MPPT needs to be vertical?

All solar controllers, heat fins, are vertical

i have not seen one, that is supposed to be mounted any other way

the larger and heavier and more powerful
the more critical it is to do it correctly

could mount a fan on it , IF you want to go horizontal because of space limitations, connect the fan to the 'load' posts and set the time functions so it only runs during the day during charging hours

Because the manufacturer said so, I know Mr. Obvious here.

Warm air rises. Natural convection keeps the air flowing over the heat sink on the back...

2oldman wrote:
When it's vertical it slows down the electrons a bit giving it more time to extract the extra wattage. No, that's not true.

I believe it's for cooling.

You beat me to it.. I was going to say it speeds up the electrons so it can pack them into the battery faster/tighter. Yep its for cooling and can make a significant difference in unit temp.

Dave

The heat sink is positioned so as to maximize cooling when it is mounted vertically.. Mounting horizontally can reduce the effiency of the convection cooling and cause it to overheat.

I read an article on this years ago. likely in QST (Arrl.org's publication) but I do not recall what they discovered. and I'm not sure it was in QST. Been a while.

But I recall that one position of the cooling fins worked best

I ignored the instructions on my epsolar tracer and installed it horizontally.
But it's only a 20A model and hopefully over-engineered.
Guess we'll find out ...

Also note the top, bottom and side clearance specifications.

Most MPPT will derate based on over temperature. Might fool you into thinking all is fine. All the while controller is clipping power and running the electronics at max temperature. OK in extreme conditions but not every day.

2oldman wrote:
When it's vertical it slows down the electrons a bit giving it more time to extract the extra wattage. No, that's not true.

I believe it's for cooling.

That makes sense...

Thanks.

When it's vertical it slows down the electrons a bit giving it more time to extract the extra wattage. No, that's not true.

I believe it's for cooling.

I’ll bet cooling.