Sol-Arc 12K PV input questions

[JamesW]

On the Sol-Arc 12K system, the manual says max PV input voltage is 500 volts. It also specifies PV max input current per MPPT = 20A (self-limiting).

To simplify: If I use a single parallel MPPT string of (8) 400 watt panels each capable of ~ 10 amps, then it would follow that the input string would carry up to 80 amps. This would put it 60 amps over rating?

What am I missing here? Sorry if this is a dumb question .....

 

[timselectric]

If I use a single parallel MPPT string of (8)

If you are talking about 8 panels in parallel. 1s8p
You wouldn't have enough voltage to wake up the MPPT.
For clarification:
A "string" is X number of panels in series.
A "circuit" goes to a charge controller (MPPT).
A circuit can be made up of one or more strings in parallel.

 

[GuyG]

I think you are confusing amps and volts, and stringing in series versus parallel. String amperage will be the same as the panels’ amperage; it’s not additive for the string, unless you combine two strings in parallel. Panel voltage is additive when panels are strung in series. The string voltage will be the voltage of the panels multiplied by the number of panels.

Solark has a string design tool that makes all of this very easy, btw.

Good luck to you and please post any other questions.

 

[GuyG]

One other thing: it’s easier for people here to help if you’ll post the specs on your panels.

 

[JamesW]

One other thing: it’s easier for people here to help if you’ll post the specs on your panels.

I was looking at these components:

SOK batteries
Sol-Arc 12K
and
Rich-Solar 400w panels

• Maximum Power(Pmax): 400W
• Maximum Power Voltage(Vmp): 41.2V
• Maximum Power Current(Imp): 9.71A
• Open Circuit Voltage(Voc): 49.6V
• Short Circuit Current(Isc): 10.3A
• Maximum System Voltage(Vmax): 1500VDC
• Temperature Range: -40°F ~ 185°F
• Max Series Fuse Rating: 20A

Looking over the original post, I see I was posting in Amps and Watts instead of Volts and Amps. Lol -- don't know what I was thinking.

Appreciate the help ......

 

[GuyG]

Eight panels wired in series gives you a string open-circuit voltage of 396. Find the temp coefficient for Voc on those panels and do the cold-weather correction calculations, but I’m guessing you’ll be under the 500 volt limit for that inverter. (But remember, that’s a HARD limit; you can damage the inverter with higher voltage, so make sure to do the calculation. Or let the Solark sizing tool do it for you).

Your mpp voltage is 41.2. That times 8 is 328 volts for the string. If the panels produce the maximum power of 9.71 amps at that voltage, then your string will deliver 328 volts times 9.71 amps equalling 3,185 watts.

 

[Quattrohead]

The 500v is not a hard limit on the Solark but it will throw an error. Not sure what the absolute max voltage is off the top of my head.
As soon as it can pull the voltage down below 500 it will start charging.
Every thing else spot on....they have great tools and documentation on their website.

 

[GuyG]

The 500v is not a hard limit on the Solark but it will throw an error.

That might well be true, but many other peeps more knowledgeable than me have stated it’s a hard limit. Do I think it will happily hum along at 500v and then blow up at 501? No. But how much can you fudge without doing damage? 10 volts over? 15? For how long? Who knows.

And, while many inverters say they will “self-limit” the current coming into the MPPT, I wasn’t aware that the SolArk will self-protect against over-voltage by simply throwing an error. I’d be interested in seeing documentation so that I’d understand it better.

I don’t mind taking calculated risks, but an essential ingredient for any calculation is knowing the variables and the formula. Otherwise I’m engaging in what I call an Anal Extraction Analysis; that is, just pulling a guesstimate out of my ass.

So unless the OP knows way more than most of us, I think it’s wise for him to treat 500 volts as a hard limit.