19.3.3
Figure 19.23: A simple model for (a) the equivalent circuit and; (b) the I-V characteristics of a battery.
Because of R i , the voltage V BB will differ from V OC-BB . In fact, V BB is also dependent
on the current I BB flowing through the battery, as seen by the equation
Note that we use the convention that I BB is positive when the battery is charged and
negative when it is discharged. The resulting I-V characteristics of the battery bank are
illustrated in Figure 19.23 (b). In this figure, the charging regime and the discharging
regime are depicted.
The current I BB determines the power loss in the battery,
This power is always lost, irrespective of the sign of I BB , and hence irrespective of whether
the battery is charged or discharged.
Battery parameters
We will now discuss some parameters that are used to characterize batteries.
Voltage
First, we will discuss the voltage rating of the battery. The voltage at which the battery is
rated and is supposed to operate is the nominal voltage. The so-called solar batteries or
lead acid batteries for PV applications are usually rated at 12 V, 24 V or 48 V. The actual
voltage of PV systems may differ from the nominal voltage. This mainly depends on the
SoC and the temperature of the battery.
Capacity
When talking about batteries, the term capacity refers to the amount of charge that the
battery can deliver at the rated voltage. The capacity is directly proportional to the amount
of electrode material in the battery. This explains why a small cell has a lower capacity
than a large cell that is based on the same chemistry, even though the open circuit voltage
Figure 19.23: A simple model for (a) the equivalent circuit and; (b) the I-V characteristics of a battery.
Because of R i , the voltage V BB will differ from V OC-BB . In fact, V BB is also dependent
on the current I BB flowing through the battery, as seen by the equation
Note that we use the convention that I BB is positive when the battery is charged and
negative when it is discharged. The resulting I-V characteristics of the battery bank are
illustrated in Figure 19.23 (b). In this figure, the charging regime and the discharging
regime are depicted.
The current I BB determines the power loss in the battery,
This power is always lost, irrespective of the sign of I BB , and hence irrespective of whether
the battery is charged or discharged.
Battery parameters
We will now discuss some parameters that are used to characterize batteries.
Voltage
First, we will discuss the voltage rating of the battery. The voltage at which the battery is
rated and is supposed to operate is the nominal voltage. The so-called solar batteries or
lead acid batteries for PV applications are usually rated at 12 V, 24 V or 48 V. The actual
voltage of PV systems may differ from the nominal voltage. This mainly depends on the
SoC and the temperature of the battery.
Capacity
When talking about batteries, the term capacity refers to the amount of charge that the
battery can deliver at the rated voltage. The capacity is directly proportional to the amount
of electrode material in the battery. This explains why a small cell has a lower capacity
than a large cell that is based on the same chemistry, even though the open circuit voltage