Possible issue with backtracking single axis trackers

[vabbaraju]

Hello,

I was comparing two configurations of single axis PV trackers (with backtracking). First configuration is 1 module up (width of sensitive PV area = 2m) and second configuration is 2 modules up (width of sensitive PV area = 4m). Both configurations have same GCR and same total sensitive PV area. During backtracking hours, I am seeing a slight difference in "AngInc", "BeamInc", DifSInc" and "Alb Inc" between the two configurations. Why is "AngInc" dependent on table width, when GCR and total sensitive PV area remains same? Are we seeing differences in "BeamInc", DifSInc" and "Alb Inc" because of the difference in "AngInc", or is there another factor causing these differences?

The second question is with near shading losses. It makes sense that there is no "ShdBLss" in either configurations. But, since GCR and sky viewing angle (slice) is same between the aforementioned configurations, why would "1 module up" have more "ShdDLss" and "ShdALss" losses compared to "2 module up" configuration?

 

 

Thank you in advance for support!!

[André Mermoud]

These are complex numerical calculations, with some approximations, tables, interpolations between tables, etc.

Perhaps your table sizes (with inter-modules or mechanical frames) are not exactly scaled.

There are also rouding effects in the Hourly values.

Do you really think that differences of the order of 0.2% to 1% on the shading losses of diffuse (most of them less than 0.5 W/m2) are significant, when the modelling uncertainties of these factors are probably of several percents ?

I find it indeed reassuring that the differences are so low.