[SOLVED] Astro group radiation explanation

mister78 · March 7, 2018, 2:33pm

Hi guys,

I am interested in understanding where the data of the radiation group comes from and which parameters influence these values.
Unfortunately I did not manage to find any documentation about that. As I am quite new to OH2 this of course may be my fault. Perhaps anyone can help me understand this or give me a link to the documentation.

Thanks
mister78

hr3 · March 7, 2018, 3:29pm

https://docs.openhab.org/addons/bindings/astro/readme.html
What do you mean concret?

hr3 · March 7, 2018, 3:46pm

github.com/eclipse-archived/smarthome

[Astro] radiation group channels dimensions

opened 11:29AM - 13 Jan 18 UTC

closed 01:55PM - 22 Jan 18 UTC

emme-g

Binding-Astro

Hello, I recently found and set up some new channels of the Astro binding in my… Openhab system, among all of them are the radiation group channels (direct, diffuse and total radiation). I searched in the documentation and in Internet but I couldn't find any information about the dimensions of the numbers that these channels provide. In my place now is Winter (I'm in the North of Italy) and the binding, approximately at midday, gives me these numbers: - direct radiation - 149,32; - diffuse radiation - 108,40; - total radiation - 257,72. I guess that these values are expressed in W/m2 (Watt / square Meters), but I would be happy if some of the people who know better this binding could confirm that and maybe insert this information in the documentation. Bye.

mister78 · March 7, 2018, 4:35pm

I wanted to know which parameters influence those values: eg. direct radiation: What about clouds, is it “just” the theoretical maximum corresponding to sun angles and local position or does it know more about the cloud conditions? Where comes this information from and how accurate is it/can it be?
Same for the diffuse radiation … I am curious what is taken into account here.

Thanks for helping …

hr3 · March 7, 2018, 5:03pm

http://stackissue.com/openhab/openhab2-addons/this-pr-adds-radiation-calculation-in-w-m2-to-the-astro-binding-1588.html
http://www.ecgllp.com/files/3514/0200/1304/2-Solar-Radiation.pdf

wawa79 · June 30, 2020, 6:01pm

I also would like to know what calculation is performed for direct radiation. First link is obsolete and 2nd is a general presentation.

I assume that direct radiation reported is DNI (direct normal irradiance). But looking at the history I captured over 2 days, it seems to take into account cloudiness. Is this correct? And if yes, what calculation is applied for cloudiness?

Thank you

mister78 · July 1, 2020, 8:21am

This was my intention as well.
I then assumed the same as you did, an my history data over here in germany looks like there is no influence of the cloudiness on the radiation value … so for me it looks like it is the theoretical direct normal irradiance value.
Perhaps someone who knows what is done in this binding can look over this again …
Thanks from me as well…

wawa79 · July 1, 2020, 8:18pm

You are right: my mistake. The direct irrandiance does not take into account cloudiness. I was logging the values after correcting them with my own (and very basic…) empiric cloudiness formula from some readings in french (sorry!)

Direct radiation is highly reduced by couds (well, anyone would have guessed it…)
sun_direct_rad = sun_direct_rad * (1 - 0.9 * cloudiness / 100)

Diffuse radiation can increase with clouds (because reflection effects increase
sun_diffuse_rad = sun_diffuse_rad * (1 + 0.15 * cloudiness / 100)

I will probably add a light sensor device “calibrated” against the irradiance to detect when I actually have couds over the house (cloudiness reported by weather bindings is not accurate enough)