A video of my home made solar wall clock, it will run with room light alone without a battery, but I do use a rechargeable battery in it which never runs down as it keeps the battery recharged with room light. In the video I am running the clock with the battery removed. Just a slight modification to the clocks circuit board, an extra capacitor and four small solar panels wired in parallel does the job. http://www.youtube.com/watch?v=Nv0BP1kV3t8 (http://www.youtube.com/watch?v=Nv0BP1kV3t8)