Mismatch panels, use an extra charge controller or go over ISC by 0.2 amps?

[BRegan87]

I have an MPP solar LV2724
Max voltage is 60 volts
Max ISC is 25 amps

Currently I have 2 parallel strings of 2 100w Ecoflow rigid panels each

I would like to double up on my panels but the problem is that the ISC of these panels is 6.3.

6.3 amps x 4 strings = 25.2 short ciruit amps

To my understanding I should NOT go above the 25 amps even by a tiny amount. Is this correct?

The ecoflow panels specs are as follows

17.1 max operating voltage
20.3 open circuit voltage
5.9 amp max operating current
6.3 amp short circuit current

I can mismatch by adding on 100w panels by Rich Solar with the following specs

19.4 max operating voltage
22.8 open circuit voltage
5.15 amps max operating current
5.46 amps short circuit current

How much power loss will I experience using these panels together? Should I get all 4 extra panels from Rich Solar or should I get 2 from each company?

Any reason I should NOT mismatch? I can also just get 2 more panels from ecoflow then add another charge controller down the line.

Any thoughts or input on my options is greatly appreciated as I am a beginner. Thank you soo much

 

[MisterSandals]

Max ISC is 25 amps

Is this exactly what the manual says?

 

[BRegan87]

Is this exactly what the manual says?

It just says the maximum charging current is 25amps.

I had assumed that the MPP would be self limiting but I contacted MPP explaing my intentions to over panel.

They responded and advised me that the panels had to stay within voltage as well as the 25amp ISC limit.

Is it possible they are giving me an overly cautious response because they have to?
My original intentions were to over panel to 1000 watts lol

 

[MisterSandals]

It just says the maximum charging current is 25amps.

That is completely different from array Isc. The charging current is the most it will put into your battery under optimal conditions.

They responded and advised me that the panels had to stay within voltage as well as the 25amp ISC limit.

This seems odd to me. The MPPT pulls the amps and controls the voltage/current ratio as it seeks maximum power.

Is it possible they are giving me an overly cautious response because they have to?

Possibly. If someone knows better, i am willing to learn.

 

[BRegan87]

Yes. TBH it seems odd to me as well.

Here is the message I sent them and the response I got.
‐‐---------------------
Me:

If I stay under recommended voltage how much can I overpanel this system?

I was considering doing either 5 or 6 parrallell strings of 2 100 watt panels each. Would overpannelling to 1000 or even 1200 watts be ok?

The specs of the panels are below.

Rated Power
100 W（+/-5W）
Open Circuit Voltage
20.3 V
Short Circuit Current
6.3 A
Maximum Operating Voltage
17.1 V
Maximum Operating Current
5.9 A


MPP Solar's response:

Hi (redacted lol),

You also need to make sure the solar panels are within 25A ISC for PIP2724LV-MR.

So the max quantity of the solar panels you can connect is 2s3p=6pcs.

 

[MisterSandals]

I was considerring doing either 5 or 6 parrallell strings of 2 100 watt panels each. Would overpannelling to 1000 or even 1200 watts ok?

Well with this much over paneling, their advice sounds more reasonable. I'd have wanted better wording but the person responding seems to understand array configurations so is probably the person to listen to.

With a 25A charge limit, the most amount of array it will process is: 28V battery x 25A charging = 700W

 

[Crowz]

I was under the impression voltage was all that mattered panel wise. So if you were within the voltage range you could have as many panels as you wanted. I have always over paneled amp wise to make up for cloudy days.

 

[BRegan87]

Well with this much over paneling, their advice sounds more reasonable. I'd have wanted better wording but the person responding seems to understand array configurations so is probably the person to listen to.

With a 25A charge limit, the most amount of array it will process is: 28V battery x 25A charging = 700W

Can I not go to above the watts provided the total ISC is below 25A?

I understand its only ever going to charge at 700watts but a 700 watt array is never going to produce that much at any given time.

If soo....is it best to run 3 strings of ecoflow panels and 1 string of rich solar panels? Or would I be better running 2 string of each?

Or would it be better to only add 1 more string until I can add another charge controller?

 

[Mattb4]

I would guess the amps matter based on physical limitations of the circuit to carry higher. Just like you do not run 30a in a 12awg wire. However since the SCC itself limits the total amount (max charge current to battery) it loads the panels it would be unlikely that you need to worry about the max current it could handle on the PV input side.

