Wearing sunlight

We’ve got smartphones, smart watches, and all sorts of wearable tech either already available or in development. You’ve got to admit though, that’s a lot of stuff to power up, and we don’t always have the luxury of stopping to plug in. Case in point – ever been to a major airport? Sometimes you can find them under your seat or on a kiosk somewhere, otherwise you’re using the ones on pillars or walls near some high-traffic places like the bathroom because that’s where the custodial staff plugs in for their cleaning appliances. And you’d better let them; I’ve seen people outright get snotty with the custodial staff because how dare they, who work for the airport, ask travelers to unplug their devices so they can get to cleaning up the airport. Don’t be that guy.

Anyway, manners rant over, back to science. Anyway, a group of researchers from China and Singapore propose a solution: how about wearing some clothing that will not only harvest solar energy, it can store it so you could charge up your portable tech right now. 

For some of the more on-the-go readers, this probably doesn’t sound all that new. After all, we’ve got backpacks with solar panels, and this is consumer-level tech that’s been around for a while – why is this particular development special? Well, you ever tried wearing a solar panel?

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Wikimedia Commons (CC-BY-SA-30 Unported, Author: David Monniaux)

I would imagine it’s about as comfortable as wearing a sandwich board all day, and let’s not even forget that it’s also highly reflective, so expect to be punched in the face by people you’re blinding and roasting with your solar-panel suit. The research by Chai et al. should make this less of a concern since the solar panels are flexible nanowire (OK, very, very small wires) systems woven into cotton thread. You can cut it up, sew it into fabric, and get it tailored if you want that clean, bespoke look. The authors figured that something like this is useful as textiles if you can actually treat it like thread. What’s the point if it’s not practical, right?

So far, so good, but all of this solar energy has to go somewhere. Can’t just wear a solar-thread shirt and just charge up things willy-nilly (stupid first law of thermodynamics), you’ll need something that can hold that charge temporarily before releasing it into, say, a smartphone or some LED slap-patch. For that, you would need a capacitor, which (in a nutshell) does a lot of things, including holding on to charge. But do you really want to be wearing these all day?

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Wikimedia Commons/Flickr (CC-BY-SA-20 Generic, Author: Eric Schrader)

I imagine that would itch.

Anyway, the authors devised a capacitor that can also be treated like thread. Weave it along with the solar thread, and now you’ve got something that can hold a charge while you plug it into the tech you’ve got on you. Works great in theory, but no good if it doesn’t do what it’s supposed to do. Time for some testing to make sure.

What did Chai et al. find? Small pieces of thread (not a whole shirt or something, just small pieces of thread) can be fully charged to 1.2 V in 17 seconds, which is quite fast, and takes more than a minute to discharge at 0.1 milliamps of current. These are small numbers, but you might get better performance if you scale up by, say, using more of this thread system that they have. Further testing shows that using more thread can increase the voltage, but I’m sure there’s a point where more material means either there’s too much resistance or a good sweat will short-circuit your shirt. Shirt-circuit…?

disapprove
Wikimedia Commons/Flickr (CC-BY-SA-20 Generic, Author: hobvias sudoneighm)

Anyway, this seems like a good idea for the smaller, hopefully more energy-efficient devices that are going to start coming down the pike (hopefully) with a lot of the strides in materials chemistry. The one thing that hasn’t been tested in the paper is how this would stand up to being washed – you’re putting in potentially (I’m not trying to pun here, I’m very sorry) live wires in water, you’re going to short out something. The other concern I have is that while some of the wires are coated in carbon for insulation, some of it is coated in a material that is actually water-soluble, which is why people in the ‘maker’ movement are keen on using it as an easily-removable support for 3D printing. I’d like to say I’m thinking about this for the good of humanity, but really it’s because dry-cleaning can get expensive and if it wasn’t for professionalism, I would only ever wear t-shirts (well, more than I already do). But at least there’s material that you could cut like (and with) cotton thread, and you’re wearing a solar battery. Now to get it to a more agreeable price-point, since I’m pretty sure manufacture-scale is going to get expensive thanks to the titanium this material uses…

Featured Article: Chai Z, Zhang N, Sun P, Huang Y, Zhao X, Fan HJ, Fan X, Mai W. (2016) Tailorable and Weable Textile Devices for Solar Energy Harvesting and Simultaneous Storage. ACS Nano, doi: 10.1021/acsnano.6b05293

Featured Image: Wikimedia Commons (CC-BY-SA-30, Author: Ingridlavid)

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