Self Shading - No Effect

Hi,

I have a question regarding the Self Shading calculator. The array I am modelling will be shaded from panels in the front rows. I have selected CEC Performance modules, fixed axis system, GCR of 0.8 and completed the self shading inputs.

When I run the simulations it seems as though there is absolutely no effect of self shading in the final results. That is, annual energy output remains constant, losses remain constant etc.

I have followed the help file instructions but have had no luck.

I wanted to ask what is the issue with the self shading calculations?

Regards.

Dear masir,

Thank you for attaching your .sam file. That makes it easier for me to answer your question.

Before I get to the self-shading question, I found one problem in your file: You are using a weather file for a location in Australia (Location and Resource page), but the Azimuth for each subarray on the System Design page is 180 degrees, which means that the subarrays are facing south, away from the equator. For southern hemisphere locations, you should use an azimuth value of zero to orient the array toward the equator.

There are a couple of reasons you are not seeing any self-shading losses. The main reason is that the modules for each subarray are on a single row. For example, Subarray 1 has 56 modules with 8 modules along the bottom and 7 modules along the side, so all of the modules are in one row. If you change the number of modules along the side to 1, then the subarray would have 7 rows, and you would see the effect of self-shading in the results.

Once you have correctly configured the self-shading inputs, you are likely to see only a small effect because the subarray tilt angles are low (5 and 10 degrees), so the rows do not cast large shadows on each other. If you increase the tilt angle you should see more self-shading losses.

Finally, to see the effect of self-shading in the results, you can compare the POA total nominal irradiance to the POA total irradiance after shading to see the reduction in diffuse irradiance, and also look at the self-shading derates for each subarray. Note that "self-shading derate" applies to the DC output of each subarray rather than reducing the POA irradiance. That's because the self-shading model reduces the incident diffuse irradiance, but because the effect of self-shading on beam irradiance is non-linear, calculates a DC derate factor for its effect on the array's output.

Best regards,
Paul.

Dear Paul,

Thank-you for your speedy reply!

In regards to your first point, there are three tabs within my project file two of which have not had the design completed (due to the problem I was having with the shading in the first design), so I should have probably deleted them before uploading! So yes, the 180 azimuth is erroneous.

In regards to the self shading, thank you, your explanation has solved the issue!
I had mistaken the parameter "Number of Modules Along Side Row" to mean the number of rows within the sub-array rather than the number of modules that are stacked/racked on top of each other.

Cheers,
Masir.