Diffuse Shade Loss Parameter for SDK

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jamesalfi
Diffuse Shade Loss Parameter for SDK

Hi,

I can see that a new diffuse shade loss factor has been added to the SDK. This number just seems to be a percentage input. How can this actually be calculated in the SDK based on the project and selecting subarray1_shade_mode=0 or is this not possible? Do we need to have a 3D shade model to be able to calculate this, or the hourly shading losses from the actual SAM program? If that is the case, it seems like the diffuse shade loss in the SDK will not be very useful, since we cannot generate hourly shading losses on the fly.

Another question, will the SDK automatically calculate and take off the subarray1_ss_derate and subarray1_ss_diffuse_derate? If the SAM SDK can automatically calculate diffuse shade loss (like in PVsyst), it would be most helpful for accurate automated modeling.

Any help or clarification regarding the diffuse shade loss in the pvsamv1 SDK would be much appreciated.

Thanks,
James

Paul Gilman

Dear James,

You have to calculate the value of the diffuse shading loss and hourly beam shading losses outside of the pvsamv1 compute module. You could use the 3D shade calculator that is part of SAM to calculate those losses and save them to a text file by running SAM manually, and then read those values into your model.

You can use the subarray[n]_shade_mode input variable to enable self shading. When it is enabled, pvsamv1 will calculate self shading losses. When you enable self shading, be sure to also set the values of subarray[n]_mod_orientsubarray[n]_nmodx and subarray[n]_nmody.

Best regards,
Paul.

jamesalfi

Thanks for the response.

I guess this confirms what I was thinking. Are there any plans to include a diffuse shade loss calculation inside of the pvsamv1 module? It would be most helpful, and allow the results from the SDK to be just as accurate (if not more) as the SAM program and other software (PVsyst).

Paul Gilman

Dear James,

We do not have plans to include the 3D shade calculator in the SDK, mostly because it is not clear, given that the SDK does not have a graphical user interface, how to work with the 3D representation of the shading scene in the SDK.

How would you imagine the diffuse shade loss calculation would work in the SDK?

Best regards,
Paul.

jamesalfi

I suppose the main goal is to just have diffuse shading, and self shadings (external shade structures are not a real concern) both accounted for in the model whether it is based on a 2D or 3D model for both fixed tilt and HSAT. I am not sure how the 3D shade model is performing the calculations (e.g. ray tracing?), so I don't know if the approach outlined below would work.

In the SDK, depending on the shading model chosen, we are already choosing the racking configuration for self shading, and the module dimensions are already included as variables. The only additional variables that I could see being required are the number of racks in x-direction, and number of rows.

From there, a shading scene could simply be constructed and/or calculated based on the module dimensions, rack configuration, # of racks, tilt, azimuth, number of rows, and GCR.

Stephen Peters

Hi Paul,

Any update on exposing an easier way to incorporate array self shading loss in the SDK?

I too am using the SDK as a automated tool and the largest discrepancy between SDK and other software (PVsyst) is that I can not easily represent self-shading losses. Like James says, external shading is not to much of a concern and most of the information for this to be calculated is already supplied to the SDK.

Best regards,
Stephen

Paul Gilman

Hi Stephen (and James),

This discussion may be a bit misleading.

The self-shading model is part of pvsamv1, so you can access it via the SDK. Use the subarray[n]_shade_mode input to enable it: A value of 1 is for the non-linear option for modules with crystalline silicon cells, and 2 is for the linear option for thin-film modules. The model will calculate self-shading losses based on the subarray nmodx, nmody, rotlim, gcr, tilt, azimuth inputs, along with the module area.

The self-shading model's non-linear option for crystalline silicon modules does account for the effect of self shading on both the incident beam and diffuse irradiance. The linear option only calculates a reduction in beam irradiance, based on the assumption that thin-film modules are affected less by the reduction in diffuse irradiance than are crystalline silicon modules.

My comments about the shading scene above are about shading of the array by nearby objects, which requires a 3D representation of the array and objects around the array which may cause shadows, which is not part of pvsamv1.

Best regards,
Paul.

Stephen Peters

Hi Paul,

Thanks for clearing that up! I have a few more questions but will start another thread.

cheers,
Stephen

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