Over Paneling, Over Inverter Voltage with Breaker

[davesmith87]

Hello all,

I've got (2) MPP LV6548 inviters. These inverters can do 250v for solar input. Each inverter can do 8000 watts.

I currently have 24 panels (435 watts) in 2s3p setup. 4 combiner boxes. This put's me using about 10,000 watts (out of 16,000) in peak sun. I want to find a way to utilize the rest of the 6000 watts.

However, if I go 3s3p, this will put be slightly over the inverters rated max. My panels are 5 years old, and about 200 ft from my house (where inverters are). In the 3 years I've had them, I've only recorded 165v once (in 2s3p) configuration (this was in January when it was -10 out and sunny). Adding a third would put me just at about 250v or slightly over.

Could I simply add a breaker at 250v for each string right before the inverter? Any cons to this other than the breaker failing and not tripping?

Ideally, I would just get a higher capacity charge controller, but don't want to replace my inverters.

https://www.amazon.com/Low-voltage-Miniature-Circuit-Breaker-Panels/dp/B0746DLP7S/ref=sr_1_5?crid=1FQ871JWGA5CK&dib=eyJ2IjoiMSJ9.rDLg3snin8AuMKq1RrH3ARbPCkV3RfzbK712r4BegKjiGjM8lSEz3EkmB1mMdGR6-15aRCGZpwNJ6Dd65vE2pvpQXJDWhpAnWN_2tYlPwoThIB-v0IEWWf1sG_Ob35zQSzxLT8CpR0h1Fjsnb3-1qD8JOJGN8JJnyRx5EXs3X-RH6hSdGmRcIBstCv9dnaLcay5CqpU8Ap4QTt8oQK2B8KwytYxdX7AzhRkh9QgfzcWJmzzXOyGQHsjgWYS3cMzRmbzWjNyC_IBBAUO5hRy4sXyL4vTHTnkz-sssy4G7wso.YAhCkSPztzu6oJBKzyvnFLxlmgrKeDt065-V2FGUMDg&dib_tag=se&keywords=250v+dc+breaker&qid=1714178134&sprefix=250v+dc+breake%2Caps%2C154&sr=8-5

Thanks in advance,

Dave

 

[timselectric]

Could I simply add a breaker at 250v for each string right before the inverter? Any cons to this other than the breaker failing and not tripping?

Breakers don't trip on voltage.
Only current.
Same goes for fuses, before you ask.

 

[davesmith87]

well thanks for the reply. can't believe I didn't know that. I just assumed because the breakers list voltage and apms, it was either or.

Is there any type of product on the market that could do this? Or do be safe, could i just cover a couple of cells on the solar panels?

 

[MisterSandals]

I currently have 24 panels (435 watts) in 2s3p setup. 4 combiner boxes.

What are the panel Voc and Isc specs?

If you have roughly 50Voc panels, 4S3P into a combiner box seems like a good setup.
Assuming you were handling amps properly with 2S3P.

 

[timselectric]

Add another separate SCC.

 

[davesmith87]

The panels are SunPower 435 watts.

VOC = 85.6
ISC = 6.43

4S3P would put me at 342v, way over 250v.

AMPS are not problem. Inverter is rated for 18, and the most it's ever is in just under 18.

 

[ruralsolar]

You have 24 panels at 435 watts each, that's ~10.4kw assuming ideal conditions, to "use" the other 6kw of your inverters you need more panels. Unless I'm missing something in your post.

 

[davesmith87]

You have 24 panels at 435 watts each, that's ~10.4kw assuming ideal conditions, to "use" the other 6kw of your inverters you need more panels. Unless I'm missing something in your post.

Your correct. I am trying to fit more panels on one string, so I can use the other solar input on 1 inverter (and of course to buy additional panels).

 

[ruralsolar]

Your correct. I am trying to fit more panels on one string, so I can use the other solar input on 1 inverter (and of course to buy additional panels).

After I posted brain clicked and went "maybe he's asking about adding more panels....". I blame the work week

 

[sunshine_eggo]

Unfortunately, those inverters are kinda shitty on the MPPT side. They fall short of the typical 450-500Voc range, but they also have severely restricting 18A on the input.

