It may be that I am confused. I plan on charging either 2 AA or 2 AAA batteries at one time. The purpose of the LED would be to indicate that charging is complete. I thought the zener would allow sufficuent back voltage, once the batteries are charged, to light the LED. The sole purpose of the circuit would be to charge batteries, not to operate a load. I'm not concerned about the season; I will use this when the sun returns to Ohio in the spring.
I found the suggestion to use the LM317 (actually an LM317T) on a U.K. solar projects website:
http://www.reuk.co.uk/Solar-Battery-Charger-With-LM317T.htm[/URL]