I would like to do a little project with a solar panel, something to measure the actual watts coming out of the thing, and an Arduino to integrate the panel's output over time.
However, I haven't any idea of how I would build a circuit to measure the actual amount of power the panel is producing. Is there an off-the-shelf component that will measure that for me? Or measure some related value(s) through which I can calculate the watts?
Any pointers to circuit diagrams, wikipedia pages, or anything to help me get going would be greatly appreciated.