Reality? You can NEVER get 4000W out of a single MPPT on these units. Period. NEVER.

Best option is about 6S 37Voc 60 cell panels at 222Voc. That puts you at about 178Vmp.

178Vmp * 18A = 3204W

In your case, with your panels, you're limited to 2S3P in terms of usable PV per MPPT, or about 2300W. You can overpanel a little... maybe to 2S4P, but you'll clip the excess above 2300W.

Math check:

I currently have 24 panels (435 watts) in 2s3p setup. 4 combiner boxes. This put's me using about 10,000 watts (out of 16,000) in peak sun. I want to find a way to utilize the rest of the 6000 watts.

24 * 435 = 10,440W

Where are you getting 16,000W from, or are you just assuming because they say are rated for 4000W?

IMHO, you're as optimal as you can get at this point. You could potentially add another string to each MPPT and get 10,440W for longer. Additionally, since you'll only be pulling 18A from an array capable of closer to 24A, you'll probably get up to a 5-7% increase in voltage since you're not pulling max current. This will equate to a 5-7% boost in peak PV output.

If you want 1:1 increase for whatever you add, @timselectric suggestion to get a separate SCC is your ONLY option. You are not going to get more out of your existing MPPT with the panels you're using unless you over-panel and give up most of the peak output of the additional string.

 

[wpns]

Adding a third would put me just at about 250v or slightly over.

And it would only slightly fail. Do not do this.

 

[Supervstech]

Hello all,

I've got (2) MPP LV6548 inviters. These inverters can do 250v for solar input. Each inverter can do 8000 watts.

I currently have 24 panels (435 watts) in 2s3p setup. 4 combiner boxes. This put's me using about 10,000 watts (out of 16,000) in peak sun. I want to find a way to utilize the rest of the 6000 watts.

However, if I go 3s3p, this will put be slightly over the inverters rated max. My panels are 5 years old, and about 200 ft from my house (where inverters are). In the 3 years I've had them, I've only recorded 165v once (in 2s3p) configuration (this was in January when it was -10 out and sunny). Adding a third would put me just at about 250v or slightly over.

Could I simply add a breaker at 250v for each string right before the inverter? Any cons to this other than the breaker failing and not tripping?

Ideally, I would just get a higher capacity charge controller, but don't want to replace my inverters.

https://www.amazon.com/Low-voltage-Miniature-Circuit-Breaker-Panels/dp/B0746DLP7S/ref=sr_1_5?crid=1FQ871JWGA5CK&dib=eyJ2IjoiMSJ9.rDLg3snin8AuMKq1RrH3ARbPCkV3RfzbK712r4BegKjiGjM8lSEz3EkmB1mMdGR6-15aRCGZpwNJ6Dd65vE2pvpQXJDWhpAnWN_2tYlPwoThIB-v0IEWWf1sG_Ob35zQSzxLT8CpR0h1Fjsnb3-1qD8JOJGN8JJnyRx5EXs3X-RH6hSdGmRcIBstCv9dnaLcay5CqpU8Ap4QTt8oQK2B8KwytYxdX7AzhRkh9QgfzcWJmzzXOyGQHsjgWYS3cMzRmbzWjNyC_IBBAUO5hRy4sXyL4vTHTnkz-sssy4G7wso.YAhCkSPztzu6oJBKzyvnFLxlmgrKeDt065-V2FGUMDg&dib_tag=se&keywords=250v+dc+breaker&qid=1714178134&sprefix=250v+dc+breake%2Caps%2C154&sr=8-5

Thanks in advance,

Dave

Wow, your panels output 82.5V each!
Must be a commercial panel.
3x would only be 247.5V by my math...

What are the VOC specs of the panel, and what is the record low temp for your area.
Also, see if there is a temp coefficient % listed

 

[wpns]

3x would only be 247.5V by my math...

His MPPT input has a maximum of 250V input. #DangerWillRobinson.

