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Panel Sizing


JohanB
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Hi all, 

I have a query I am planning a hybrid system with a Deye/SunSynk 5kw inverter. I see on the stats it has 2 mppt trackers rated at:

Max. DC Input Power (W): 6500W.
PV input Voltage (V): 370V (100V-500V).
MPPT Range (V): 125-425V.
Full Load DC Voltage Range: 240V-425V.
Start-up Voltage (V): 150V.
PV Input Current (A): 11A + 11A.
No. of MPPT Trackers: 2
No. of Strings Per MPPT Tracker: 1+1.

The panels I am looking at is wired in series (I have a open roof no shading and the lower current is better from what I have read):
410W Canadian solar

PMAX: 410.0W
VMP:      39.10V
IMP:       10.49A
VOC:       47.60V
ISC:        11.06A

So what I want to know:

  1) Would it be best to split the panels over the 2 controllers or will it not make that big of a difference? (ie. 6 panels on one tracker or 8 (4*2) over 2 trackers)
  2) Would 4 panels per tracker work? Voltage is what concerns me?
  3) The ISC is rated at 11.06A would this be safe on the 11A input of the inverter or should I be looking at the IMP?
  3B) if not  can someone recommend a better suitable panel.  

I want to maximize the amount of watts on the roof now seeing as the installation cost is not that much more for a few more panels, but still staying within a budget. 

 

Thanks.

 

Edited by JohanB
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Impp vs Isc - whichever is higher. For my panels 9.89 Impp, I've seen 12-15A suggested due to MPPT adjusting the charge current upward somewhat. Probably just go with 15A in this case - or whatever is inscribed on your factory-attached cables leading out from the panel(mine are 15A 4mm MC4). Re other panels - better to just work with what you've got? 400+W is a decent output. I know JA Solar do similar to Candian Solar at similar costs if you want to look at other 400W.

Will be interesting to see what others say about splitting across 2 MPPTs.

Edited by Wick
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1 hour ago, Wick said:

Impp vs Isc - whichever is higher. For my panels 9.89 Impp, I've seen 12-15A suggested due to MPPT adjusting the charge current upward somewhat. Probably just go with 15A in this case - or whatever is inscribed on your factory-attached cables leading out from the panel(mine are 15A 4mm MC4). Re other panels - better to just work with what you've got? 400+W is a decent output. I know JA Solar do similar to Candian Solar at similar costs if you want to look at other 400W.

Will be interesting to see what others say about splitting across 2 MPPTs.

"I've seen 12-15A s"

What is the Voc of your string ? What inverter are you using?

I would assume that the higher the string voltage, the lower the current should be, if the 15A is a problem just increase the no of panels in series... 

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2 hours ago, JohanB said:

Hi all, 

I have a query I am planning a hybrid system with a Deye/SunSynk 5kw inverter. I see on the stats it has 2 mppt trackers rated at:

Max. DC Input Power (W): 6500W.
PV input Voltage (V): 370V (100V-500V).
MPPT Range (V): 125-425V.
Full Load DC Voltage Range: 240V-425V.
Start-up Voltage (V): 150V.
PV Input Current (A): 11A + 11A.
No. of MPPT Trackers: 2
No. of Strings Per MPPT Tracker: 1+1.

The panels I am looking at is wired in series (I have a open roof no shading and the lower current is better from what I have read):
410W Canadian solar

PMAX: 410.0W
VMP:      39.10V
IMP:       10.49A
VOC:       47.60V
ISC:        11.06A

So what I want to know:

  1) Would it be best to split the panels over the 2 controllers or will it not make that big of a difference? (ie. 6 panels on one tracker or 8 (4*2) over 2 trackers)
  2) Would 4 panels per tracker work? Voltage is what concerns me?
  3) The ISC is rated at 11.06A would this be safe on the 11A input of the inverter or should I be looking at the IMP?
  3B) if not  can someone recommend a better suitable panel.  

I want to maximize the amount of watts on the roof now seeing as the installation cost is not that much more for a few more panels, but still staying within a budget. 

 

Thanks.

 

You want to keep the power produced by the panels as close to the 3250W that the MPPT allows (6500W/2).

So put 8 strings in series, that will give you 400V max , 11A max (maybe a little more at 0C but close enough, so no problem on exceeding the MPPT voltage, A  limits).

At best,  you will get 90% consistently of installed panel power, so 8*410 = 3280*0.9 = 2.9kW production, even at 100% 8 panels will not give you much more than 3280 which is still in the range for the MPPT.Capture.PNG.ecb5f830d12c2bdb7b9dea32a0aa9a1d.PNG

The current will only get to 11A (as the voltage decreases) at 65C (as per the chart below).

In JHB with the same panels I've never seen more than 320V on my 8 panel string.

I'm keen to see what the professionals have to say........

 

Canadian_Solar-Datasheet-HiKu_395-415W.pdf

Edited by FixAMess
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34 minutes ago, FixAMess said:

You want to keep the power produced by the panels as close to the 3250W that the MPPT allows (6500W/2).

