Roberto,IZ7VHF has shared his solar cell builds here -
Should give you an idea what you may want to try.But to power the entire U3S kit would require a lot of solar I would think having the LCD and all.
Most are using minimal builds to operate from solar power.The GPS modules can be key to how many cells you will need.I found a uBLOX NEO-6M draws much more current than the NEO-7M.This is just an example,but key to reducing current required when using solar power.
I have had great luck using only 6 52x19mm connected directly to the 3.3v LDO reg...no battery.It fires up the boards fine even with low sunlight.Solar cells produce more energy at altitudes...so if they work on the ground...you got it made.
Once the U3B is available,I am sure your solar requirements will be much easier to accomplish.
Jim,N2NXZ
