[newbie] Info about pvlib for solar position

[El Berto]

Hi to all users!
It's first time I use pvlib.
I'm making a solar tracker using Raspberry pi and I'm having some doubts....

Position: 46.0° N, 13.0° E

Time: 22th Feb 2022, 12:00, Timezone Rome

solpos2 = solarposition.get_solarposition('2022-02-21 12:00:00+01:00', 46.0, 13.0)

gives me:

                           apparent_zenith     zenith  apparent_elevation  elevation     azimuth  equation_of_time
2022-02-21 12:00:00+01:00        56.665351  56.690862           33.334649  33.309138  173.650818        -13.568558

                   

Comparing data to different online calculator:

https://www.dossier.net/utilities/calcolo_posizione_solare/index.html

http://www.centrometeo.com/articoli-reportage-approfondimenti/astronomia-meteo-matematica-calcoli-utili/5229-calcolo-posizione-solare-azimuth-declinazione

Azimuth: 178°, elevation: 33.56°
Why 5° error on azimuth?
Thanks.

[Kevin Anderson]

Hi, and welcome to the group!

First, I will point out that the website has a diagram indicating that azimuth is the angle measured anti-clockwise from south, but I don't think that's what the website actually uses.  In pvlib, azimuths are measured clockwise from north, and I think that's what this website actually returns too.  I think one issue is the website's sign convention for longitudes: it uses negative longitudes for east of the meridian.  The sign convention for UTC offset is also confusing to me. 

Anyway, here is a screenshot that matches the pvlib output:

You might also compare with other solar position calculators, for example: https://gml.noaa.gov/grad/solcalc/

Kevin

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[El Berto]

Hi Kevin!
Thanks for quick answer.
I'll investigate about references taking as origin Greenwich at noon.... it looks be according to pvlib output results, thanks.

[SHEILA OBI]

Hello El,

I have been working on that too.

Did you use any key for the code?

Can you send me a complete program you used?

Thanks

Sheila

[El Berto]

Hi Sheila, I'm sorry but I have no code yet, I'm just starting using pvlib to make simulations...