Ampage question that NAPIT cannot answer.

[bobbiecool]

Hi. Attached are data sheets for a Growatt SPH5000 inverter and for a Eurener solar panel, these were installed at my property in November. I have 2 strings of 12 and 6 panels. Im currently in dispute with the installers through NAPIT initially due to a voltage problem on the 2nd string of 6. I'm also concerned that due to the ampage of the panels being outside of the working parameters of the inverter that these panels should not have been installed in the first place. Am I correct in questioning this or does it not matter in the long run? Not being an electrician I have no idea whether intalling these panels would cause a problem due to the ampage.
NAPIT, having had this info for 3 months, are being very unhelpful in answering this question. I get the feeling they're understaffed and/or not up to the task of giving me an answer.
Any help would be appreciated.

 

[SamDeleted]

Hi. Attached are data sheets for a Growatt SPH5000 inverter and for a Eurener solar panel, these were installed at my property in November. I have 2 strings of 12 and 6 panels. Im currently in dispute with the installers through NAPIT initially due to a voltage problem on the 2nd string of 6. I'm also concerned that due to the ampage of the panels being outside of the working parameters of the inverter that these panels should not have been installed in the first place. Am I correct in questioning this or does it not matter in the long run? Not being an electrician I have no idea whether intalling these panels would cause a problem due to the ampage.
NAPIT, having had this info for 3 months, are being very unhelpful in answering this question. I get the feeling they're understaffed and/or not up to the task of giving me an answer.
Any help would be appreciated.

Hi Bobbie


Can you give us your real world solar panel strings amp & voltage outputs , for both strings separately if possible

It is hard to diagnose the issue without the data

 

[SamDeleted]

.

 

[zanydroid]

Nit: current > amperage > ampage

I took a quick look and 6 * VoC, 6 * Vmpp, for various combinations of NOCT and STC, are marginal vs the start voltage and operating range. With a high enough cell temperature it might drop below on both fronts?

6 / 126 / .0025 = drops below operating range of 120V at ~40C cell temperature.

And the 126V is outside the MPP range anyway, I'm not sure what implications this has. Probably not good for efficiency.

Not enough data to proceed beyond this without your amp & voltage readings.

Is there shading on second string?

 

[zanydroid]

My shot-in-the-dark theory of what happened here is that the installer did not realize they were using 40s cell configuration (quite low voltage), and used a panel count more appropriate for > 54s

Another consequence of this, even on your 12s string, is that the current is high for the MPPT (12A input) so some output is wasted. IE this MPPT is designed for the other types of solar modules. OOPS!

(The specs on the module say 2x (8 x 5) config of cells, and the name implies 80 half-cut cells)

 

[zanydroid]

For some context, I ran into a similar issue when deciding between 108 half-cut vs 144 half-cut 400W modules, and decided to go with the latter because the microinverters I wanted to use were marginal for 108 half cut output current, and I didn't want to deal with that. The newer generation of that microinverter worked perfectly fine with either type but the cost delta was not worth it to me.

 

[bobbiecool]

Nit: current > amperage > ampage

I took a quick look and 6 * VoC, 6 * Vmpp, for various combinations of NOCT and STC, are marginal vs the start voltage and operating range. With a high enough cell temperature it might drop below on both fronts?

6 / 126 / .0025 = drops below operating range of 120V at ~40C cell temperature.

And the 126V is outside the MPP range anyway, I'm not sure what implications this has. Probably not good for efficiency.

Not enough data to proceed beyond this without your amp & voltage readings.

Is there shading on second string?

Many thanks for your reply. I've looked and I cannot see any real world amp readings, however my voltage readings 10mins ago was 251v on 1st string and 124v on the troublesome 2nd string. A moment later it went below 120v and shut of the 2nd string, 5 mins later it went back up to 150v to start producing again (a common occurrence).
My installer are contemplating using Tigo devices to increase the voltage on the 2nd string (there is no shading at all), and I'm wondering, given the ampage, would it be advisable to do that?

 

[zanydroid]

My installer are contemplating using Tigo devices to increase the voltage on the 2nd string (there is no shading at all), and I'm wondering, given the ampage, would it be advisable to do that?

