Solar-Panel to Controller Loss
Much has been made of the lower losses on the panel to controller path with MPPT because the amps are less. So once you have your loss measured, how valuable is it to improve on that if you don't lik...
Forum Discussion
Salvo wrote:
No, didn't miss anything. I came to the same conclusions as the Morningstar 60-cell Tech Tip. You can not use just one 60-cell panel in a 24V battery system.
http://support.morningstarcorp.com/wp-content/uploads/2014/07/tech-tip-60-cell-PV-module-sizing.pdf
There's no voltage headroom for higher panel temperatures. The lower the voltage headroom, the worse the mppt controller looks. We could have figured this out long ago had you mentioned the 255W panels had only 60 and not 72 cells.BFL13 wrote:
"A single 60-cell panel can only be used with a 12V battery."
Salvo must have missed where I got the four 6s as a 24v bank to 30 volts with my single 60 cell 255w panel easy as pie. Panel at 45C too, which is its NOCT. We'll see how it goes when the panel is at 50C.
There is a difference between saying you can't do it (which means ever) and saying sometimes you can't do it. The question is how high must panel temperature be so you can no longer get the 24v battery to say 29.6v ( twice 14.8)?
I will be testing it again with panel at 50C or a bit more which is as high as I have seen it here. if it will do 30v then, there is nothing to prevent us choosing 24v vs 12v battery if so desired, with the single 60 cell panel. Or else we just stay with 24-12.
The other thing is low light reducing panel voltage vs battery voltage. I don't have any experience with that, but it must be a factor for many campers depending where and when they camp.
Morningstar says to just use two 60s in series to crank up the array voltage, but then points out that you will exceed the input Voc rating of many controllers. Amazingly, they then say that they can sell you a controller that can do it! :)
