The other day I was strolling around Tokyu Hands and these bags and backpacks with built-in solar cells grabbed my attention. The biggest backpack is able to produce 15W in ideal conditions, the small ones only 4W. The interesting thing is that they also include a battery so even when there’s not a laptop, cellphone or iPod plugged to the backpack, if you are walking in sunlight the battery will recharge so that you can plug any gadget later on to recharge it. It looks like a great idea to me, the problem is that the prices are around 300~500 euro, depending on the model.
The company that produces these bags and backpacks is not Japanese but American. If you are interested you can buy them online in their website.