Panel options

[Tyler702]

Epever 4215bn (150V/40A)
24V 100Ah LFP
4x250W used santan panels arriving soon.
(Voc 37.6 isc 8.85)
Options:
1. 4S (150.5V / 8.85A)
2. 4p (37.6V / 35.4A)
3. 2s2p (75.2V / 17.70A)
Either option is within range, although #1 is barely over the 150V max..but..
Will stress tested this exact cc awhile back, and it passed with flying colors. He indicated you could over panel it.
My question is:
Assuming all 3 options are doable, do cc's like, or operate more efficiently in either of these configs?
Add'l info: these will be ground mounted so its easy to access and re-tool if necessary, and the panels to CC is a run of 30' 10guage windy nation wires.
Lastly, IF I go with 4p, will I need additional protection, like an inline fuse? My current setup is 1x250 panel to rapid disconnect to CC.
Thanks!
Tyler

 

[snoobler]

4S Voc is too high - you need to allow margin below the 150V limit. Going over this limit can destroy a controller.
4P is borderline too low (60 cell panels are not typically best for 24V systems).
2S2P is what I would choose.

If you can fit them, over panel to 3S2P. Yeah, you're over the power limit, BUT the used panels and conditions will likely never produce rated power, and the controller will just ignore any extra.

 

[Tyler702]

Ok, so:
2S2P..easy enough..
3S2P= 112.8V@17A=1917W
Within the 150V/40A rating. Good
According to manual though, that exceeds the 1040W/24V rated charge power but well below the max PV array power (3120W/24V)
So then..the difference of 1917W minus 1040W (877W) will just be ignored? how? Burned off? Resistors, fetts?
I still wonder however, if cc's prefer higher input volts + moderate amps (pv series) or the opposite, high amps and moderate volts (parallel).
For instance, if I attach a bench PS set to 30A@34V= 1020W
Or set to 15A@68V= 1020W
Does it operate any more or less efficiently either way? Both being 1020W.?

 

[Tyler702]

Sorry..didnt mean to attach duplicates..

 

[snoobler]

Ok, so:
2S2P..easy enough..
3S2P= 112.8V@17A=1917W
Within the 150V/40A rating. Good

It s not within the rating. The 40A is for charging. PV current may be the same or a separate rating.

According to manual though, that exceeds the 1040W/24V rated charge power but well below the max PV array power (3120W/24V)
So then..the difference of 1917W minus 1040W (877W) will just be ignored? how? Burned off? Resistors, fetts?

This concept is no different than a battery being topped off or a load on a battery. When a battery is nearly full, they will only accept so much power at the set voltage. The MPPT just doesn't pull any more than that from the array to feed the battery. Same as putting a 10W 12V light bulb on a 12V battery - the load only pulls what it needs.

Think of the MPPT as "load" on the PV array taking only what it can provide to the batteries or system loads.

I still wonder however, if cc's prefer higher input volts + moderate amps (pv series) or the opposite, high amps and moderate volts (parallel).
For instance, if I attach a bench PS set to 30A@34V= 1020W
Or set to 15A@68V= 1020W
Does it operate any more or less efficiently either way? Both being 1020W.?

The only "preference" SCC have is to operate within their rated limits. There are implications with choices, but they're generally trivial.

1S - Voltage may be too low to effectively charge 24V systems. LFP is generally okay. Voltage too low for lead-acid if equalization is needed.

2S vs. 3S:

2S: higher efficiency converting panel voltage to battery voltage, 0.5-1.5%.
3S: higher efficiency due to lower voltage drop between panels and SCC.

The affects of the above two choice often offset themselves resulting in a negligible change in overall efficiency.