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10x 540w Panels in 1 string?


EugeneS

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Hi all,

Need to get some advice.  I'm installing 10x 540w JA Solar panels and trying to save some costs. The installers feels I should be fine installing them as 1 string on 1 MPPT. 

However, I'm getting apprehensive as the VOC is 49.6 per panel (496 total) and recommended max on my Sunsynk 8KW is 500. 

Any views or recommendations? Should I rather do 2 strings of 5 panels each?

Thanks in advance,

Eugene 

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Some practical examples may help...

I run 2 strings with 12 panels each and the strings *just* breach 500V on a partly cloudy day (String 2 had a 510V peak on Sunday).  Voc on my panels are 45.6V (for a 547.2V theoretical max) and my roof has a 17.2 degree angle.

PS: My inverter is capable of 900V per string, so I'm actually thinking of adding more panels 😁

image.thumb.png.65eb8744bf8eabb750d212b89b670689.png

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4 hours ago, EugeneS said:

Hi all,

Need to get some advice.  I'm installing 10x 540w JA Solar panels and trying to save some costs. The installers feels I should be fine installing them as 1 string on 1 MPPT. 

However, I'm getting apprehensive as the VOC is 49.6 per panel (496 total) and recommended max on my Sunsynk 8KW is 500. 

Any views or recommendations? Should I rather do 2 strings of 5 panels each?

Thanks in advance,

Eugene 

I have those exact panels. Those panels are supper efficient.
Be careful for partially cloudy days, then they far exceed their max rates at times.

If your recommended max voltage is 500 then I personally would aim for 450max on the safer side.
It's the voltages that makes the smoke :)

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14 hours ago, EugeneS said:

Model Sunsynk-8K-SG01LP1

Location: Kempton Park, Gauteng

Don't have exact pitch, but not steep. Don't know azimuth.

I was talking about the panels' model # / specs. 😀 Or maybe you have the spec sheet that you can share?

Azimuth is the direction that your roof (and thus your panel) is facing relative to True North. You can get it to a reasonable degree of accuracy using Google maps.

Azimuth and pitch (or tilt angle) are important to know, because the panel's specs are derived at optimal conditions, and your own installation probably deviates from this. If you know what this  deviation is, then you can more accurately assess the degree at which the panel's performance would be degraded, and those voltages might not be so scarily high after all.

Kempton Park is roughly 26° 6' 0" S / 28° 13' 59" E. As a rule of thumb, optimal pitch is equal to the Latitude, so for your install this will be slightly over 26 degrees (relative to level ground).

Here's a vid explaining it: 

 

Location is also important for historic weather conditions, to size panel arrays you will need the lowest temperature recorded in the past say 10 or 20 years, this is because the panels' specs are derived at STC and / or NOCT, and lower temperatures than these cause the panel to produce more power than the spec sheet. You can get this information from a site like this.   

Once you have all of this info, here is a good guide on how to use it to do string sizing, and to take into account temperature coefficient.

Edited by YellowTapemeasure
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1 hour ago, YellowTapemeasure said:

I was talking about the panels' model # / specs. 😀 Or maybe you have the spec sheet that you can share?

Azimuth is the direction that your roof (and thus your panel) is facing relative to True North. You can get it to a reasonable degree of accuracy using Google maps.

Azimuth and pitch (or tilt angle) are important to know, because the panel's specs are derived at optimal conditions, and your own installation probably deviates from this. If you know what this  deviation is, then you can more accurately assess the degree at which the panel's performance would be degraded, and those voltages might not be so scarily high after all.

Kempton Park is roughly 26° 6' 0" S / 28° 13' 59" E. As a rule of thumb, optimal pitch is equal to the Latitude, so for your install this will be slightly over 26 degrees (relative to level ground).

Here's a vid explaining it: 

 

Location is also important for historic weather conditions, to size panel arrays you will need the lowest temperature recorded in the past say 10 or 20 years, this is because the panels' specs are derived at STC and / or NOCT, and lower temperatures than these cause the panel to produce more power than the spec sheet. You can get this information from a site like this.   

Once you have all of this info, here is a good guide on how to use it to do string sizing, and to take into account temperature coefficient.

Thank you for all the valuable information. 

This is the spec sheet I could find: JAM72S30 525-550 MR (shopify.com)

Azimuth seems to be around 20-25 degrees.

What is the worst case scenario if the system goes into over voltage? I would assume there are sufficient safeguards to ensure shutdown or errors etc and that nothing should blow or burn out?

