Have two PV arrays facing north and the are both the same.  One sometimes dip in output to about half it should give. The amps drop although the voltage stays normal.

Some say it is shading.  I do have a 150mm chimney that gives a shadow on half of one of the panels but this has not caused any significant reduced capacity in the past.

The reduced capacity also seem to occur at similar times each day.  Around 11am give or take 30min the output jumps back to normal (doubling on the one array/string or 25% higher)

 

Where do I start looking?

25 minutes ago, Pietpower said:

Have two PV arrays facing north and the are both the same.  One sometimes dip in output to about half it should give. The amps drop although the voltage stays normal.

Some say it is shading.  I do have a 150mm chimney that gives a shadow on half of one of the panels but this has not caused any significant reduced capacity in the past.

The reduced capacity also seem to occur at similar times each day.  Around 11am give or take 30min the output jumps back to normal (doubling on the one array/string or 25% higher)

 

Where do I start looking?

I am also keen to learn on this issue as I have two 6 x 450w strings that are similar and one always is different to the other in watts, amps etc and hope to learn from your issue. Maybe post a picture on your panels and what you see??? The visual may help

Changing season  is probably changing when and where the shadow falls, i have a similar issue, summer there is a shadow on the panels between 9:30 and 12, but in winter since the sun is at a lower angle, so no such problem

35 minutes ago, Pietpower said:

Some say it is shading.  I do have a 150mm chimney that gives a shadow on half of one of the panels but this has not caused any significant reduced capacity in the past.

Is each array a single string?  If yes, it is almost certainly shading.  All panels in a string are affected by shade on one.

The effect is more pronounced if the shade is across the short side of a panel.  Shading a long row will normally lose you at most 1/3rd of the power - shading a short row can lose you most of the whole string.

You can find a lot of information online - search for "pv panel shading effect"

 

I have a funny case, my one string seems to always measure 0.4 amps irrespective of it being night with no sunlight. This is on the 5kw sunsynk MPPT 1.

This of course means that PV 1 is always showing higher amps than PV2

Anyone else experience something like this:

What could be the reason?

3 hours ago, Calvin said:

Is each array a single string?  If yes, it is almost certainly shading.  All panels in a string are affected by shade on one.

The effect is more pronounced if the shade is across the short side of a panel.  Shading a long row will normally lose you at most 1/3rd of the power - shading a short row can lose you most of the whole string.

You can find a lot of information online - search for "pv panel shading effect"

 

Is a single string all connected in series?  I presume it is in my case.  Below is an image of panels.  PV1 is the row above and PV2 the row below.

You can see the shading is very little.  Reluctant to move panels or chimney to address shading before investigating other possible causes for the following reasons.

1) Today PV2 took a dip between 12:30 and 13:00 and then shot back up when the shading from the chimney was solid on the panel.
2) Although it follows a pattern it does not happen at exactly the same times each day.
3) The output for the string dips by 50% while the shading is only on one panel.
4) Last year and the year before I never had this issue but the shading was exactly the same.

 

Someone told me that panels are not designed for shading and might be damaged.  Could this be the case?

What other reasons could there be for current drop?

- damaged panel?
- loose connections? (already checked the incoming protection panel)

 

Everything points to shading - the chimney is terribly placed.  I am not surprised that it sometimes causes a 50% drop in the lower string.

The problem with this diagnosis is: "Last year and the year before I never had this issue but the shading was exactly the same."

What time of day was this picture taken?

14 hours ago, Calvin said:

Everything points to shading - the chimney is terribly placed.  I am not surprised that it sometimes causes a 50% drop in the lower string.

The problem with this diagnosis is: "Last year and the year before I never had this issue but the shading was exactly the same."

What time of day was this picture taken?

Panels face exactly north, so that would be around 3pm

Please explain to me how a 3-4% shading can have a 50% dip in output for the whole string?  I do understand that the one panel that is experiencing shading can have a big drop but why the whole string?
And then why would it suddenly jump back to normal (maybe 1% lower than the top string) without removing the shading or doing anything. How can both conditions exist.