Not sure how TIGOs would help, I thought they decreased voltage to gain current. Opposite of what you want.

Do you have space for another panel? Are the two strings on the same roof surface? If they are then you can pull one panel from first string to boost voltage on second string. The first string would still be comfortably above start voltage.

The other approach would be to install another grid tie inverter with lower start voltage, I doubt it would be that much labor, provided the inverter exists. Or the installers replace the solar panels with same number of higher voltage versions on the same racking. Not much more work than installing TIGO.

Or replace the existing grid tie inverter with another two MPPT one that is better matched to these solar panels.

A DIYer would most likely try the inverter route.

This is UK right? I think you do solar with electricians and roofers as separate trade with one of them being the master contractor. Inverter add should be electrician only.

 

[zanydroid]

https://support.tigoenergy.com/hc/en-us/community/posts/4409145936403-Some-curiosities-about-optimizers-that-I-can-t-seem-to-find-info-on

 

[Vigo]

So if im understanding the complaint correctly, the 12s string is just fine and the 6s string is marginal because it will not consistently hit the 'startup' voltage for the MPPT to start doing anything with that string.

Technically BOTH strings are slighlty mismatched to the inverter in another way which is that they can make 14amps and the controller will only ever use 12a, which is leaving power on the table aka wasted, at least under ideal conditions.

For me the real question is how are the panels currently installed? Moving 2 or 3 panels from the 12s string to the 6s string would be a major improvement.

But, if you ever want to get close to the 'nameplate wattage' of solar panels you have installed, you'd either want panels that made <12amps, or an MPPT that would allow 15a+. So one end of that equation has got to change or you will always be 'down' a bit of power compared to the theoretical max.

 

[chrisski]

Sounds as if you could ass one more panel in series to the string of 6, it would stop the low voltage shutoff.

Is rewiring two strings of 9 possible or is adding a seventh panel possible?

 

[bobbiecool]

Not sure how TIGOs would help, I thought they decreased voltage to gain current. Opposite of what you want.

Do you have space for another panel? Are the two strings on the same roof surface? If they are then you can pull one panel from first string to boost voltage on second string. The first string would still be comfortably above start voltage.

The other approach would be to install another grid tie inverter with lower start voltage, I doubt it would be that much labor, provided the inverter exists. Or the installers replace the solar panels with same number of higher voltage versions on the same racking. Not much more work than installing TIGO.

Or replace the existing grid tie inverter with another two MPPT one that is better matched to these solar panels.

A DIYer would most likely try the inverter route.

This is UK right? I think you do solar with electricians and roofers as separate trade with one of them being the master contractor. Inverter add should be electrician only.

The 1st string of 12 is on a roof facing west, the 2nd string of 6 is on a roof facing south. There is not enough space on the south facing roof to add another panel.
My ideal scenario would be to replace the 2nd string with higher voltage panels, however my concern is the amp parameter of the inverter. Would leaving the 12 panels on the 1st string cause any issues due to the amp being higher than the inverter allows in the spec sheet?
The installer wants to avoid replacing panels and install TIGOs to help with the voltage issue, but as I'm no electrician or solar expert I've no idea if it would work.

 

[bobbiecool]

So if im understanding the complaint correctly, the 12s string is just fine and the 6s string is marginal because it will not consistently hit the 'startup' voltage for the MPPT to start doing anything with that string.

Technically BOTH strings are slighlty mismatched to the inverter in another way which is that they can make 14amps and the controller will only ever use 12a, which is leaving power on the table aka wasted, at least under ideal conditions.

For me the real question is how are the panels currently installed? Moving 2 or 3 panels from the 12s string to the 6s string would be a major improvement.

But, if you ever want to get close to the 'nameplate wattage' of solar panels you have installed, you'd either want panels that made <12amps, or an MPPT that would allow 15a+. So one end of that equation has got to change or you will always be 'down' a bit of power compared to the theoretical max.

See my reply above

 

[bobbiecool]

Sounds as if you could ass one more panel in series to the string of 6, it would stop the low voltage shutoff.

Is rewiring two strings of 9 possible or is adding a seventh panel possible?