Or do I spend an extra R3,000 for a larger protection box in order to essentially cater for one extra panel (from 9 panels to 10) - I realise I will string them 5 each then, but the expense is really for one more panel.

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4 minutes ago, EugeneS said:

Thank you for all the valuable information. 

This is the spec sheet I could find: JAM72S30 525-550 MR (shopify.com)

Azimuth seems to be around 20-25 degrees.

What is the worst case scenario if the system goes into over voltage? I would assume there are sufficient safeguards to ensure shutdown or errors etc and that nothing should blow or burn out?

Or do I spend an extra R3,000 for a larger protection box in order to essentially cater for one extra panel (from 9 panels to 10) - I realise I will string them 5 each then, but the expense is really for one more panel.

Thanks, will take a look.

Over the specified voltage will result in expensive damage. The MPPT can easily clip the amps, but not the voltage.

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15 minutes ago, EugeneS said:

Thank you for all the valuable information. 

This is the spec sheet I could find: JAM72S30 525-550 MR (shopify.com)

Azimuth seems to be around 20-25 degrees.

What is the worst case scenario if the system goes into over voltage? I would assume there are sufficient safeguards to ensure shutdown or errors etc and that nothing should blow or burn out?

Or do I spend an extra R3,000 for a larger protection box in order to essentially cater for one extra panel (from 9 panels to 10) - I realise I will string them 5 each then, but the expense is really for one more panel.

Wire in series/parallel. Problem solved, surely? You can expect catastrophic failure on overvoltage. 

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My calculations based on the information supplied above.

Inverter Input Voltage: 370V (100V-500V) - thus max should be 500V

MPPT range 125 - 425V

Panel VOC 49.6v x 10 = 496V

Panel VMP 41.64 x 10 = 417V

So, whilst 10 panels are within max without accommodating weather and also in MPPT range, I suspect it would be best to either drop to 9 panels total or to spend the extra R3k and do two strings of 5 each.

 

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47 minutes ago, EugeneS said:

Thank you for all the valuable information. 

This is the spec sheet I could find: JAM72S30 525-550 MR (shopify.com)

Azimuth seems to be around 20-25 degrees.

What is the worst case scenario if the system goes into over voltage? I would assume there are sufficient safeguards to ensure shutdown or errors etc and that nothing should blow or burn out?

Or do I spend an extra R3,000 for a larger protection box in order to essentially cater for one extra panel (from 9 panels to 10) - I realise I will string them 5 each then, but the expense is really for one more panel.

OK so here are my calcs using this method:

 

  String size calculations            
               
  JA Solar 540W panel JAM72S30 525-550/MR   8k Sunsynk inverter      
VoC 49,600000 volts          
Vmp 41,680000 volts          
Max panels 10,080645            
      Max Voltage 500,00      
      MPP 125,00 425 volts  
      Max input DC power 10400,00 watts    
Minimum string size 2,999040 therefore    3,00 panels per string minimum    
maximum string size that doesn’t exceed operating voltage 8,568548 therefore    10,00 panels per string max    
Does max string size fall within MPP range 416,800000 therefore    YES      
               
Would extreme temperatures cause us to fall outside a safe operating range?                                               
Coldest day ever       4 degrees celsius    
Temperature Coefficient of Voc       0,275 percent    
NOCT       45      
Difference       41      
VoC * temp coefficient (voltage change /degree celsius)       0,1364      
Multiplied by temp difference (what each panel will produce extra on a cold day)       5,5924      
What each panel will actually produce on a cold day       55,1924      
All panels together 6     331,1544      
  7     386,3468      
  8     441,5392      
  9     496,7316      
  10     551,924      
  11     607,1164      
  12     662,3088      
Warmest day ever?       26 degrees celsius   so not over NOCT

So yes, it is possible to use 10 per string, but you will run into problems if the temp drops to 4 degrees in Winter. Will it ever be 4 degrees in Kempton Park between 11H00 at 13H00 is anyone's guess, and further research is needed, but note that you start running into problems once you go lower that 43 degrees C already 😀

You could argue that your azimuth (at 20-25 degrees) and pitch is not optimal, and therefore could negate the temp co-efficient, but those are quite complicated calculations to make, and remember that real-time azimuth changes every second because the earth moves and wobbles.

Practically speaking, if I were you, I would go with 9 panels (and leave space for a tenth one) and then monitor the system over 1 year at least before making a decision on the 10th one.

