We have 24 260 wp panels installed with 2 combiner boxes to 2 Mecer 5 kW inverters installed in parallel. Currently due to various constraints, we have 12 panels connected to one of the combiner boxes in 3 strings of 4 panels in series. These are showing Voc of 139v but wildly swinging Amperage from zero up to only 7 Amps and barely charge our bank of 6 Mecer M3000 batteries. Tried to use the system in PV mode during recent load shedding but it could not support the relatively small load requirements of 1.1kW and went to battery mode. I guess our question is why we cannot seem to get the PV system to produce this relatively modest load?

Check your other topic, a few of the guys have answered, we need more info. You need to provide the panel specs on the back of the panel (Voc, Vmp, Isc) and also the inverter model and specs (preferably a pic of the sticker on the side). If you have a high voltage solar controller then it is likely trying to pull the voltage too low when searching for the max power point. If you have a low voltage model then the panel voltage is way too high and will blow the MPPT.

 

Thanks for the response. Lots of life getting in the way of overcoming problems in completing our installation but need to get out from under the Eskom. Attached photo of inverter label. Panel WP 270 VoC 38.7. isc 9.12A. Vmp 30.95. Imp 8.37A. Think we have a problem with dirty/corroded M40 couplings and busy replacing with crimps and heatshrinks. Will finish tomorrow and report. 

28 minutes ago, John Brady said:

Thanks for the response. Lots of life getting in the way of overcoming problems in completing our installation but need to get out from under the Eskom. Attached photo of inverter label. Panel WP 270 VoC 38.7. isc 9.12A. Vmp 30.95. Imp 8.37A. Think we have a problem with dirty/corroded M40 couplings and busy replacing with crimps and heatshrinks. Will finish tomorrow and report. 

Well this should go some way towards explaining some of your problems. Your four panels in series (4 x 38.7Voc = 154.8V) are exceeding the Max Solar Voltage (VOC) of 145VDC on your low-voltage MPPT. You are at risk of damaging your inverter.

I'd suggest placing connecting your panels 3 in series, with four such strings in parallel, or if circumstances really prevent that, try 3x3 on the one inverter, and add the other 3 in parallel on the other inverter.

@John Brady, @GreenFieldsis correct, with your model inverter you need to hook the panels up in strings of 3 in series and then parallel them, so you can make 8 strings of 3 in series (3S8P). As you have 2 inverters and 2 combiner boxes the best would be to set up 3S4P into each combiner box and then on to each inverter.

I would agree. Series parallel is your best option to go with. As you are already maxing out your allowed solar voltage you run the risk of damaging your contoller.

Finally got our system up and running as follows (after lots of con fusion and mistakes!)

2 Strings X 10 panels:

String 1 - 10x275W panels  - 38.6 VOC

String 2 - 10x270W panels - 37.8 VOC However only getting 3.07kW output. 

VOC readings - String 1 = 346 - String 2 = 336. Max cable length 12 m x 8mm2. All joints now crimped and heat shrink insulated. 
many suggestions on how to check/test?

On 2023/05/06 at 7:04 PM, GreenFields said:

Well this should go some way towards explaining some of your problems. Your four panels in series (4 x 38.7Voc = 154.8V) are exceeding the Max Solar Voltage (VOC) of 145VDC on your low-voltage MPPT. You are at risk of damaging your inverter.

I'd suggest placing connecting your panels 3 in series, with four such strings in parallel, or if circumstances really prevent that, try 3x3 on the one inverter, and add the other 3 in parallel on the other inverter.

Sorry to say @John Brady but you did not listen to what @GreenFields told you.

Your string total VOC  should not exceed 145 vDC 

1 hour ago, John Brady said:

Finally got our system up and running as follows (after lots of con fusion and mistakes!)

2 Strings X 10 panels:

String 1 - 10x275W panels  - 38.6 VOC

String 2 - 10x270W panels - 37.8 VOC However only getting 3.07kW output. 

VOC readings - String 1 = 346 - String 2 = 336. Max cable length 12 m x 8mm2. All joints now crimped and heat shrink insulated. 
many suggestions on how to check/test?

Apart from exceeding the 145V Voc you have also perhaps exceeded the maximum PV power that your inverter can handle by going more than 20% over the maximum. This is a 2nd risk to your inverter to be damaged. 

1 hour ago, John Brady said:

Finally got our system up and running as follows (after lots of con fusion and mistakes!)

