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Do I have the voltage headroom to expand my array?

TheTallOne

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Joined
Mar 10, 2023
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Location
Broadstairs, Kent, UK
Hello everyone. Beginner here with a professionally installed array that I'm looking to add to.

TL:DR: My inverter has two PV inputs. Do the calculation for max string size apply to the array in total, or each string going into the inverter individually.


I think I must be missing something obvious here, so I can only apologise if it's staring me in the face. Here's the situation:

We have an East/West 4.4kw PV Array consisting of two strings of 7 LG Neon2 All Black 320w panels (14 panels total). I assume they are wired in series, I don't know for sure as I didn't wire them but I gather that's by far the most common setup for this kind of array.

The inverter is a Goodwe 3600 D-NS String inverter. (2 MPPT)

Here's the question.

I would like to expand the array on the West facing roof side (I don't have space on the East side). I've got enough space to add another four panels of similar size. The problem is the inverter.

If I've done my sums correctly, my Voct for the array as a whole right now stands at 604. The maximum input voltage on the inverter is 580. So, I'm already over the absolute edge of what the inverter can take at the lowest all time temperature (-7°C here)

(For ref: Panel VOC: 40.8. NOCT temp 20°C. Temp delta: 27°C Temp coefficient -0.27% Voct 43).

But am I interpreting the numbers correctly? I've looked at a bunch of inverters rated for higher output and they all have a max input voltage of no more than 600. How can this be? Surely this would put a hard limit on the number of panels that falls WAY below the max DC power input of the inverter.

Am I missing something here? Is the max input voltage per input (my inverter has two) instead of total?

I'm not adverse to changing the inverter for a hybrid as I'm considering a battery in the long term anyway and I gather that would simplify matters, but I feel like I'm missing a crucial element of this puzzle.

Any and all help appreciated!

Jon.
 
Are you already using both MPPT inputs? I’m guessing you are because you said you have 2 different strings and they are facing different directions. I would even call them different Arrays if they are facing different directions.
The max voltage is probably for each MPPT. It just reads a little funny the way they say it. (My inverter also displays this info in the same confusing way and it is 500v per MPPT).
I posted a place where I found info on ur inverter below and it states the “range” per MPPT is 80-550v.
So to be calculating the voltage you should just multiplying the 7x panels in series x 40.8 VOC. So each MPPT is getting 285v max. Well within the range I saw posted for this inverter which says 80-550. (600 max).
Got this info here:

The only issue I can see with adding more panels is that you are already close to the Power limit (Watts) max for the inverter (4680W). But, if your solar arrays are truly facing different directions then it is unlikely that you will ever see the full 4.4KW that your panels can produce at once.

People do add more panels than their inverters can take. It is called “over-paneling”. I am no expert in the subject, but I believe it is usually not a problem to go over the Power limit of your inverter (within reason) as long as you stay within Voltage and Amperage limits.

I hope this helps. Maybe someone else more familiar with over paneling can supply more info.

I've looked at a bunch of inverters rated for higher output and they all have a max input voltage of no more than 600. How can this be?
You can’t simply multiply the max voltage times max amperage and expect it to equal the max power. As I understand it they are all hard limits and you can’t go over any of them. For instance my inverter has 2x MPPTs 500v 18a. That would mean 18KW power if you just did the math. But the real max power is 8KW.
 
Hello everyone. Beginner here with a professionally installed array that I'm looking to add to.

TL:DR: My inverter has two PV inputs. Do the calculation for max string size apply to the array in total, or each string going into the inverter individually.


I think I must be missing something obvious here, so I can only apologise if it's staring me in the face. Here's the situation:

We have an East/West 4.4kw PV Array consisting of two strings of 7 LG Neon2 All Black 320w panels (14 panels total). I assume they are wired in series, I don't know for sure as I didn't wire them but I gather that's by far the most common setup for this kind of array.

The inverter is a Goodwe 3600 D-NS String inverter. (2 MPPT)

Here's the question.

I would like to expand the array on the West facing roof side (I don't have space on the East side). I've got enough space to add another four panels of similar size. The problem is the inverter.

If I've done my sums correctly, my Voct for the array as a whole right now stands at 604. The maximum input voltage on the inverter is 580. So, I'm already over the absolute edge of what the inverter can take at the lowest all time temperature (-7°C here)

(For ref: Panel VOC: 40.8. NOCT temp 20°C. Temp delta: 27°C Temp coefficient -0.27% Voct 43).

But am I interpreting the numbers correctly? I've looked at a bunch of inverters rated for higher output and they all have a max input voltage of no more than 600. How can this be? Surely this would put a hard limit on the number of panels that falls WAY below the max DC power input of the inverter.

Am I missing something here? Is the max input voltage per input (my inverter has two) instead of total?

I'm not adverse to changing the inverter for a hybrid as I'm considering a battery in the long term anyway and I gather that would simplify matters, but I feel like I'm missing a crucial element of this puzzle.

Any and all help appreciated!

Jon.
The mppt inputs are two separate mppt controllers you can run up to 600 volts max per mppt this is a hard limit do not exceed it will not end well

the recommendation for the voltage per string is 80 to 550

Depending on how cold it gets in your area if your voc is 40.8 you could run 11 panels in series with a large safety margins -30f

if your area doesn’t go below 32f you could run up to 13 panels per string in series 40.8x13x1.1=583 volts

so adding 4 more of the same panels is not a problem
 
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