Hybrid cars exist. The regular (gas) engine also charges the battery when it's running.
Having a windmill on top of the car would not be very efficient, but an alternator/generator attached to the engine is quite efficient. You still need to charge the batteries overnight, but they last longer this way. Gas engine shuts down automatically when the electric drive engages, and I have heard that the car is actually nice to drive.

http://www.toyota.com/prius/

Harnessing wave power has been tried with land installations, but without much success so far. Taking advantage of currents can be risky, you dont want to change them. Also, the fishermen dont like large underwater installations..
The latest plans I read about, was to put some large underwater 'windmills' on the bottom.. Wonder how they will maintain them and keep seaweed off them.

Please dont shut off the gulfstream yet, that would mean a new ice age here in Norway.