Calculate acceptable over paneling.

[Ampster]

Granted, some "inverters" (all-in-ones) have a solar charge controller as part of the system but still, over paneling has nothing to do with the inverter portion or its rated output wattage. Two completely different and unrelated ratings.

Thanks for the explanation. I will try to use those terms correctly. I do not have a separate charge controller and see the term AC to DC ratio used in GT systems all the time.. I ocassonally see people describe high DC to AC ratios as over paneling or over stringing and now see why that is not correct. I agree the important issue is not to exceed the voltage and current limits of the charge controller when discussing this topic.

 

[McDubsy]

There is an inconsistency between the 150V and the 12V above that needs to be clarified?

100 Amps at 150 Volts is 15,000 Watts.

I agree. There is an inconsistency.
Here is a clip of the stat sheet I am getting that info from. I may be reading it wrong but it seems to say that with a 12v battery bank I should only have a 1300w pv array max. Am I correct in that assumption?

New item by Aaron Green

photos.app.goo.gl

 

[McDubsy]

So what is the maximum PV Amperage? There was some ambiguity in the original post by @McDubsy

Max PV Amperage is 40a

 

[McDubsy]

Okay. I think I follow

So, for instance...if I connected 2 strings of 4 325w/40v/10a panels I would end up with 80v/80a going to the charge controller.
Since that is lower than the posted VOC and ISC it would work safely. Is that correct or am I completely off?

 

[Bud Martin]

Okay. I think I follow

So, for instance...if I connected 2 strings of 4 325w/40v/10a panels I would end up with 80v/80a going to the charge controller.
Since that is lower than the posted VOC and ISC it would work safely. Is that correct or am I completely off?

What is the Voc and Vmp of your panel? is it 40V for Voc?
If each string has two panels in series, the Voc for each string will be 80V, the Isc will be 10A, then when you put the two strings in parallel, the Voc will be 80V, the Isc will be 20A, the panel configuration is called 2s2p for the 4 panels you have.

 

[rmaddy]

I agree. There is an inconsistency.

What inconsistency are you referring to?

The SCC has a max input Voc of 150V.
The SCC has a max input Isc of 40A.
The SCC has a max battery charge current of 100A.
When the SCC is used on a 12V system and you are charging a battery at about 13V and the max charge current of 100A then that means it will make use of no more than 1300W.
You can put more than 1300W of panels on the SCC as long as you don't exceed the 150V input and the 40A input. Whatever total wattage you end up with (within those two input limits), the SCC will never make use of more than about 1300W.

if I connected 2 strings of 4 325w/40v/10a panels I would end up with 80v/80a going to the charge controller.
Since that is lower than the posted VOC and ISC it would work safely. Is that correct or am I completely off?

2 strings of 4 sounds like 4S2P. That would be 160V and 20A. Definitely no good due to too much voltage.
4 strings of 2 would be 2S4P and that would be 80V and 40A.

 

[rin67630]

There are two limits, when determining the maximum array size that can be connected to an MPPT:

1. The Maximum PV open circuit voltage (Voc at STC)
2. The Maximum PV short circuit current (Isc at STC)

Both values are specified in the datasheets of all our MPPT Solar Charge Controllers. Those two ratings of the PV array must not exceed these MPPT limits.

No. The MPPT controller will limit the current to its capability. Matching both is only a requirement for PWM controlers.

 

[rin67630]

You can put more than 1300W of panels on the SCC as long as you don't exceed the 150V input and the 40A input.

The max 40 A Input are controlled by the MPPT SCC controller. Even with more panels you will not exceed that rating.

 

[Ampster]

What inconsistency are you referring to?

The first post where @McDubsy said, "rated at 100A/150V max pv input. Also 1200w at 12v max pv input“. The 40 Amp limit was not mentioned in that statement. Later it was clarified that the 100A was the max charge current, and even later that the max isc was 40 Amps.

 

[rmaddy]

rated at 100A/150V max pv input

Ah. I hadn't noticed that the 100A was being referred to as max input as opposed to max output.

The max 40 A Input are controlled by the MPPT SCC controller. Even with more panels you will not exceed that rating.

Most spec sheets for Victron MPPT SCCs clearly state that exceeding the max short circuit current can harm the SCC. So the input current isn't simply clipped, you must stay below that value, just like the Voc.

Since we seems to be talking about the Victron 150/100 at the moment, its spec sheet states a max short circuit current of 70A (not sure where the 40A came from). And the 70A value has a footnote that states: "A PV array with a higher short circuit current may damage the controller."

 

[Ampster]

(not sure where the 40A came from).

It came from post #23, in which the poster said, "Max PV Amperage is 40a"
Thanks for your posts which have brought this thread back to reality.

