For designing off-grid PV system it’s a must. Controllers should buy externally or integrated into inverters. The main missions both of them are; charge the battery or battery bank with an optimum process and protect PV panels reverse current during the nights. There is also a DC power pin that is an opportunity for DC loads to supply power constantly.
The goal is the charge the batteries but the methods that used are different.MPPT charge controllers seem like on grid inverters ( most of them have MPP tracker) the aim is continuous to find out the maximum power point (maximum producible energy ) less energy is not satisfied MPPT device, on the other hand, price little expensive.
PWM charge controllers cheap alternative but they are not always insist to search maximum power. Batteries connect to the system and the device decides the operating voltage (lots of devices are compatible with 12/24 V design). After that PWM consider all possible loses and specify charge voltage This corresponding value (intersection point) on the PV production current graph determine the operating power point of the PWM charge controller. Pv power increase not so much important at that instant if we observe results it will be the same as before. Total production comparison shows us %15-20 less than MPPT devices.
MPPT specify charge voltage automatically and always check the PV input values, that means if high voltage comes from PV panels (more than charge voltage) device decrease the voltage and increase the current that gives us more efficient power output, in other words, charge batteries faster.
The below graph explain the reaction of the two charge controllers at the same 24V battery bank ( DC power supply set constant current 1A) MPPT device is more efficient you see the more power yellow zone.
Let’s talk about the scenarios about a system that does not use charge controllers. Such as what happens if connect PV panels directly to the battery? A battery should be charged up but when it’s full nobody informs PV panels that means they continue to charge the battery, this is not good for battery health, battery voltage increase and increase over up the limit of it, in this case, the damage is possible.
On the other hand, most of the PV panels do not include blocking diodes that means stored energy can able to flow back to the PV panels during the nights. Charge controllers design to prevent all these negative events also they give chance to see battery fill factor via LCD or LED indicators.
Sum up Solar Energy is a long-term investment, for sure PWM should be a possibility and not the wrong choice, however, buying MPPT charge controller or inverter which is equipped MPPT will be the more efficient way.
Teknik Destek Mühendisi