My question is actually: What do I need to look into before I look at the shading.
- Can a damaged panel cause the throttle in amps? How do I find the problem panel
- What else?

20 minutes ago, Pietpower said:

Please explain to me how a 3-4% shading can have a 50% dip in output for the whole string?

It is because this panel is in series with the rest of the panels in the string.

There is a relatively easy way to test this.  Take a picture of the shade when the power is low.  Now take a piece of cardboard (or similar) and cut it to roughly the same size.   Wait until the shade is gone, and put the cutout on the panel in the same place as the shade was.  If the power is low again, shade was your problem. If not, look elsewhere.

1 minute ago, Calvin said:

It is because this panel is in series with the rest of the panels in the string.

There is a relatively easy way to test this.  Take a picture of the shade when the power is low.  Now take a piece of cardboard (or similar) and cut it to roughly the same size.   Wait until the shade is gone, and put the cutout on the panel in the same place as the shade was.  If the power is low again, shade was your problem. If not, look elsewhere.

As explained above I already know that. I mostly have normal output with the shade full on the panel.  Just certain times of the day the output dips for 30min to an hour. 

4 minutes ago, Pietpower said:

As explained above I already know that. I mostly have normal output with the shade full on the panel.  Just certain times of the day the output dips for 30min to an hour. 

Could be a broken diode. Either way, moving the chimney is probably the best solution.

17 minutes ago, tetrasection said:

Could be a broken diode. Either way, moving the chimney is probably the best solution.

What is a broken diode and how do I find it?

 

Edited June 24, 20215 yr by Pietpower

17 minutes ago, Pietpower said:

What is a broken diode and how do I find it?

 

Solar panels have bypass diodes inside which bypass a string of cells when there is shading. If a bypass diode doesn't work, a small bit of shade can effect your whole string of panels.

It seems fairly likely that, because you have the same area shaded every day, the same bypass diode is being worked every day and probably wore out. 

 

I don't know if you can repair that... You could try to dismantle the panel but I think getting a new panel would be easier and safer.

Edited June 24, 20215 yr by tetrasection

9 minutes ago, tetrasection said:

It seems fairly likely that, because you have the same area shaded every day, the same bypass diode is being worked every day and probably wore out. 

I don't know if you can repair that... You could try to dismantle the panel but I think getting a new panel would be easier and safer.

Thanks, that makes sense.  I presume the diode could be working intermittently or maybe when the shadow is on a certain spot on the panel.

Yes replacing the panel is the what I would do.  How do I test the panel?  Could I bypass the panel and see if my problem disappears?
Dammit I don't think they made it easy to get to the panel wiring underneath.

3 minutes ago, Pietpower said:

Thanks, that makes sense.  I presume the diode could be working intermittently or maybe when the shadow is on a certain spot on the panel.

Yes replacing the panel is the what I would do.  How do I test the panel?  Could I bypass the panel and see if my problem disappears?
Dammit I don't think they made it easy to get to the panel wiring underneath.

You could just switch the possibly broken panel with one that never gets shade. That would serve as a test and a solution (if it solves the problem).

Thanks again.  Will try that.

From your image and my photo the panels most likely have three strings per panel and the shadow would bypass 1-2 strings at a time losing max 2/3rd of the output per panel.  That equates to a 5% loss in output per array of panels.  A broken diose could place a restriction in the system causing a much higher loss in output.

The comment above about the panels not being designed for shading and being damaged also makes more sense now.

I had a similar shading problem on Sunday, I realized my six 330WATT panels were not performing to well in the morning, round about 9H00. I thought maybe the panels are dirty and on investigating found my small Telkom aerial making a small shade on one string of two series panels. When measuring the current to that string it was 3.4A and the next two strings was at 8.9A. I got on the roof and lowered the aerial and the pv jumped up with about 200Watt. The small drop in the graph was my shade passing the panels on the roof. Please ignore the time on the ICC graph as it was not correct at the time.