PVWatts calculation of solar zenith (and sun above horizon variable)

Hi all

I'm wondering if anyone knows how SAM (or more specifically PVWatts/detailed solar module) is calculating the solar zentih/sun above horizon variable. This seems to be causing issues when running with ERA5 data that has been put into the SAM CSV format.

I am unsure if it relates to a) the input time-zone, b) lat/lon and/or c) datetime index. Basically, I am inputting in local time but the solar zenith (according to the detailed PV module) is completely off. I have tried changing the UTC time, but it seems to have issues.The problem is that the solar position is completely wrong in addition to the output being clipped by the 'Sun above the horizon' variable.

Any help in understanding the interaction of these different variables would be greatly appreciated. 

Regards,
Craig

Hi Craig,

The Detailed Photovoltaic model sun angle equations are described in Section 4.2 the SAM photovoltaic reference manual, which you can download from the PV Publications page of the SAM website.

Best regards,
Paul.

Hi Paul

Many thanks for this reference. It is very helpful. I was getting quite confused with the sun-up variable being a non-binary flag, which now is explained. 

I would also like to applaud those who are responsible for the new PySAM module. This is a fantastic piece of work which has made many aspects of the SAM workflow so much easier, quicker and more manageable! 

Regards,
Craig