Help required to estimate VOC of panel strings compatible with inverter

[NSsolar]

Hi everyone
I'm going to add one more panel to already installed panels (9 panels and all connected in series).
The panels are of JA solar, Deep Blue 4.0, JAM66D42-580/MB bifacial N-type.
I'm unable to understand if I could hook the new panel with the existing panels in series or I have to make two strings of 5 panels each and parallel them..
Inverter Specs.
Nominal DC/Max DC= 360/500 VDC
Start up/Initial Feeding= 120/150 VDC
MPP range = 120-430 VDC
Max input Current= 27 A
No of tracker= 1

Panels specs are
VoC = 48.18
Vmp = 40.42
Isc = 15.21
Imp = 14.35
Temp Coefficient of Isc = +0.046%/°C
Temp Coefficient of Voc = -0.36%/°C

Minimum temperature that we encounter in winters is around 3°C while maximum temperature reaches 46°C in summer.
If anyone can tell if I hook all the panels in series, will the VOC of inverter be crossed of it will be in limits. And if make two strings of 5 panels each, will it exceed the Isc of inverter?

 

[hwy17]

VOC 48.18

SCC Vmax: 500

9 is definetely the most anyone here will recommend you run in series. Some will say 9 is already risky.

10 is out of the question.

Those are cool panels. I hope we get 580 class panels in the USA soon.

 

[BentleyJ]

I'm calculating 462Voc at 0 deg C. so 9 in series should be OK.

The MPP range of the Inverter Charger is 120V to 430V so under normal operating conditions the Voltage of the string should be around 365V.

(40.5V is the Vmp)

 

[NSsolar]

If I make two strings of 5 panels, won't it exceed the Isc of inverter too?

 

[NSsolar]

I'm calculating 462Voc at 0 deg C. so 9 in series should be OK.

The MPP range of the Inverter Charger is 120V to 430V so under normal operating conditions the Voltage of the string should be around 365V.

(40.5V is the Vmp)

I'm running 9 panels already for a couple of months and it giving great results (achieved 4960 watts on 24th March). I'm interested to get the inverter to maximum of it's capacity (7000W). So, exploring the options to hook three more panels. But at the moment, I have only one panel at the disposal.

 

[NSsolar]

VOC 48.18

SCC Vmax: 500

9 is definetely the most anyone here will recommend you run in series. Some will say 9 is already risky.

10 is out of the question.

Those are cool panels. I hope we get 580 class panels in the USA soon.

If I make two strings of 5 panels, won't it exceed the Isc of inverter too?

 

[BentleyJ]

If I make two strings of 5 panels, won't it exceed the Isc of inverter too?

Yes, but Current is only used by the charge controller up to the limit of what can be accepted. In other words, the panels do not force current through the charge contoller. The CC only uses as much current as is available (up to the maximum) based on prevailing irradiation conditions. PV's will only produce Imp and Vmp under ideal conditions. Any PV power that is available, but not used is called clipping.

It is standard practice to "over panel" with regard to Amperage because the system will perform better under cloudy conditions at the expense of maybe wasting some available power at Noon under rare perfect conditions.

 

[hwy17]

If I make two strings of 5 panels, won't it exceed the Isc of inverter too?

Yes, there's no perfect way for your charge controller to make use of 10 of these panels. The lost production will probably be very minimal though.

But there's also wiring concerns. If you have 2.5mm2 or 4mm2 between the inverter and array, then you might need new wires to run in parallel.

 

[NSsolar]

Yes, there's no perfect way for your charge controller to make use of 10 of these panels. The lost production will probably be very minimal though.

But there's also wiring concerns. If you have 2.5mm2 or 4mm2 between the inverter and array, then you might need new wires to run in parallel.

I have already used 6mm2 wire during installation of system just for the sake of future enhancement.
I'm confused either to hook only one more panel to reach 5800W or hook 3 more to reach 7000W and get around 6kw output from inverter (as it is rated 6kw). Actually, it is grid feeding inverter being used with net metering, so, I really can't decide if 10 panels or fine or I should go to maximum of inverter. Suggestions will be highly welcomed

 

[hwy17]

I have already used 6mm2 wire during installation of system just for the sake of future enhancement.
I'm confused either to hook only one more panel to reach 5800W or hook 3 more to reach 7000W and get around 6kw output from inverter (as it is rated 6kw). Actually, it is grid feeding inverter being used with net metering, so, I really can't decide if 10 panels or fine or I should go to maximum of inverter. Suggestions will be highly welcomed

More is better if you ask me. 6+6, 7+7.

 

[Hedges]

Different Orientations for Different Strings, I always say.
More hours of high production, lower peak for less clipping.
That should support panels with PTC or NOCT rating 1.4x of inverter (more or less) without clipping. Based on relative area presented to sun.

 

[NSsolar]

Different Orientations for Different Strings, I always say.
More hours of high production, lower peak for less clipping.
That should support panels with PTC or NOCT rating 1.4x of inverter (more or less) without clipping. Based on relative area presented to sun.

Hi Hedges
I have a customized structure, so, the orientation of the panels will be same. as the inverter can support 7000W PV, I can hook 3 more panels to make 6+6 strings. Since, the inverter is capable to deliver 6000W, what if hook only one more panel and make two strings with 5 panels. will these 10 panels be more efficient or 9 panels in series (specially in cloudy days) due to low Vmp and VoC of 5 panels. The answer could help me reach a conclusion.

 

[Hedges]

I don't see inverter model number quoted. Have a link to data sheet and manual? Do those give efficiency curves?

