​ ​I recently bought for camping​ ​RAVPowerOf 15 W Dual USB Solar Charger​ ​
It’s fairly efficient, giving an iPhone a full-charge in about 3 hours if the weathers good, and since the USB port is two-fold, its possible to charge two devices or a mobile batteries simultaneously.
Just using for camping is a bit of a waste, so I tried providing it with some sunlight to charge an iPad and iPhone with, instilling in the window of the house, with it always connected to the companies​ ​1600mAh mobile battery.
Not a problem. It’s good because it can be used in case of an emergency as well as camping out.