See my reply above above )

 

[zanydroid]

The installer wants to avoid replacing panels and install TIGOs to help with the voltage issue, but as I'm no electrician or solar expert I've no idea if it would work.

Since I linked a thread from TIGO saying the optimizers work opposite to what installer claims I would suggest forwarding them that thread to the installer and having them justify the dissonance between their plan and that info. and also emailing or calling tigo yourself. Though the latter is awkward because you would need to find the right support engineer and then communicate effectively with your starter knowledge of solar.

15A Isc into a 12A max MPPT is fine safety wise but you're leaving some production on the table due to the clipping.

It really feels like they messed up the design and are continuing to mess up in some ways.

 

[bobbiecool]

Since I linked a thread from TIGO saying the optimizers work opposite to what installer claims I would suggest forwarding them that thread to the installer and having them justify the dissonance between their plan and that info. and also emailing or calling tigo yourself. Though the latter is awkward because you would need to find the right support engineer and then communicate effectively with your starter knowledge of solar.

15A Isc into a 12A max MPPT is fine safety wise but you're leaving some production on the table due to the clipping.

It really feels like they messed up the design and are continuing to mess up in some ways.

Thank you so much for your response, I will definitely forward the thread to them. And yes, your last comment is spot on. Not only that they refuse to accept any of this is their fault, hence me contacting NAPIT to help resolve the situation. However they are dragging their heels on the matter (3 months and counting) hence me obtaining as much info as possible to help my case.
I've attached some info that may or may not be of interest. Its today's voltage data from Growatt, you can see at 12.17pm the 2nd string shut down.
So as it stands the best way forward is to replace the 6 panel 2nd string with higher voltage panels, is this correct?

 

[bobbiecool]

And for 40 mins the 2nd string didn't produce while waiting to get back up to 150v :-(

 

[zanydroid]

So as it stands the best way forward is to replace the 6 panel 2nd string with higher voltage panels, is this correct?

(I talked about the options in one of my replies above).

Best is always hard to say, but if you can find narrower but higher 400W cells they will definitely fit on the rails, the question is whether it'll still fit on your roof taking into account any setbacks required by local regulations. I'm also not sure about how much margin it will buy you. 40s -> 54s will give 30% more buffer. If there's no shading (which may activate bypass diodes, dropping voltage) and this is the hottest temperature / most overcast (I think both will drop the VOC) you expect then 30% is feels pretty good.

FWIW, it's just 6 modules, it's not going to kill their business. Maybe US$1200 + labor. If they're still using these modules they really should have the more appropriate string inverters in stock, if they were competent I guess.

 

[Vigo]

If you can force the installer to deal with it then i think the best solution is different panels in that location with greater string voltage.

If YOU are fixing it, you may consider just buying a standalone MPPT controller which is more compatible with the voltage and amperage from the existing panels, and adding it to your setup. The advantage of that is that all the work which would need to be done to install it would be inside your house (or wherever the Growatt is, but likely indoors and with a level surface to stand on and no ladders or harnesses or buddy system involved). Downside is if you are trying to do a bunch of logging/tracking through the growatt inverter itself, running the 6s string through a separate mppt would take that information 'offline' or to a 2nd system which may be undesirable to you.

Another option may be to add more roughly-south-facing panels to the 6s string, but in another location. Even if you had room for only 2-3 panels on another south-facing surface, there is no reason you couldn't wire them in series with the existing 6.

 

[zanydroid]

Keep in mind also what's easier / best depends on regulations... I think most people in the US are authorized to swap their own inverters (with varying levels of involvement of grid to update operating agreement), but that may not apply to you.

I think in most places you can have licensed electricians swap any solar components. And if it's not on a roof they'll be happy to do it.

My concern about adding solar on a similar facing but separate plane is that it really encroaches on more knowledge/skillset and regulations on who can do the work. In the US everything is easier to do to code, and with low incremental labor, on contiguous arrays. That's why both DIYers and installers heavily prefer it...

Anecdotally I have a current project where I'm installing on 4 separate planes , was going to add a 5th comprising a single panel, all to NEC2017. Cut that last one because that was pure torture for the incremental production, lol.