[TRNSYS-users] Potential Bugs with Type94a

Amir Nashed nashed.amir at gmail.com
Thu Apr 24 22:12:57 PDT 2014


I previously sent 2 emails regarding potential bugs in Type94a (PV 4
parameters model) and i can conclude the following:

1-      The equation used to calculate the IAM has a wrong sign in the
third term (should be -6.26E-6 rather than +6.26E-6) (this error actually
in some cases made the IAM to be larger than 1 which is incorrect as far as
I know)

2-      The last term in the equation used to calculate the IAM in the
manual is 1.4272E-8 while in the code is 1.472E-8

3-      Different equations than those indicated in the manual are used to
calculate the effective angle of sky diffuse and ground diffuse radiation

4-      The variable SUNGND (surface ground diffuse radiation) is not
calculated anywhere in the code and it is not one of the inputs

5-      The reference efficiency EFFREF does not account for the module
surface area so I believe it should equal:  Vm*Im/SUNR*Area instead of

6-      Equation 5.2.5-21 used to calculate the cell temperature in the
manual (page 74) I believe is incorrect [It should be
UL*(Tc-Ta)=TAU_Alpha*Gt*(1-Eff/TAU_Alpha) thus Tc=Ta+
TAU_Alpha*Gt*(1-Eff/TAU_Alpha)/UL ] (The equation is however applied
correctly in Type94 code script)

7- Finally, I found out why Type94a overestimates the IAM losses (when the
option is activated). This is because the SUN variable, (Effective global
tilted irradiance) is calculated after multiplying each irradiance
component IAM multiplier (i.e. TADIR, TAGND, TADIFF) by TAMAX (TAU-ALPHA at
normal incidence), which i believe is incorrect as the IL at reference
conditions already includes the effect of TAU-ALPHA at normal incidence.
This error is however corrected when the IAM mode is disabled where the SUN
variable is not multiplied by TAMAX

 could someone confirm the aforementioned bugs?

Thank you


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