How SAM handle tilt angle in System Design and tilt angle for the active surface

How SAM handles the module tilt angle in System design with tilt angle for the active surface in the 3D shading scene. For example, the roof in 3d shading scene has 23 degrees and the active surface tilt angle in the system design is 23 degrees. Is that correct? And how is the GCR affected by these variables?

Hi Rodrigo,

The 3D Shade Calculator that is part of SAM's Detailed Photovoltaic and PVWatts models calculates a set of time series beam irradiance shading factors based on your drawing of the active surface and nearby shading objects like trees and buildings. The active surface represents the photovoltaic array. When you close the shade calculator, it populates the time series beam shading loss table input in SAM with values representing the reduction is solar irradiance caused by shadows on the array.

The shade calculator does not read any inputs from SAM, so you have to be sure that the active surface you draw is consistent with the inputs on the System Design page. For the example you give, if the tilt angle on the System Design page is 23 degrees, then you should set the active surface Tilt property to 23. You should also make sure the active surface's Azimuth property matches the Azimuth value on the System Design page.

The GCR (ground coverage ratio) on the System Design page is a way to represent space between rows of modules in a rectangular array with more than one row of modules. It is used by SAM's self-shading model to calculate shading losses caused by one row of modules on a neighboring row. To model self-shading, you do not need to use the 3D shade calculator.

Best regards,
Paul.

Hi Paul, thank you for the fast reply!

In 3d scene, I added 2 active surfaces side by side with the same tilt angle and I choose one active surface for each subarray in the system design. as you can see in the pictures below.
3d scene: drive.google.com/file/d/1KItQ4Ye6N_rS8vHr-1nsqGBXdxEam5tk/view?usp=sharing
system design: drive.google.com/file/d/1yhrsaBn5NQhwQSBg2psFnWg69NnBqCEG/view?usp=sharing

The right value for GCR, as the solar modules are installed over the roof I'm assuming the max value which is 0.99. I was based in the following picture to calculate this.
GCR: drive.google.com/file/d/1vcL7oNBmhWkt36RsUxdiL7CELy5fg614/view?usp=sharing

But I am getting very high (DC module deviation from STC) losses as you can see in the picture below.
Losses: drive.google.com/file/d/1BwB_3eaBxX1yfTQS3jHg54sMMlxxNXrk/view?usp=sharing

Any idea how to decrease the DC module deviation losses?

Best regards,
Rodrigo

Hi Rodrigo,

The GCR of 0.99 would be for rows of modules that are almost touching. If you have enabled "Standard (non-linear)" self-shading on the Shading and Layout page, that could explain the high DC losses you are seeing.

It's hard for me to tell what might be causing those results without seeing some of the other inputs. I would be happy to review your .sam file if you attach it to this thread.

Best regards,
Paul.

Hi Paul, thank you.
The file is attached.
Btw, the standard (non-linear) is not enabled.

Hi Rodrigo,

I don't see a file attached to your latest post. Please use the Attachments button below the editor to upload your .sam file. You may need to use the "Reply" option instead of the "Quick Reply" option to see the Attachments button.

Best regards,
Paul.