Fixed tilt with greater GlobEff than HSAT at critical hours

[Agustín Doña]

Hello everyone,

I was running some cases in PVSyst 7.2.17 with bifacial panels. I simulated one HSAT (backtracking enabled) and one fixed tilt (16° tilt, 90° azimuth, South hemisphere) configuration, all else being equal. For the fixed tilt configuration I used a Near shadings 3D scene together with "According to module strings" for shading loss calculation.

When retrieving hourly results, I obtain greater GlobEff for the fixed-tilt configuration even close to midday and with no relevant diffuse  component. I attach an image with some of these cases (I found ~60 hours with this behavior throughout the year).

Even if the differences are low in absolute value (decimal differences) this caught my attention, given that at those hours the tracking system should be receiving more irradiance than the fixed tilt configuration. Maybe there is some modeling configuration I am not looking at.

Thank you very much in advance for your answers !

 

[Michele Oliosi]

Hi,

Can you give a few more specifics on the orientation definitions. You mention: 16° tilt, 90° azimuth, South hemisphere fpr the fixed tilt. Your tracker axis azimuth is 0° correct ? Do you have a shading scene for the trackers or are you using the unlimited trackers option ?

[Agustín Doña]

Hello Michele,

Thank you for your reply. The tracker axis azimuth is -180°, which should be equivalent to 0° (?). Well, actually I simulated both: unlimited sheds and 3D scene with linear shading/according to module strings.

Although I found a greater yearly GlobEff in the Unlimited sheds case (compared to the According to module strings case), in fact I observe fewer times of the year in which GlobEff is higher at those critical hours (at 13:00 I observe 4 hours for the unlimited sheds case compared to 36 for the 3D scene case), as it is shown below:

If you need any further information please let me know!

[Michele Oliosi]

Still difficult to say at this point. Are there any shadings at that time? Possibly you can also try the slow calculation mode. It is possible that interpolations of shadings are affecting the results in some specific cases.

Anyway, you may send us the project at support@pvsyst.com. We should then be able to look in details at some point.