I have a rooftop that is not small, but it is surrounded by walls. There is a slightly higher building on the left side and a very tall building on the eastern side that deleys the sun rise till 08:40 in summer and 09:30 in winter . Because of this, my roof is heavily affected by shading.

This situation left me with only a small area where I could install four solar panels that are not affected by shade from 9 a.m. until 4 p.m.

Recently, I had to add three more panels. However, sunlight reaches these new panels one to two hours later in the morning compared to the original four panels. In the evening, sunlight disappears from the old panels while it is still available on the new ones.

I assumed that the bypass diodes would handle this issue by isolating the shaded panels so they would not affect the illuminated ones. However, it seems that this does not happen in reality: the shaded panels limit the performance of the illuminated ones and pull their output down. Maybe my inverter doesn’t do global sweep/scan

I considered connecting the three new panels to a separate MPPT input, but I am concerned that I would lose the advantage of higher voltage achieved by connecting the panels in series. In other words, the performance gain I might achieve in the early morning could be lost during peak production hours.

What do you recommend?

Bypass diodes only protect cell groups inside a single panel. They do not isolate an entire shaded panel from a string.

In your case: Morning: The new panels are shaded they limit string current Midday: All panels clear OK .Afternoon: The old panels shade first same problem, reversed. Because a series string must pass the same current through every panel, the weakest (shaded) panel dictates the operating point. The MPPT can only track one compromise point, not two different irradiance profiles.

Put the 2 strings on diffrent Mppt's. Most systems gain more kWh/day by separating shaded arrays, even if each string runs at a lower voltage. Just ensure adequate start up voltage on the 3 panel string .

Edited December 22, 2025Dec 22 by TaliaB
Spelling

2 hours ago, TaliaB said:

Bypass diodes only protect cell groups inside a single panel. They do not isolate an entire shaded panel from a string.

In your case: Morning: The new panels are shaded they limit string current Midday: All panels clear OK .Afternoon: The old panels shade first same problem, reversed. Because a series string must pass the same current through every panel, the weakest (shaded) panel dictates the operating point. The MPPT can only track one compromise point, not two different irradiance profiles.

Put the 2 strings on diffrent Mppt's. Most systems gain more kWh/day by separating shaded arrays, even if each string runs at a lower voltage. Just ensure adequate start up voltage on the 3 panel string .

This would be the better option for the 7 panels. As the inverter has 2 MPPT's the 3 panels might at times not start the MPPT due to the requirement of a 130V start up. It does seem as if the roof allows the new 3 panels to be increased to 4. This I belief would allow them to work well and will be money well spend.

On 2025/12/21 at 11:36 AM, esmail-kassir said:

I have a rooftop that is not small, but it is surrounded by walls. There is a slightly higher building on the left side and a very tall building on the eastern side that deleys the sun rise till 08:40 in summer and 09:30 in winter . Because of this, my roof is heavily affected by shading.

This situation left me with only a small area where I could install four solar panels that are not affected by shade from 9 a.m. until 4 p.m.

@esmail-kassir I'm a bit confused - could you please clarify: Is east to the right in the photo above? If so, then are your panels not facing south - I do note that all the other panels visible in the photo are also facing the same direction, so I'm probably understanding this wrong...

Regardless, would it not be possible to move your panels further to the left (of the photo above), and have the highest part of the panels cover the red (water?) tank visible in this photo? Obviously if east is to the left then the panels are facing north, and moving the panels closer to the high building would not be an option as that area would be covered more by shade.

6 hours ago, Scorp007 said:

It does seem as if the roof allows the new 3 panels to be increased to 4. This I belief would allow them to work well and will be money well spend.

I concur.

I think this pic was taken in Northern Hemisphere?

23 hours ago, Scorp007 said:

3 panels to be increased to 4. This I belief would allow them to work well and will be money well spend.

On 12/22/2025 at 8:00 AM, TaliaB said:

Put the 2 strings on diffrent Mppt's. Most systems gain more kWh/day by separating shaded arrays, even if each string runs at a lower voltage. Just ensure adequate start up voltage on the 3 panel string .

