Excellent - how many trees can I grow on my roof? Can they be retrofitted?

/s

You know what cools roofs and generates electricity? Magic!

Another trick: bifacial panels oriented to pick up the reflected light from highly reflective roofs

What about Ultra white ceramic trees?

True though this is still practical for folks who live in deserts and other treeless places

Tech Ingredients did a video about it as well. https://www.youtube.com/watch?v=dNs_kNilSjk

The biggest problem with making stuff white and using fancy materials is the amount of crap they get exposed to.

Moisture is one issue, both in the form of water vapor / condensation as well as rain. But there's also smallish animals, like birds and cats that crawl around on roofs. Not to mention all the insects. Then there is the normal sand and dust in the air, plus all the pollution. Depending on where you live, white stuff gets really dirty within weeks or months.

I work in a white office building and they have it cleaned with pressure washers twice a year, it takes a whole climbing team a good two weeks to clean the whole thing and it looks dirty again after a few months. And that's just a white form of plastic (HPL) you can blast away on, without causing damage. With these fancy meta materials often they are really fragile and any damage undoes the special properties.

Here is an alternative Piped link(s):

https://www.piped.video/watch?v=N3bJnKmeNJY

Piped is a privacy-respecting open-source alternative frontend to YouTube.

I'm open-source; check me out at GitHub.

What's the gains in contrast to regular white bathroom tiles? (Not a joke question)

There is a difference between mirror like reflection and diffuse reflection. Mirror reflection is what you get with metal roofs which beam the sun directly to a target resulting in one spot being blinded. Diffuse reflection will spread it around, resulting in more light all around which is what we can handle as humans.

It's not visibly reflective. Yes, it's white, but it's cool to the touch because the majority of the energy is radiated out into space via non-visible wavelengths. Someone has already posted a great YouTube video from Night Hawk In Light in a comment where he explains how this tech works and makes his own paint!

Probably yeah, but more likely it would have to be atmospheric and not surface based. When Mount Pinatubo erupted in 1991 it was estimated that the global temp dropped about 0.5 degrees C over the ensuing year due to the ash cloud blocking the sun

https://pubs.usgs.gov/fs/1997/fs113-97/

The only feasible plan we have for increasing the albedo of the planet overall is atmospheric engineering. Basically you can make a reflective cloud that’s millions of square miles in area, many orders of magnitude more cheaply than any other kind of structure.

Covering our roofs with it would certainly make a difference. BUT, it works in the winter too, cooling the house when we want it warm. So, that might increase the need for heating in the winter.

Personally, I'm waiting for a commercial product, because my NM house has a large, south-facing stucco wall that is currently white, but not ultra cool white. Given my experience with the house, which is well insulated, I expect I could paint the house with such paint and not need any other cooling, even when it hits 100+F here. That wall is my bedroom wall, and I can feel the heat pushing through it in the late afternoon after a full day of exposure to the sun.

My thoughts exactly at first glance! At least, now we know why some people think storm troopers are so cool.

The article addresses that. It is because ceramics are durable while paints and coatings are not.

Most coatings like paint that have this effect include ceramics to do most of the reflection, but the other paint stuff the ceramic substrate is emulsified in does not have near the reflectivity, so you're impairing yourself if reflectivity/heat rejection is the only goal.