Step 1: Introduction
The panel consists of eight 1"x3" solar cells wired in series with a blocking diode mounted on a board and protected by clear plastic. In this configuration the panel provides about 250 milliamps at 4 volts, which will charge two batteries in a day or two, depending on the weather and the batteries' capacity. Other solar cell configurations are possible to provide more or less power to, for instance, directly charge a 3.6 volt cell phone battery, or to provide a faster charge to AA batteries.
There are a number of off-the shelf small solar panels available on the web, but building one yourself gives you the flexibility to configure it to provide exactly the voltage and amperage your project needs. And it could be cheaper.