I can't add 8th panel due to the chimney

so my options are

7 on one MPPT VS 4/3 2 MPPTs

13 hours ago, Demo said:

I think this pic was taken in Northern Hemisphere?

you are correct , It is in Damascus Syria

Once you have two strings you don't have to have them physically adjacent to each other. You could have two arrays, positioned to take advantage of different light and shade on your roof space.

34 minutes ago, esmail-kassir said:

I can't add 8th panel due to the chimney

so my options are 7 on one MPPT VS 4/3 2 MPPTs

you are correct , It is in Damascus Syria

OK, thanks - that clarify matters 🙂

So, why can you not move your first string of panels further west, with the highest panel being over the red water tank as I previously suggested? You could even let the panels overhang (cantilever) some distance (one panel width...) over the western wall to make room for the second string to be placed further away from the eastern wall, thus reducing the effect of the shadow of the high eastern building to some extent.

1 hour ago, Bobster. said:

Once you have two strings you don't have to have them physically adjacent to each other. You could have two arrays, positioned to take advantage of different light and shade on your roof space.

With a NOCT Vmp of only 39V it could be iffy to start the 2nd MPPT that needs 130V. This is for 3 panels. For this reason @TaliaB also mentioned it in his previous reply. One should rather try other suggestions to get to 4 which seems a challenge. This is a classic case where instead of buying similar panels to those in use a better call would be for panels with a higher voltage even if it is only 2V more per panel. CS6W-555T-F30-T6 comes to mind. Similar to the new string you added recently.

Edited December 23, 2025Dec 23 by Scorp007

3 hours ago, Scorp007 said:

With a NOCT Vmp of only 39V it could be iffy to start the 2nd MPPT that needs 130V. This is for 3 panels. For this reason @TaliaB also mentioned it in his previous reply. One should rather try other suggestions to get to 4 which seems a challenge. This is a classic case where instead of buying similar panels to those in use a better call would be for panels with a higher voltage even if it is only 2V more per panel. CS6W-555T-F30-T6 comes to mind. Similar to the new string you added recently.

Assuming the array is just able to start the MPPT , which configuration harvests more energy: two independent strings that each sit exactly at the MPPT lower-limit voltage, or a single string whose Voc is close to the inverter’s nominal MPPT value but is partially shaded?

Edited December 23, 2025Dec 23 by esmail-kassir

4 hours ago, esmail-kassir said:

Assuming the array is just able to start the MPPT , which configuration harvests more energy: two independent strings that each sit exactly at the MPPT lower-limit voltage, or a single string whose Voc is close to the inverter’s nominal MPPT value but is partially shaded?

Once an MPPT is active, operating near its minimum tracking voltage does not materially reduce energy harvest.

By contrast, placing panels with different shading profiles on the same MPPT forces current compromise and causes large, unavoidable energy losses.

Therefore, two independent strings that each barely satisfy the MPPT voltage requirement will consistently harvest more energy than a single higher-voltage string that is partially shaded. If a string repeatedly drops below MPPT start voltage, it will cycle on/off and lose energy. But if it stays above the threshold, even marginally, it operates normally.

Wow! Having @TaliaB around is like going to PV school.

14 hours ago, TaliaB said:

Therefore, two independent strings that each barely satisfy the MPPT voltage requirement will consistently harvest more energy than a single higher-voltage string that is partially shaded.

Thant is the answer that I was looking for , thaaaaaaaaaank you 🤩. maybe operating near nominal voltage increase the MPPT efecincy and reduce thermal stress the looses wont be that much

25 minutes ago, Bobster. said:

Wow! Having @TaliaB around is like going to PV school.

indeed !

9 hours ago, esmail-kassir said:

Thant is the answer that I was looking for , thaaaaaaaaaank you 🤩. maybe operating near nominal voltage increase the MPPT efecincy and reduce thermal stress the looses wont be that much

indeed !

The real test is during winter with those extra long shadows and lower irradiation that can reduce PV output to less than 50% of the summer value. I do see you are quite a bit away from the equator at 33.5 degrees north.

On 12/24/2025 at 7:48 PM, Scorp007 said:

The real test is during winter with those extra long shadows and lower irradiation that can reduce PV output to less than 50% of the summer value. I do see you are quite a bit away from the equator at 33.5 degrees north.

it is winter now, so I am testing the worst scenario