Replaced panel array with existing inverter now PAC reading "0"

Hello All,

Yesterday I replaced 20 old Sunpower 210 watt panels from 2010 on a house roof array.
The system was professionally installed and has been trouble free.

Once the new array was installed (14 Canadian Solar CS6R- 390MS-HL panels) two strings of 7 panels each. Everything connected, checked and panel and rack grounding secured.

it was dark when finished so just checking this morning - I have no error codes but a flashing green light on the SPR 4000m inverter

the system reads
Pac 0W and VPV 256V
Gridtype 240V
L1 120V L2 119V
indicates "waiting"


I have rebooted inverter twice shutting inverter off, then PV disconnect, waiting a minute then inverter then ac reconnect. Inverter seems to boot up fine but right back to situation above.

Any advice on what to work back or forward from to rectify this situation? I read a lot about how the inverter could fail but it doesn't seem to be that from what im experiencing


Thanks G

Am I deducing correctly that i probably have a bad string?

Im getting 240-260 volts but 2 strings of 7 panels should be at least 420 volts, right? (panels VOC is 36 volts ea)

reading that the inverter needs about 325 volts to start up (Sunny boy 4000/Supower 4000 branded)

Sure sounds like something changed! What are the specs on your old panels, the specs on your new panels, and what kind of strings did you have and do you have the old and new panels in?

so I had 2 strings of 10 panels originally. Sunpower 201Watt (40 w amp) one panel failed so we disconnected another one to keep two (balanced) strings of 9
bought and installed 14 canadian solar 390 watt panels. (30.6 watt VMP) Using existing set up (new rails on roof though) connected panels in two strings of 7.
Sorry if i am underexplaining but I essentially plug and play swapped these 14 390 watt panels. Did discuss and research before purchase that it should be within spec/

I will be testing each string and then up on roof to see either what connection issue might be going on...have to get a new multimeter first (it failed when dropped by my kid off roof yesterday. ( family solar affair!)

Thanks G\

7 of the new panels in series would be ~254V at standard conditions, and for the old sunpowers it would have had to be two strings in parallel. Sun powers are MUCH higher voltage, looks like 47.7V so 10 in series would have been ~477V in standard conditions.

Looking online the operational range of the inverter is 100V-480V so it should be working

Open circuit voltage (VOC) on the new panels is 36.6 volts
x14 = 512.4v
so you think a single string would be OK/ acceptable?
inverter spec lists DC input range as 250-600 @ 240AC, so that seems ok

now up on roof to create one string I guess

I there any issue with leaving the wiring for the second string in place but not connected?

pretzelboy said:

now up on roof to create one string I guess

Click to expand...

Just tie the two strings in series at the inverter for now, no need to visit the roof.

WPNS=
Im only getting 250 VOC doest that indicate I have a bad string?
I was going to test at outside PV shut off box first to see if there is power from both strings

pretzelboy said:

WPNS=
Im only getting 250 VOC doest that indicate I have a bad string?
I was going to test at outside PV shut off box first to see if there is power from both strings

Click to expand...

Seven panels in series at 36.6 V (I can’t really tell because you have not given us the specs on the old panels and the new panels) is 256 V, and that’s pretty much what you’re getting so it sounds right. Two strings in parallel is going to give you that same 256 V, but at twice the current.
If your inverter input range starts at 250 V, then I’m not surprised it doesn’t work.
Put both strings in series to get 512 V and see if that works.

Hello all

Humbly asking some assistance.
yesterday replaced the solar array on my house from twenty 14 year old Sunpower 210 panels (4.2kw system)
left current wiring mode in place, which was 2 strings of 10 panels. the layout was 5 over 5 series on left of array 5 over 5 on right.

New panels were fourteen larger Canadian Solar CS6R-390MS panels I mimicked the old config by connecting the 3 over 4 panels on left of array and 4 over 3 panels on right. so 2 strings of 7 panels ( see photo of roof array) There

It was almost dusk as I finished on roof so when pulled all the switches to on again i did notice the flashing green light with the "waiting" message
this morning it seems that im not producing enough voltage for the inverter to operate. No error messages but flashing green and (see image 4764) zero watts and varying 240-250 Vpv

I went to the outside PV disconnect box today and put a multimeter agains the two hots. If I have it on the right setting I seem to be getting 220 or so from each when I bridge the breaker on each (images 4779, 80, 81)

Ive included a crude drawing of how the array lays out with the 2 strings of seven panels with mc4 connection in series image 4783

FWIW I also opened up the inverter to show the DC connect ( image 4778)

OK please help me get this thing working. Im 62 and trying to keep my butt off the roof as much as possible

Thx G

wpns said:

Seven panels in series at 36.6 V (I can’t really tell because you have not given us the specs on the old panels and the new panels) is 256 V, and that’s pretty much what you’re getting so it sounds right. Two strings in parallel is going to give you that same 256 V, but at twice the current.
If your inverter input range starts at 250 V, then I’m not surprised it doesn’t work.
Put both strings in series to get 512 V and see if that works.

Click to expand...

WPNS

so looking at the post I just made - I think i need to go to roof and reconnect all 14 panels into one series (string)?

pretzelboy said:

WPNS

so looking at the post I just made - I think i need to go to roof and reconnect all 14 panels into one series (string)?

Click to expand...

You should be able to convert them into a single series string of 14 panels without going to the roof. I don’t know if both strings go directly to the inverter, or if there is a DC combiner box outside, but you should not need to go up to the roof to test this out. Just put the two strings in series.

