
9.1 State of the Battery
9.1.1 Available Battery Capacity
The available capacity of a new battery is equal to the rated capacity specified by the battery
manufacturer. During operation of an off-grid system, the available battery capacity decreases for the
following reasons:
• Increasing age of the battery
• Frequent, insufficient charging
• Temperatures below the rated temperature
Currently available battery capacity:
Battery management reports the currently available battery capacity as a percentage of the rated
capacity (SOH). After initial start-up of the off-grid system, battery management requires a few
charging cycles before it can measure the currently available battery capacity with sufficient
accuracy. For this reason, battery management initially uses the rated capacity specified in the QCG.
Automatic correction of the currently available battery capacity:
The available capacity of a battery falls significantly at temperatures of 20°C and below.
Battery management corrects the currently available battery capacity by –1% per °C.
9.1.2 Current State of Charge
Battery management reports the current state of charge (SOC) of the battery.
Estimated error of the state of charge:
The estimated error of the state of charge provides information concerning the accuracy of the current
calculation of the state of charge of the battery.
The deviation between the displayed state of charge and the actual value decreases with every
charging procedure.
9.1.3 Battery Temperature
Battery management continuously monitors the battery temperature. The off-grid inverter adjusts the
reported currently available battery capacity and the charging voltage based on the current
operating battery temperature (see Section 9.2.3"Automatic Temperature
Compensation",page128).
Battery management issues a warning message if one of the following events occurs:
• The battery temperature is within 5°C of the maximum permissible battery temperature.
• The battery temperature is less than − 10°C.