Solar panel math

This is my first time on a forum, so bear with me. How do you figure how many solar panel for a Growatt 5000w ES off grid 240v inverter, maximum PV input voltage is 450VDC and 6000w of solar power? I have 60 cell, polycrystalline, 250w, VOC 37.6 and I think 8.27 amp if I reading it right. I guess I don't understand the math, I have watched a lot of video, but maybe I'm over thinking it. Can someone explain it to me, thanks James.
 

Alphacarina

Solar Enthusiast
If you wanted the maximum allowable, you could series/parallel 24 of your 250 watt panels. 12 in series paralleled with another string of 12 in series. That would give you 450 volts and 6,000 watts

Don
 

iamrich

Solar Addict
You have three measurements that matter:

Input Voltage Max = 450V, so if you are running your panels in series (which you will be), you add the voltage of each panel in a string to get a total number. So if you run 10 panels, you have VOC 37.6v x10 which is under 450V which is good. 10x250w =2500w output

Input current max = 100A, so your strings will be 8.27a x how every many you have. So let's say you run 2 of the above strings you would have 5000w total.

Total wattage input = 5500w, so two strings would be good...
 
Thank you, I thought my math was right, I'm just overthinking, but that sure is a lot of panels. I will probably run 20 panel in series and parallel, and go from there, thanks, James
 

iamrich

Solar Addict
If you don't mind adding a combiner box and breakers I think I would probably run 24 panels 6S4P. That would give you plenty of safety margin (~300v/~10a strings) and redundancy in case one panel craps out. 24 panels would be 6000w, but you could turn off any string for maintenance and still have 4500w of output. Or point them in different directions to get power over a longer time period. You could also run 8S3P (same output, one less string). Lots of good options for that size array.
 

schmism

Solar Addict
series you add voltage
parallel you add current

so 6S4P with "VOC 37.6 and I think 8.27 amp" would be 6*37.6 = 225v @8.27*4=33a

wire size depends on current, length of run, type of wire, and what its run in.

most jurisdictions require panel frames to be earthed for lightning, however the specifics are going to depend on your location requirements.
 

iamrich

Solar Addict
What about wire size running 24 panels in a 6S4P, I like that idea, especially if you lost a panel. And what about lightning protection?

Depends on your setup, but I would run 12awg from the panels to a combiner box and then run the biggest wire you can from the combiner box to the charge controller which would be close together. I think most solar wire is rated 600v plus so no issues, and obviously 9a is no issue for 12awg, probably even 14awg as long as the run isn't super long. I would go 12.
 

iamrich

Solar Addict
I am using a Midnite Solar MNPV6, but at that voltage you would need the double breakers so you would probably need the MNPV12. I think the breakers are like $40 each and the box is probably $200, so not cheap. There might be better solutions, but I don't have any experience running over 150vdc breakers.
 

Supervstech

Administrator
Staff member
Moderator
Solar math.
Bank size in KWh
Daily sun
Charge controller max wattage
Useage KWh per day.
Inverter max wattage
Inverter continous wattage

If your inverter is capable of 5000W, that is 120Kwh a day possible...
6000W solar is average 30KWh some days more, some days less... some days a LOT less.

What I'm saying is know what you use, know what you need.
 

wattmatters

Solar Enthusiast
If you wanted the maximum allowable, you could series/parallel 24 of your 250 watt panels. 12 in series paralleled with another string of 12 in series. That would give you 450 volts and 6,000 watts
That panel configuration has the potential to significantly exceed the specified voltage limits of the inverter's MPPT input.

Add ~20% to the panel Voc rating if expecting very cold weather, increasing their Voc from 37.6V to ~45V.

With a max inverter DC input limit of 450V, I would not be putting any more than 10 of those panels in series.

To get the max of 6000W with 250W panels, that's 24 panels. To keep string at 10 or fewer then parallel 3 x strings of 8 panels.

BUT - do we know what the maximal MPTT input current rating of the inverter is?

If it's less than 30A then not sure I'd suggest paralleling 3 arrays.

Best you'll get from those panels is 2 arrays of 10 panels = 5000W
 
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