The problem with solar charge controllers.

Well, more accurately, the problem with every solar charge controller - regardless of whether it is PWM or MPPT or even direct charging is that they just don't work well.

Picture this scenario: Loads of sunlight, full batteries and the charge controller is doing what it should be - trickle-charging the battery. That's fine. Then say you want to run something like a pair of electric fans that demand a hefty current. That's where the charge controllers all go belly up.

What seems to happen is that they keep trickle-charging the battery while the fans draw current from the battery at a higher rate.  Picture this - fans drawing 4A from the battery and 7A of solar panels in full, glorious sunlight. What you'd imagine would be happening is that the charge controller would be saying "hey, we have plenty sunlight so we can run these fan things directly from the panel power, supplementing that as needed from the battery. That would be the sane, sensible thing to do.

Um, no. That kind of thinking is far too advanced for makers of solar charge controllers. What actually happens (it doesn't matter if it's MPPT or PWM or any other flavor) is that the charge controller keeps putting that trickle charge in until the voltage of the battery drops low enough to merit drawing more power from the panels. So the net effect is the solar panel power is just being wasted and the battery used instead. It's akin to having a free lunch offered to you but opting to go to a restaurant and paying instead.

As far as I can see, most of the solar charge controller engineers need to be lined up against a wall and used for ballistic testing by the ammunition companies. That's all they're worth. What a cockamamie way of building charge controllers!