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<p><span style="color: rgb(33, 33, 33); font-family: arial, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: pre-wrap; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">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</span></p>
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