Solar backpacks work by absorbing sunlight and storing the energy collected into a battery. Whenever your backpack is in the sunlight -- for example, while you're walking to class, going on a hike, or just relaxing outside -- you can store solar power.
The problem with many solar powered backpacks available for purchase is that they're so small (and they can be costly!) and there aren't as many choices. By buying your own regular backpack, you'll have a lot more selection and can choose the size and configuration that suits you best. Turning the backpack into a solar powered bag isn't that hard, either.
The first step in converting your backpack is to purchase a solar panel charger that fits your pack. Look for a thin, flexible solar panel charger with a USB cable for connecting to your iPod, cell phone, etc. You will probably want to get more than one panel, for maximum impact. Try to find panels that are weather resistant.
Once you have purchased the solar panel(s), you need to connect it to the backpack. Sew a pouch to hold the panel, and then attach the panel in its pouch to the side of the backpack that's exposed to the sun (ie. not the side that rests against your back). That's all there is to it.
Keep the solar panels clean so that they operate at their most efficient. Learning how to build a solar powered backpack is a neat idea for students, travellers, hikers, cyclists, campers, and anyone who spends time outdoors yet wants to stay connected!