I've tried solar charging, it's way to much harassment. You must keep the panel aligned with the sun to do any serious recharging and unless your on a perfectly straight road you'll never be able to maintain a good charge. Here is the circuit I use on my touring bike for recharging USB devices including a GPS receiver and a PDA.
The 2 1N5818 diodes convert AC to DC. S2 isolates the batteries to prevent discharge when the bike is parked for a while. The 4 Ni-MH batteries automatically regulate voltage, absorb excess current, and supply clean power for any devices connected to the USB connector. S1 I isolates the LED headlight and taillight when using the USB connector. There is simply not enough power to use the lights and have devices plugged into the USB connector. The 470mF capacitor allows the LED lights to be used in the event the batteries were lost or damaged. The resistors used with the lights limits current to 380mA allowing 120mA excess current to recharge the batteries to compensate for stops and hill climbing when little or no power is being produced by the dynamo.
I use a Palm TX PDA and bluetooth GPS unit with both being recharged from the USB connector. The Palm has WiFi and bluetooth allowing access to the internet and e-mail in WiFi hot spots. The Palm also has an SD card slot allowing me to remove the SD card from my camera and upload photos and video via e-mail attachments with the Palm. I can blog and post ride reports as the Palm has full internet capability. The Palm is not a replacement for a Lap Top but for touring with the ability to access the internet and post photos, videos, and write updates about the tour I've found it does all I need to do and it's so small and easy to carry unlike a Lap Top.
Last edited by n4zou; 02-16-08 at 08:25 AM.