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Solar generation down 25% from last year ??


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Posted (edited)

Hi all

Hoping someone can shed some light and point me in the right direction to solve my problem.  I have had my current installation in since Mid 2020 and all has been running perfectly until recently. During the Cape Town summer seasons we would peak at just over 4000w of PV with it averaging around 3500 during mid day. We did not have great weather in December and January, so I did not notice exactly when the problem started but I have noticed over the last two months that we peak just over 3000w and average at 2600w. The daily generation is obviously down and batteries are rarely getting fully charged, so it is not a lack of demand issue.

I have cleaned the panels with soap and water, I have cleaned the air vent "filters" on the inverter and opened it up to check that fans are spinning and nothing is clogged up inside. Nothing seems to make a difference.

My setup is as follows

1x Axpert King 5KW
2x Narada NPFC100 batteries
12x 350w Canadian Solar panels. The panels are setup in 3 strings connected in parallel with each string being made up of 2 parallel sets of 2 in series (i.e 2S6P)

When putting a volt meter to each of the 3 strings individually (without load), I am reading around 82 to 85v which is a little higher than rated but I would presume normal, so I know that the strings are semi equal and nothing would seem to have come apart in the wiring. When applying load to each string individually, the inverter / ICM reads between 700 and 900w in mid day which shows there is an issue but it is the same between the strings with leads me back to the inverter.

I have a volt meter permanently connected to the inverter on the PV input and the odd thing which concerns me with the inverter, is when the load is disconnected the meter is still showing 40 odd volts which over time drops down (15 to 30 mins)

If you look at the below image, the generation curve is normal, it is just 25% / 1kw lower than the last 2 years

Any ideas of things to look at? How does one test if my MPPT has gone faulty?

Thanks in advance

image.thumb.png.a424b2c2d46d8366e0d01f922888aa50.png

Edited by Jay-Dee
typo
Posted
10 hours ago, Jay-Dee said:

I have noticed over the last two months that we peak just over 3000w and average at 2600w.

We're now well past Equinox, so the sun will be further north than it was. What is the tilt of your panels?

10 hours ago, Jay-Dee said:

How does one test if my MPPT has gone faulty?

It's pretty unlikely that the MPPT has faulted in such a way that the output is reduced but still working. Unless the PV voltage measurement is way off. You can check that with a multimeter versus data from the display or monitoring software. If it thinks the voltage is too high, it could start derating the output. But you appear to have perfect sine waves for PV output, no clipping, so that seems unlikely.

Similarly, if you have a cooling problem, the output could be derated, but again this would result in flat tops to the sine waves.

It's possible that you have high resistance in one of the cables or panels. It would be good to measure the current in each string with a clamp meter, so make sure that no string is far behind the others.

Posted
14 hours ago, Jay-Dee said:


If you look at the below image, the generation curve is normal, it is just 25% / 1kw lower than the last 2 years
 

 

It is the weather for sure. My PV production is also down about 25% this year and it can be attributed to the abnormal amount of cloud cover and rain we have had this year. This is my 6th year of solar and definitely the worst production ever.

Posted
3 hours ago, GVC said:

It is the weather for sure. My PV production is also down about 25% this year and it can be attributed to the abnormal amount of cloud cover and rain we have had this year. This is my 6th year of solar and definitely the worst production ever.

Still not 100% convinced as every day is the same on system, no matter the weather and it never peaks or averages over the above but sadly, that makes me feel a lot better as I am at the point of trying to get a new inverter to test with.

Posted
10 hours ago, Coulomb said:

We're now well past Equinox, so the sun will be further north than it was. What is the tilt of your panels?

It's pretty unlikely that the MPPT has faulted in such a way that the output is reduced but still working. Unless the PV voltage measurement is way off. You can check that with a multimeter versus data from the display or monitoring software. If it thinks the voltage is too high, it could start derating the output. But you appear to have perfect sine waves for PV output, no clipping, so that seems unlikely.

Similarly, if you have a cooling problem, the output could be derated, but again this would result in flat tops to the sine waves.

It's possible that you have high resistance in one of the cables or panels. It would be good to measure the current in each string with a clamp meter, so make sure that no string is far behind the others.

Thank you for the insight... I am not sure on the degree of the tilt but I am comparing to the same months last year, so in theory the sun would be as far north as it was previously.

