Sunny Boy SB1700 Waiting Fault (170 VDC)

[Deyedreamer]

Hi, i have a Sunny Boy SB1700 Grid Inverter approx 12 years old. (Installed 2011)
It has 10 x Suntech STP190s Solar Panels.
The inverter is displaying a fault saying "Waiting".
I noticed the input DC voltage at the inverter is 170VDC. (Confirmed with a multi meter)
The specs on the panels say Optimum Operating Voltage = 33.1v
Calculation: 10 x 33.1v = 331 volts.
Am I right to assume the inverter is not switching on due to low DC input voltage of 170VDC?
As the panels are 12 years old (installed in 2011), could the panels have degradated over time and is now below the DC input voltage minimum of 180v.
See images below.
My thoughts are that 1 panel has failed bringing the whole system down to 170VDC.
Should the panels be replaced due to their age.
Any advice appreciated.

Thanks.

 

[sunshine_eggo]

The open circuit voltage is likely > 400V.

Shorted bypass diodes will cause a panel voltage to read low, and I believe a a shorted bypass diode in a string could cut the remainder of the string out of the circuit.

You likely need to check voltage of every panel looking for outliers starting with the panel with the (-) connected to the inverter and working out.

 

[Deyedreamer]

Hi, thanks for the info.
I disconnected the DC cables into the inverter and checked the voltage and it was 170V.
When you say Open Circuit Voltage > 400, do you mean if the panels were working correctly it would be >400v and not 170.
I have some new old stock panels I may just replace them all and be done with it.

Thanks again.

 

[sunshine_eggo]

Hi, thanks for the info.
I disconnected the DC cables into the inverter and checked the voltage and it was 170V.
When you say Open Circuit Voltage > 400, do you mean if the panels were working correctly it would be >400v and not 170.
The specs on the panels say Optimum Operating Voltage = 33.1v

Optimum operating voltage is Vmp. You should be measuring maximum open circuit voltage, Voc. If you're not pulling power from the array, you should measure closer to Voc. If your Vmp is 33.1V, your Voc is around 40V, so 10S @ 40Voc should be closer to 400Voc.

DOH! I missed that you posted the datasheet. I just noticed your panels say 45Voc and 36.6Vmp (not 33.1V), so you should be measuring much closer to 450V.

I have some new old stock panels I may just replace them all and be done with it.

I'd rather find the offending panel and remove or re-route it unless the array is clearly degraded.

Do you have to consider any restrictions on this with your utility feedback contract?

 

[kommando]

Your SB1700 will need 139V to 180v dc before it starts drawing power depending on the internal settings, 180V is the out the box setting, so your panels are the issue. No need to drop the 180V to 139V as once your panels are working the 180v is not a problem.

 

[Deyedreamer]

Hi Guys, thanks for the replies.
The Utility contract says to replace "like for like".
I have new old stock of 225 watt panels I will use to replace the old 190w.
I am removing the old panels today, so we will see what the result is.

Thanks again for your advice.

 

[Deyedreamer]

The panels I planned to use as replacements are not suitable due to voltage limitations of the inverter.
I have found the faulty panel which was reading only (5v).
I have a CSUN panel I can use that has the same specs as the old Suntech Panels.
I will re-install the panels and check the results.

 

[sunshine_eggo]

The panels I planned to use as replacements are not suitable due to voltage limitations of the inverter.
I have found the faulty panel which was reading only (5v).
I have a CSUN panel I can use that has the same specs as the old Suntech Panels.
I will re-install the panels and check the results.

Same specs - it's critical that the replacement panel have a max power current (Imp) equal to or greater than the panels in place.

Where was it relative to the panel connected to the inverter PV (-)?

 

[Hedges]

I have new old stock of 225 watt panels I will use to replace the old 190w.

The panels I planned to use as replacements are not suitable due to voltage limitations of the inverter.

What are the specs of the old panels, and of the new panels?
What are the specs of the inverter?

There is likely some series or series/parallel combination for the new panels which fit within the inverter's limits.

You had 10, 190W panels for 1900W (STC) feeding a 1700W inverter. Probably put out no more than 1500W except under ideal conditions, and lss the rest of the day.

With the newer panels you may be able to overpanel a bit using same mounts, clip during middle of the day and make more kWh total.
If you can mount both but of different orientations you might make significantly more power per day.

 

[Deyedreamer]

Same specs - it's critical that the replacement panel have a max power current (Imp) equal to or greater than the panels in place.

Where was it relative to the panel connected to the inverter PV (-)?

