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ianhager

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Hi,

I'm no expert so your help will be greatly appreciated.

I've been asked to look at somebodies PV system comprising of 12 of Jetion 250w black fram, black back solar panels installed as a single string using as SMA sb2500 inverter on a west facing roof.

I've been told the inverter sometimes flashes saying input DC voltage too high. The maximum input from what I can see for this inverter is 600v DC and after visiting when this has happened, i took a reading of 657v DC, obviously too high.

What I'm asking is that if you agree with me that the problem is these panels all wired as a single string, and with the maximum dc voltage of these panels @ 61.7v DC (in series a possiblility of , not probability of 740v DC) could the wiring be re-arranged to split the array into 2 seperate strings of 6 panels each? Could this inverter take this voltage spread over the two strings or is this inverter not capable of doing this? I know that it takes 2 strings but am unsure of the combined voltages.

The customer want's to know if he should go back to the installer if a different inverter is needed or to just get them back to alter the configuration?

Thanks in advance for any help you can offer.

Ian:29:
 
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Gavin A

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Arms
as you say, it needs to be run in 2 equal strings of 6.

whoever installed it obviously didn't realise that those panels are much higher voltage panels than standard, so even though the HF inverter's operate best at higher voltages and have a wide voltage range, 12 of these panels is too high for it.

it'll work fine at 2 x 6 panels though if you can get to the panels to reconfigure it (if it's run in 4mm cable you can probably just parallel the system on the roof and just use the existing cables to connect to the inverter if that's simpler. It's the ampages that combine when run in 2 strings, not the voltages btw.


eta - ah, actually I see it's just the SB2500 not the HF version. That will work with 2 x 6 panels, but I'd be less happy about having 3000W DC input into that inverter, as they're not as well designed for running at those sort of higher power levels as the HF, and I'd suspect it will end up limiting itself to a greater degree.
 

SolarCity

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Arms
Yep, needs to be wired into two strings. This will bring the amperage up but still within the parameters of that inverter.

Another bizarre error.

I wonder if the rest of Europe is suffering from this kind of nonsense too?
 

widdler

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Mentor
Arms
It seems a simple rearrangement to a two string array should do it - have you worked out the adjustments?
DO you know which inverter it is?
 
Think this has to be an issue for the installer to fix as the installation is clearly incorrect. Not having the specs on me I'd take a punt that the voltage is fine but you'd have to double check that the input current isn't too high as to damage the inverter.

When wiring pv panels in parallel as with battery's voltage remains the same but current increases

Bottom line. Problem for the installer IMO
 
Id say the inverter is too small 12 x 250 = 3000 I would of gone for a 3000HF .

you can under rate an inverter upto 80% of array size but I try to match it.

also two strings might be better on a 2500
 

Gavin A

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Arms
to sum up / clarify...

2 strings is an absolute none negotiable must for this panel / inverter combo to even switch on due to the voltage of the panels.


the inverter is arguably a little undersized, BUT the system is within the manufacturers design specs once it's run in 2 strings, so as long as it was the inverter specified originally, the customer has no legal right to demand a replacement (presuming it fires up properly once it's been run in 2 strings).
 
to sum up / clarify...

2 strings is an absolute none negotiable must for this panel / inverter combo to even switch on due to the voltage of the panels.


the inverter is arguably a little undersized, BUT the system is within the manufacturers design specs once it's run in 2 strings, so as long as it was the inverter specified originally, the customer has no legal right to demand a replacement (presuming it fires up properly once it's been run in 2 strings).
You could argue (manufactures words) - over voltage on the dc side of the inverter can seriously damage the inverters internal components. No doubt your client could ask for the inverter to be sent back to manufactures for a thorough inspection to assess any possible damage as the inverter has been overloaded (is that the correct terminology? Over volted?)

Joe
 
W

wstevew

  • Thread Starter Thread Starter
  • #10
If it has been subject to over voltage then it will be logged and warranty void I would guess.
 

Worcester

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Mentor
Arms
as per Gavin A's comments

2 strings is a must, whiched of the SMA SB inverters you use.

According to PVSOL, the SB2500, rated at 2300W is massivley undersized (130%), either the 2500HF or 3000HF both with 2 strings are suitable (the difference in annual aoutput is 4kWh so not worth worrying about) and according to Sunny Design the 2500HF gives a slightly hogher output kWh/annum. I couldn't even get Sunny Design to say that an SB2500 was acceptable...

The client should report the faults to the installer and ask them to rectifiy it, getting the installers proposals for rectification first and agreeing them before allowing him to change it, simply changing to two strings will fix the overvoltage, but not the bad design / sizing of the inverter.

Wether the client can get an inverter change is down to their persuasive skills, it is once again, not a good design...

Though seeing the above comments it wouldn't take too much to get them to change it, and if they are changing it, I'd go for the 2500HF.
 

Gavin A

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Arms
I couldn't even get Sunny Design to say that an SB2500 was acceptable...
It says it's fine for me. 99.9% usability, 90% nominal power ratio at 2 x 6 panel strings.


re overvoltage damage - it'll only affect the varistors until the varistors are destroyed, after which the rest of the inverter would swiftly follow. As the varistors have a design life of 1000 uses (IIRC), and there are 2 of them, I seriously doubt that's going to be an issue at this stage, presuming it's a recent install. They could ask for a pair of replacement varistors if they wanted, but I doubt they'd need them.
 

Worcester

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Mentor
Arms
@Gavin A what software did you use? 12 x 250 - 3000W

The SB2500 is rated at Max DC Power 2700W and Rated AC output of 2300W.
The SB2500HF is rated at Max Power DC 2600W and Rated AC output of 2500W.
 

BruceB

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Arms
I have just put 12 x Jetion JT250SBb + SB2500 into Sunny Design using grid voltage of 240 and it does not complain.
 
M

moggy1968

  • Thread Starter Thread Starter
  • #15
I was suprised at this, until I looked up the spec sheet, those panels produce some serious voltage!!!
 

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