How to Choose a Solar Charge Controller

Charge Controller: PWM or MPPT?

How to Choose a Solar Charge Controller

Do you need a charge controller for your off-grid solar power system but you don't know which one to choose? The market offers different types of solar charge controllers at different prices. But which one is the most suitable for you?

It's therefore very important to know their characteristics and their principle of operation in order to make a safe and lasting purchase. For this reason, MPPTSOLAR has selected two charge controllers for solar panels, one PWM and the other one MPPT, and decided to create this informative article to help you choose the right charge controller for your solar power system based on the type of panels and the battery you want to install.

If during the design of your solar power system you decided to choose certain panels instead of others, it is good to know that this choice may suggest one charge controller instead of another. The PWM and MPPT charge controllers that we will use in this comparison are manufactured by the same company, the German company Steca Solar.

Where to use an MPPT controller and where to use a PWM?

As we said, the choice of charge controller technology depends both on the type of panels we have (or want to install) and on the battery bank. The PWM charge controller normally costs less than an MPPT charge controller, but the MPPT controller is able to fully exploit a solar panel with much higher voltage than the battery bank and therefore it allows to produce more output power than a PWM controller. If the solar panel voltage is slightly higher than the battery voltage (typical case of a 12V 30-cell panel and 12V battery), the PWM charge controller is recommended as it has a daily yield in this case similar to the MPPT.

So we have created a very simple table where you will find which charge controller technology to use based on:

•   Number of cells in your panels
•   Voltage of the battery bank you want to charge

Panels and Batteries Controller Type
36-cell Panels and 12V Batteries MPPT
48-cell Panels and 12V/24V Batteries MPPT
54-cell Panels and 12V/24V Batteries MPPT
72-cell Panels and 12V/24V Batteries MPPT
114-cell Panels and 48V Batteries MPPT
30-cell Panels and 12V Batteries PWM
60-cell Panels and 24V Batteries PWM
120-cell Panels and 48V Batteries PWM

How to know the voltages of the panels according to their cells?

Panel Cells Rated voltage Open circuit voltage
30 cells 12V 18V
36 cells 12V 21V
48 cells 18V 30V
54 cells 18V 33V
60 cells 24V 36V
72 cells 24V 42V
120 cells 48V 72V
144 cells 48V 84V

How do the two charge controllers behave?

And now let's see two photos that we took to show you the behavior of the current in the PWM charge controller (PR3030) and in the MPPT charge controller (Solarix). Regarding the solar panel, we used a 100W monocrystalline solar panel. The angle of the panel was not exactly perpendicular to sunlight for a "photographic" need. The battery is a 12V lead-acid Fiamm battery.

1) PWM charge controller (PR3030)

test on the pwm charge controller Pr3030

As you can see from the photo, at the output from the solar panel we have a current of 1.60A which is used almost completely by the PWM charge controller (1.57A) to recharge the 12V battery.

The PR3030 charge controller can accept currents up to 30A and it has the displaying function of the percentage of battery charge. In this case, he tell us that the battery is 76% charged.

Here is the data:
•   Input current: 1,60A
•   Output current: 1,57A
•   Technology: PWM

2) MPPT charge controller (Solarix)

test on the mppt charge controller Solarix

Unlike the PWM charge controller which considers only the current in order to charge the battery, the Solarix MPPT controller considers all the power of the solar panel (therefore voltage and current).

In fact, the difference between the voltage supplied by the panel (example 36V) and the voltage required by the battery at that moment (example 14V) is not lost but is transformed by the MPPT regulator into current useful for the recharging process.

From the photo we can see that the input current to the charge controller is 1.68A, but the current that goes to the battery is even 2.07A.

In this case the data is:
•   Input current: 1,68A
•   Output current: 2,07A
•   Technology: MPPT

With the Solarix MPPT charge controller we use all the power of the panel! But with the MPPTSOLAR charge controllers the benefits don't end there. In fact, in addition to taking advantage of the MPPT technology and accepting panels with high voltages, the MPPTSOLAR charge controllers offer also the possibility to recharge different types of batteries (such as modern LiFePO4 batteries), to easily choose the charging program, to remotely monitor the state of charge, and much more. Would you like to know more? Discover our MPPT solar charge controllers