[TRNSYS-users] Type 94a

[Maximilian Bernat]

Hello, I am currently using Type94a in TRNSYS 17. When parameterizing 
with the help of the data sheet of a standard PV module, some questions 
or comments arose. When calculating il (photocurrent), the irradiation 
is reduced by a value that depends on the tau-alpha product, see code 
excerpt: ! Calculate incidence angle modifier for direct radiation 
        tadir = tamax * (1-1,098d-4 * (theta) + 6,26d-6 * (theta ** 2) + 
6,583d-7 * (theta ** 3) -1,472d-8 * (theta ** 4 ))                If 
(tadir <0) tadir = 0        sundiff = sundiff * tadiff        sungnd = 
sungnd * tagnd        sundir = sundir * tadir        tau_al = (sundiff + 
sungnd + sundir) / sun        sun = sundiff + sungnd + sundir The 
variable "sun" is, as already described, used to calculate il:       il 
= (sun / sunr) * (ilr + misc * nprl * (tc-tcr)). Now the question arises 
whether this il calculation is correct, because in my opinion the ratio 
of sun / sunr when entering the STC conditions is reduced by the above 
reduction of sundir by tadir (under STC conditions tadir = tau alpha 
product). In principle, the code says: tadir * current irradiation 
(input model) / sunr, so with input radiation = sunr -> exactly the 
value of Taualpha. From my point of view, sunr should also be reduced by 
TauAlpha, since the values ​​are then never related to the incident 
radiation but to the values ​​reduced by optical losses, ie: il = (sun / 
(sunr * tau_al)) * (ilr + misc * nprl * (tc-tcr)) I do not know now if 
that is a model error or somewhere is a mistake in thinking? Many Thanks 
Best regards Maximilian Bernat

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