PV voltage tripping the inverter

[mudk]

Hi all,

I have a 5Kva PV inverter - hybrid. I don't have any batteries connected at the moment though.

The booklet says that Max PV voltage is 500Vdc
I have 11 250w plates in series.
occasionally (at odd times of day) the inverter will trip saying that PV voltage is beyond specification. eg. at 8 am.

Any ideas?

during the day it hovers around 450 volts. Tested the input from before and after the DC panels breaker and the numbers are identical +/-3 as on the inverter screen

but when i run any load on the inverter I do not get the max i would expect (250x11 = 2750 Watts of power) i only get around 1.2kw

Why is voltage from panels always at it's maximum?

 

[gnubie]

Can you post a link to the manufacturer's web page for the unit? I'm guessing you have a MPP brand unit, but perhaps not. Also if you can post a link to the panel specs, or a picture of the spec sheet that is found on the back of the panel.

Are you operating the panels in a cold environment? What is the temperature at 8am?

 

[mudk]

Sunglow VM II 5000 Off-Grid Inverter - Maxpower

Quick Overview Regardless of whether it is a photovoltaic system for a single - or multi-family home, an agricultural or industrial building, or a megawatt power station; MaxPower inverters reliably and efficiently convert direct current into mains-compliant alternating current. Brand Max...

www.maxpower.com.pk

The manual I have is also there in PDF
This is a video of the system today, a new issue i noticed today. When i switch on the utility breaker the inverter dumps the load there instead of the solar. Even though it is set to SBU.

switch on util.mp4

drive.google.com

This following is an hour later, everything seemingly working. https://drive.google.com/open?id=12UEPQkAz9NXNg605KEAWBIIrXFof08hC

It is very cold here in the morning close to 0 C i would say.

 

[gnubie]

The inverter has two voltages to note on the PV side. Maximum permissible 500v, but MPPT range of 120v to 450v. Early in the morning before the panels warm up from the sun you may well be seeing > 450v from the panels (no load, during MPPT search the panels will be lightly loaded at some stage so they will float up in voltage) and that is probably what it is complaining about.

If you post a link to the panel's specs or a picture of the label on the back of the panels so I can see the ratings I can see if that is the explanation.

 

[Maast]

How are you even turning it on without any batteries attached to it? Every battery based inverter I've ever heard of needs a battery attached to even turn on.

 

[mudk]

The inverter has two voltages to note on the PV side. Maximum permissible 500v, but MPPT range of 120v to 450v. Early in the morning before the panels warm up from the sun you may well be seeing > 450v from the panels (no load, during MPPT search the panels will be lightly loaded at some stage so they will float up in voltage) and that is probably what it is complaining about.

If you post a link to the panel's specs or a picture of the label on the back of the panels so I can see the ratings I can see if that is the explanation.

I've attached the image.

The voltage on the panel doesn't seem to vary much throughout the day though, it seems to be stay around over 450V.

Also, does the voltage not effect how much watts i should be receiving? around that time i get a max of 150watts before the system trips from over loading.

 

[mudk]

How are you even turning it on without any batteries attached to it? Every battery based inverter I've ever heard of needs a battery attached to even turn on.

I was sold on it BECAUSE it didn't need the battery attached.
In Pakistan the electricity is out any where up to 8-10 hours a day. For days when the sun is also having a vacation batteries would only power my full house for a few hours max.

I have a separate inverter + batteries set up for when this happens for essential lights/fans (in summer) and a socket for my laptop.

(pic attached for the curious.)

 

[mudk]

The inverter has two voltages to note on the PV side. Maximum permissible 500v, but MPPT range of 120v to 450v. Early in the morning before the panels warm up from the sun you may well be seeing > 450v from the panels (no load, during MPPT search the panels will be lightly loaded at some stage so they will float up in voltage) and that is probably what it is complaining about.

If you post a link to the panel's specs or a picture of the label on the back of the panels so I can see the ratings I can see if that is the explanation.

also, is there a lower limit where the inverters would prefer NOT to use solar?

e.g in the video i shared we were using around 100watts of electricity in total (a couple of bulbs in the house) and the inverter seemed to prefer utility instead of solar unless I switched off the utility power.

 

[Maast]

We still need a image of the panel sticker, or at least its VOC and VMC voltage ratings and how many of them you have in a series.

If you're running during the day at 450v you could VERY easily overvolt your charge controller on a cold morning in bright sunlight at 0C. Overvolting is bad as it kills most charge controllers quick unless they have a "hyperVOC" like the Midnite Classic charge controllers have and even they're not immune if it's bad enough.