Re the failing MPPT, this is exactly my thought of I am keep in the perfect wave with no clipping, just lower than expected. The heating idea was a long shot but was worth the clean as they were dirty.

Re the high resistance... I have a clamp on a Multi Meter but have never tried it on DC current? Will it work? Should I be on the positive site or the negative side for best results?

What I am currently doing to test each of the 3 strings, is I am cutting them off in my combiner box and running 1 at a time... All 3 are performing similarly and all 3 are around 25% lower than expected... I am getting between 700 and 950w depending on the time of day which at a push will give me 2850w instead of 3500 to 4000w and this is why I keep on coming back to the inverter instead of a panel or wiring issue.   My 3 strings are split between 3 different sections of roof but all face the same direction. So the likelihood of something damaging all 3 strings at the same time equally is extremely slim

Posted (edited)
5 hours ago, Jay-Dee said:

every day is the same on system, no matter the weather

Oh. That sounds very suspicious. On the short term, solar irradiation is as random as, well, as the weather.

Maybe your monitoring software is returning some default values under certain conditions, and these result in the perfect sine wave every day??

Edit: Or some testing code was accidentally left in place?

Edited by Coulomb
Posted
6 hours ago, Coulomb said:

Oh. That sounds very suspicious. On the short term, solar irradiation is as random as, well, as the weather.

Maybe your monitoring software is returning some default values under certain conditions, and these result in the perfect sine wave every day??

Edit: Or some testing code was accidentally left in place?

Those that is some very interesting food for thought... I changed over in the beginning of March from ICC (v4.8) to ICM (the new product from ICC Software) and never thought there could be an issue in the new software, how ever I have check the actual values on the inverter and they are displaying the same.

My old Pi was freezing every other day but I have re-installed it for now... I have gone back to look at the history and I may be worrying about "nothing"... This year's March, I know we had funny weather, so I cant compare but April 2022 is comparing to May 2021, so while it is off... It may be completely seasonal and I could have jumped the gun.

Either way, I have put my old Pi back on the system and will see what it does tomorrow as the weather going to be very similar to what it was today. My parents also live down the road and have a similar setup where we always managed to get similar outputs but they have a single battery and lower draw, so are normally fully charged by 11am and then just power the house. I am going to plug some high load items into their system to see what I can push it do in the middle of the day which will also provide a point of comparison.

Will keep you posted but thanks again for all the insight so far 

Posted

GoodDay. I am also from CapeTown South africa. And yes you can definitely see less production this year. To my small brain its definitely more pollution in the air. In 2020 when we were in lock down the air quality was a lot cleaner so no smog in the air the production on my solar panels were off the charts. I was getting over 2200 watts from my 1600 watts string panels. 4x405 Mono Panels halve cell. now 1000watts on average, My 4x545watts string is only producing 1600watts on average so all down facing north . Yes we always have smog especially now the last couple of weeks with very little wind. You can see even the sun looks a bit yellow/brown some days. That why the day after rain production ramps up again. Drive up to durbanville and look back towards capetown. From strand all the way to westcoast all you can see is a thick smog layer. Horrible. Cape town is know for its bad quality air especially now when the wind is not howling. if you fly you can see the smog all over the lower cape town area basically all the way from somerset west to almost as far a Yzerfontein the whole of bottom corner of the western cape is covered in smog. So sad, i hope we get lots off rain soon to clean the air.

This is all just based on my opinion and offcoarse i can be wrong 😉

Posted

@Coulomb Sorry for the delayed reply and feedback.. We have an 9 week old and needed to focus that way this week but managed to get some testing in-between. The old Pi with ICC went back in the other day and exactly the same issue. I re-checked all settings on the inverter to make sure they were still as they have always been and not just relying on what was showing in ICC.  I then returned ICM and the new Pi and forgot about it for most of the following day but when checking, I noticed some decent spikes and a non-solid / perfect curve.

Yesterday the weather was all over the place and we maintained over 3000w for a period and peaked at just under 3500w

image.png.6c64eb5f1926b634a3c3cddf9f2427d6.png

 

I am going to have to "give in" and agree with @Henry2501 and @GVC sadly as I think it is just different weather and more air potentially pollution then the previous two years. Hopefully the winds in Cape Town today and tomorrow, clear things up a little as it really bothers me to use Eskom on daily basis (even if it is still only a little)


Thanks to all, the feedback has been greatly appreciated 

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