My idea is to integrate a central battery pack and power regulator stored underneath the bike seat. The lithium-ion battery would power front head lamp and rear tail lamp, both are LED lights. The battery pack/regulator, tail light, and fold out solar panel would package all together under the bike seat. The bike seat rails would be good place for mounting the assembly.
An optional generator at the front hub would power the battery pack intermittently because the generator only turn on when braking, therefore no drag during normal riding. This typical setup called regenerative braking for electric bikes.
This idea I think is best for a commuter bike application, because the battery pack could charge while work or school, and ready to go for the commute home.