So put 8 strings in series, that will give you 400V max , 11A max (maybe a little more at 0C but close enough, so no problem on exceeding the MPPT voltage, A  limits).

At best,  you will get 90% consistently of installed panel power, so 8*410 = 3280*0.9 = 2.9kW production, even at 100% 8 panels will not give you much more than 3280 which is still in the range for the MPPT.Capture.PNG.ecb5f830d12c2bdb7b9dea32a0aa9a1d.PNG

The current will only get to 11A (as the voltage decreases) at 65C (as per the chart below).

In JHB with the same panels I've never seen more than 320V on my 8 panel string.

I'm keen to see what the professionals have to say........

 

Canadian_Solar-Datasheet-HiKu_395-415W.pdf 1.05 MB · 1 download

Thanks, 

So what you are saying is that the 410w panels would not exceed the current limits if I do 8 * 410. I'm in pta.

And secondly if I understand correctly putting 8 on one input is beter or equal to splitting 4 over the 2 inputs? I was wondering if 4 panels would fall under the minimum.

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Why do you want to split the string? If you want to expand later, just adding a second string will be easier than adding new panels to 2 strings.

The startup voltage, 150V, is when there is no battery or Escom power input so you will need a minimum of 150V PV for the inverter to start working, in fact mine is rated as 150V as well but in a footnote they mention that without battery or escom then 200V is required from PV. (Goodwe)...Not sure how, why this is so.??????

What I have noticed on my setup is that with 7 Panels, I usually have a lower voltage and higher current than the 8 panels..

But even at 90V, at dusk, 0,1A I'm still getting power produced by the MPPT's on both strings, but I do have batteries and escom..Never tried without batteries.

 

 

Capture.PNG

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4 hours ago, FixAMess said:

"I've seen 12-15A s"

What is the Voc of your string ? What inverter are you using?

I would assume that the higher the string voltage, the lower the current should be, if the 15A is a problem just increase the no of panels in series... 

Per string, maintaining the same current through those 15A rated cables attached to the panels.

Quote

And secondly if I understand correctly putting 8 on one input is beter or equal to splitting 4 over the 2 inputs?


Yes. For most, people 1 series string will do the trick, and you would generally purchase your series of panels with the MPPT max input voltage in mind (or vice versa if you already have panels), never exceeding the voltage rating on your MPPTs - or even coming close, to play it safe. Series adds voltage. Parallel adds current. More current = more copper = higher cost for cabling. So get away with the highest voltage, lowest current, and shortest cables possible. If this means splitting across 2 MPPTs, do so, although there will be more copper AFTER the MPPTs outputs merge (say 15A x2 = 30A) - the only benefit I can see to two MPPTs (aside from partial shading conditions) is if each panel string's voltage is so high that you cannot run off one MPPT alone.

Edited by Wick
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3 hours ago, FixAMess said:

Why do you want to split the string? If you want to expand later, just adding a second string will be easier than adding new panels to 2 strings.

The startup voltage, 150V, is when there is no battery or Escom power input so you will need a minimum of 150V PV for the inverter to start working, in fact mine is rated as 150V as well but in a footnote they mention that without battery or escom then 200V is required from PV. (Goodwe)...Not sure how, why this is so.??????

What I have noticed on my setup is that with 7 Panels, I usually have a lower voltage and higher current than the 8 panels..

But even at 90V, at dusk, 0,1A I'm still getting power produced by the MPPT's on both strings, but I do have batteries and escom..Never tried without batteries.

 

 

Capture.PNG

Hi,

I don't want to split it, I was just wondering what would be best. I was thinking if there are two inputs would it not be better to populate both, for performance or optimisation. 

If there is no benefit obviously sticking to one string would be easier and as you say to expand later I will just add a string. 

 

 

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1 hour ago, Wick said:

Per string, maintaining the same current through those 15A rated cables attached to the panels.


Yes. For most, people 1 series string will do the trick, and you would generally purchase your series of panels with the MPPT max input voltage in mind (or vice versa if you already have panels), never exceeding the voltage rating on your MPPTs - or even coming close, to play it safe. Series adds voltage. Parallel adds current. More current = more copper = higher cost for cabling. So get away with the highest voltage, lowest current, and shortest cables possible. If this means splitting across 2 MPPTs, do so, although there will be more copper AFTER the MPPTs outputs merge (say 15A x2 = 30A) - the only benefit I can see to two MPPTs (aside from partial shading conditions) is if each panel string's voltage is so high that you cannot run off one MPPT alone.

Thanks good explanation. I think I am going to do 8 * 410w panels in series runs will be short. 

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4 minutes ago, FixAMess said:

You MUST do them in series, if you do in parallel then you will reach your current limit. So the short, long run, more cable combiner boxes argument is mute.

Ok thanks.

Yes, the current limit, was the concern from the onset, I was afraid I would reach it with series so parallel I will most certainly exceed the 11A limit. 

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