2 Strings X 10 panels:

String 1 - 10x275W panels  - 38.6 VOC

String 2 - 10x270W panels - 37.8 VOC However only getting 3.07kW output. 

VOC readings - String 1 = 346 - String 2 = 336. Max cable length 12 m x 8mm2. All joints now crimped and heat shrink insulated. 
many suggestions on how to check/test?

Sounds like you're on the right track now and much better positioned in terms of close enough to the right panel config for your inverter. 

In terms of your reduced generation - likely seasonal related. It's winter after all. Everybodys generation is taking a knock

On 2023/05/06 at 7:00 AM, John Brady said:

we have 12 panels connected to one of the combiner boxes in 3 strings of 4 panels in series

All you needed to do was change this from 3 strings of 4 panels in series to 4 strings of 3 panels in series for each combiner box and it should work fine and produce just under 40A at full power and stay below the 145V limit of the solar charge controller.

13 hours ago, LumexClipsal said:

Sounds like you're on the right track now and much better positioned in terms of close enough to the right panel config for your inverter. 

In terms of your reduced generation - likely seasonal related. It's winter after all. Everybodys generation is taking a knock

Hmm i don't share your opinion.

10 x 275w panels at 38.6VOC = 2750w / aprox 35vmp = 78.57 Amps. That's a hell of a lot of amps going down the PV lines to me. I would really hope these lines are super large in size and super short in length.

Do what @jumper has said and make your system groups of 3 panels in series.

3 in series x 38.6V = 115.8V VOC so even with 10% extra on a really cold sunny day there is plenty of margin before you reach the 145V the inverter supports.

4 in parallel x 7.85 amps = 31.4 Amps Much safer loads for the PV cables to handle.

So the 3 in series combined with 4 in parallel is by far the safest option for you.

Far safer to have higher voltages and lower amps but make sure you stay well under the 145VOC the inverter can handle. Just under is not good enough because at colder temps to the 25 Deg C they rate the panels at the VOC will increase. In my case i get 10% extra voltage at 3 deg c compared to the 25 deg so it is something you need to account for or you learn the hard way like i did when in the middle of winter the inverter shuts down due to the excessive solar voltage coming in.

2 hours ago, Webbie said:

Hmm i don't share your opinion.

10 x 275w panels at 38.6VOC = 2750w / aprox 35vmp = 78.57 Amps. That's a hell of a lot of amps going down the PV lines to me. I would really hope these lines are super large in size and super short in length.

Do what @jumper has said and make your system groups of 3 panels in series.

3 in series x 38.6V = 115.8V VOC so even with 10% extra on a really cold sunny day there is plenty of margin before you reach the 145V the inverter supports.

4 in parallel x 7.85 amps = 31.4 Amps Much safer loads for the PV cables to handle.

So the 3 in series combined with 4 in parallel is by far the safest option for you.

Far safer to have higher voltages and lower amps but make sure you stay well under the 145VOC the inverter can handle. Just under is not good enough because at colder temps to the 25 Deg C they rate the panels at the VOC will increase. In my case i get 10% extra voltage at 3 deg c compared to the 25 deg so it is something you need to account for or you learn the hard way like i did when in the middle of winter the inverter shuts down due to the excessive solar voltage coming in.

How do they say:"You learn the hard way" 🤔

 

39 minutes ago, Scorp007 said:

How do they say:"You learn the hard way" 🤔

 

The operating voltage is 40v to 115v. So any thing above 115v is a waste. 145VOC is the absolute max. The next thing you hear is BOOM.

I got my popcorn, interested in whats happening next

4 hours ago, Webbie said:

it is something you need to account for or you learn the hard way like i did when in the middle of winter the inverter shuts down due to the excessive solar voltage coming in

I see you speak from experience... as do I 😳

22 hours ago, Chris Louw said:

The operating voltage is 40v to 115v. So any thing above 115v is a waste. 145VOC is the absolute max. The next thing you hear is BOOM.

Good point @Chris Louw

Operating voltage of 40V to 115V means no charge happening until full sun voltages are achieve in the 10 panels in parallel. If they are getting charge at 35v odd then they are lucky but wasting so much potential lower sunlight generation.

This is something i didn't think about in my reply

2 hours ago, Webbie said:

10 panels in parallel

He has the 10 panels in series in 2 strings with voltages of 346V and 336V each into 1mppt, not in parallel. It should produce about 10A, but the voltages are way too high, I'm surprised the mppt is still alive,