Dear Britt,
SAM's self-shading model uses the ground coverage ratio (GCR) instead of module dimensions. It makes the following assumnptions about the module dimensions:
The module's area the value from the Module input page, which, depending on the module model option you choose, might be from the CEC database, Sandia database, or the value you specify.
The module has an aspect ratio of 1.7: Length = Width x 1.7.
The GCR is the value you specify on the System Design page.
The row layout is based on the values you specify on the Shading page.
If you are using the CEC module library and would rather use a different value for the module area than the one in the CEC database, you can choose the "CEC Performance Model with User Entered Specifications" to enter values from the manufacturer's data sheet.
This means that the module dimension variables on the Module page that you describe do not affect the self-shading calculations. The module width and length inputs on the Module page are for the temperature correction model that estimates the effect of temperature on the module's performance. By default, SAM uses the NOCT method, which uses the two NOCT method parameters: Mounting standoff and array height. The NOCT method does not use the module dimensions, which is why the module width and length inputs are inactive and greyed out on the input page. If you use the "Heat transfer method" instead, then you have to specify the module's width as an input -- its default value is 1 m, but it is up to you to choose a correct value because only the module area is available in the CEC database. SAM then calculates the length by dividing the area value from the library by the width that you specify.
Best regards,
Paul.
