I wanted a case I could throw outside in the elements and not have to worry too much about it. It also needed to be big enough to fit the solar cell.
I went with this 4-1/2" x 2-1/2" x 1-5/8" case from McMaster. It's IP65 rated and should be good enough for a prototype. I had to make a hole in the front cover to be able to connect the solar cell:
In this picture you can also see the little board I used for the buzzer and driver transistor. The idea was that if the buzzer was glued against the solar cell, the sound would be louder than if it was just in the box. Nice theory. :) In practice, it didn't work out that well.
To attach the solar cell to the case, I used some VHB tape and then put silicone around the edge of the solar cell so hopefully no water can get behind it:
Now this may look pretty good and work decently for a prototype, but I have no illusions about it being the final solution. I have a lot to learn when it comes to the design of rugged systems that need to endure years of exposure to the elements.
For one thing, the idea about the current enclosure is that it's sealed. Of course, making a hole in it and sealing it with silicone probably compromised that.
Also, when this thing sits in the sun, it will get very hot inside and pressure will build up. Some of this pressure will escape and may compromise the silicone. The worst thing about that is that when it cools back down, the pressure inside will drop, pulling air, and possibly moisture, back in to the case.
My #WiFi Logger project is an effort to hopefully learn about these kinds of issues. It will monitor the charging system and also environmental conditions inside the case.