Solar Position Algorithm

[estewan]

Dear Andre,

(I have tried to look on PVsyst's help file but had no luck)

How does PVsyts calculate the sun position (solar height and azimuth)?

Does it use NREL's algorithm?

http://www.nrel.gov/midc/spa/

On the other hand, I realized (reading this post: http://forum.pvsyst.com/viewtopic.php?f=24&t=1754&p=4674&hilit=sun+position#p4674) that the "sun's position is taken in the middle of the hour during the simulation". This is a bit confusing since the hourly output file gives o'clock hours. Does this apply to other hourly values like, for example output power? Is the output power at hour 3 the power for 3:30?

Thank you,

[André Mermoud]

The algorithms used in PVsyst are probably a little bit simpler than those of this NREL publication. But the results should nt differ by more than 1-2 minutes.

However I will not give all of them here. Perhaps we will give an extended description in the help in the future.

In PVsyst, the hourly values are averages over one hour.

The time stamp 8:00 concerns accumulations (averages) of instantaneous values from 8:00 to 9:00. Therefore it is natural to compute the solar geometry at the middle of this interval.