Someone on a Solar Panel forum said something along the lines of: a portable PWM regulator only uses 125Watts out of a 12V 250W panel compared to a MPPT regulator which can use the full 250W.
I wan’t to use 2 separate 250Watt panels connected in parallel to increase amps charging one 12V battery at a time.
In all the reading about solar I have never read anything like the above, to such a degree I think the guy miss read my post, he did not reply back to clarify.
Does anyone know what he could have meant? perhaps it’s true for some regulators with Lithium chemistry?
This is sort of true, but confused and incomplete.
A MPPT regulator is a DC-DC converter. The value of this is that no matter what voltage your solar panel is developing (and the voltage does vary) the converter can output any desired voltage with minimal loss. Where this matters is that your battery will have an optimal charge voltage depending upon a range of factors as well. The MPPT regulator can match the panel to the battery no mater what the panel is doing or the battery needs. So it is able to use whatever power the panel can provide.
A PWM regulator can only reduce the voltage - it can’t increase it - and it can only reduce the voltage by essentially throwing energy away (in this case by never taking it from the panel). In the best of circumstances there might not be too much of a mismatch, but there will almost always be some, and the regulator will not be using the power generated by the panel to best effect. In the worst case, the panel might not be able to generate a high enough voltage to charge the battery at all, and you lose the lot. So 50% is a very glib approximation. Even the MPPT will never be 100% - nothing in this universe is 100% efficient - but it can get close.
The question is not anything to do with the battery chemistry, although lithium batteries do have somewhat stringent requirements that might make things a bit worse compared to others.
Adding to what FV said, a decent MPPT regulator will allow you to tailor the charge requirements like temp compensation, float voltage, and other parameters to the specific battery type. We use Outback and Midnight Solar regulators on our remote sites and have very little issue with them.