micro-inverters or optimizers when shading is major issue ?

[nwdiver]

Well except the MPPT range for SMA Sunny Boy 7.7-US inverters is 270-480V



So you put 22.77kW of solar on 15.4kW of inverter. I see why you are not worried about optimization there.

Check the data sheet again. 270-480v is the 'Rated band'; since the channel is limited to 10A you need 270v to get the rated power... not really an issue if ~70% of your panels are in shade. The remaining unshaded panels will still function in the MPPT band which is 100 - 550v.

For the 22.77kW project 15.5kW of inverter would have required a ~$5k service upgrade... not worth it. So we have 15.1kW facing SW and 7.6kW facing SE on 15.4kW of inverter; Works great

[bcroe]

There's no reason to ever have parallel strings on a residential system with current inverter options. I don't think anyone makes an inverter with 1 MPPT channel anymore. All the new inverters I've seen have 2-4 channels.

There are 12 strings operating here. The thought is that they are arranged so a whole string
gets shaded at a time, at day extremes. Bruce Roe

[nwdiver]

There are 12 strings operating here. The thought is that they are arranged so a whole string
gets shaded at a time, at day extremes. Bruce Roe

On 1 MPPT? Jeeze... what's the voltage and current?

[bcroe]

On 1 MPPT? Jeeze... what's the voltage and current?

There are 2 inverters 6 years old (single MPPTs). Running about 360VDC at 42A total summers, up to
420VDC winters. Bruce Roe

CombAug18.JPG

[nwdiver]

There are 2 inverters 6 years old (single MPPTs). Running about 360VDC at 42A total summers, up to
420VDC winters. Bruce Roe

Ah... that makes sense. If your inverters die it would be interesting to see the change in production if each string had its own channel. I've got an old SMA inverter with 3 parallel strings. My production drops off a lot in the evenings when 3 panels get shaded around ~5pm. I effectively end up with 2 strings of 14 and a string of 11 so the 11 unshaded panels do ~nothing where as if they had their own channel they would do ~something.

I helped design a 27kW ground mount on 2 old 11.4kW Fronius inverters. 4 Strings per inverter. ~November - February the front array shades the rear array a bit in the mornings and evenings. Once a single panel gets shaded the rest of the string pretty much drops out.

The ~23kW array with 6 independent strings actually 'lost' a panel in a bad wind storm. The other ~65 panels carried on just fine. It also gets some shade from nearby trees in the evenings... production barely budges since only the shaded panels are effected.

IMO string level optimization is where it's at. Even optimizing a single module is technically 'string level' it's just a string of ~60 or 72 cells instead of ~800 cells. I just don't see much of a benefit optimizing every ~60 or 72 instead of the full ~800... You really only run into issues when you try to run parallel strings... and even then it mostly works unless there's shade.

[bcroe]

Ah... that makes sense. If your inverters die it would be interesting to see the change in production if each string had its own channel. I've got an old SMA inverter with 3 parallel strings. My production drops off a lot in the evenings when 3 panels get shaded around ~5pm. I effectively end up with 2 strings of 14 and a string of 11 so the 11 unshaded panels do ~nothing where as if they had their own channel they would do ~something.

I helped design a 27kW ground mount on 2 old 11.4kW Fronius inverters. 4 Strings per inverter. ~November - February the front array shades the rear array a bit in the mornings and evenings. Once a single panel gets shaded the rest of the string pretty much drops out.

The ~23kW array with 6 independent strings actually 'lost' a panel in a bad wind storm. The other ~65 panels carried on just fine. It also gets some shade from nearby trees in the evenings... production barely budges since only the shaded panels are effected.

IMO string level optimization is where it's at. Even optimizing a single module is technically 'string level' it's just a string of ~60 or 72 cells instead of ~800 cells. I just don't see much of a benefit optimizing every ~60 or 72 instead of the full ~800... You really only run into issues when you try to run parallel strings... and even then it mostly works unless there's shade.

I will leave that experiment to someone else. I will not be trenching in wiring for each string for
the 200 to 400 feet to the inverter location. As it is I use a clamp on DC ammeter to make sure
all is well some sunny days. If/when they do die, I have an identical spare inverter set bought
at closeout price. Whiz bang features on newer models I perceive as a threat to simple and
reliable operation.

