Thanks for the responses. I'm mostly thinking of measuring and data-logging the output voltage of a small (5.5V, 320 mA) solar panel throughout the day, as a gauge of whether or not -- on average -- it makes sense to invest in solar power at my house. I live in an area (Puget Sound Convergeance Zone) where direct sun is hit & miss throughout the year.
Peak voltage of my solar cell is over 6VDC, so that would probably fry the Uno. perhaps I should find a smaller panel for my experiment. But the question is, can I just plug the output of a smaller panel directly into an analog port on my Uno (assuming its peak voltage is under the 5V limit) and read the voltage through code?