PV array voltage significantly higher than expected

[donsolarak]

• 18x Renogy 100w panels wired in series
• 24.3voc per panel
• 20.4vmp @ 25C
• voltage temp coefficient -0.28%/C
• current outside temp +12F/-11C
• coefficient 0.28x36 = 10.08%
• panel voltage 22.45v at -11C
• string voltage 404vdc at -11C
• also string voltage 434vdc at -40F/-40C which is what I spec'd for as that's my lowest expected temps with output
• power is running through 600v 10g wire
• EG4 supports 500voc
• EG4 supports 120v-450v operating voltage

With all that said I'm seeing voltage today as high as 443vdc with the array at only generating about 25% rated output at +12F/-11C. This voltage is significantly higher than I was expecting to see. 443v vs the 404v. I verified the line voltage with a volt meter which also showed 443vdc.

Oddly enough I'm often seeing array voltage in the 300v range (much lower than expected) a lot of the time as the array is often only generating about 10-20% of rated output. Much of this is due to the fact that I live in a boreal forest with lots of trees which creates lots of small shadows on the panels. I'm waiting for the snow to melt so I can go cut down a few hundred birch trees to go green to save the planet by using solar.

Any thoughts why I'm seeing voltage this high?

Pictures were taken at time of very high voltage. Was only able to catch 433v at the charge controller. Witnessed 443v max. -45F temps for reference to spec.

Attachments: sun/shadows/specs/array/temp/voltage

 

[ricardocello]

Unless I missed something, 18 panels in series x 24.3 Voc = 437.4V
and that is at 25 deg C, the voltage goes up when it is colder.

Need to use the specification on the label, not what you measure.
You are too close to the 450V limit, probably safe from the 500V. Edit: Not safe!

 

[seneysolar]

Wow thats cold!

24.3 x 18 = 437.4 @ stc rating, voltage goes up as temps go down. Id expect much higher in full sun at those temps for sure.

 

[42OhmsPA]

Please disconnect immediately and restring to 9s2p.
You're flirting with a magic smoke party.
Cold temp is driving up your 437VOC string.

 

[donsolarak]

Unless I missed something, 18 panels in series x 24.3 Voc = 437.4V
and that is at 25 deg C, the voltage goes up when it is colder.

Need to use the specification on the label, not what you measure.
You are too close to the 450V limit, probably safe from the 500V.

That's open circuit voltage. I'm not measuring open circuit voltage. I'm measuring the voltage with a load connected.

 

[ricardocello]

That's open circuit voltage. I'm not measuring open circuit voltage. I'm measuring the voltage with a load connected.

Yes, but the MPPT in the SCC goes from open circuit to dead short by varying resistance to determine the optimum power point!
So at some point it will see that voltage.

 

[RCinFLA]

That's open circuit voltage. I'm not measuring open circuit voltage. I'm measuring the voltage with a load connected.

You must design for Voc max at coldest temperature. Usually in the morning after a cold night. Without any load on panel, the panel will approach Voc when illumination level generates current that exceeds the inherent shunt leakage current of panel. This is common in morning sunlight levels.

During MPPT searching a controller will approach Voc. Also before it starts up in the morning it will have to initially take Voc when is first fires up DC to DC converter.

 

[donsolarak]

Yes, but the MPPT in the SCC goes from open circuit to dead short by varying resistance to determine the optimum power point!
So at some point it will see that voltage.

Ok, the EG4 manaul says

Max PV array open circuit: 500vdc
PV array: 120vdc-450dvc

It's not clear why the voc and array max voltages are different then.

 

[ricardocello]

Ok, the EG4 manaul says

Max PV array open circuit: 500vdc
PV array: 120vdc-450dvc

which model EG4?

 

[donsolarak]

which model EG4?

