Clipping loss outside of MPPT Range, how significant is it?

[Rocksteady2R]

alright... Got some odd blow-back today from a boss, and I want to clarify to get my #'s.

Max string voltage is 600V - essentially set by NEC and subsequently, manufacturers. That's simple enough.
Inverters also have an "MPPT Operating Voltage Range" of ~500V.

My boss was surprised to see my max voltage up near that 600 mark. My justification is that we wattage is more significant a gain than loosing MPPT tracking is a loss. I don't care, and honestly, my salesmen and my other bosses don't really care about mppt range if it means leaving KW on the table. I'm still inside warranteed limits. I'm not breaking code.

My understanding is that if I'm outside of that MPPT range, I'm just going to clip Currents and Voltages - but since my panels are fairly identical (w/in that 3% power tolerance), then that clipping should be relatively minimal.

So what're common production losses due to setting my string voltages at the upper limits?
Anyone know of any articles on this?


And, as an aside, since I'm asking about similar topics -
SMA has an "Operating MPPT Voltage Range" (125-500V) and a "Rated MPPT Voltage Range" (175-480V). Can anyone tell me the difference before I give them a call?


Alright, thanks in advance! What've you got for me?

[sensij]

Just to be clear, it is the temp corrected Voc that is getting set near 600 V, right?

[Rocksteady2R]

Just to be clear, it is the temp corrected Voc that is getting set near 600 V, right?

Indeed it is.

[Naptown]

what are the string calculations at STC temps?

[sensij]

Let's say the array is someplace relatively warm, so 0 deg C is design minimum temp. That is a 10% temp factor per 2011 NEC 690.7. The max STC string voltage is then 540 V. Let's say Voc per panel (72 cell panel) is about 45 V, with an MPPT voltage of around 36.5 V. 12 panels would be 540 Voc, right at the limit, and the Vmp is 438 V, safely in the inverter's MPPT range. I don't know what string construction could give you values that comply with the 600 Voc limit and fall outside the 480 V MPPT range of the inverter.