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This panel, built by ICP solar is a good small-scale panel weighing 13.5 pounds and measuring 46in x 15in x 2in. The longest side of the panel is slightly larger than a typical windowsill.
Although all good panels are in short supply nowadays, i purchased this panel on amazon for i think between $140-$180.
ICP panels have cabling which allows for linking/chaining them in series or parallel (meaning you could take two 18watt panels and combine for 36watts of charging to a single output). The panel either came with, or i purchased separately) cable connectors allowing for various output methods... a 12volt socket, red/black leads or red/black clips for connecting to 12v battery terminals, or adapters can be purchased to convert the link cable (for linking two panels) into various dc charging port socket sizes. For directly charging a raw 12volt battery (such as marine) you should purchase a charge controller for roughly $40 to ensure the battery is charged safely.
If need be, in best conditions, this panel could charge a 20 amp-hour battery (such as the Xantrex Powerpacks) in around 13 hours of full sun. That would be approximately two to three days of full sun. This would provide me the capability to run a device like a notebook computer for 5 hours (@48 watts) - 10 hours (@24watts). These are rough orders of magnitude to guage your own applications and scale... essentially the panel could thoretically run an 18watt device continuously in full sun.