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What is MPPT and PWM on solar charge controllers and what is the difference?
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What is MPPT and PWM on solar charge controllers and what is the difference? What is better? What should I go for?

To understand this you need to know that solar panels work basically like a power supply. By design they have a sweet spot where they work at their highest possible efficiency. For solar panels this is called their maximum power point. Power is voltage * current, see Electrical units / Electrical characteristics of a battery if you are not familiar with the concept.

Without any load the panel will be at its idle voltage, assuming there is decent sunlight. This is usually called their open circuit voltage, or Uoc for short.
When putting a load on the panel, i.e. drawing current to charge a battery, the voltage will drop while the current goes up. With power being voltage * current, you see that both effect the power output of the panel. Very high current will lead to very low voltage. As a result the total power will be very low as well.

• Uoc is the open circuit / idle voltage
• Imp is the current at maximum power (point)
• Ump is the voltage at maximum power (point)
• Imp*Ump is the maximum power, Pmax or Pmp. This is usually the rated power for the panel.
For a "12V panel" rated for 100W it will, for example, look like this:

Uoc = 23.2V
Isc = 6.2A
Ump = 17.5V
Imp = 5.71A

Sometimes mpp instead of mp is used. Isc is the short circuit current which is of no relevance at this point.

This is where MPPT comes into play. It stands for Maximum Power Point Tracking. That means the solar charge controller will search for, or "track", the maximum power point of the connected solar panels, i.e. the current where the panels operate at their highest efficiency. Imagine it's like trial & error, monitoring the power output while adjusting the current and then locking the current where the power is the highest. This is done on a continual basis as a cloud, leaf, dust, or temperatures can effect where this sweet spot is. So even a nice wind across the panels could effect where the MPPT is located.

PWM on the other hand stands for Pulse Width Modulation. Instead of looking for the maximum power point there will be pulses of voltage, resulting in a current. That means the voltage is turned on and off very quickly, and for different periods of time. This is called the duty cycle, a value in % that shows for how long the output is activated. 50% could mean 1ms on, 1ms off. 1000ms = 1s, so we are talking about very short periods of time. It could also mean it's on for 500ms, then off for 500ms. So we need to make sure we also know the frequency at which the PWM operates at.
The frequency is how many times the switch is turned from the on state to the off state. This is usually shown in Hz (Hertz), but could also be shown in kHz, MHz, etc. So, with 1ms on/off times, this would be 500 switches on in a second, or 500Hz. For the 500ms on/off times, or 1 time on in a second, this would be 1 Hertz.

PWM is generally cheaper to implement. All cheap solar charge controllers will use PWM technology. The problem is that this is very inefficient and with that you will never use the maximum power (or even close to that) of the panel. MPPT is more expensive, but more efficient.

If every penny counts, then you have to stick with PWM. But if possible you should always choose an MPPT solar charge controller. It also doesn't hurt to start off with PWM, then later upgrade to MPPT when budget allows.



Quote:DISCLAIMER: I am by no means an expert on any one or all of these fields/questions/topics. The results of this FAQ is a collaboration of multiple different members to come up with a common list of questions that would be asked and we have tried to answer. I was the member who was chosen to post the FAQ. If you have question that goes beyond the FAQ, please post your questions in the relevant section pertaining to your inquiry. Thank you and have a nice day
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