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Comment by gotocake | Hacker News Reader

More concerning to me is that I’m unclear how much heat capacity this thin film has. If you can’t layer it, then you’d neee vast sheets of the stuff to be useful as an energy source. Maybe it could be useful, but at the moment it seems more interesting than practical. Of course that could change, but I don’t think applications will be in the realm some here are hoping for.

It could make for a great solar shower lining though...

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Back-of-the-napkin:

> 90-nm ultra-thin

I don't know the density, but let's say 2g/cm³. That means a 1cm² piece of this film weighs 18 micrograms.

> 30°C to 150°C in 30 seconds

If by "sunlight" they mean 1000 W/m², which is generous, then our 1×1 piece would catch 0.1 W. Over 30 seconds, that makes 3 joules.

3 joules to heat 18 micrograms by 120 degrees – that's a specific heat capacity of 1.388 joules per gram and K (a bit more if the density is lower than 2, a bit less if it's higher). So: a bit more than typical metals, probably, but not by much.

Thanks, why can't this type of information be included in the article. A comparison with a common material would be useful to ok. Like copper or something.

Could you explain why the specific heat capacity is the important metric? It seems like the rate of absorption would be more important. (In other words, the percentage of incident photons absorbed.)

I just wanted to answer the question. The limiting factor is indeed the sunlight and how much of it is absorbed – thus my comment that 85% is nothing special.

You’re a champion, thanks!

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