What kind of radio module are you using on this?

Very cool, clean design. Any reason for cutting out the board for the solar cell area? I've used a smaller version of them and I don't remember anything in the documentation about that. I could have missed it though. 

I realize you are using some monocrystalline photovoltaic cells (i recognize the IXYS cells) but I don't know if you will get get the power you expect out of them if they are at the incorrect angle.  I very much suggest looking into the use of amorphous photovoltaic cells because they aren't designed to work at a particular angle.  There is a lower maximum power that you can get but it will be more consistent regardless of their positioning.