MPPT or PWM solar charger - what's the difference?
Do I really need an MPPT charge controller, or is a cheap PWM controller sufficient? And what's the difference anyways?
What is a solar charge controller?
A solar charge controller is connected between the solar panel(s) and the battery bank. Its main task is to manage the power that goes in to the battery:
- Make sure that the battery is not overcharged, by regulating the voltage from the solar panel.
- Cut the connection to the solar panel if the solar panel voltage drops below the battery voltage, to avoid the solar panel from draining the battery e.g. during the night.
There are two main types of solar charge controllers: PWM (pulse-width modulation) and MPPT (maximum power point tracking).
PWM charge controllers
A PWM controller reduces the voltage from the solar panel to match a little more than the voltage of the battery, so that the battery will charge without being overcharged. They a relatively cheap; you can get a working PWM controller for a small solar setup from around $10.
- Cheap, small and light weight
- Well tested technology
- Not as energy efficient as MPPT
- Low current only, no PWM controller above 60A
- Low voltage only
- Not very scalable
MPPT charge controllers
An MPPT does what the PWM controller is doing on the battery side, but is a little smarter on the solar panel side. Instead of just limiting the voltage, it will find the maximum power point (watt) by adjusting the voltage and current from the solar panel to the point where it gets the most power out of it.
More information on how MPPT works:
- Up to 30% more efficient than PWM controllers
- Higher voltage
- Higher current (Amps)
- More expensive than PWM, although prices are constantly dropping
- Generally larger and weigh more than PWM controllers
Can I replace a PWM controller with an MPPT controller?
Yes. If you want to start off with a small solar power setup, there is no problem in using a cheap PWM controller first, and replace it with an MPPT controller later on.
How to spot a fake MPPT controller?
There are some really cheap charge controllers on the market that claims to be MPPT, but is actually just an advanced PWM controller. But how to you separate a real MPPT controller from a fake one? Here is what you should look for:
- Size and weight: A real MPPT controller uses more metal for coils and usually a heat sink. Higher Amp rating will result in a larger and heavier charge controller, if it's a genuin MPPT controller.
- Voltage rating: While a fake MPPT controller usually is limited to around 60V, a real MPPT controller can often take 100V, or even up to 150V or 200V.
- Price: If it seems to be too good to be true, it often is. Controllers that claims to be MPPT with a current rating of 50A, but doesn't cost more than $20, is probably just a fancy PWM charge controller.
- Brand: If you buy an MPPT controller from a well known brand (Victron, Renogy, Outback, Epever/Epsolar etc.), you're probably buying a real MPPT charge controller.