homeassistant @lemmy.world sytone @lemmy.world 5 mo. ago

Automating skylights with blinds to block direct sun

Looking for a solution on how to determine when to close and open skylight blinds. I can just do hours of the day but would like it to be a bit more intelligent.

Anyone looked at using something like the math used for solar panels? I was thinking that when max solar power was generated in the summer that is when they are closed to keep heat out.

Ideas?

12 comments

So there is a calculation for what time the sun is at a particular angle in the sky which will be relative to your area and factors in the time of year etc. You could use that as it will give you a very specific to your area mathematical answer to when you should close your shades. This is a good start. If you mix that with a light sensor and set minimums that will get you the rest of the way there (no sense run blocking lightning a cloudy day.) You can just use a light sensor but it will be more erratic if you don't correct for weather and seasonal light levels.

The rest is personal to how sensitive to light changes and seasonal settings you apply to it.

As far as the physical control goes - there are several commercial devices available as well as diy solutions involving motors and 3d printing on YouTube.
- Additional information regarding Home Assistant:
  
  The sun component (which should be enabled by default) already computes the sun position for you.
  
  Elevation and azimuth are available as standalone sensors sensor.sun_solar_azimuth (might be disabled by default) or as attributes on the sun.sun entity.
Light sensor threshold, and a rule to trigger the blinds. Pretty simple.
Hey, I have a Shelly window/door sensor on my bifold door. It includes a lux and temperature sensor, which i’m using to close the blinds (luxaflex/hunter douglas) if the temperature exceeds a certain level along with a high light level.

In practice where I live it is easier to close the blinds based on the current outside temperature, but the window/door sensor makes a good second check. it also prevents the blinds from operating if the door is open!
- Out of curiosity: how long does the battery last on those devices?
  
  I’ve had this one (it’s the Wifi version not Bluetooth) for about four months and it claims that the battery is at 81%. I’ve not owned it long enough to say if that is a linear or exponential (or totally made up) value.
It's not clear to me if you have photovoltaic panels and can use the data from them or not.
- I don't have panels. I was wondering if I can apply the same math and if so has anyone done this in home assistant already.
Just a few ideas for very easy math:

Start with the sunrise and sunset times. You can have them automatically for your location.

Calculate the middle between these: this is your best "noon" time (free of DST etc).

Calculate the duration between these: the longer it is, the warmer.
If your goal is just to prevent glare from direct sunlight? Maybe a purely passive diffuser is what you're looking for

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