Advise on panel optimization

We’re finally up and running and have enjoyed the setup thus far, but I need advise on two things, but first, context:

context 1: I’m working with the 18kPV inverter. I have 3 series functioning right now. I have a place on my roof where I’d like to put a 4th series which would run in parallel with the 3rd string.

Context 2: The panels spec sheet is attached.

Context 3: my I am using Tigo 2-for-1 RSD, not optimizers.

Question 1. I separated my series two to account for the immediate shade it would get from the chimney. In the later afternoon my series 1 is then shaded. If I use optimizers on the panels that are shaded in my series 1, would that help account for the late afternoon shading?

Question 2: I purchased my panels from SanTan Solar new but the are not willing to restock that panel. Because my 4th series needs to be identical to the 3rd due to those being paralleled, what advice do yall have on specific panels or configuration? I understand the series need to be identical, but I can’t get them unless i want to buy a whole pallet from Santan’s source.

counting:
10 panels in string 1
8 panels in string 2
10 panels in string 3

Q1: if you put optimizers on shaded panels, it will improve string performance.

Q2:


whelp, I have good news.

You don't need identical panels. You need panels that have series Vmp of 410V ±10%

Generally speaking, you need to match Vmp within about 10% to ensure the panels will perform normally; however, both strings may experience that 10% penalty to rated output (there will be a penalty, but it may not be the full 10%). You can also use different panels in series, but they will operate at the current of the lowest rated panel.

Generally speaking, while you may pay a penalty for dissimilar panels, it is almost always worth it if it enables you to add another string.

Another idea...
Connect the new string with a separate MPPT charge controller straight to the battery bank.

sunshine_eggo said:

counting:
10 panels in string 1
8 panels in string 2
10 panels in string 3

Q1: if you put optimizers on shaded panels, it will improve string performance.

Q2:


whelp, I have good news.

You don't need identical panels. You need panels that have series Vmp of 410V ±10%

Generally speaking, you need to match Vmp within about 10% to ensure the panels will perform normally; however, both strings may experience that 10% penalty to rated output (there will be a penalty, but it may not be the full 10%). You can also use different panels in series, but they will operate at the current of the lowest rated panel.

Generally speaking, while you may pay a penalty for dissimilar panels, it is almost always worth it if it enables you to add another string.

Click to expand...

What if I put series 1 and series 3 in parrarel into the 1st port? I think I’m reading elsewhere that orientation doesn’t matter if it will take the average of the two?

I guess I need to find panels that can get me to that 410v that also satisfy the wife’s aesthetics review

GXMnow said:

Another idea...
Connect the new string with a separate MPPT charge controller straight to the battery bank.

Click to expand...

yea that could work, I’m trying to keep it simple with just the eg418k inverter and power wall though

Jdcarrol said:

What if I put series 1 and series 3 in parrarel into the 1st port? I think I’m reading elsewhere that orientation doesn’t matter if it will take the average of the two?

Click to expand...

It's important that all panels in a single string be facing the same direction. Unshaded parallel strings can be at different orientations with little to no penalty; however shading on a single string in that scenario will have adverse effects on the overall. Optimizers will help.

sunshine_eggo said:

It's important that all panels in a single string be facing the same direction. Unshaded parallel strings can be at different orientations with little to no penalty; however shading on a single string in that scenario will have adverse effects on the overall. Optimizers will help.

Click to expand...

Ok, I think I’m going to run the east facing 10pv string with the west facing 10pv string and place optimizers on few that get shaded. Thanks!

Read the installation notes for paralleled strings of optimizers . I am not sure that Tigo, for instance, allows “partial deployment” in that case. I have placed their jargon in quotes, search for tigo partial deployment for more details.

Jdcarrol said:

Ok, I think I’m going to run the east facing 10pv string with the west facing 10pv string and place optimizers on few that get shaded. Thanks!

Click to expand...

Even with optimizers note that if you have two shaded panels on one string, you may effectively lose the performance equivalent to two panels on the unshaded string. To bypass a panel, the voltage of that panel is lost. If you lose the voltage of the two shaded panels, the MPPT moves down to the -2 panel voltage of the string.

sunshine_eggo said:

Even with optimizers note that if you have two shaded panels on one string, you may effectively lose the performance equivalent to two panels on the unshaded string. To bypass a panel, the voltage of that panel is lost. If you lose the voltage of the two shaded panels, the MPPT moves down to the -2 panel voltage of the string.

Click to expand...

I think that is why Tigo says partial deployment on parallel strings is not supported. I think if the whole of both strings are optimized it can adjust the buck amount on both strings to match in voltage.