 

[mudk]

VOC on the panels is 37.7 and VMP 30.1

I have 11 panels. What is the best solution for this?

 

[Maast]

Unused power on panels means the panel voltage goes up towards its "VOC" or Volts Open Circuit (aka disconnected) voltage. Depending on how cold it is a cold bright morning can boost voltage output 15-25% so you could easily reach 518V if your panels are lightly loaded.

Option 1 - remove one panel and see how things go.

Option 2 - Add on the Tigo TS4-L panel optimizers to each panel, they're designed for just this situation and will bring your panel voltages down about 30% without you losing any power generation. They're about $55 US if you shop around.

Option 3 - Add a automatic dump load from the panels when voltage goes above 400VDC, this is technically challenging if you dont have a electronics background.

Option 4 - Buy another 9 panels and arrange them in two parallel strings of 10. You'll end up with more power but at a lower input voltage.

Option 5 - Put a generic battery pack on the inverters DC input, get a separate charge controller that can handle the high voltage and feed it to the inverter through the battery connection. The battery pack will act as a buffer, it doesnt need to be a good battery pack, just there so the new charge controller has something to see and will turn on.

I believe either the high voltage is messing with inverters' charge control input, or has already damaged it, or it's just not working right. You should be getting more power than you have and if it's not taking in ALL the power the panels are producing (this is a grid tie system?) then that would explain why the panel voltage is climbing so high. Is there a current limit setting in the inverter that would be restricting it?

 

[mudk]

option 1 seems like the best option so far.
i doubt option 2 will be available here, i don't think i will understand how to do option 3 and 4 is not financially possible.

Not sure I fully understand option 5.
The inverter has a +ve and -Ve underneath to connect batteries to. Once i connect the batteries there, how do I add the charge controller?


in full summer swing mid-day I get roughly full power around 2.2kw from my panels. Now that it is winter and sun is dimmer they don't produce as much, today they were pulling 1.5k. for about 30 minutes.

if i remove one panel, should open votage stay around 400 even on a dim winter morning when sun isn't direct on panels/ at full strength?

 

[mudk]

in terms of current limitation the handbook says:

Maximum charging current:
To configure total charging
current for solar and utility
chargers.
(Max. charging current =
utility charging current +
solar charging current)

from 10 up to 80A in increment of 10. Default is currently 60A

that is the only thing that i can make sense of as a form of current limitation, but not sure if that is anything close to what you were asking...

 

[mudk]

i was given the wrong info on the solar panels. Sorry, asking or help and giving you dud info...

i've attached a pic of the label on the panel.

When we bought the set up (inverter + panels) the shop were clear not to go over 11 and instead go for 14 (2 parallel of 8 series panels). 12 was our max budget. So we went with 11.

 

[gnubie]

The STC open circuit voltage of the array is 495.77. That's already really close to your inverter's maximum permissible voltage and outside of its MPPT operation range.

I don't know the temperature derate of your panel's voltage but let's say its 0.4% per degree C. There will be a window early in the morning when the sun is on your panels but the cells haven't warmed up and are at 0c. STC is measured with the cells at 25c. At 0c you might find you have a 10% increase in voltage from your panel. Voc will rise to over 545v, Vmp will rise to over 454 volts. This is likely what your inverter is complaining about.

As a test remove one panel from the array. That should bring the voltages back down to where your inverter is happy. Remember to not disconnect a panel from this array with current flowing as the voltages present are dangerous and will cause substantial arcing too. If you don't have a disconnect switch do it when ambient light is very low.

 

[Maast]

That 45v VOC certainly explains things. I think your best bet is if you can afford it is buy one more panel and arrange it in two parallel strings.

 

[mudk]

Whatis the minimum voltage required for the unit to start up?
I have "cold star voltage 48vdc"
"Nominal voltage 230Vdc"
"Mppt range 120-450vdc"

If i split 12 into 2parallels of 6 in series will there be enough to start the system early on in mid-light with such few panels?

 

[Maast]

Usually its 10-15V above your battery bank voltage, since you dont have a battery bank I'm guessing its around 60V

 

[Maast]

I'd be very interested in how your system would perform with a battery bank. Not to necessarily store any power but just to have something there for the inverter to work with, even 4 motorcycle batteries in series would do. Just set the charging voltage to something low like 54V so you dont cook the batteries.