They’re very hard to keep clean, especially in urban environments, which soak up most of the power used for cooling and where this product would be most beneficial.
How easy is this stuff to clean? Is it easily damaged by pressure washing? What kind of cleaners are needed for this to function reliably? Are those cleaners safe for the environment?
You are absolutely right to be skeptical. There are a great many downsides to this technology. Getting it grimy, pointing it out of the sky, cloud cover, etc. will nullify any cooling effect. And yes, the DIY preparation shown would be completely destroyed by a powerwasher, or even a moderate storm. That said, I read recently of a university of maryland research team made an improved coating, allowing the nanospheres to withstand significantly increased weathering while still remaining effective.
If I understand it right, it's not a laser shooting heat into space. It doesn't require a clear sky to function. It's just moving the heat effectively away from itself by bypassing the atmospheric insulation, wherever that might be. And that goes for pointing it as well, except you wouldn't really want it under direct sun for best heat transfer
My white building is currently covered by spiders and crud. Luckily it'll soon be cleaned spotless by the first blizzard of the season, which would also polish off this paint.
However this is really just some science YouTubers replicating an experiment, far from a commercial product. It's just for interest. I like Tech Ingredients, they try to do fairly rigorous work on the border of pure and applied science.
You're right: it's probably not practical to paint a building with the stuff. Nighthawkinlight briefly comments on this. I believe the idea is to use it on passive radiator panels to sink heat from a pumped coolant fluid. That way you can strategically place panels (e.g. on the roof) and control them, just like solar heating panels.
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