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The original was posted on /r/homeassistant by /u/jorgo1 on 2024-09-28 23:13:59+00:00.

TLDR. Automated curtains to close on hot days with high UV and low cloud cover. Preventing living space from heating up and as such lowering the cost of air conditioning. Energy savings paid for entire system in 4 months. 

I started automating my blinds to enable privacy within my home. I want them up when it’s bright enough outside such that someone can’t see inside, and I want them down when it is dark outside so the lights inside don’t present us to the people walking past. 

This is simple enough, when the sun is x mins past sunrise, raise the curtains, when the sun is x mins prior to sunset, lower them.

Sitting on the couch to watch TV one afternoon I noticed the sun was in my eyes. 

When the TV turns on and it’s after 2pm then lower curtain 2 to 40%.

When the TV turns off and it’s after 2pm then set curtain 2 to curtain 3’s position.

Solved.

Last summer I walked past the window and realised the raw heat being injected into my living space by the windows.

For reference I have double glazed windows, UV block out screen blinds then black out blinds. In summer the UV screens are down all day but the heat still gets through. (UV here is about 12+ through summer).

So while the sun is cooking my living space my air con is trying to remove this heat. 

So I created an automation, when the temperature outside is above 27c and the time is > 12pm and the sun is up and the UV is greater than 5 and cloud cover is < 40% then lower the curtains. (UV, Temperature and cloud cover are all sliders in the UI, < 12 pm is not needed due to coverage on the Eastern side).

This puts the block out blinds down and prevents the heat from entering further into the living space and as such the air con has less work to do.

We noticed an immediate drop in power consumption. With electricity usage down 40% on hot days.

The ROI of the curtains paid for itself in the first 1.5 months. It then paid for the lights and other hardware 2.5 months later. Power company raised prices by 30% and without this automation we would be in a world of hurt. So I wanted to share it to hopefully help others who are in a similar situation to save some energy.

A few points of note, blocking the windows from outside the house would be a better solution, however this is not possible with this building. Tinting was considered however as Winter gets to 0-5c having sun heat the living space good, this is why there are UV blinds to enable us to add or remove protection as required. The buildings insulation is new, however there is more work to be done pending the repair of a unknown source water leak. The location is Australia. Blind controllers are Aqara controlled via HA. Without Air con and with no curtains, interior will easily get above 30c in summer. Solar is not practical on this building, the roof shape can currently yield 2kw which doesn’t justify itself, we are looking at investing in a communal solar farm as an alternative.

Would be very interested in other energy saving ideas.