One more panel provides about 10% more energy to make use of, probably better.
Under cool clear conditions when PV panels make full Imp, the current being 10% higher than inverter would not be utilized. That is when I see highest kWh/day, so could be OK that it clips
I think 5s2p does meet minimum voltage, but not if you get any shade. If a shadow would hit the array, better to do 9s.
9s can use smaller wire, has less IR loss. And hits nominal 360Vmp.

I think 9s would be best of the two choices.

The 6kW inverter usually won't make full power.
I would prefer 9s2p, with the two strings oriented differently. That could make full power or close to it for several hours.

 

[NSsolar]

I don't see inverter model number quoted. Have a link to data sheet and manual? Do those give efficiency curves?

One more panel provides about 10% more energy to make use of, probably better.
Under cool clear conditions when PV panels make full Imp, the current being 10% higher than inverter would not be utilized. That is when I see highest kWh/day, so could be OK that it clips
I think 5s2p does meet minimum voltage, but not if you get any shade. If a shadow would hit the array, better to do 9s.
9s can use smaller wire, has less IR loss. And hits nominal 360Vmp.

I think 9s would be best of the two choices.

The 6kW inverter usually won't make full power.
I would prefer 9s2p, with the two strings oriented differently. That could make full power or close to it for several hours.

Inverter Specs are here

Voltronic Power On-Grid with Energy-Storage Inverter InfiniSolar V II 6KW TWIN

voltronicpower.com

No shadow could hit the array (No trees, or other object around, which could shade the panels) as the panels exposed to Sun throughout the day.
So, you recommend 5S2P if no shade hits otherwise 9S would be recommended?
what if I put 6S2P? after clipping, could I get max output from inverter under clear condition? would 6S29 outperform 5S2P or the results would be similar due to clipping effect?

 

[Hedges]

No shadows, you should be able to get away with 5s. Although I like reaching "rated voltage".
I didn't find any efficiency curves from that link. Just 93% DC/AC, nothing about MPPT PV to battery DC.

Overpaneling 6s2p should make full power for more hours. And off-season or some clouds, you'll get more power.
But I like multiple orientations, so power doesn't drop off much when sun's angle changes. In that case maybe 10kW or so of PV panels.
Panels are cheap, put up what you can. Even if it was 9s2p, that just means power won't be as low during overcast.

 

[LydMekk]

I would go down to 8 in series.
9 are too much IMO.

 

[Hedges]

How come?

"VoC = 48.18" x 9s = 434Voc under nominal conditions

"Nominal DC/Max DC= 360/500 VDC", 500V / 434Voc = 1.153

Temp Coefficient of Voc = -0.36%/°C, 0.153 / -0.0036 = -42.5 (relative to 25C)
25C -42.5 = -17C coldest temperature before 500V exceeded.

"Minimum temperature that we encounter in winters is around 3°C"


"Vmp = 40.42" x 9s = 364Vmp nominal, just what the inverter calls for.

 

[NSsolar]

How come?

"VoC = 48.18" x 9s = 434Voc under nominal conditions

"Nominal DC/Max DC= 360/500 VDC", 500V / 434Voc = 1.153

Temp Coefficient of Voc = -0.36%/°C, 0.153 / -0.0036 = -42.5 (relative to 25C)
25C -42.5 = -17C coldest temperature before 500V exceeded.

"Minimum temperature that we encounter in winters is around 3°C"


"Vmp = 40.42" x 9s = 364Vmp nominal, just what the inverter calls for.

Hello Hedges
"Nominal DC/Max DC= 360/500 VDC", 500V / 434Voc = 1.153
What's meaning by this and how to use this ratio?


Secondly, as shown in attachment, yesterday, it was over caste, cloudy day. I noticed that around 11 am, the system reached 5330 W (Installed capacity is 5220 W). Since, the panels are bifacial, I guess, due to scattering, the panels were producing from lower side as well. My questions are
1. What if I use some sort of reflecting surface (sheets, mirrors etc.), could these 9 panels reach VOC of inverter?
2. How much gain is expected if some sort of reflecting surface is spread beneath the panels to get output from lower side of panels?

Cheers

 

[Hedges]

"Nominal DC/Max DC= 360/500 VDC", 500V / 434Voc = 1.153
What's meaning by this and how to use this ratio?

Based on data sheet specs, expect 434Voc from string under nominal 25C temperature.
Inverter allows up to 500V input. The ratio 500V / 434V = 1.153 says that we can tolerate up to 15.3% voltage increase before 500V is exceeded.
I then used temperature coefficient of Voc = -0.36%/°C to determine what cold temperature would boost Voc of string as high as 500V.
The answer was -17C.

So long as your ambient temperature never, ever gets below 17C, we don't have to worry about over-voltage damaging the inverter.

Therefore, regarding "I would go down to 8 in series. 9 are too much IMO.", I asked, "How come?"

 

[NSsolar]

Based on data sheet specs, expect 434Voc from string under nominal 25C temperature.
Inverter allows up to 500V input. The ratio 500V / 434V = 1.153 says that we can tolerate up to 15.3% voltage increase before 500V is exceeded.
I then used temperature coefficient of Voc = -0.36%/°C to determine what cold temperature would boost Voc of string as high as 500V.
The answer was -17C.

So long as your ambient temperature never, ever gets below 17C, we don't have to worry about over-voltage damaging the inverter.

Therefore, regarding "I would go down to 8 in series. 9 are too much IMO.", I asked, "How come?"

Thanks for your response.
What about other questions regarding the bifacial gain observed and could this bifacial gain increase the VOC as well? I have posted the real time output images if inverter where we can see that the output was around 5330W (against installed capacity of 5220W). Images have been attached in previous post