# Sun tracking outside shutters

In our house on the south side, I have a large glass wall around the front door with blinds on the outside that I can control via somfy io.

I have been looking for some time now for a way to make the blinds automatically move with the sun angle, but without success.
I started logging manually by setting the angle each time so that no direct sunlight comes in, but this is impossible and the flows become too long…

I would like to control my blinds so that points A and B are in line with the sun as above and continue to follow the sun’s altitude.

Is there anyone who can help me calculate what position the blinds should be in based on the azimuth and altitude.

My blinds are 200mm wide, center distance is 180mm and my house faces 187°

You can try this app. Maybe it will work.
https://homey.app/nl-nl/app/com.cyclone-software.sunevents/Zonnestanden/

I use the app (Zonnestanden App voor Homey | Homey) already for the azimuth and altitude, but I am looking for a calculation that takes into account the dimensions of my blinds.

When the sun shines on the blinds at an angle, the length of the slats changes, which becomes longer and so the angle of the slats must also change.

As your slats most likely have a just a few positions, you might as wel experiment with these few positions, depending upon the actual altitude of the sun. Like a lookup table.

By the way, I don’t think that azimuth is important for the position of the slats. See Azimuth - Wikipedia. The azimuth does define during which hours of the day the slats shall be lowered. This is defined by 2 values, one for in the morning as the slats shall be put down and one value for when the slats shall be raised. You can calculate this 2 values from the orientation of your house in relation to the sun (azimuth) or by measuring this value in the real world.

Shouldn’t the slats always be perpendicular to the sun rays? As in that case they block the sun rays optimal? So depending upon the way you measure the position of the slats, the slats position is (90 decrees minus altitude) or equals the altitude.

I can set my slats in any position I want, it is fully adjustable from 0-100%.

I found this interesting article where everything is described, but how can I apply this in homey?
https://www.mdpi.com/683254

Well, that is a complicated way of controlling the slates. To me the ideal positioning of the slats is when as much as possible lights come in, but no direct sunlight comes in.

The biggest challenge for me was determining when to turn on the shading on individual windows and when to turn it off. The position of the sun doesn’t even play that big of a role here. An important thing is the internal temperature and solar contributions to understand whether to prioritize or block solar contributions. Every day is different and every day has different solar contributions, so it’s not that easy. I have abandoned the implementation of shading according to the position of the sun.

Regarding the positioning of my venetian blinds, I didn’t go into too much detail, I chose one position and always set to that position.

That is also difficult, but I have already completed the part when I want to keep the sun out in a flow.

The only thing I’m looking for is a calculation that the slats just keep the sun out based on the position of the sun.

I initially thought this would be quite simple by calculating the height of the sun. But unfortunately the angle is very different if the sun is not directly in front of the shutters.

So the calculation must take into account the azimuth and altitude of the sun.

Just suppose the sun is at a certain position, and the slats are closed enough to keep the sun out. Then imagine you rotate your house. Then you don’t need to reposition your slats, as the rotation of the house is parallel to the slats. The same is true when not your house rotates but the sun. So the position of the slats is independent of the azimuth and equals the altitude, ie always perpendicular to the sun.
The azimuth does determine the time the slats shall be lowered or raised. As your hous faces 187, the slats shall be lowered between (187-90) and (187+90).

It is true what you say that the sun does not change in height. What does change is the width of the slat when the sun shines on the window at an angle. When the slat becomes wider, the angle must be adjusted again.

L changes and therefore the angle relative to the slat must also change.

I am looking for a calculation that takes the azimuth and altitude of the sun into account and adjusts the shutters accordingly.

I just don’t understand your reasoning. Might be due translations problems.
If you make the angle of the slats equal to the altitude, you almost have the ideal solution. As d is almost L. Even when d equals L the sun would still be blocked.
So when L is a litle bit more then D, the angle of the slats could be a little bit less then the altitude, but I don’t think that is a great difference.