[TRNSYS-users] Potential Bugs in Type94a and/or erros in the manual

[Amir Nashed]

Hello

I have previously sent an email regarding an overestimation* of the IAM losses by the type94a so I opened the Fortran code for the model and I realized 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 --> what value is used?

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  Vm*Im/SUNR

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)


Under the same conditions, the results of another PV special software (PVSYST) are 8-9% higher than those estimated by Type94a and when I deactivated the IAM in the model and calculated it separately I got similar results to those of PVSYST

I still cant find out why the model overestimates the IAM losses

Please advise

Regards,
Amir Nashed
PhD Candidate
School of Renewable Energy and Photovoltaic Engineering
University of New South Wales
Phone:+61405979282
Email:a.nashed at unsw.edu.au

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