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Solar layout - Does this need optimizers?

GrantD

New Member
Mar 17, 2021
2
0
Connecticut
I am having a 16.32Kw Tesla string solar system installed. Tesla’s equipment would include the following equipment (NOTE: no optimizers or mini inverters):
  • 48 x Hanwha 340 Kw panels (Q.PEAK DUO BLK-G6+)
  • 2 x Tesla 7.6Kw Inverters (model 1538000-00-E)
I have been told by a competitor that the Tesla system is a waste because a string system is not appropriate for my roof. They say this because Tesla uses a string system and the chimney shadow that will be over some panels from mid to late afternoon will reduce the output to “the output of the most shaded panel”. They say that because of the chimney shadow, I would need a system with either Optimizers or Micro-inverters.

My Tesla Project Advisor says that since Tesla uses MPPT, which does the same thing as an Optimizer and thus the rest of the system will not be affected by shadow over a few panels.
Who is correct? NOTE: the chimney shadow will cover at least 3 panels from 3pm in the afternoon until sunset (see photo below taken at 3pm in March).

Also, since the total KW of the two inverters is only 15.2kw, does that mean that my output will be capped? Why would Tesla sell a 16.32kw system when the inverters are only rated for 15.2Kw? I have the option to add another 2 panels but what would be the point if the inverter capped it?

Advice greatly appreciated!

Tesla solar design.png


Roof with Chimney 4pm on 3_9_21.jpg
 

rxlawdude

Active Member
Jul 10, 2015
2,268
1,556
Orange County, CA
I am having a 16.32Kw Tesla string solar system installed. Tesla’s equipment would include the following equipment (NOTE: no optimizers or mini inverters):
  • 48 x Hanwha 340 Kw panels (Q.PEAK DUO BLK-G6+)
  • 2 x Tesla 7.6Kw Inverters (model 1538000-00-E)
I have been told by a competitor that the Tesla system is a waste because a string system is not appropriate for my roof. They say this because Tesla uses a string system and the chimney shadow that will be over some panels from mid to late afternoon will reduce the output to “the output of the most shaded panel”. They say that because of the chimney shadow, I would need a system with either Optimizers or Micro-inverters.

My Tesla Project Advisor says that since Tesla uses MPPT, which does the same thing as an Optimizer and thus the rest of the system will not be affected by shadow over a few panels.
Who is correct? NOTE: the chimney shadow will cover at least 3 panels from 3pm in the afternoon until sunset (see photo below taken at 3pm in March).

Also, since the total KW of the two inverters is only 15.2kw, does that mean that my output will be capped? Why would Tesla sell a 16.32kw system when the inverters are only rated for 15.2Kw? I have the option to add another 2 panels but what would be the point if the inverter capped it?

Advice greatly appreciated!

View attachment 645387

View attachment 645386
While I don't have a Tesla solar installation, I'm assuming (and expect) they will have two strings, the lower roof being on its own string. I have a similar situation with a chimney shadow, and that string definitely generates less when the shadow hits one or two panels. We do not have optimizers. Frankly, if I had to do it over again, I'd consider microinverters.

Obviously, that solution has its own challenges, and as far as I know, Tesla doesn't do these.
 

h2ofun

Active Member
Aug 11, 2020
1,731
276
auburn, ca
While I don't have a Tesla solar installation, I'm assuming (and expect) they will have two strings, the lower roof being on its own string. I have a similar situation with a chimney shadow, and that string definitely generates less when the shadow hits one or two panels. We do not have optimizers. Frankly, if I had to do it over again, I'd consider microinverters.

Obviously, that solution has its own challenges, and as far as I know, Tesla doesn't do these.
with all the comments about strings and shading, sure glad I went with solaredge stuff, since I have a lot of shading on various parts of the day. Now did I spend more. Yep, Would the total cost of Tesla still have been cheaper, probably. Tough decisions.
 

