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Electrical shade losses at Tracker Limits (Phi) - Backtracking vs Truetracking vs Fixed Tilt


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I am looking for some clarification on how PVsyst treats electrical shade loss with different type of simulations. I have three simulations with same exact loss assumptions,weather file and other global project settings.

1. 1-axis N-S axis tracker (backtracking ON)

2. 1-axis N-S axis tracker (backtracking OFF)

2. Fixed Tilt with 60deg tilt and -90 azimuth (facing East)

I have an 8760 output for all three cases above (attached), comparing the output from #1 & #2 and fixed tilt output (#3) for the hours where tracker tilt/azimuth angles matches with fixed tilt (facing east, PhiTilt is 60deg). I then looked at hourly DC energy (Earray), electrical shade loss (ShdElec) and GlobEff which got me to the following questions related to how PVsyst treats electrical shade loss.

a. For the same plane tilt (PlTilt), azimuth (PlAzim) and tracker angle (PhiAng), I expect the electrical shade loss (ShdElec) to be the same across all three cases (irrespective of tracker or fixed tilt) with rest of the assumptions being the same. But I am noticing different hourly energy output during these hours (see highlighted columns). Is this something to do with any angle rounding error in backtracking algorithm when plane tilt angles reach the tracker limits?

b. Does PVsyst assume zero electrical shade loss based on the value at middle of every hour or is it an average loss reported for a specific hour?

It would be of great help to get responses to these questions and understand the shading loss treatment better.

Thanks in advance!

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