Since it is evident a 9V battery won’t last near long enough I decided to start playing with solar power to charge a NiMH 9V battery.
Doing some research I found someone that was using solar cells from garden lights to charge a 9V battery. I went to Harbor Freight and got a NiMH 9V battery and 8 of these lights for $20:
I parted the lights and got some switches, LEDs, and 1.2v AA batteries as well:
I connected 4 of the solar cells together and built a charging circuit:
This was kind of clumsy to deal with so I connected all of the solar cells onto a piece of cardboard. 4 cells didn’t seem to generate quite enough voltage so I tied in a 5th. The other 3 are available, but unused:
I only had a few hours of sun, but I did get the battery charged enough for an Uno to run for about an hour.
Next I will program the Uno to sleep all except for a few events a day and see if the solar cells can keep the battery going.