generated by the PV array, such that the battery is heavily discharged. Over discharging
the battery has a detrimental effect on the cycle lifetime, as discussed above. The charge
controller prevents the battery from being over discharged by disconnecting the battery
from the load.
For optimal performance, the battery voltage has to be within specified limits. The
charge controller can help maintain an allowed voltage range in order to ensure a healthy
operation. Further, the PV array will have its V MPP at different levels, based on the
temperature and irradiance conditions. Some charge controllers perform an appropriate
voltage regulation to ensure the battery operates in the specified voltage range, while the
PV array is operating at the MPP.
However, most simple charge controllers available on the market have no MPP
tracker included. In this case the battery will determine the voltage at which the module is
operated. In is then important to size the module such that it fits the battery. For example,
for systems that are connected to a 12 V battery, crystalline silicon panels with 36 cells in
series are often used, while for 24 V batteries modules with 72 cells connected in series
are appropriate.
As we have seen above, certain C-rates are used as battery specifications. The higher
the charge/discharge rates, the lower the coulombic efficiency of the battery. The optimal
charge rates, as specified by the manufacturer, can be reached by manipulating the current
flowing into the battery. A charge controller that contains a proper current regulator is also
able to control the C-rates. Finally, the charge controller can impose limits on the maximal
currents flowing into and out of the battery.
If no blocking diodes are used, it is even possible that the battery can ‘load’ the PV
array, when it is operating at a very low voltage. This means that the battery will impose a
forward bias on the PV modules and make them consume the battery power, which leads
to the solar cells heating up. Traditionally, blocking diodes are used at the PV panel or
string level to prevent this back discharge of the battery through the PV array. However,
this function is also easily integrated into the charge controller.
We distinguish between series and shunt controllers, as illustrated in Figure
reffig:comcharge-controller. In a series controller, overcharging is prevented by
disconnecting the PV array until a particular voltage drop is detected, at which point the
array is connected to the battery again. On the other hand, in a parallel or shunt controller,
overcharging is prevented by short-circuiting the PV array. This means that the PV
modules work under short circuit mode, and that no current flows into the battery. These
topologies also ensure over discharge protection using power switches for the load
connections which are appropriately controlled by the charge controller algorithms.
the battery has a detrimental effect on the cycle lifetime, as discussed above. The charge
controller prevents the battery from being over discharged by disconnecting the battery
from the load.
For optimal performance, the battery voltage has to be within specified limits. The
charge controller can help maintain an allowed voltage range in order to ensure a healthy
operation. Further, the PV array will have its V MPP at different levels, based on the
temperature and irradiance conditions. Some charge controllers perform an appropriate
voltage regulation to ensure the battery operates in the specified voltage range, while the
PV array is operating at the MPP.
However, most simple charge controllers available on the market have no MPP
tracker included. In this case the battery will determine the voltage at which the module is
operated. In is then important to size the module such that it fits the battery. For example,
for systems that are connected to a 12 V battery, crystalline silicon panels with 36 cells in
series are often used, while for 24 V batteries modules with 72 cells connected in series
are appropriate.
As we have seen above, certain C-rates are used as battery specifications. The higher
the charge/discharge rates, the lower the coulombic efficiency of the battery. The optimal
charge rates, as specified by the manufacturer, can be reached by manipulating the current
flowing into the battery. A charge controller that contains a proper current regulator is also
able to control the C-rates. Finally, the charge controller can impose limits on the maximal
currents flowing into and out of the battery.
If no blocking diodes are used, it is even possible that the battery can ‘load’ the PV
array, when it is operating at a very low voltage. This means that the battery will impose a
forward bias on the PV modules and make them consume the battery power, which leads
to the solar cells heating up. Traditionally, blocking diodes are used at the PV panel or
string level to prevent this back discharge of the battery through the PV array. However,
this function is also easily integrated into the charge controller.
We distinguish between series and shunt controllers, as illustrated in Figure
reffig:comcharge-controller. In a series controller, overcharging is prevented by
disconnecting the PV array until a particular voltage drop is detected, at which point the
array is connected to the battery again. On the other hand, in a parallel or shunt controller,
overcharging is prevented by short-circuiting the PV array. This means that the PV
modules work under short circuit mode, and that no current flows into the battery. These
topologies also ensure over discharge protection using power switches for the load
connections which are appropriately controlled by the charge controller algorithms.