Solar USB Charger for Cellphone

This is a simpledevice that uses solar energy for charging mobile phones via USB port, it is very useful if your phone need's recharging in a place where there   is no electricity or if you are on a  camping trip this is a great gadget for recharging phone batery.
I did not put a spare battery in case you can not rely on the sun's energy and it would be good to put two rechargeable AA batteries so that they can recharge the phone battery.
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Materials 

-2x solar panels (one is 3 volts)
-1x USB Charger
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Solar panels connected serial in order to obtain higher voltages
(http://cleangreenenergyzone.com/solar-power-panels-or-cells-in-parallel-circuits/) and don't
forget to use diode on solar panel to prevent it  from damage (1N4041 diode )
Positive end connected to the positive part of the USB board  and negative from the panel to the negative on the USB board.
The panels can give 6v .