The basic design is very simple. Each solar panel has an output of 3V, so I connected four of them in series to charge up 12V gel cell batteries. A diode was used in series to prevent current backflow. Alligator clips connect the wires to the battery terminals.
The solar charger puts out 18V in direct sunlight, supplying around 50 mA of current. This will not overcharge a gel cell battery and will give it a good trickle charge, but may take some time to charge up a dead battery. More current can be obtained by adding four more solar panels arranged as above, and connected in parallel with the original four panels.
Using the solar charger, a gel cell battery can keep a QRP rig supplied with power virtually forever. The only limiting factor is the number of recharges the battery can take, but this system should be able to last for many years.