How to measure solar energy collected?
So I am pretty knowledge-less about solar energy, so I decided to do some research on it a couple hours ago. Is there a simple way to measure the solar energy that is collected? From what I understand, determining if it is cost efficient to implement solar energy is very dependent on how much sunlight is collectible, which seems to be very location-dependent.
The only solar device I really have available are the $2 outdoor solar lights made by Westinghouse (purchased at Walmart, impossible to miss). Anyways, the device works by collecting solar energy with the panel on top, and converted to be stored in the rechargeable Ni-Cd AA Battery.
Would I be better off trying to measure the amount stored in the battery for a period of time, or is there a way of measuring the solar light collected accurately?
As I said, I am extremely new to this topic, so I apologize if any of this was too vague or incorrect. Constructive criticism never hurts :).
Any ideas or suggestions?