 

[cs1234]

I was under the impression voltage was all that mattered panel wise. So if you were within the voltage range you could have as many panels as you wanted. I have always over paneled amp wise to make up for cloudy days.

I've seen some fairly smart sounding people here on the forums say that excessive over-paneling can possibly damage the charge controller and let it's magic smoke out. I've also seen fairly smart sounding people here on the forums arguing that it doesn't matter.

I'm in the it doesn't matter camp, but I'm not very smart, so my opinion is of little value.

If I were doing it for myself, I would overpanel the heck out of it and not care. If I were doing it for somebody professionally, I would follow whatever the manufacturer says in their documentation. If the documentation doesn't say max amps of panels connected, I probably wouldn't use that equipment professionally.

 

[Crowz]

On the first system I built using the 4215bn's they have a stated max watts. This bugged me and after reading up on everything I could find I even found somewhere in the docs that it was actually over voltage that was a no no. So I went WAY over max amps. I mean WAY over. Never had a problem with it. That system ran 5 years without me even paying attention to it with it working fine. I think I had 3kw on it and its rated at a max of 1000 watts.

The final reason I decided that I didn't think it mattered was the part about "if you don't have a load you wont see the watts". So if its not running something or charging a battery it will show x voltage and zero watts on the readouts and since the charge controller can't put out more than its rated charge rate I didn't see how it could pull more watts than that no matter how much wattage was available.

Again not claiming I'm right that's just how I think it works.

 

[HRTKD]

I'm over paneled on my Victron 100/20 by almost 2x. But it's within the Maximum PV Input Voltage as well as the Max PV Short Circuit Current limits as defined in the Victron data sheet.

The data sheet has this to say about going over the input current:

A PV array with a higher short circuit current may damage the controller.

Over paneling on wattage is OK, as long as you don't exceed the other two limits.

 

[sunshine_eggo]

I'm over paneled on my Victron 100/20 by almost 2x. But it's within the Maximum PV Input Voltage as well as the Max PV Short Circuit Current limits as defined in the Victron data sheet.

The data sheet has this to say about going over the input current:


Over paneling on wattage is OK, as long as you don't exceed the other two limits.

I'm fanatical about this on Victron MPPT because they actually publish PV input current limits. When you dig into the issue over at community from Victron employees, this limit is based on the reverse polarity protection circuit, i.e., if you hook your array up backwards, if you're under the PV input current limit, the MPPT will protect itself. If it exceeds that, you may blow the unit up.

HOWEVER, outside of reverse polarity protection, the PV input current limit is a soft limit, i.e., if you don't reverse polarity, there really isn't a limit.

I apply the same logic to all other controllers unless they explicitly state otherwise, i.e., the EPEVER units recommend no more than 50% overpaneling.

 

[HRTKD]

When you dig into the issue over at community from Victron employees, this limit is based on the reverse polarity protection circuit, i.e., if you hook your array up backwards, if you're under the PV input current limit, the MPPT will protect itself. If it exceeds that, you may blow the unit up.

Good to know that it's based on that.

 

[BRegan87]

Lots of good information and feedback provided. Thank you everyone.

From what I gather I would be OK to add another 4 like panels and have slightly over limit ISC of 25.2 provided I dont accidentally reverse polarity.

With that said I would like to have more information to weigh this option against taking the conservative route and keeping my ISC under 25 Amps.

Say I add 2s2p rich solar panels to my system as is without an additional controller...What inefficencies am I going to experience?

Am I correct that the Ecoflow panels would throttle back amperage to 5.15 amps to match the Rich Solar panels?

 

[cs1234]

I believe the amperage will not be throttled back, at least not in the way you might think.

What's going to happen is the new higher voltage panels are going to have their voltage reduced to more closely match the other lower voltage panels. The MPPT controller is going to try and find the sweet spot in the voltage/amperage across all the the panels in the paralleled strings.. but it can't go any higher in voltage than the lowest voltage serialed panels on the paralleled strings are willing to go.

If it's still within voltage limits, you might actually want to have mismatched panels on every serial string.. one rich one ecoflow so there is no difference in voltage between the strings.. hard to say though, because the amps would then be brought down to the lowest amped panel.

One way you lose volts, the other way you lose amps. You do the math. I'm sure somebody else here might do it for us though.