I am reworking a rotating stage for a display case. I've attached a PDF of my circuit. The motor (which I am in the process of replacing) ran on 4 UV cells wired in parallel, producing up to 2.6 volts in that configuration. The motor needed 1.5 volts and could alternately be run on a AA battery. The new motor I am installing runs on 12 VDC. I have rewired the UV cells in series, so that they now produce a maximum of about 10.5 volts under optimal lighting conditions (i.e. shining a bright light directly on them). The problem is that these cells will be under different lighting at different times. My question is, how should I size the battery I add into the attached circuit?

 

Well, maybe it is because you didn't give the information needed to answer your question. The important missing pieces are the current drawn by the motor, and how long you expect it to run on the battery.

Oh, and you would not put the battery in series with the solar cells as in your diagram. You would put it parallel, with a diode to isolate it from the solar cells.