Solar iPhone Charger That Actually Works?

jyl · jyl's Garage

I'm looking for a solar panel/charger that uses an easily portable panel (say, not more than 10 inches diagonal) and, in full sun, will deliver enough current to an iPhone to offset the drain of having the iPhone "on" and running GPS (Location Services) and a 3G connection.

In other words, suppose you start with your iPhone at 100% charge, then you leave the phone on when you are hiking or riding or whatever, and running your GPS mapping/training app (Garmin, etc) as well maintaining your cellular connection - but you aren't actually gabbing on the phone or surfing Pelican. And let's suppose you are doing this in full sun and the panel is appropriately positioned - on your hat or the top of your backpack or something.

The goal would be for the solar panel/charger to keep your iPhone at 100% indefinitely, even if you're in the backcountry for weeks or riding your bike across America.

Does anyone know of such a device, that actually works? And would any of our resident engineers be able to check, via back-of-envelope calculations, if such a device is possible?

red-beard · red-beard's Garage

Maximum solar = 1 kilowatt per square meter. Efficieny of solar panel = 10-17%.

10" diagonal = maximum of 7.07 on a side = 50 sq inches

a sq meter = 1550 sq inches. So maximum solar flux = 50*1000/1550 = 32 watts. Using a poly panel @ 10%, you'll get a maximum of about 3 watts. In practice, if there is any voltage conversion or mismatch, it will be lower. And this is at NOON with the panel oriented perfectly to the sun. The maximum you can expect from a panel that size is about 15 watt hours per day. If the battery is 3.6v (pretty standard Li-ion) and 2000 mAh, that is about 7 watt hours.

Again, this is if the panel is perfectly oriented...

jyl · jyl's Garage

Ah, so, if the GPS and 3G would drain the battery in a day, then if all was perfect the postulated panel would 2X offset the drain (15 vs 7) In the real world, might be challenging to 1X offset. If I read your post correctly.

Thanks. Looking around isn't coming up with much in commercial products that seem like they'd actually work. Maybe have to build one.

stomachmonkey · 02-14-2012, 06:37 PM

Guy that works for me got one of these.

Voltaic OffGrid Solar Backpack

I can get some usage data from him if you want.

red-beard · red-beard's Garage

Quote:

Originally Posted by jyl

Ah, so, if the GPS and 3G would drain the battery in a day, then if all was perfect the postulated panel would 2X offset the drain (15 vs 7) In the real world, might be challenging to 1X offset. If I read your post correctly.

Thanks. Looking around isn't coming up with much in commercial products that seem like they'd actually work. Maybe have to build one.

It looks like it would. The issue is building a solar panel to put out 5vdc with that size cells.

I might be able to experiment. I just had 30 panels delivered and 10 were shattered. If the shiping company does not collect the "debris", I might try to experiment for you.

There are places to buy just cells.

Here is a 7" x 7" cell, but the voltage is wrong. You'd need a dc-dc converter.

SUN 2.5 7 x 7 [SUN-2.5] - $21.00 :

at $21, the price is right.