Meteonorm vs PVGIS horizons

[laurahin]

We have compared the effect of Meteonorm and PVGIS horizons and found that the far shading loss was typically greater for the PVGIS version.  In making the comparisons, we noticed that the profiles as shown in the PVsyst report "Sun Paths" diagram have different characters.  Even though the number of points used to define the profiles is similar, the PVGIS profile always appears smooth whereas the Meteonorm profile is blocky.  Is there any particular reason for that?

I would expect the Meteonorm and PVGIS horizons to be the same, since they use the same spatial resolution (90m) and likely both rely on data from the Space Shuttle Radar Topography Mission, although I haven't been able to confirm this.

[dtarin]

1. Meteonorm and PVGIS both use SRTM (depending on the coordinates); Meteonorm with 3 x 3 degree tiles, PVGIS with 2.5 x 2.5.
2. PVGIS calculates to the first decimal while Meteonorm rounds to whole numbers. 
3. PVGIS uses 48 points (excluding 0 degree), 7.5 degree increments, whereas Meteonorm uses 1 degree increments. This causes the difference in smoothness. Repeated values are excluded in PVsyst. If you evaluate a complex site, you will find there is a significant difference in the number of horizon data points between the two. For example, one project site evaluated shows 29 points for PVGIS and 56 for Meteonorm.
4. I would conclude that the differences lie with PVGIS and Meteonorm and the methods by which each is performing the calculations. PVsyst is importing the correct values one would retrieve directly from each source. 

Edited June 1, 2023 by dtarin

[dtarin]

My only comment to PVsyst is that when PVGIS is used, the comment which displays the coordinates incorrectly shows the minutes ' and seconds " notations. The coordinates should read (degrees, minutes, seconds), but it is displays as such:  40°5"17', Long=-77°39"53', which shows degrees, seconds, minutes. Whether this is from PVGIS or PVsyst, I do not know. 

Edited June 1, 2023 by dtarin

[Agnes Bridel]

Dear @dtarin, thank you for pointing out this error. The display error was identified and will be corrected in the upcoming release. 

Best regards, 

[laurahin]

Thanks for your reply, @dtarin   I did believe that the issue was with the data sets, not PVsyst, but couldn't find documentation of the data sets beyond what you included.  Thus your statement in point three concerning the resolution of the horizons is quite useful. 

Laura