If you only have one optimizer in a string then you don’t have the flexibility to tradeoff current for voltage without throwing out power.

sunshine_eggo said:

counting:
10 panels in string 1
8 panels in string 2
10 panels in string 3

Q1: if you put optimizers on shaded panels, it will improve string performance.

Q2:


whelp, I have good news.

You don't need identical panels. You need panels that have series Vmp of 410V ±10%

Generally speaking, you need to match Vmp within about 10% to ensure the panels will perform normally; however, both strings may experience that 10% penalty to rated output (there will be a penalty, but it may not be the full 10%). You can also use different panels in series, but they will operate at the current of the lowest rated panel.

Generally speaking, while you may pay a penalty for dissimilar panels, it is almost always worth it if it enables you to add another string.

Click to expand...

I was reading along in this thread and I had a related thought that I wanted to run it by @sunshine_eggo.

If you made a parallel string with the same Maximum Power Voltage per string regardless of per panel specs could you not still achieve maximum output rating?

Example s-1 10×38.1v=381v s-2 12×31.6v=379.2v and parallel s-1 and s-2 99.47% efficiency by my calculations of course one panels low light efficiency may exceed the others.
Amps do not in parallel they just add together. Correct?

I got the 31.6v example from my panels.

Bananaman321 said:

I was reading along in this thread and I had a related thought that I wanted to run it by @sunshine_eggo.

If you made a parallel string with the same Maximum Power Voltage per string regardless of per panel specs could you not still achieve maximum output rating?

Example s-1 10×38.1v=381v s-2 12×31.6v=379.2v and parallel s-1 and s-2 99.47% efficiency by my calculations of course one panels low light efficiency may exceed the others.
Amps do not in parallel they just add together. Correct?

I got the 31.6v example from my panels.

Click to expand...

Depends on the details & how you define it.

If there is no shading, you can parallel a string comprising 100W panels with another comprising 400W panels, and the performance will be the same. In fact half-cut 400W panels are to a level of approximation 2 200W panels in parallel, and this doesn't "hurt" them in aggregate output.

If you don't care about shading in your model / situation then you can stop here.

If there is shading, then you need to factor in the bottlenecked, non-bypassed power at full string voltage; and the bypassed, reduced string voltage. Both of those cases reduce output, and there is an interaction with the fact that two parallel strings impose mutually exclusive constraints on the MPPT optimization, that are not present with a single string.

Just an FYI I did a little experimenting with my 18KPV

The number one port likes to be driven a little harder amps wise in my experimentI found that 6S2P with put out more power and low light then 12S.

zanydroid said:

Depends on the details & how you define it.

If there is no shading, you can parallel a string comprising 100W panels with another comprising 400W panels, and the performance will be the same. In fact half-cut 400W panels are to a level of approximation 2 200W panels in parallel, and this doesn't "hurt" them in aggregate output.

If you don't care about shading in your model / situation then you can stop here.

If there is shading, then you need to factor in the bottlenecked, non-bypassed power at full string voltage; and the bypassed, reduced string voltage. Both of those cases reduce output, and there is an interaction with the fact that two parallel strings impose mutually exclusive constraints on the MPPT optimization, that are not present with a single string.

Click to expand...

I'm not telling anybody to do this it was just something that came to mind and I thought I would run past @sunshine_eggo if I had some other panels I would experiment with it myself.

From an electrical standpoint the configuration is sound in optimal conditions. I just thought it a good place to pop the question And get everybody scratching their heads a bit.

Bananaman321 said:

If you made a parallel string with the same Maximum Power Voltage per string regardless of per panel specs could you not still achieve maximum output rating?

Click to expand...

That's essentially what I was saying here:

sunshine_eggo said:

Generally speaking, you need to match Vmp within about 10% to ensure the panels will perform normally; however, both strings may experience that 10% penalty to rated output (there will be a penalty, but it may not be the full 10%).

Click to expand...

if you match them perfectly, no penalty.

On my DC system, I have 3 rows of panels running in parallel. 2 rows are 5 x 100 watt matching panels in series. The third row is again 5 panels, but they re 200 watt panels. The VOC and VMP are virtually identical. The 200 watt panels have 32 full size square cells. The 100 watt panels look like the identical cells, but they are just half cut versions. Looking at the 200 watt panels, you can eve see scribe lines where they would be cut to make the half cuts. I think the cells came out of the same fab. On a nice sunny but cool day, I saw 5 amps on each row of 100 watt panels, and 10 amps on the 200 watt row. I had 20 amps into the charge controller and nearly 1,800 watts going into the battery bank. As long as the voltage of each string matches, they add up nicely.