Ampster

Active Member
Oct 5, 2012
1,690
432
Sonoma, California
Your panel will rarely reach their maximum output. It is common to have DC to AC ratios larger than 1 to 1. Mine is 1.50 to 1. As far as chimney shadow ask Tesla for an estimate and compare to PV Watts.
 

bevo

Member
Mar 10, 2021
39
16
Irvine
Each Tesla 7.6kW inverter can support up to 4 strings, each with it's own MPPT. Since you have 2 of these, you can have up to 8 strings. There are other considerations such as minimum panels per string but I don't know the details.
Tesla could design such that these panels are separated out and not impact much of the system. You would have to review the design with them.
 

bevo

Member
Mar 10, 2021
39
16
Irvine
Ask Tesla for the Electrical Layout document (at least that's what mine was titled). This should show the groupings and other interesting details.
 

bevo

Member
Mar 10, 2021
39
16
Irvine
Also, since the total KW of the two inverters is only 15.2kw, does that mean that my output will be capped? Why would Tesla sell a 16.32kw system when the inverters are only rated for 15.2Kw? I have the option to add another 2 panels but what would be the point if the inverter capped it?
You will not be limited by the inverters. Your panels are facing West. I don't think they will be able to produce 340W. Add the 2 panels if you like.
 

nwdiver

Well-Known Member
Feb 17, 2013
7,644
9,777
United States
While I don't have a Tesla solar installation, I'm assuming (and expect) they will have two strings, the lower roof being on its own string. I have a similar situation with a chimney shadow, and that string definitely generates less when the shadow hits one or two panels. We do not have optimizers. Frankly, if I had to do it over again, I'd consider microinverters.

Obviously, that solution has its own challenges, and as far as I know, Tesla doesn't do these.

Well.... yeah... if there's less sunlight hitting a panel it's going to produce less energy. Micro-inverters or optimizers aren't going to stop that... they're not magic. The effect is going to be nearly identical with a string inverter so long as that string is on an independent MPP... which according to the OP it should since he'll have 8 independent MPP channels. So long as all panels on each channel are in series and facing the same direction there's no significant advantage to micros or optimizers.
 
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GrantD

New Member
Mar 17, 2021
2
0
Connecticut
Ok, so if I have this straight. As long as I have the design engineer put all the panels that will be affected by the chimney shade on the same MPP and all the ones that have uninterrupted sun on their own MPP(s) then I will be close to the same output as if I had optimizers for each panel?
 

nwdiver

Well-Known Member
Feb 17, 2013
7,644
9,777
United States
Ok, so if I have this straight. As long as I have the design engineer put all the panels that will be affected by the chimney shade on the same MPP and all the ones that have uninterrupted sun on their own MPP(s) then I will be close to the same output as if I had optimizers for each panel?

Yep. Possibly even outperform optimizers. There isn't any good 3rd party research but optimizers don't work for free and there's reason to believe properly installed string systems can outperform optimized systems.

SMA Shadefix

'Shade fix' is just a fancy name for a MPP tracker smart enough to find the best MPP. I'm sure Tesla inverters are just as good.
 
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rxlawdude

Active Member
Jul 10, 2015
2,268
1,556
Orange County, CA
Well.... yeah... if there's less sunlight hitting a panel it's going to produce less energy. Micro-inverters or optimizers aren't going to stop that... they're not magic. The effect is going to be nearly identical with a string inverter so long as that string is on an independent MPP... which according to the OP it should since he'll have 8 independent MPP channels. So long as all panels on each channel are in series and facing the same direction there's no significant advantage to micros or optimizers.
Um, if one panel is not producing, the total output of that string drops significantly more than if each panel had its own inverter. But an MPP on the channel will help mitigate the loss.

I agree that optimizers (or MPP channels!) aren't magic. If he has 8 MPP channels, the installation should isolate the panels that are subject to shade into its own channel, considering sun's position at various times of the year that affect the shadow cast by the chimney.
 

nwdiver

Well-Known Member
Feb 17, 2013
7,644
9,777
United States
Um, if one panel is not producing, the total output of that string drops significantly more than if each panel had its own inverter. But an MPP on the channel will help mitigate the loss.

It does not. If one panel becomes a 'load' due to shade the bypass diodes are activated effectively removing the shaded section from the string. Unshaded panels continue producing unaffected by the shaded section.

