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

Amir Nashed a.nashed at unsw.edu.au
Thu Apr 24 01:43:19 PDT 2014


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

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

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