You should check out Lumos thrillseeker solar hydration backpack. It is a light weight (800g) hydration backpack which features a unique 3W solar fabric paired with a 4000 mAh battery. The battery helps you to charge your smartphone or bikelights . Apart from that it’s a full featured hydration backpack with a 3L bladder compartment, reflectors and whistle buckle for safety and a high visibility rain cover.
Do check it out at iwearlumos.com.
PS: Do get an independent review for the bag because I work with the above company.