7 ms·
This is cool, but at 85% absorptivity it's no better than coatings you can already buy. Absorber plates in glazed solar water heaters you can get in your hardwa
by skosch 8y ago
This is cool, but at 85% absorptivity it's no better than coatings you can already buy. Absorber plates in glazed solar water heaters you can get in your hardware store today have numbers in the 90s.
Edit: I recommend a look at the original paper instead [0]. The significant feature appears to be the ability to absorb light at a wide range of angles, rather than simply the absolute absorptivity.
[0] https://www.nature.com/articles/s41566-019-0389-3 https://www.nature.com/articles/s41566-019-0389-3
- wilg 8y agoSo is there anything interesting about this "new" development then?
- skosch 8y agoI didn't mean to come across as cynical — it's still a cool discovery, and it might turn out to be useful in some surprising niche context. The researchers do speculate that it might be > suitable for a wide variety of uses, including desalination of seawater, color displays, photodetectors, and optical components for communication devices. So: time will tell!
- gotocake 8y agoMore 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...
- skosch 8y agoBack-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.
- DEADBEEFC0FFEE 8y agoThanks, 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.
- gotocake 8y agoYou’re a champion, thanks!
- nardi 8y agoCould 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.)
- skosch 8y agoI 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.
- lostmsu 8y agoAre they water-proof? Could you put them in a pool to heat it up?
- ineedasername 8y agoDo you mean absorber plates? They may or may not be water proof, but don't need to be to heat a pool. It's a relatively common application [0] [0]http://www.alternative-energy-tutorials.com/solar-hot-water/solar-pool-heating.html http://www.alternative-energy-tutorials.com/solar-hot-water/...
- lostmsu 8y agoThe kind of system with circulation is overcomplicated. Would be much better to just put the heater into the pool/take it out.
- ineedasername 8y agoWhat are these other materials' physical characteristics and cost to produce? Apart from absorptivity, a key factor here is the thinness and potential for inexpensive mass production. In contrast, absorber plates tend to be large and heavy. 1lb per square foot isn't uncommon. They are also often produced with (relatively) expensive copper. This might not be a breakthrough in terms of new capabilities, but it could allow a scale of use not currently practical.
- gotocake 8y agoThe thing is a pound of copper has a pretty significant specific heat, and that’s a feature rather than a bug. A thin graphene film may be more conductive, but what is it thermal capacity? If it’s just a thin film that gets blazing hot it’s not necessarily useful in that way.
- ineedasername 8y agoTrue. It looks like they made a few square centimeters of this stuff. If they make a bit more and slap it on a coffee mug & eliminate the need for a microwave, there could be some very interesting applications. Though also consider their applications weren't limited to desalination and other "macro" applications, but also electronics, sensors and such. It sounds like this might be significantly cheaper than current monolayer graphene on substrate.
- Zenst 8y agoOnly if the thermal transfer is one way, otherwise you may find your coffee getting colder quicker as surfaces that capture heat, equally have a penchant to radiate it. For example two metal balls, one painted white, one painted black. Whilst in the sun the black one will heat up more than the white one, at night it will radiate heat much quicker - even if they start at the same temperature. Though the prospect of sending a coffee mug that only works in the sun to some geeks I know, does bring with it some wry humour opportunities. As for other uses, agreed, much potential if it has an edge over alternative offerings.
- strainer 8y agoFrom the very first sentence of the article: "...a new graphene-based film that can absorb unpolarized incident light striking it over a wide range of angles up to 60 degrees."
- bigbadgoose 8y agoI hold that solar energy is the optimal solution, and consists of 1/ capture, 2/ storage, 3/ transmission Focus on (1) is great, but (2) is the breaker of chains. Solving (2) at enough efficiency should largely obviate the need for (3). Store and ship massively efficient solid state "batteries" instead of building (ie, owning) transmission infra