Can we calculate NOCT from STC ?

[nidalls]

I have a lack of understanding of the difference between STC and NOCT.
Why do with that NOCT is more accurate than STC, we rely on our calculations on the STC?
and can we we calculate NOCT from STC? How?

[sensij]

STC is "standard test conditions"... 25 deg C with 1000 W/m2 of irradiance.

NOCT (nominal operating cell temperature) is the temperature at which the panel comes to thermal equilibrium when it is not generating any power under a different set of test conditions: 20 deg C ambient, 800 W/m2 irradiance, and 1 m/s wind.

The NOCT electrical property data is taken when the panel is at NOCT, under the NOCT conditions.

The NOCT conditions are generally thought of as more "real-world", but there needs to be a standard to compare between panels, and STC is it. You can not just calculate to go from one to the other, the test must be performed.

[J.P.M.]

I've never had a lot of use for NOCT. For starters, I'd think Normal Operating Cell Conditions would at least imply there was some power being produced.

Also,and IMO only, the term is somewhat misleading if for no other reason than because the cell or panel temp. is f(environmental conditions) which are never constant, the cell/panel temp. will rarely be at NOCT. Then, since most panels are in arrays, there's the matter of the cell/panel temp. being substantially different in different parts of the array for a lot of reasons. That's why, as Sensij points out, you can't go from one to the other in a simple way. Estimates are possible, but those involve energy balances and a lot of estimates of heat transfer coefficients and other things.

Bottom line: In trying to figure out what's "normal", or NOCT, the time is better spent on actual measurements if estimates of performance are needed.