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PV panels and Max Voc

EPicTony

Solar Enthusiast
Joined
May 29, 2022
Messages
225
Location
NE Ohio
I'm now running my EG4-6500 system.
I need to stay under 450vdc (Max Voc).
Running 8 Solarever 455w panels per string. On the panels Voc is 49.3v.
8x49.3= 394 I wanted to give a safety factor so I stopped at 8 / string.

It's 12 deg F outside and I'm only getting 349v from each string. 349/8= 43.6v
Would it be safe to add 1 more panel ? 9x43.6= 392v
I thought the Voc was supposed to increase in cold weather but I'm not seeing that.
FYI this is with the panels connected to the EG4 and under load.
 
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Make sure that you do your test when it’s not under a load. The high voltage restriction has to do with voltage not anything else. So you need the voltage unloaded to make that determination.
 
Make sure that you do your test when it’s not under a load. The high voltage restriction has to do with voltage not anything else. So you need the voltage unloaded to make that determination.
Ok thanks I will definitely re-measure with no load ! I don't know what I would do without help from this forum.
 
The "oc" in Voc stands for "open circuit" AKA there is nothing connected to the panels. You must not exceed the Voc limit of the inverter at any point otherwise smoke production is imminent...
Yes, now I understand. I'm sticking with my original 8 panels to stay 50vdc under the Voc max.
 

At 12F/-11C I have you x 1.16 = 457V.
You are pushing it unfortunately. Might recheck @ calc link in same link above with specific temp coefficient data for your panels...??
 

At 12F/-11C I have you x 1.16 = 457V.
You are pushing it unfortunately. Might recheck @ calc link in same link above with specific temp coefficient data for your panels...??
From the manual:
1675289656199.png
1675290490988.png
From this am I ok ? It looks like I am (fingers crossed) -13F is about as cold as it gets where I live. 394x1.13= 445. I could also add a shunt wire when super cold so I would only be using 7 panels instead of 8.
 
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Rather than eyeballing the chart you can just use the numbers from the spec sheet

Temp coefficient is -0.29%/C so -25C would be -50C*-0.29%/C=14.5%

49.25V * 8 * 1.145 = 453.42V

At -13F that would be you Voc which is over the 450V by a hair. I don't know how much overhead that inverter has built in and I don't know what the odds are of -13F weather at your place but these are the numbers.
 
Looks good. :) I thought you were saying smoke at 450V, you've added that it's at 500V. You are spot on, don't change a thing without additional research. From the calculator, of course agrees with the chart from your panel spec. Assuming you have the same Solarever 455W that "everbody" is selling at this time.

Result​

You entered

  • Total string OC voltage: 394
  • Nominal maximum power: : 3640
  • Worst case temperature: -25
  • Temperature coefficient (Voc): -.29
  • Temperature coefficient (Pmax): -.35
For these, your:

  • Total worst case differential is: 50
  • Your voltage increase (%) is: 14.5
  • Your voltage increase (V) is: 57.13
  • Your maximum voltage (V) is: 451.13
  • Your Pmax increase is (%): 17.5
  • Your Pmax increase is (W): 637
  • Your total Pmax at this temperature is (W): 4277


Go back to the form
 
Greg, I was admiring your awesome system in Show and Tell, thx for sharing. You should be very proud...

So. Since I *am* a Newbie and we're already here, what is going on with an Inverter between the Maximum Vmppt (450V in Tony's case) , and Maximum PV array Voc to inverter (500V here..)??

Power flatlining from 450 to 500V then POOF!! ?? One spec is under load, one not or ?? Please explain if anyone can, or point me to a resource if its already explained somewhere. Thanks ?
 
I have a Sol-Ark so I can only speak to that one, but I would assume other inverters are similar in terms of specifications.

They would have an MPPT Voltage Range, in the Sol-Ark's case it's 125-425V which means that the MPPT will track and find the optimal power generation point between these two points. If your PV string's peak power voltage falls outside of these two voltage values, it won't find it. Usually if it's under the minimum the inverter just won't even power on.

The other value they provide is Voc Max, on the Sol-Ark it's 500V so any voltage higher than that will possibly cause permanent damage to the inverter. Actually in Sol-Ark's case they additionally write "Damage will occur if PV VOC > 550V" in the manual.

A 500Voc of a string would likely have working voltage under 425V as the difference is ~17% which would mean a working temperature ~-30F to -40F for your standard PV with -0.26 to -0.29%/C Voc coefficient. The math checks out and there is not a whole lot to worry about.

Note that even if the temps are -40F and you have a Voc of 500V, the second you hook up the inverter the voltage will drop to the Rated Voltage Vmpp which is 20% lower than Voc and you will be well within the MPPT operating range of the inverter.

I think the risk/confusion/concern with the EG4-6500 specs is that the gap between the 450V Max MPPT voltage and the 500V Voc Max is only 11% which is far tighter than the 17% of the Sol-Ark, therefore gives you more concern with maximizing number of panels in series and being concerned with colder temperatures.

With the Sol-Ark you practically can't overrun the Voc even in the coldest weathers as long as you stay under the MPPT voltage limit (unless you're up really far north) while with the EG4 it's a lot easier to get there.

And thanks for the kind words about my system, it is doing really well and I could not be any happier with it!
 
Thanks for expanding on this, Greg. It's a debate, but if I were Sol-Ark I think I would have kept the fudge-factor to myself... :LOL:
 
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