EG4 3kW Off-Grid Inverter | 3000EHV-48 | 3000W Output | 5000W PV Input | 500 VOC Input

Power your off-grid setup with the EG4 3kW Off-Grid Inverter (Model 3000EHV-48), ensuring reliable energy conversion and performance for residential and small commercial applications. Available now at Signature Solar.

signaturesolar.com

 

[ricardocello]

I don’t think you will damage it, but since EG4 is not clear about the meaning, what is the point of those upper 50V?
I assume it means you will not get more than 450V out of it, but it is ok if Voc goes up to 500V.

EDIT: See Voc calculation below, you are at 517V!!

 

[timselectric]

Ok, the EG4 manaul says

Max PV array open circuit: 500vdc
PV array: 120vdc-450dvc

It's not clear why the voc and array max voltages are different then.

The usable voltage range is what it can turn into production.
The maximum VOC is what it can handle without releasing the magic smoke.

 

[donsolarak]

I don’t think you will damage it, but since EG4 is not clear about the meaning, what is the point of those upper 50V?
View attachment 206663

I don't know! I'm asking you!
I'm not doubting your logic, but if we use that the VOC and max PV array voltage should be the same value no?

 

[ricardocello]

I don't know! I'm asking you!

Listen to @timselectric

 

[donsolarak]

The usable voltage range is what it can turn into production.
The maximum VOC is what it can handle without releasing the magic smoke.

Ok this makes sense. Sort of. Is it likely that above 450vdc the mppt controller shuts off like it does below 120vdc?

 

[zanydroid]

Ok this makes sense. Sort of. Is it likely that above 450vdc the mppt controller shuts off like it does below 120vdc?

It will smoke above 500

Operating voltage above 450 likely means VOC will be above 500, so it’s a dangerously academic question. To ponder after you disconnect your string.

And by operating I mean the voltage you measure when it’s running and use for various calculations

 

[timselectric]

Ok this makes sense. Sort of. Is it likely that above 450vdc the mppt controller shuts off like it does below 120vdc?

It will try to load the circuit enough to pull the voltage down below 450v.
But it's limited by its amperage rating.
VOC is a hard limit. Do not exceed it, unless you are planning to replace the equipment, anyway.
Watching things burn, can be entertaining sometimes.

 

[ricardocello]

RED Alert!

 

[donsolarak]

It will smoke above 500

Operating voltage above 450 likely means VOC will be above 500, so it’s a dangerously academic question. To ponder after you disconnect your string.

And by operating I mean the voltage you measure when it’s running and use for various calculations

Ok,

So what is really want then is to use Voc multiplied by the temp differential at -40C/-40F multiplied by the number of panels and keep that value below 450vdc not 500vdc to be safe.

 

[donsolarak]

View attachment 206665

I was multiplying Vmc to the temp differential times the number of panels and keeping that value below 450vdc which it is. In reality though I want to multiply Voc times the temp differential times the number of panels and keep that voltage below 450vdc instead of 500vdc.

Now it makes sense.

 

[G00SE]

I’d say you’re flirting with disaster with cold temps, snow, cloud edge, etc

 

[ricardocello]

Please disconnect immediately and restring to 9s2p.

This is the best advice, you have plenty of voltage range, and current limit is 18A.
2 in parallel Isc is 10.42A.

Plus, you could add 9 more panels in parallel later for future expansion (use fuses if you do).

 

[donsolarak]

RED Alert!

It's only a red alert when we approach -40F!

 

[ricardocello]

-40F!

or -40C!!

 

[zanydroid]

So what is really want then is to use Voc multiplied by the temp differential at -40C/-40F multiplied by the number of panels and keep that value below 450vdc not 500vdc to be safe.

I think it's safe to target 500VDC for Voc

After that, you can see whether Vmpp is below 450VDC, probably if you go outside that range the MPPT will derate. You can also apply the temp adjustment too. I'm not sure if it is a hard cutoff like the low range, curious like you what people think. I believe Vmpp is usually far enough below Voc that this won't make a big difference.