I noticed lower than expected output from my north facing string compared to my west facing string during peak sun hours and I am not sure why. 

I have two strings of 8x 550w panels. One string is facing North and one string is facing West. There is no shading on both strings during this time.

I would like to find out why my West string is producing more at 12pm - 1pm compared to my North string. I would reasonably expect it to be quite similar. I have a 12kw Sunsynk inverter so I dont think it is a clipping issue. 

The voltage is quite similar but the current is different. Any ideas on what could be causing this?

Below are the current, voltage and power graphs: 

PV2 = North & PV1 = West

 

 

Edited November 5, 20223 yr by Milan188

Scratch that, I think I've got myself confused.

 

Edited November 5, 20223 yr by GreenFields
Confusion

Some additional info which might be causing the different is:

My West string is mounted on a pitched roof and my North string is mounted on a flat roof. 

It appears the angle of the West string is flatter than the North string which may be resulting in better production on the West string.

MPPT2 clips at 12A as can be seen from your graphs. MPPT1 is rated at 25A. Swap the MPPTs and you should get better overall yield.

 

I'm not sure why it is clipping at 12A, the datasheet states 12.5A, but they often change things if they don't work in the field...

Edited November 6, 20223 yr by P1000

1 hour ago, P1000 said:

MPPT2 clips at 12A as can be seen from your graphs. MPPT1 is rated at 25A. Swap the MPPTs and you should get better overall yield.

 

I'm not sure why it is clipping at 12A, the datasheet states 12.5A, but they often change things if they don't work in the field...

Great reply as to why. I notice on the current graph that the clipping string did exceed 12.5A and while clipping there are a number of periods that the MPPT does provide 12.5A before dropping to 12A.

Moving the strings around as suggested would cause the clipping string to clip for a shorter period.

@Milan188

If in the southern hemisphere the flatter string should be providing more power this time of the year if both were in the same direction. In winter the greater angle will provide more yield.

Edited November 6, 20223 yr by Scorp007

Thanks for the awesome replies. Really appreciate it 

4 hours ago, P1000 said:

MPPT2 clips at 12A as can be seen from your graphs. MPPT1 is rated at 25A. Swap the MPPTs and you should get better overall yield.

 

I'm not sure why it is clipping at 12A, the datasheet states 12.5A, but they often change things if they don't work in the field...

@Scorp007& @P1000I just saw that I have the SG04LP3 model which has 34a and 17a according to the datasheet. So not sure why it is this.

Edited November 6, 20223 yr by Milan188

19 minutes ago, Milan188 said:

@Scorp007& @P1000I just saw that I have the SG04LP3 model which has 34a and 17a according to the datasheet. So not sure why it is this.

Looks like the max panel current you can put on it that the MPPT will still manage to control. The MPPT will still limit to 26A+13A (according to the Deye brochure attached). I have never seen Isc ratings in Sunsynk manuals - they really should put them in there.

23 minutes ago, P1000 said:

Looks like the max panel current you can put on it that the MPPT will still manage to control. The MPPT will still limit to 26A+13A (according to the Deye brochure attached). I have never seen Isc ratings in Sunsynk manuals - they really should put them in there.

Thank you. 

I found the latest datasheet from the Sunsynk website and it matches this also.

 

Did some calculations. 

Definitely leaving some peak performance on the table with this setup but not as much as I would expect after taking into account the reduction in output from the West String if I swap the MPTTs.

Edited November 6, 20223 yr by Milan188

59 minutes ago, Milan188 said:

Did some calculations. 

Definitely leaving some peak performance on the table with this setup but not as much as I would expect after taking into account the reduction in output from the West String if I swap the MPTTs.

Yes, those panels usually don't spend a lot of time above 12A, and there is very little area under the curve of the difference. Getting just-about 4kW from 8 of those 550W panels for that many hours is actually quite impressive. That said, swapping MPPTs costs nothing and would be a worthwhile experiment IMO.

Edited November 6, 20223 yr by P1000

4 hours ago, Milan188 said:

Did some calculations. 

Definitely leaving some peak performance on the table with this setup but not as much as I would expect after taking into account the reduction in output from the West String if I swap the MPTTs.

Having a "loss" of about 2A at best when the throttle takes place should not keep you awake at night. Those 16 panels are doing well enough if you ask ME even with the throttle from 10h to 15h if my guess is right. Graph does not show until what time.

Edited November 6, 20223 yr by Scorp007

1 hour ago, Scorp007 said:

Having a "loss" of about 2A at best when the throttle takes place should not keep you awake at night. Those 16 panels are doing well enough if you ask ME even with the throttle from 10h to 15h if my guess is right. Graph does not show until what time.

Yes its between 10am and 2.30pm. After 2.30pm the current from the West string drops below 12 again. 

The net loss is actually quite small. I got all the data from both strings, used the PV1 voltages with the PV2 current and vice versa making adjustments for timing, estimated current and clipping on the West string. What I found was the net effect was around 6% better performance. 

Overall I am very satisfied with the panels. They are performing better than I initially expected and I am not going to haggle the installer to come change it right away. However, I definitely want the MPTTs swapped because in Gauteng there is usually afternoon showers and clouds and I want to get all my geysers and batteries ready in the morning as quickly as possible. 

Edited November 6, 20223 yr by Milan188

1 hour ago, Milan188 said:

Yes its between 10am and 2.30pm. After 2.30pm the current from the West string drops below 12 again. 

The net loss is actually quite small. I got all the data from both strings, used the PV1 voltages with the PV2 current and vice versa making adjustments for timing, estimated current and clipping on the West string. What I found was the net effect was around 6% better performance. 

Overall I am very satisfied with the panels. They are performing better than I initially expected and I am not going to haggle the installer to come change it right away. However, I definitely want the MPTTs swapped because in Gauteng there is usually afternoon showers and clouds and I want to get all my geysers and batteries ready in the morning as quickly as possible. 

Interesting how we differ. Some want their battery charged as early as possible while I feel if it is by about 15h00 it is fine. I will rather use the power during peak times. But again it depends on loading in the late afternoon and during the night and battery size.

Although cloud is mostly in the afternoon tomorrow it could be in the morning in Gauteng-blue blocks on the right? This forecast is for 2hrs full sunshine.

Edited November 6, 20223 yr by Scorp007

5 minutes ago, Scorp007 said:

Interesting how we differ. Some want their battery charged as early as possible while I feel if it is by about 15h00 it is fine. I will rather use the power during peak times. But again it depends on loading in the late afternoon and during the night and battery size.

Although cloud is mostly in the afternoon tomorrow it could be in the morning in Gauteng-blue blocks on the right?

Yes. I still prioritise my load before battery throughout the day but like the battery to charge up quickly because then it can start to supplement my non essential loads when PV is a bit low due to clouding. 

Some days in Gauteng there are clouds in the morning but on average we usually get afternoon thundershowers so on most days it will be fine.