 

[rmaddy]

It came from post #23, in which the poster said, "Max PV Amperage is 40a"

OK, let's clarify a few things. Post #23 is from the OP. Post #1 is referencing a Renogy 150V 100A SCC. I have not looked at the specs for that specific SCC. So perhaps the OP is stating that the Renogy 150V 100A SCC has a 40A max input current.

I got sidetracked with Victron details in post #30 while responding to post #28 who also made a similar reply in post #27 which was a reply to post #19 which linked to a Victron document. Did anyone just follow that?

Either way, the OP needs to determine, for their specific SCC, what the actual max short circuit current is. And it needs to be determined whether the SCC simply clips the input at that max value or whether exceeding that max is actually harmful to the SCC or not (like the Voc).

 

[McDubsy]

Thank you everyone for your helpful replies.

I'm seeing several places in this thread a mention to an ISC of 40a for the SCC.

The SCC I am using is the Renogy 100a MPPT
The specs are as follows:
-Nominal Voltage: 12V/24V/36V/48V
- Rated Charge Current:100A
-Max. PV Input Power: 1300W/12V; 2600W/24V; 3900W/36V; 5200W/48V
-Max. PV Input Voltage: 150VDC (25°C), 140VDC(-25°C)

I understand the importance of keeping my PV input under the VOC of 150. I don't see or know how to find the ISC of this SCC.

I guess I am confused on what is meant by "PV Input Power: 1300W/12V"
Does that refere to how many Watts the SCC can push to the batteries at 12v, or is that a limit I need to keep in mind when building my PV array?
-

 

[rmaddy]

I'm seeing several places in this thread a mention to an ISC of 40a for the SCC.

That came from you in post #23. But the specs for the Renogy 100A SCC don't make any reference to a max input current.

"PV input Power: 1300W/12V" means that on a 12V system, the most power the SCC can make use of is 1300W. This is simply based on the fact that the SCC has a max battery charge current of 100A and an assumed battery charge voltage of 13V (13V x 100A = 1300W).

Basically, keep your temperature adjusted panel array Voc under 150V and you can safely add up to at least 2000W of solar panels. Just keep in mind that the SCC will only make use of at most about 1300W. Any extra potential beyond that won't be taken advantage of.

BTW - if you are willing to spend $700 on the Renogy 100A SCC, I suggest spending $795 on the Victron 150/100 SCC instead. You'll get a top-of-the-line SCC that can easily run at max specs 24/7 without worry.

 

[rmaddy]

One other thought. When get to the point where you need a 100A SCC, you really should consider a higher voltage system. If you went to 24V then you would only need a 50A SCC to support the same amount of solar panels. That would save you hundreds of dollars. Something to consider.

 

[timselectric]

$795 for a charge controller?
Ouch
I agree with upping the battery voltage.

 

[McDubsy]

One other thought. When get to the point where you need a 100A SCC, you really should consider a higher voltage system. If you went to 24V then you would only need a 50A SCC to support the same amount of solar panels. That would save you hundreds of dollars. Something to consider.

Thanks for the help. That clarifies a ton!

When I upgraded the system, I was going to upgrade to a 24 volt battery bank.
I am currently using 2 12v 300ah lithium batteries.
My understanding was that wiring them in series for a 24 volt system would save me when it comes to cost on charge controller but, the battery bank would have less of a capacity than it does now.

The capacity was my biggest concern at this point. My family and I live completely off grid so we're trying to make the system as robust as possible.

 

[timselectric]

Thanks for the help. That clarifies a ton!

When I upgraded the system, I was going to upgrade to a 24 volt battery bank.
I am currently using 2 12v 300ah lithium batteries.
My understanding was that wiring them in series for a 24 volt system would save me when it comes to cost on charge controller but, the battery bank would have less of a capacity than it does now.

The capacity was my biggest concern at this point. My family and I live completely off grid so we're trying to make the system as robust as possible.

Capacity remains the same.
Voltage will double.
Amp hours will be halved.
Watt hour remains the same.

 

[wiseacre]

My understanding was that wiring them in series for a 24 volt system would save me when it comes to cost on charge controller but, the battery bank would have less of a capacity than it does now.

Capacity remains the same
12v x 200ah = 2400wh
24v x 100ah = 2400wh

say you had a 100w load
100w / 12v = 8.333a
100w / 24v = 4.166a
so pulling a 100w load would take 1/2 the amps at 24v than a 12v system would require
Basically, higher voltages need less amps to provide the same wattage

 

[McDubsy]

Capacity remains the same
12v x 200ah = 2400wh
24v x 100ah = 2400wh

say you had a 100w load
100w / 12v = 8.333a
100w / 24v = 4.166a
so pulling a 100w load would take 1/2 the amps at 24v than a 12v system would require
Basically, higher voltages need less amps to provide the same wattage.

So regardless of the battery bank voltage, it could run a heater that pulls 500w and 10a for the same amount of time because the watt/hour capacity is the same?