I did something like this to my trike years ago as a test. I used 3 small solar panels that trickle charged the 3 batteries. It was good enough to ride once or twice a week. These show much bigger solar panels and you could ride once a day for a good distance. I like the overhead version better. The one in the picture below looks like it would be hard to see the road. The one above looks like it would get some sun no matter which way you are facing and it would also keep the rain off on those rainy days.
You can find more at http://www.solartrike.com/electricrecumbenttrike.html
And here is an instructable http://www.instructables.com/id/Solar-Powered-Trike/