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PV panel amps and volts on Axpert 5kva inverter


gertc
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Hi all

Would appreciate your help on this.  My setup:

3 Axpert 5 Kva inverters in parallel
27 Yingli 260 Watt panels (3 sets, a set for each inverter, of 3 series by 3 parallel)
800 ah Gel batteries @ 48v

The Yingli panels' spec at 1000 w/m2 solar radiation:
- Voltage at maximum power = 30.3
- Current at maximum power = 8.59
- Open circuit voltage = 37.8
- Short circuit current = 9.09

What happens during the peak sunshine hours of the day, when the panels are reaching their max output is that current climbs to over 12 amps (40 amps per set of 9 panels) while the volts stay well below their max, at around 20 volts (60 volts per string).  When the solar radiation and resulting power output is lower, the volts are between 25-30 volts, but as the solar radiation increases the volts drop and the amps increases above the max.  Overall the power output in Watt is still close to spec, but the amps and volts are not what I expect. 

This in turn causes issues with the 40 amp circuit breakers I have for each set of solar panels, causing them to trip in the middle of the day.

Would appreciate any help

PS Yingli panel specs attached - I have the 260 Watt panels

DS_YGE60Cell-29b_35mm_EN_v04.pdf

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If you using the Axpert to report PV current then there is an anomaly within Axperts in that they report PV volts before the MPPT and PV Amps after the MPPT. So in my case it often reports 44A whereas if you do the calculation it is closer to the maximum of 32A for my PV array. I have 12x250W Yingli panels in 4 strings of 3 and never have any hassle with a 40A DC breaker. The voltages you are seeing seem a bit low. I would expect to see figures of 68 to about 75V at maximum power and your Isc is 9.09A so I would not expect anything over 28 -29 A. Are you sure your breakers are DC rated? (It is not DC rated unless it says so on the outside- don't let some wiseass electrical supplier tell you it is DC rated check for yourself). That is the only thing that I can think of. You low PV panel voltage troubles me but I cannot put my finger on it. There may be a wiring fault somewhere. Did you use a contractor to do your install or is it DIY? 

Edited by Chris Hobson
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44 minutes ago, gertc said:

Hi all

Would appreciate your help on this.  My setup:

3 Axpert 5 Kva inverters in parallel
27 Yingli 260 Watt panels (3 sets, a set for each inverter, of 3 series by 3 parallel)
800 ah Gel batteries @ 48v

The Yingli panels' spec at 1000 w/m2 solar radiation:
- Voltage at maximum power = 30.3
- Current at maximum power = 8.59
- Open circuit voltage = 37.8
- Short circuit current = 9.09

What happens during the peak sunshine hours of the day, when the panels are reaching their max output is that current climbs to over 12 amps (40 amps per set of 9 panels) while the volts stay well below their max, at around 20 volts (60 volts per string).  When the solar radiation and resulting power output is lower, the volts are between 25-30 volts, but as the solar radiation increases the volts drop and the amps increases above the max.  Overall the power output in Watt is still close to spec, but the amps and volts are not what I expect. 

This in turn causes issues with the 40 amp circuit breakers I have for each set of solar panels, causing them to trip in the middle of the day.

Would appreciate any help

PS Yingli panel specs attached - I have the 260 Watt panels

DS_YGE60Cell-29b_35mm_EN_v04.pdf

This does not make sense at all. Does this happen on all 3 inverters or perhaps only on one of them?  The short circuit current per panel is only 9A, so for 3 parallel strings it will be 27A @ 1000w/m2. Say you have clouds and the cloud effect, you might get up to 25% more from the panels - then they would give you 11.25A per string, 33.75A per set and that is at short circuit, so the V would be 0.  You get 20V per panel when this happens, so you are running at less than short-circuit current. I cannot explain why you would measure 12A per string and how a 40A breaker will trip.

I'm going with Chris' comment, probably the breakers are not DC rated.

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Hi Gertc

 

Please send model numbers of your breakers used on the strings.

If possible maybe even a picture of the inside of your combiner boxes.

12A per string also does not make sense to me, how are you measuring this?

The voltages lets me think you have 4 strings of 2 panels per string

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Just a thought that I learned once when I got strange readings on my charge controllers during peak production.

Climbed up to have a look. As I touched the panels I could feel one was very hot. I mean not sunlight hot, I mean hot. Checked the panel's connection box. It was deformed.

Opening it up I saw there was a short caused by a failed diode, which we found when we tested the diodes.

