Near Shading Losses

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Near Shading Losses

I am trying to replicate in SAM a solar PV system model that I have created in both PVSyst and PlantPredict. The models in these two systems are within a <1% error, but the SAM model is showing about a 4% error in comparison. The biggest discrepancy I see is that my SAM model shows .271% shading loss, while PVSyst shows 2.6% and PlantPredict shows 2.46%. There are also a couple of other smaller gaps.

What percent error should I be expecting between SAM and these other programs, can I solve the discrepancy between the near shading losses, and are there other things I can do to bridge the gap?


Paul Gilman


The difference between the different models depends in part on how consistent the inputs are. We have posted some papers describing comparisons between SAM and other PV models here:

I suspect there may be differences between the way shading is represented in the different models. Which shading options did you use in SAM? For example, did you specify shading loss percentages by time step, using the month-by-hour table, or the solar-azimuth-by-altitude angle table? If you used the time series option, did you enable the partial shading model? For the comparison, you should be sure to choose options in SAM that are the most similar to the options in the other models.

Best regards,

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