19.4.1
Figure 19.26: Basic wiring scheme of (a) a series; and (b) a shunt charge controller.
As we have seen above, temperature plays a crucial role in the functioning of the
battery. Not only does temperature affect the lifespan of the battery, but it also changes its
electrical parameters significantly. Thus, modern charge controllers have a temperature
sensor included, which is attached to the battery back. This sensor allows the charge
controller to adjust the electrical parameters of the battery, such as the operating voltage,
to the temperature. The charge controller thus keeps the operating range of the battery
within the optimal range of voltages.
Charge controllers for lead acid batteries used for
PV applications
The role of the overcharge protection part of controllers will be discussed in more detail
now for the case of lead acid batteries. A typical mode of operation of an autonomous PV
system is that the battery will be discharged partly during the night and will be charged
again during the day. High states of charges will be reached after noon. This implies that
the time available subsequently in the afternoon to charge the battery fully is limited, or in
other words, the time available to convert all the lead sulphate into lead and lead dioxide is
limited. This conversion is crucial because if lead sulphate stays too long in the
amorphous state it will change into polycrystalline lead sulphate which cannot then be
changed into lead and lead oxide. In order to convert all the amorphous lead sulphite into
lead and lead oxide in the short time available, sufficient overvoltage is required. This
voltage, however, is not allowed to be too high for too long a period, otherwise voltageinduced corrosion of the plates takes place.
In practice, during charging of the batteries, the battery voltage will rise gradually in
the course of a day. A good controller will switch off the array current once a certain
voltage level is reached and will switch the array on again at a slightly lower voltage.
Keeping the voltage within a narrow voltage band close to the gassing voltage, the
Figure 19.26: Basic wiring scheme of (a) a series; and (b) a shunt charge controller.
As we have seen above, temperature plays a crucial role in the functioning of the
battery. Not only does temperature affect the lifespan of the battery, but it also changes its
electrical parameters significantly. Thus, modern charge controllers have a temperature
sensor included, which is attached to the battery back. This sensor allows the charge
controller to adjust the electrical parameters of the battery, such as the operating voltage,
to the temperature. The charge controller thus keeps the operating range of the battery
within the optimal range of voltages.
Charge controllers for lead acid batteries used for
PV applications
The role of the overcharge protection part of controllers will be discussed in more detail
now for the case of lead acid batteries. A typical mode of operation of an autonomous PV
system is that the battery will be discharged partly during the night and will be charged
again during the day. High states of charges will be reached after noon. This implies that
the time available subsequently in the afternoon to charge the battery fully is limited, or in
other words, the time available to convert all the lead sulphate into lead and lead dioxide is
limited. This conversion is crucial because if lead sulphate stays too long in the
amorphous state it will change into polycrystalline lead sulphate which cannot then be
changed into lead and lead oxide. In order to convert all the amorphous lead sulphite into
lead and lead oxide in the short time available, sufficient overvoltage is required. This
voltage, however, is not allowed to be too high for too long a period, otherwise voltageinduced corrosion of the plates takes place.
In practice, during charging of the batteries, the battery voltage will rise gradually in
the course of a day. A good controller will switch off the array current once a certain
voltage level is reached and will switch the array on again at a slightly lower voltage.
Keeping the voltage within a narrow voltage band close to the gassing voltage, the