How to size your MPPT Solar Charge Controller?
What is a charge controller?
A solar charge controller is a regulator for your solar battery that prevents it from overcharging. Batteries are rated for a certain voltage, and exceeding that voltage can lead to permanent battery damage.
Types of solar charge controllers
There are two types of charge controllers to consider: Pulse Width Modulation (PWM) controllers and Maximum Power Point Tracking (MPPT) controllers. PWM controllers are generally less expensive and can only be used for smaller systems where the voltage of your solar panel system and your battery have matching voltages.
Most larger solar panel systems do not have the same voltages as the batteries, and therefore a MPPT solar charge controller is highly recommended. MPPT charge controllers can pair non-matching voltages from panels and batteries. MPPT controllers adjust their input to bring in the maximum power possible from your solar array, and can also vary their output power to match the attached battery. This means that MPPT charge controllers are more efficient than PWM controllers, and more effectively utilize the full power of your solar panels to charge a home battery system.
Size of your Charge Controller
There are two things important in selecting your charge controller, Voltage and Amperage.
Voltage: You will need to ensure that your Solar Charge Controller can handle the voltage that your Solar Panels strings produce. For example if you have 3 x 410 Wp solar panels in a string, which are roughly 50 V each, you would need at least a 150 V MPPT charge controller.
Amperage: Find the current (in A) by using power (W) = voltage (V) x current (A). Take the power produced by the solar panels and divide by the voltage of the batteries. For example: the solar panels are producing 3.5 kw and charging a battery of 48V. The controller size is then 4000/48 = 72.9 amps. Introduce a safety factor by multiplying the value you have found by 1.25 to account for variable power outputs: 72.9 x 1.25 = 91.1 Amps. In this example we would need at least a 91.1 amp controller (e.g. 100 amps).
You want more details?
Victron has a MPPT sizing calculator online: Click Here, but you would need all the detailed characteristics of you panels at hand to fill in the online calculator.
MC4 or Tr connections?
The price for these two is exactly the same for Tr and MC4; we prefer Tr as the MC4 connectors are more fragile.
Have a look at SunStore’s range of MPPT charge controllers, Click Here.
Source: adapted from energysage.com