[Difference between Pvsyst and NREL's Solar Position Algorithm]

Hello,

Does someone know where the difference between PVsyst and NREL's Solar Position Algorithm (SPA) comes from?

I get an important difference in the incident angle between those models.

SPA calculator : http://www.nrel.gov/midc/solpos/spa.html

The parameters used :

- Site location : latitude = 20.5°S ; longitude = 55.3°E ; elevation = 14 m ; time zone = UTC+4 ; No skyline nor shading

- Pannel position : tilt = 0° ; azimuth = 0° (from north, negative toward east)

- Simulation : start date = 01/01/1990 ,end date = 31/12/1990

- The meteorological data for PVsyst simulation comes from Meteonorm. Thus the label "12:00" should represent 12:30.

Difference observed between the models : from +1° to +3° at sunrise (NREL - PVsyst)

Changing the pannel position to : tilt = 2° ; azimuth = -135° (from north, negative toward east), I get :

+3° to + 6° at sunride / +2° to + 3° before 12:00 / -2° to - 3° after 12:00

Based on the Beaminc (incident beam irradiation in the collector plane) calculation (BeamInc = BeamHor * sin Hsoli / sin Hsol), I assume the two models give very different results for the sun heigth on horizontal plane.

Cheers,

Sébastien

[Plane orientation]

Thank you Bruno. Indeed, I thought the red dot was on the top of the collector (as it appears on the drawing on the left)!

[Plane orientation]

Hello,

PVsyst guide states : "In southern hemisphere, the plane azimuth is defined as the angle between north and collector plane.This angle is taken as negative toward east".

However, if I put -135° in the "Orientation" pane (projet in the south hemisphere), I get a north-west orientation (instead of south-east).

Should I believe the PVsyst guide or the drawing?

Thanks in advance,

Sébastien

[Difference between GlobEff & GlobIAM]

Hi there,

In the PVsyst 6 Help, I can find :

- GlobIAM : Global on collectors, corrected for horizon, near shadings and IAM

- GlobEff : "Effective" global, corrected for IAM and shadings simultaneously

I don't get the difference between those two variables?

Thanks in advance for your help

Sebastien