Could I have Matched the Panels Better? Check my Figures Please.

[Onehand]

6000XP's -2 of them. 4000wats MAX ALLOWABLE, per MPPT, 480VDC MAX ALLOWABLE per MPPT - 2 MPPT's per XP

Below figures based on ONE MPPT's input maximums.

8 - 455 watt panels, per MPPT = 3640 watts, per MPPT, voltage = 394VDC.

On a 15 degree day, voltage increases to 435VDC, MPPT MAX ALLOWABLE 480VDC. (OK here I assume)

Total watts per MPPT (15 degree day), (V x A) = 435VDC X 10.96A = 4767 watts. MAX ALLOWABLE per XP, BOTH MPPT's = 10,000 watts, 5000 watts each, (I assume) as per manual.

Subtract 4VDC for voltage drop (150' run, 10ga PV wire) = 431VDC x 10.96 A = 4723 watts, per MPPT.

XP's MPPT's track best between 120 and 385VDC

Could I have matched the panels to the MPPT's better?

 

[AZ Solar Junkie]

Are those voltage calculations based on Vmp, VoC, or just measuring the actual voltage with a meter? Be sure you're calculating to stay below the 480 volt limit based on the VoC (with temperature adjustment). If you are measuring 435V with a multimeter, I would be concerned you could be close to over the limit re: the temperature-adjusted VoC. Certainly wouldn't want to fry those shiny new 6000XP's. Just got one myself and loving it.

 

[AZ Solar Junkie]

Honestly I don't totally get the VoC vs Vmp and how it all works. I do know that if I have my panels disconnected from the MPPT (with a breaker, for example) and measure the voltage on the line, it is a good bit higher than when they are connected and under load. I suppose that is the fundamental difference between VoC and Vmp - one under load and the other as the name says when the circuit is open. That VoC being over 480 volts is what can fry the mppt even when the string voltage is lower than that when under load if I understand correctly.

 

[Onehand]

VDC is based on the VOC spec for the panels, from the spec sheet. Ya, last thing I want to do is cut the smoke loose...

 

[AZ Solar Junkie]

VDC is based on the VOC spec for the panels, from the spec sheet. Ya, last thing I want to do is cut the smoke loose...

Sounds to me like you're in good shape as long as it doesn't get much colder in your area than the 15 degrees you mentioned.

My panel setup is pretty similar to yours though a bit smaller. I only have so much room to play with in the backyard and I haven't wanted to fool with permitting the system to be able to put panels on the roof. This time of year I'm getting a LOT of shading which I can't do anything about - looking forward to the return of summer to see how it all performs. Living in the Phoenix Arizona area I never would have thought I would hear myself saying that - lol.

 

[Onehand]

If it gets below15 here, I have far bigger issues to deal with.

Tracking efficiency being best up to 385VDC seem like resources going to waste with a 480 max dc input..

 

[G00SE]

WIf it gets below15 here, I have far bigger issues to deal with.

Tracking efficiency being best up to 385VDC seem like resources going to waste with a 480 max dc input..

I designed my strings based on nominal rating as well. I had over 120v of headroom if utilizing the high voltage limit but seemed better to stick to the mid/upper 300s

 

[AZ Solar Junkie]

If it gets below15 here, I have far bigger issues to deal with.

Tracking efficiency being best up to 385VDC seem like resources going to waste with a 480 max dc input..

Yeah it would be interesting to see someone do an efficiency study of the unit to see just how much less efficient the MPPT is at different voltages above and below what the manual says is the optimal voltage of 320 volts.

 

[Onehand]

This is what I was wondering about. How efficient are theses inverters with voltages on my system ranging from 394 to 431 when optimum is 320vdc? Guess were just splitting hairs at this point.

 

[AZ Solar Junkie]

This is what I was wondering about. How efficient are theses inverters with voltages on my system ranging from 394 to 431 when optimum is 320vdc? Guess were just splitting hairs at this point.

And what exactly does it mean when it says the MPPT Operating Voltage Range / Range where the MPPT can track is 120-385VDC? Does this mean that if the string had voltage above 385 that the charge controller would just start pulling as many amps as it could but at 385 volts? I don't know...