An RF-powered cordless phone
wired.com
wired.com
Because the phone relies on those signals for its energy harvesting, it has a range of just 15 meters from the basestation.
This is neither a cellphone nor solar-powered. It's an RF-powered cordless phone. Interesting nonetheless.
Like non-traditional solar panels; a company called Ixys has some interesting small "solar bits"[1] which are what they sound like. Or old-school amorphous solar cells, like the kind that used to power calculators. They're not very efficient, but they perform okay in indoor lighting and they're cheap.
Also, PIN photodiodes[2] are intended for detecting whether an object is in light or not, but they can actually deliver around 25 microAmps @ 5V in less than 5 sq. mm. Not much, but it could charge something ambiently for short bursts of usage. (Edit: and I'd be remiss if I didn't point to the project that made me aware of this: https://hackaday.io/project/21342-bpw34-solar-powered-led-wa...)
So, you know. Hop to, everyone.
[1]: http://ixapps.ixys.com/DataSheet/KXOB22-04X3F_Nov16.pdf
EDIT:
I looked up the spectrum PV cells tend to respond to and some sources on the usual meaning of the word "light", and I admit my original comment was me being pedantic about the more obscure usage of the word. Sorry :(.
Also consider what of the sun's radiation makes it to the surface of the Earth.
"The prototype basestation uses an unlicensed frequency, limited to low-power transmissions. ... Real cell towers have a hundred times as much power, and would increase the range to perhaps a kilometer,"
To be fair, we used more sites closer together instead of a few larger ones, but the point stands. Cell sites biggest advantage is elevation and line of site, not massive transmit power.
Elevation and line of sight are important but power is too!
Ctrl-f "watts" on this page to see what I'm talking about:
https://www.ericsson.com/en/networks/offerings/connecting-th...
However because the base has multiple (hundreds) of low-power transmitters, it must cater for a very large instantaneous peak power when they momentarily add up.
And more importantly, excess Transmit power reduces the re-use ability of that frequency in nearby cells.
Late response, but that assumes that the mobile RX is as good as the tower's RX, and I can assure you that's not the case.
The gear up on a tower has a way better low noise amplifier than a mobile phone, so it's able to "hear" the phone at a greater distance than you'd expect. That's why it's a-okay to have a base transmitter with a quite a bit more power than a mobile TX.
The what? The only thing I can find about reciprocity is that antennas have the same characteristics in either direction. That doesn't mean your noise levels are the same, and you very often have different bandwidth requirements in each direction.
Any excess power prevents re-use of the frequency in adjacent cells.
So it sounds like not only this should be very useful according to those numbers, but would also imply that solar chargers for smartphones are not complete bullshit fake non-product I always assumed they were?
Achieving those numbers does require the panel to be aimed at the sun and the sky to be clear, though; cloud or off-axis aiming drops the efficiency dramatically.
Works well on sunny days if you adjust it to point directly at the sun, and it charges in 6-8 hours.
Is it practical even then? I'd gladly carry a few extra batteries so that I don't have to sit around camp and keep adjusting the panel every hour.
$100 isn't practical for most people either.
My phone has a battery of around 12 Wh and lasting maybe 30 h on a full charge, that's a power consumption of 0.4 W on average. With a surface area of about 70 cm², we get about 60 W/m².
Phone eats 60 W/m².
Sun provides 1000 W/m².
Okay, let's cut that into a fourth because, you know, clouds and nights and stuff. Retake.
Phone eats 60 W/m².
Sun provides 250 W/m².
Essentially, if you find a solar panel with 25% efficiency and the right size, you can slap that on the back of your phone for a very tiny size increase, and you now have a phone that powers itself as long as you put it down in the sun instead of in your pockets when you don't use it!
Obviously it varies a lot depending on where you are. For example, in Germany the total sunshine you have to work with is approximately 1000 kWh/year[1], or 115W/m2 on average. I think that still assumes you find a way to perfectly align your phone to be perpendicular to the sun's rays; otherwise you get less energy still.
[1] http://www.solar.lucycity.de/index.php/sonnenenergie/9-sonne... I think the technical term may be solar irradiance, here's a global map: https://en.wikipedia.org/wiki/Solar_irradiance#/media/File:S...
1. This sounds very useful both as a backup capacity to make calls when your battery died; a smartphone could run in a restricted, super-power-saving mode off that. Could be handy in cities, where there's lots of RF background.
2. Energy that can be harvested this way from human-made RF is energy wasted. I expect less and less of such background RF to be enabled as time goes on and people figure out more tricks to do hyper advanced magic with beamforming.
Just make 5% battery the new 0% and whatever super-power-saving mode magic you have to run off that 5%. I think that might make more sense in terms of power envelope than to bother with all this stuff.