This panel should be connected to the external solar panel connector. As shown in the picture below, it has identical shape as sensor connectors, but is placed on the control side of the enclosure, below the on/off button.
External solar panel features:
Max power: 3 W
Max power voltage: 5.8 V
Max power current: 520 mA (max current input is 300 mA in Plug & Sense!)
Dimensions: 234 x 160 x 17 mm
Weight: 0.54 kg
Cable length: 1.5 m
Do not connect any sensor on this connector and also do not connect the solar panel to a sensor connector. Waspmote can be damaged and warranty will be void.
In the next picture a typical installation with external solar panel is shown. Notice that the enclosure is placed just under the solar panel, using it as a protection against sun and rain.
Libelium provides special brackets in order to install it correctly.