I have thought about building some optimizers for certain sections. But so far the chain saw
and careful location have preempted electronic intervention. Bruce Roe

[nwdiver]

I will leave that experiment to someone else. I will not be trenching in wiring for each string for
the 200 to 400 feet to the inverter location. As it is I use a clamp on DC ammeter to make sure
all is well some sunny days. If/when they do die, I have an identical spare inverter set bought
at closeout price. Whiz bang features on newer models I perceive as a threat to simple and
reliable operation.

I have thought about building some optimizers for certain sections. But so far the chain saw
and careful location have preempted electronic intervention. Bruce Roe

Oh... you combined the strings at the array? Yeah... that won't work then

[RShackleford]

Argh, flagged for moderation again. All I was trying to do was figuring out how to edit my post so the quotation from the link could be smaller, or different color or font.

Look at this bit of double-speak at a comment thread at SMA website (http://www.smainverted.com/sma-redef...comment-132444) appearing to come from an SMA person:

Hi Andrew, thanks for your question. When the TS4 platform is used for selective deployment and TS4-R-O units are attached only to modules with shade impact, the Secure Power Supply function will still work. In this case, SMA’s Rapid Shutdown System will also still function as needed to meet code requirements.

When the TS4 platform is used specifically for Rapid Shutdown, the shutdown signal will be sent to all TS4 units, and in this case, Secure Power Supply will no longer work.

Does that make ANY sense to anybody ? I think SMA/Tigo is doing a very poor job of explaining the interaction between rapid-shutdown and secure-power, and not really owning up to the fact that SPS may not work for many installations.

[solar pete]

Hi R Shackleford, I think I was trying to approve you post while you were trying to edit it, all good now, cheers

[nwdiver]

Argh, flagged for moderation again. All I was trying to do was figuring out how to edit my post so the quotation from the link could be smaller, or different color or font.

Look at this bit of double-speak at a comment thread at SMA website (http://www.smainverted.com/sma-redef...comment-132444) appearing to come from an SMA person:

Hi Andrew, thanks for your question. When the TS4 platform is used for selective deployment and TS4-R-O units are attached only to modules with shade impact, the Secure Power Supply function will still work. In this case, SMA’s Rapid Shutdown System will also still function as needed to meet code requirements.

When the TS4 platform is used specifically for Rapid Shutdown, the shutdown signal will be sent to all TS4 units, and in this case, Secure Power Supply will no longer work.

Does that make ANY sense to anybody ? I think SMA/Tigo is doing a very poor job of explaining the interaction between rapid-shutdown and secure-power, and not really owning up to the fact that SPS may not work for many installations.

I think that's in relation to the old -40 inverters. TIGO communication is integrated into the -41 so SPS will now work with the S and the O TS4s but not the 'Fs' for some reason.

[bcroe]

I try to avoid moderation by cutting off much of any link, why repeat it. Bruce Roe

[RShackleford]

I think that's in relation to the old -40 inverters. TIGO communication is integrated into the -41 so SPS will now work with the S and the O TS4s but not the 'Fs' for some reason.

I don't get that from the quote at all, or from any other part of that comment thread, except maybe the very last thing (from a Mike who also seems to work there): "please be advised that the Sunny Boy US-41 will support the SPS functionality, but only when used with the TS4-O and -S. The TS4-F in combination with the Sunny Boy US-41 will not support the SPS functionality." But it's still unclear if you have to omit the RCK for SPS to work, thereby possibly disabling rapid shutdown.

The lack of clear communication, about what is and isn't possible, by this company is ridiculous.

[nwdiver]

I don't get that from the quote at all, or from any other part of that comment thread, except maybe the very last thing (from a Mike who also seems to work there): "please be advised that the Sunny Boy US-41 will support the SPS functionality, but only when used with the TS4-O and -S. The TS4-F in combination with the Sunny Boy US-41 will not support the SPS functionality." But it's still unclear if you have to omit the RCK for SPS to work, thereby possibly disabling rapid shutdown.

The lack of clear communication, about what is and isn't possible, by this company is ridiculous.

The article you cited is from 2017... before the -41s were released. I don't understand why the Fs don't work...

[SunEagle]

I try to avoid moderation by cutting off much of any link, why repeat it. Bruce Roe

A post with more than one weblink is usually flagged for Moderation.

[RShackleford]

The article you cited is from 2017... before the -41s were released. I don't understand why the Fs don't work...

The comment thread goes thru until this past July. If interested, I'd encourage people to read the whole thing; lots of conflicting info.