These PowerFilm flexible solar modules can be used alone to direct-power your small DC project (anything that runs off 3V or less and requires 22mA of current or less) - or, they can be used in your battery-charger project to store energy for later use.

BATTERY-CHARGING TIPS
For battery charging, the voltage of your solar panel MUST be higher than the voltage of the battery that you want to charge. We recommend using the following guidelines:
at least 2.0 volts to charge one 1.2 volt battery
at least 3.6 volts to charge two 1.2 volt batteries wired in series
at least 4.8 volts to charge three 1.2 volt batteries wired in series
at least 6.0 volts to charge four 1.2 volt batteries wired in series.

Multiple panels can be wired together to increase voltage or current, and the panels can be cut (following directions!) for your special project.
Each module is encapsulated in 3 mil clear polyester film.

Specs:
Output 22mA @ 3V
Open-circuit voltage: 4.1V
Total size: 2.5" X 1.5"
Solar cell area: 2" X 1.5"
Thickness 0.22mm (8 mil)
Weight: a few grams