The CSUN panel is 5.21A compared to the old Suntech 5.2A.
I am not sure where the panel was as it was removed before testing.
But I can tell you there were 2 strings in parallel which was a surprise.
I would have thought that the string without a faulty panel would continue to work as normal.
Maybe the minimum voltage of 180v isn't being met on the remaining string of 175v.
Maybe the faulty string was above 180v when in normal operation keeping the system running.

Regarding Hedges comment.
Yes I will investigate series / parallel combination to see if it works with the new panels.

Specs attached.
ZNSHINESOLAR (275W Replacements) I thought they were 220w
CSUN ( 190W Single Replacement)
SUNTECH (Old Panels)
SMA 1700 Specs

I just did a quick calculation using the new 275 watt panels.
Solution:
7 panels in series.
275w x 7 = 1925w (1850w Inverter max) over paneled.
31.32 (Vmp) x 7 = 219.24v (139-320v Inverter range)
Current (Imp) - 8.75A (Max 12.6A)

Any advice appreciated.
Thanks

 

[Hedges]

With Sunny Boys, don't worry about the max PV power spec, and don't worry about the max current spec (so long as you don't connect the panels reverse polarity.)

The efficiency curve for SB3000 (600V max) shows most efficient at 300V, so for your SB1700 (400V max) shoot for 200Vmp from the array. This will minimize heating of the inverter. HOWEVER, if panels will sometimes be shaded, make sure Vmp still within MPPT range; if not, add another in series.

https://files.sma.de/downloads/SB1200_3000-DEN110712W.pdf

12.6A max input current, but over-paneling for more current is OK.

3 strings of 5.2A would be 15.6A, wasting significant percentage when sun directly overhead. If strings can be of different orientation, would be great.

One string 8.7A Imp and one string 5.2A Imp would be 13.9A, reasonable. So long as similar Vmp, if too different would waste power.

219V from 7s sounds good. Wattage is near inverter capability (but panels typically put out 15% to 25% less than spec, except in ideal cool conditions.
A second string of significantly different angle, same or other model panels, extends hours of production.

 

[Deyedreamer]

With Sunny Boys, don't worry about the max PV power spec, and don't worry about the max current spec (so long as you don't connect the panels reverse polarity.)

The efficiency curve for SB3000 (600V max) shows most efficient at 300V, so for your SB1700 (400V max) shoot for 200Vmp from the array. This will minimize heating of the inverter. HOWEVER, if panels will sometimes be shaded, make sure Vmp still within MPPT range; if not, add another in series.

https://files.sma.de/downloads/SB1200_3000-DEN110712W.pdf

12.6A max input current, but over-paneling for more current is OK.

3 strings of 5.2A would be 15.6A, wasting significant percentage when sun directly overhead. If strings can be of different orientation, would be great.

One string 8.7A Imp and one string 5.2A Imp would be 13.9A, reasonable. So long as similar Vmp, if too different would waste power.

219V from 7s sounds good. Wattage is near inverter capability (but panels typically put out 15% to 25% less than spec, except in ideal cool conditions.
A second string of significantly different angle, same or other model panels, extends hours of production.

Hi Hedges, thanks for all your advice, its much appreciated.
As I am replacing existing panels, I can only use existing orientation with 1 string to keep it simple.
I may go with an extra panel after I examine the output.
I will post my results when finished.

One other question:
Due to the age of the system installed in 2011, there is no earthing on the rails or the panels to the inverter.
Should I be retrofitting earthing purely for safety reasons or is it not important.
Its a big job to run an earth back to the inverter through a tile roof / ceiling etc.

Thanks again.

 

[Hedges]

Newer panels may pack more watts into same space. The ones I bought recently put out 150% of the ones I bought 20 years ago.

If two parallel strings fit your voltage and current needs, that could be done with "Y" connectors on the roof. But the ones you're considering look good with a single string.

In terms of code compliance, perhaps replacing hardware without updating grounding is legal in your jurisdiction.
Although, I thought in Australia when you changed anything you had to change everything, and that is why so many used panels that some people acquired for their own systems.

The grounding of PV frames is for safety, if someone touches the frames. Or, they have continuity elsewhere (like a metal roof), and someone touches the roof. If on the roof they are out of reach of most people most of the time.

A fault in the panels could apply several hundred volts DC.

Some people have received AC shocks from the frame, with cheap inverters. I don't think Sunny Boys have that problem.

I would prefer to have panel frames bonded back to inverter chassis. Safety first.

 

[Deyedreamer]

Update.
New panels installed and system working again.
1423 Watts and 176 volts.
I still have room for 1 additional panel which should raise the voltage slightly.
Last few days have been around 9KWH per day production.

Thanks for all of your advice, much appreciated.