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An IPhone battery has a capacity of roughly 10Wh. The energy density of the sun is approx. 1kW/m2 on earth. Let's assume a solar cell with 20% efficiency, so 20

An IPhone battery has a capacity of roughly 10Wh. The energy density of the sun is approx. 1kW/m2 on earth. Let's assume a solar cell with 20% efficiency, so 200W/m2. To charge the iPhone battery in 4h you would need a solar panel with an area of 11cmx11cm. So the phone is probably not very powerful. Certainly it's power draw is nowhere near current smartphones. (It's mentioned in TFA, 800mW when calling, tens of microwatts when on standby)

TeMPOraL 9y ago
That... sounds too good to be true. 11x11cm panel is basically a pocket one; hell, my S7 has surface area (one side) of ~80% of that. And 4h for charging a smartphone is a typical time. 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?
- pjc50 9y ago
  They're definitely a real product. Popular with campers; someone was selling a backpack with integrated solar panels. 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.
  - parametrek 9y ago
    They aren't worth the money or the weight. You are almost always better off bringing the equivalent in spare rechargeable batteries. I've written an article on it: https://www.reddit.com/r/flashlight/wiki/solarcharging https://www.reddit.com/r/flashlight/wiki/solarcharging
    - 24gttghh 9y ago
      4.9oz or .139 kg: https://www.amazon.com/LightSaver-Roll-up-Solar-Charger-Battery/dp/B016N2NMBC/ref=lp_3039010011_1_3?srs=3039010011&ie=UTF8&qid=1490118799&sr=8-3 https://www.amazon.com/LightSaver-Roll-up-Solar-Charger-Batt... Works well on sunny days if you adjust it to point directly at the sun, and it charges in 6-8 hours.
      - parametrek 9y ago
        While that is extremely light, it still weighs as much as 3x18650. Breakeven point would be after four days of perfect 100% utilization of solar power. 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.
- kqr 9y ago
  Huh, I guess you're right. 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!
  - morsch 9y ago
    250 W/m2 is still rather optimistic -- though not absurdly so! 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-sonnenstrahlung 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:SolarGIS-Solar-map-World-map-en.png https://en.wikipedia.org/wiki/Solar_irradiance#/media/File:S...
  - ccozan 9y ago
    This sounds like the perfect application for a MotoZ mod.
  - fencepost 9y ago
    Likely I don't know enough about the components involved, but I've wondered for years about the viability of a solar cell as the bottom layer for AMOLED screens since those don't need a white/reflective back layer for lighting behind an LCD panel. Even if the diode electronics blocked a big chunk of the light I suspect there are plenty of places where a low usage always charged phone might be desirable.

TeMPOraL 9y ago

That... sounds too good to be true. 11x11cm panel is basically a pocket one; hell, my S7 has surface area (one side) of ~80% of that. And 4h for charging a smartphone is a typical time. 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?

pjc50 9y ago
They're definitely a real product. Popular with campers; someone was selling a backpack with integrated solar panels. 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.
- parametrek 9y ago
  They aren't worth the money or the weight. You are almost always better off bringing the equivalent in spare rechargeable batteries. I've written an article on it: https://www.reddit.com/r/flashlight/wiki/solarcharging https://www.reddit.com/r/flashlight/wiki/solarcharging
  - 24gttghh 9y ago
    4.9oz or .139 kg: https://www.amazon.com/LightSaver-Roll-up-Solar-Charger-Battery/dp/B016N2NMBC/ref=lp_3039010011_1_3?srs=3039010011&ie=UTF8&qid=1490118799&sr=8-3 https://www.amazon.com/LightSaver-Roll-up-Solar-Charger-Batt... Works well on sunny days if you adjust it to point directly at the sun, and it charges in 6-8 hours.
    - parametrek 9y ago
      While that is extremely light, it still weighs as much as 3x18650. Breakeven point would be after four days of perfect 100% utilization of solar power. 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.
kqr 9y ago
Huh, I guess you're right. 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!
- morsch 9y ago
  250 W/m2 is still rather optimistic -- though not absurdly so! 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-sonnenstrahlung 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:SolarGIS-Solar-map-World-map-en.png https://en.wikipedia.org/wiki/Solar_irradiance#/media/File:S...
- ccozan 9y ago
  This sounds like the perfect application for a MotoZ mod.
- fencepost 9y ago
  Likely I don't know enough about the components involved, but I've wondered for years about the viability of a solar cell as the bottom layer for AMOLED screens since those don't need a white/reflective back layer for lighting behind an LCD panel. Even if the diode electronics blocked a big chunk of the light I suspect there are plenty of places where a low usage always charged phone might be desirable.