negative PAO front-side shading losses...

Dear Paul,
when simulating vertical pv systems I get

(1) negative POA front-side shading losses

(2) negative system power generated during night hours

(3) when sorting the system power generated numbers descending, the highest ten or twelve values are identical. Looks like they are cut off.

Any idea what I'm doing wrong?

Thanks,
Mirko 

Hi Mirko,

I was not able to replicate the negative POA front-side shading loss (%) value. Please attach a .sam file along with your .csv weather file if you would like me to troubleshoot.

The negative "system power generated" values at night are probably for inverter nighttime consumption. That is caused by the Power use at night input on the Inverter page.

SAM does limit the system output to the inverter's AC capacity rating, so those identical values of system power generated are probably due to inverter power limiting.

Best regards,
Paul.

Hi Paul,
thank you for your fast response. Enclosed you'll find the .sam file as well as the weather file that I downloaded from PVGIS. Do the same values show up on your screen?

Greetings from Munich
Mirko

 

   

Hi Mirko,

Thank you for attaching the files.

I think the negative POA losses are caused by the combination of the "standard non-linear" self shading option and vertical (tilt = 90 degrees) array. I would recommend using the "thin film (linear)" option to estimate the self shading loss. The "standard" option is an empirical model based on measurements from systems with non-vertical arrays.

Best regards,
Paul.

Hi Paul,

thanks for troubleshooting. The "thin film" option works better, although the calculations might overestimate the actual energy yield, especially for systems with high gcr. Paul, do you have any idea how to roughly estimate the differences in yield (between thin film and non-linear self-shading) depending on gcr for vertical panels? A rule of thumb or so?

Anyway, thanks for your assistance.

Greetings from Munich
Mirko

 

Hi Mirko,

I don't have a suggestion of a rule of thumb for this adjustment. You might try comparing results for the linear and non-linear self shading options for a non-vertical array in SAM to get a sense of the difference in yield.

Best regards,
Paul.