I have some more questions.

Instead of a capacitor, can I instead use my dynamo to charge two AAA rechargeable NiMH batteries ?

Of course, batteries have a life limit unlike capacitors (theoretically speaking if I understand things correctly). If the batteries die, I always carry an extra non-charged pair. I think it would be awesome, but I have a problem: although NiMH are rechargeable, can they be "charged" and "discharged" continuously like during the stoplights scenario? Would they deteriorate faster than if I use them normally (use until they run out of juice completely and then charging them for 9 full hours as instructed)?