After replacing all three diodes, panel is honky dory again, but the panel is compromised, it cannot go back on the roof.

This is what it looked like.

 

Tenesol panel problem.jpg

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Thanks for all the quick and detailed responses!

To all:
- Apologies, I made a mistake on the voltages (getting older so the memory is not that good).  I am looking at it now and (for one set of 3x3) the voltages are around 78v with reported amps of 33 amps and 1715 watts.  So given Chris' explanation the real amps are around 22 which makes senses.  Apologies again about the incorrect voltage readings.
- So the question remains - why do the circuit breakers trip?

Some further information as requested
- Circuit breakers are Noark Ex8BP-N K 40A (photo attached)
- Installation was done about a month ago by an installer
- Only one of the strings trip (but that string also produces slightly higher watts) - but I guess that this points to something wrong with that string or breaker
- One other thing to note - initially the installer made a mistake and setup one string as 4 x 3 and another as 2x3, instead of both as 3x3.  So this of course resulted in higher amps that tripped the circuit breaker (although it should have still been under 40 amps).  Although this has been corrected now, it is still this string that causes the problems

@viper_za: pardon my ignorance but what is a combiner box?

@TTT - the panels are fairly new (1 month old) but I will get on the roof this afternoon and check.  But all 3 strings are producing roughly the same watts / amps / volts - so seems a bit less likely that all 3 strings will have a faulty panel

Thanks a lot for the help!
Gert

IMG_3719.JPG

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Gertc a quick explanation for the combiner box

"In all but the smallest PV systems, modules are wired together in series strings, where the positive leads of one module are connected to the negative leads of the next module. This results in cumulative voltage output, with current (amps) staying the same. The box where the output wires from multiple series strings are joined is the combiner box. Rated for outdoor use, it contains overcurrent protection devices (OCPDs) and the necessary bus bars and terminals for combining the inputs."

What we add extra normally are fuses per string and some of us even have breakers/disconnects for each string.

The combiner box should be located before the DB with your 3 Noark 40A breakers. Most of the time closer to your panels to keep the wiring to a minimum.

For you I would expect 3 separate ones to keep it neat and tidy.

Your Noark breakers are DC breakers so all should be fine.

 

Edit: Might even have one faulty 40A breaker?

Edited by viper_za
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1 hour ago, gertc said:


- So the question remains - why do the circuit breakers trip?

- Only one of the strings trip (but that string also produces slightly higher watts)

I am still not sure where all 3 CB trip. Do all 3 trip but one more often than the other 3 or is it only 1 CB that trips.

Since 2 strings where wired up in-correctly in the first place I would guess that the problems you are having are related to an ID-Ten-T error. Get the installer to come back and sort it out.

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Ditto ... mine was caused by a ID-10-T error ... had the panels connected the wrong way for a maybe 10 munites before correction. Fault only became obvious 4 weeks later.

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It does sound like a faulty CB possibly caused by a high contact resistance. (internal or external)

The resistance will cause heating and a de-rating of the current tripping characteristic.

For example your Noark breaker will trip at 32.5 Amps if the ambient temperature has risen to 70o C.

If you feel comfortable with having exposed DC voltages, remove the front cover off your circuit breaker Gewiss enclosure and allow the heat to escape. See if that has any effect on the tripping. 

 

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  • 1 month later...

Hi guys I need advice, I have 2 4kw axpert macer connected in parallel, 20 * 235 w panels, and 24 ml 500ah 2v batteries. My panels is connected in series 5 strings of 4 , each string push out 120 volts, 2 strings supplying inverter 2 and 3 strings supplying inverter 1. But my power only goes up to 1.2kw for inverter 1 and 1.1kw for inverter 2. What can I do to increase my power? Do I need to connect my panels in a different way maybe less strings or more? Help please.

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Also remember that you need load on the inverters. It only makes power whe something needs power. So if your bank is full and nothing is on.  You will only see a couple of watts. So to see what your max is you will need to put a load greater or equal to the array size. 

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  • 3 years later...
5 hours ago, vataleni paulus shikale said:

i got macer inveter  and 4batteries plus 4 panels. my connection of my panels are not showing on an inverter its not charging  the batteries, should i connect them in series o parrell so it can appear on screen of the inverter

You should connect them two in series, and parallel the two strings of 2 series panels. We call that 2S2P.

That's assuming you have a Mecer inverter with a 145 V max solar charge controller. If it's a model with 450 V or 500 V max PV voltage, then four panels might not be enough, and you need to connect them all in series.

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