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...