My intial "solar station" included this one 15 Watt amorphous silicon solar panel fitted to the metal roof above the shack. It's used to trickled-charge a 12V deep-cycle battery. Diode-blocking in the panel protects the panel from reverse current as the battery reaches full charge. In direct sunlight, the panel produces 20V open-circuit. However, it is able to provide charge even in overcast and rainy conditions. It was purchased from Silicon Solar for under $120.
I recently added three more 15W panels as a package from Harbor Freight for under $200. These panels look exactly like the Silicon Solar panel. The package came with a charge controller that includes a 5V USB outlet. In this photo I've placed them safely, but inefficiently behind one balcony window. All four panels daily re-charge my AGM battery to operate WI7B and to charge my cellphone and Acer One netbook.
The deep-cycle 12V 33AH SLA AGM battery with the finished wire set. Although it is capable of working in a range of temperatures, maximum efficiency is maintained by keeping the battery inside. Absorbant glass mat technology allows 99% of produced hydrogen and oxygen gases to recombine in the battery, while acid leaking is mitigated. It was purchased at a Battery-Plus mall outlet for under $80.