 

[davesmith87]

VOC is 85.6.

85.6 *3 is 256.8, greater then 250v.

What if I intentionally shaded covered the bottom cells? Or put 1 panel of different size in series in the middle of the 435?

Would the panel with the lowest voltage bring the others down? I know I would lose some capacity here.

 

[wpns]

VOC is 85.6.

85.6 *3 is 256.8, greater then 250v.

What if I intentionally shaded covered the bottom cells? Or put 1 panel of different size in series in the middle of the 435?

Would the panel with the lowest voltage bring the others down? I know I would lose some capacity here.

The string voltage is a sum of all the panel voltages, so you could bring the string voltage down by using a lower voltage panel, but unless the Isc and other parameters (Imp anyway) matched, you might get some weird effects.

Personally I'd leave it at 2S or get a SCC with a higher voltage input (do you have batteries?) or swap out your inverters , though I realize that's non-trivial. [In fact, I'm abandoning my poor inverter choice for a pair of EG4 18Kpv inverters, but that's neither cheap nor easy.]

 

[Supervstech]

VOC is 85.6.

85.6 *3 is 256.8, greater then 250v.

What if I intentionally shaded covered the bottom cells? Or put 1 panel of different size in series in the middle of the 435?

Would the panel with the lowest voltage bring the others down? I know I would lose some capacity here.

Wow... 85.6V, with -10F low temps, the panels could output far more voltage before the mppt picks a load... no, certainly no way to go 3S with those.
Its back to adding another MPPT to get use of more wattage.

 

[sunshine_eggo]

VOC is 85.6.

85.6 *3 is 256.8, greater then 250v.

What if I intentionally shaded covered the bottom cells?

Nothing and something:

Voltage would be unaffected:
Light gives voltage.
Intensity of light gives current.

You would effectively disable all output from the shaded panel.

Lower temperature would present even greater risk.

3S with your panels is not an option. Period.

Or put 1 panel of different size in series in the middle of the 435?

This is a thought. Stick with your 2S, but add a ~50Voc panel with the same or higher Imp rating. You could add about 700W per MPPT.

 

[davesmith87]

Nothing and something:

Voltage would be unaffected:
Light gives voltage.
Intensity of light gives current.

You would effectively disable all output from the shaded panel.

Lower temperature would present even greater risk.

3S with your panels is not an option. Period.



This is a thought. Stick with your 2S, but add a ~50Voc panel with the same or higher Imp rating. You could add about 700W per MPPT.

Does it matter where this 50voc panel would be placed? For example, in the middle of each 435 panel, or on the side (of each string). Maybe I'm misunderstanding, but I thought the lowest voltage wins. So if I had a 50voc panel, it would bring down by 85voc panels?

 

[timselectric]

Does it matter where this 50voc panel would be placed? For example, in the middle of each 435 panel, or on the side (of each string). Maybe I'm misunderstanding, but I thought the lowest voltage wins. So if I had a 50voc panel, it would bring down by 85voc panels?

In parallel, voltage is pulled down by the lowest.
In series, voltage (whatever it is) is added together.

 

[sunshine_eggo]

Does it matter where this 50voc panel would be placed? For example, in the middle of each 435 panel, or on the side (of each string). Maybe I'm misunderstanding, but I thought the lowest voltage wins. So if I had a 50voc panel, it would bring down by 85voc panels?

Yes. One would be placed in series with each string. It doesn't matter if it's the panel #1, #2 or #3 in the string, but it must be in series. Again, target 50Voc panels with > 6.43A Isc.

MPPT (+) ----> (+)85.6Voc panel(-) ----> (+)85.6Voc panel(-) ----> (+)50Voc panel(-) ----> MPPT (-)

or

MPPT (-) ----> (-)85.6Voc panel(+) ----> (-)85.6Voc panel(+) ----> (-)50Voc panel(+) ----> MPPT (+)

or either of the above with he 50V in the middle suitably oriented.

BTW... a 50Voc panel is only suitable if you never experience temperatures below -7°C.

If you do, a 40Voc panel is a better choice.