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i was going to use ten 355 watt panels ( Voc 46.8 volts ), so a total of 468 volts, i am based in Cape town, so the chances were extremely slim that the voltage would ever hit 500 volts, but then on second thought decided to use nine panels, why take a chance of blowing an mppt for an extra 250-300 watts, so yes, for the additional few watts, i would say, don't take a chance, as Sunsynk will surely NOT cover the mppt under warranty.

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43 minutes ago, YellowTapemeasure said:

OK so here are my calcs using this method:

 

  String size calculations            
               
  JA Solar 540W panel JAM72S30 525-550/MR   8k Sunsynk inverter      
VoC 49,600000 volts          
Vmp 41,680000 volts          
Max panels 10,080645            
      Max Voltage 500,00      
      MPP 125,00 425 volts  
      Max input DC power 10400,00 watts    
Minimum string size 2,999040 therefore    3,00 panels per string minimum    
maximum string size that doesn’t exceed operating voltage 8,568548 therefore    10,00 panels per string max    
Does max string size fall within MPP range 416,800000 therefore    YES      
               
Would extreme temperatures cause us to fall outside a safe operating range?                                               
Coldest day ever       4 degrees celsius    
Temperature Coefficient of Voc       0,275 percent    
NOCT       45      
Difference       41      
VoC * temp coefficient (voltage change /degree celsius)       0,1364      
Multiplied by temp difference (what each panel will produce extra on a cold day)       5,5924      
What each panel will actually produce on a cold day       55,1924      
All panels together 6     331,1544      
  7     386,3468      
  8     441,5392      
  9     496,7316      
  10     551,924      
  11     607,1164      
  12     662,3088      
Warmest day ever?       26 degrees celsius   so not over NOCT

So yes, it is possible to use 10 per string, but you will run into problems if the temp drops to 4 degrees in Winter. Will it ever be 4 degrees in Kempton Park between 11H00 at 13H00 is anyone's guess, and further research is needed, but note that you start running into problems once you go lower that 43 degrees C already 😀

You could argue that your azimuth (at 20-25 degrees) and pitch is not optimal, and therefore could negate the temp co-efficient, but those are quite complicated calculations to make, and remember that real-time azimuth changes every second because the earth moves and wobbles.

Practically speaking, if I were you, I would go with 9 panels (and leave space for a tenth one) and then monitor the system over 1 year at least before making a decision on the 10th one.

Thank you very much for this very comprehensive reply.

I think I'll either go with your suggestion of only linking 9 panels or getting a second protection box

 

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1 hour ago, JoeyhZA said:

Wire in series/parallel. Problem solved, surely? You can expect catastrophic failure on overvoltage. 

Sure, but his panels produce 12.97 Amps Imp, so 2 panels in parallel means 25.94. The 8K Sunsynk will clip it to 22A. That's almost 18% loss before it even hits the cable to the inverter. He would be better off buying 445W panels, because they would be cheaper for the same performance.

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On 2021/10/16 at 8:31 AM, Tariq said:

i was going to use ten 355 watt panels ( Voc 46.8 volts ), so a total of 468 volts, i am based in Cape town, so the chances were extremely slim that the voltage would ever hit 500 volts, but then on second thought decided to use nine panels, why take a chance of blowing an mppt for an extra 250-300 watts, so yes, for the additional few watts, i would say, don't take a chance, as Sunsynk will surely NOT cover the mppt under warranty.

And with more than one years' worth of data at your disposal (if I recall correctly), has the conservative approach paid off for you?

Edited by YellowTapemeasure
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On 2021/10/16 at 11:20 AM, YellowTapemeasure said:

Sure, but his panels produce 12.97 Amps Imp, so 2 panels in parallel means 25.94. The 8K Sunsynk will clip it to 22A. That's almost 18% loss before it even hits the cable to the inverter. He would be better off buying 445W panels, because they would be cheaper for the same performance.

I also opted for the 455w panels. Can install a max of 10900w on the 8kw Sunsynk with losing a few watts due to max of inverter. I was never aware that exceeding the current rating of the mppt is a non-issue

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I have 28 x 455watt JA Solar panels installed on my Sunsynk 12,740W altogether.

2x6 on one string and 2x8 on the other string. Max voltage I have seen on the  longer string is 390V and that is with a probably 25mtr cable run so I would guess I am loosing a few volts there. 

Max Amperage I get is 19.9A on both strings so I am assuming that the inverter is clipping slightly.

My suggestion would be to stay well clear of the max voltage of the MPPT and just split it into two strings and leave some space for more panels when you have some spare cash. 

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