Solar Panel Shading
 

dareed1

Member
Jan 15, 2021
34
26
Belmont, CA
Um, if one panel is not producing, the total output of that string drops significantly more than if each panel had its own inverter. But an MPP on the channel will help mitigate the loss.

I agree that optimizers (or MPP channels!) aren't magic. If he has 8 MPP channels, the installation should isolate the panels that are subject to shade into its own channel, considering sun's position at various times of the year that affect the shadow cast by the chimney.
Nope. If one panel is completely shaded and all other are in clear sunlight, a string inverter will output nominally the same power as an optimizer or microinverter system.

And each MPP channel should preferably have 10-13 panels to keep within the MPP range of the inverter, both on bright days (13 panels to avoid overvoltage) and on overcast days or at times noticeably different than solar noon (~10 panels). So in the OP's situation, it is probably best (if using a string inverter) to have 11, 12, 12, and 13 panels on 4 strings. Even better would be to add 2 panels in the open spots, if that is cheaper than going with a non-Tesla installer and an optimizer/microinverter setup.

Optimizers can help. To take a simple example for the OP's setup, if the chimney is casting a shadow anywhere on the bottom half of a single panel, then a string optimizer will probably get zero power from that panel (and full power from the others). But these are half cell panels, which means the upper half is capable of generating half the current that a fully illuminated panel can. An optimizer setup can use that upper half's output, or up to 170 watts more total output than a string setup. It is difficult to justify this increased power financially, however.

As already suggested, putting 12 unshaded panels on the east side will give just as much power as 12 unshaded panels on the west side. The maximum output will occur in the morning instead of afternoon, if that is an issue.
 
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nwdiver

Well-Known Member
Feb 17, 2013
7,644
9,777
United States
Optimizers can help. To take a simple example for the OP's setup, if the chimney is casting a shadow anywhere on the bottom half of a single panel, then a string optimizer will probably get zero power from that panel (and full power from the others).

Yep. And to see a benefit of an optimizer the ENTIRE panel needs to be in shade. If a single cell group is unshaded the optimizer will likely pull full power from that cell group causing the shaded portion of the panel to be bypassed in the same way it would be as part of a string.

There's a really narrow operating case where optimizers can outperform and it's really not by much. Pulling power from fully shaded panels is basically blood from a stone...
 

DrSmile

Member
Nov 7, 2018
219
138
Northern NJ
If enough panels on a string are shaded you will have no output from that string if the total string voltage is below the inverter minimum. So you may want to consider that when figuring out how to run your strings. 8 strings for 48 panels seems like a bad idea because on a 6 panel you may only need to lose one panel to have the whole string drop out.
 

charlesj

Active Member
Oct 22, 2019
1,083
220
Monterey, CA
I am having a 16.32Kw Tesla string solar system installed. Tesla’s equipment would include the following equipment (NOTE: no optimizers or mini inverters):
  • 48 x Hanwha 340 Kw panels (Q.PEAK DUO BLK-G6+)
  • 2 x Tesla 7.6Kw Inverters (model 1538000-00-E)
...
Has Tesla mentioned larger panels for those inverters so you can have a much larger DC to AC ratio. You have a 1.07 ratio now. You'd produce much more over a year with a ratio of 1.5 even though the max would be inverter limited, you'd have more power over a longer time span each day.

I have a 1.09 system that is 9 years old. It almost reached max inverter only 1 day in 9 years and that was only a short time on either side of peak.
 

nwdiver

Well-Known Member
Feb 17, 2013
7,644
9,777
United States
Has Tesla mentioned larger panels for those inverters so you can have a much larger DC to AC ratio. You have a 1.07 ratio now. You'd produce much more over a year with a ratio of 1.5 even though the max would be inverter limited, you'd have more power over a longer time span each day.

I have a 1.09 system that is 9 years old. It almost reached max inverter only 1 day in 9 years and that was only a short time on either side of peak.

Can't say this is always true but I've never matched panels to inverters. It's always been the other way around. I predict we're gonna see a lot of wonky ratios since Tesla inverters now need to be in multiples of 3.8kW. 11.4kW would work but an oversize ratio of 1.43 is a bit stiff. The cost of a 7.6 over a 3.8 is probably worth it.
 
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