STC vs NOCT

[Ozark]

Sorry, I know this must have been asked and answered a hundred times but I can't find it.

I understand the difference between the 2 specs but would just like a simple answer:
Which spec should I use for comparing and sizing panels to my charger; STC or NOCT?

Many panels that fit using NOCT numbers would be a blow out if they "accidentally" coughed out the STC value.
OTOH, those that fit using the STC would leave lots on the table if they "never" made the STC numbers.

Whichever is best is fine, just need to know which to use.

Thanks in advance!

 

[sunshine_eggo]

STC for establishing limits, i.e., max voltage or max current the equipment may experience.

NOCT for a more realistic expectation of performance.

 

[MichaelK]

What I've found in the real world is that the values I actually see are about half way inbetween the two numbers. I'd take an average of the two and use that.

 

[RCinFLA]

Mostly depends on what your actual panel temperature is. NOCT is usually 45 degs C,, 113 degs F

Panel temps depend on sun intensity that heats it up and environmental temp & breeze to cool it down.

In S. Fla my panels at noon in summer are greater temp than NOCT (about 55 degs C, 131 degs F) so I see worse than NOCT numbers.

 

[Hedges]

Hard and fast limits for SCC are Isc of panel (given at STC) and Voc (given at STC, but adjusted for record cold.)
"Watts" limits aren't usually actually limits. They do affect self-heating of SCC and lifespan.

If panels are oriented multiple directions, you can get more hours of output at lower current (lower most of the time.)

 

[Ozark]

Perfect! Thank you all.

 

[1201]

Hard and fast limits for SCC are Isc of panel (given at STC) and Voc (given at STC, but adjusted for record cold.)
"Watts" limits aren't usually actually limits. They do affect self-heating of SCC and lifespan.

If panels are oriented multiple directions, you can get more hours of output at lower current (lower most of the time.)