WPNS
In img 4780 and 4781 I'm getting readings of +/- 220 v from each of the leads from roof array going into my outside PV shutoff. In img 0443 (attached here) it shows that after the breaker the two leads are combined with a polaris tap into one black.
So there is only one DC hot going from here to the inverter? If that is so why am I only getting the 240 or so Vpv reading from the inverter (img 4764)
here's a shot of the open inverter (img 4778 )It looks like there is a pair of DC feed wires then a a block on the right which has a pair of AC wires (black and red)

here's a shot of the open dc connect box (img4784) this is right below/attached to inverter. looks like a single DC lead (black) going to a combiner, a red and white to grounded.

Scratching my head because Im reasonably sure I had 2 strings at inverter ( as was spec'ed in original install way back in 2009), but my learning curve here has me seeing things wrong I think

Canadian Solar 390 watt panels
Opt operating voltage (VMP) 30.4V
Opt operating current (IMP) 12.4 amp
Open circuit voltage (VOC) 36.4v
Short circuit voltage (ISC) 13.7 A

Sunpower ( Sunny boy) 4000m
4800 w recommended array
DC input voltage range 250-600v @240AC
DC max input 18A

thx--G

I can’t parse your pictures or make sense of your prose or figure out your color codes or why you are measuring across your disconnect. Please step back and take a breath and either document your system properly or (preferably) get an electrician or experienced solar installer to help you. DC can kill you!

measuring across the disconnect because the disconnect has to be open in order to open the access door
Im trying here. I just dont understand strings. If there are two strings feeding into my inverter then why are the two leads at the disconnect box spliced into one just after the breaker?
remember you had said I could combine the two strings into one in series?

Im trying to be careful AND learn.

Anyway thanks for the help you did provide I apologize for not meeting your expectations.

I agree it looks like all 14 panels in series is what is needed.
And that handling DC PV wires can be hazardous - I burned a tiny hole in my thumb and felt a strong shock in my arm when I bushed an exposed 480VDC lead.

Unless there is a disconnect to let you do the rewiring cold (and check/wait for capacitors to discharge too), shut off AC breaker and unplug the four MC4 connectors for two strings PV+ and PV-. Then after confirming zero voltage you can rewire.

(Check for voltage both AC and DC, because some inverters backfeed AC into PV strings.)

36.4Voc x 7 panels = 254.8V
36.4 Voc x 14 panels = 509.6V

Inverter max input 600V?
600V / 509.6V = 1.177

I know that 17.7% is enough headroom. If it was less than 16% I'd say check data sheet for temperature coefficient of Voc for PV panel, and consider record coldest temperature to see if it always remains under 600V.

Sunny Boy 4000m? Is that 4000US, the one in this manual?


see page 46 about positive vs. negative grounding of PV array.

SunPower panels of some generation were highly susceptible to PID, degraded badly when negative grounded (panels biased positive). Solution was to use an inverter which positive grounds the string.

Most other panels are best off negative grounded, suffer some degradation when positive grounded.

The newer crop of inverters are transformerless and PV string floats with half the panels positive biased, half negative. That could degrade some of the panels.

Good thing that most newer panels are PID resistant. But I prefer to use these older transformer type inverters and ground PV string in preferred way.

These panels?


I don't find mention of PID.
Preferred grounding depends on whether N-type silicon doping with P implant, or P type silicon with N implant.
It does say PERC, not sure if that implies one or the other.
I've got some PERC and have to figure that out before commissioning.

Maybe manufacturer of panels can tell you whether negative or positive ground is better. Or which silicon type they're made with.

pretzelboy said:

WPNS
In img 4780 and 4781 I'm getting readings of +/- 220 v from each of the leads from roof array going into my outside PV shutoff. In img 0443 (attached here) it shows that after the breaker the two leads are combined with a polaris tap into one black.
So there is only one DC hot going from here to the inverter? If that is so why am I only getting the 240 or so Vpv reading from the inverter (img 4764)
here's a shot of the open inverter (img 4778 )It looks like there is a pair of DC feed wires then a a block on the right which has a pair of AC wires (black and red)

here's a shot of the open dc connect box (img4784) this is right below/attached to inverter. looks like a single DC lead (black) going to a combiner, a red and white to grounded.

Click to expand...

I noticed your DMM across one open switch pole shows (almost) the voltage that inverter shows.

Modern installations usually isolate both poles PV+ and PV- of a string.
Early installations isolated only one pole, usually PV+, but in your case the array is probably positive grounded so switch isolates PV-

Maybe red wires are PV- of one string, and black wires are PV- of other string.
Try measuring voltage between the two wires on top, measuring between the two wires on bottom, and between each of the four wires to ground.
Double-check which color wire goes to positive input of DMM, which to common, to be sure you're seeing polarity correctly.

I'm guessing the two negative (because it is SunPower) PV leads go through the two switch poles and combine at Polaris, while the two positive leads combine elsewhere.

Be sure to shut off AC breaker, shut off DC disconnect at bottom of inverter, disconnect four MC4 connectors between PV array and wires leading to equipment, check for zero volts between leads and between leads and ground before working on them.

Definitely positive grounded.
Definitely the Sunpower branded Sunny Boy 4000 US

For this thread (to I think close it!)

Hi

connected the 14 panels into one series at roof
capped and weatherproofed the two mc4 connectors left open/unattached.
took DMM reading at pv disconnect red lead zero black lead fluctuating up to high 400's (neg polarity)
close breaker at disconnect, go to basement turn on/reconnect Sunny Boy

very satisfying watching it read MPP establish connection and green flashing light goes from waiting to operation

cloudy day today but quick photo of operation ( from inverter)

Thank you my friend.

Next project buying what's needed to repurpose 16 of the 210 watt panels as an array on the barn (the original backed to subpanel project)

Thank you again

Greg

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