Hi @jonamleonel -
If you use Boron module, you will use the solar panel to power the device. The Gen3 devices (Argon/Boron) has lipo charger build in so the module will in turn charge the Lipo Battery. The battery will therefor be used to power the device when sufficient power from the Solar panel is not available.
Of course you will have to had some small components (i.e transistors, resistors, diodes) to regulate the power coming from the Solar panel to supply steady voltage to the Boron. There are some extensive threads on Solar charging. If you opt for the B-series SoM’s… you will have to build your own power management and recharging ‘section’ on your PCB as these are not included as on the Argon/Boron.
In my proof of concept I simply used a Schottky diode to prevent current from flowing back to the solar panel, some capacitors and a 5V voltage converter to supply steady output form panel to device. See the image below, it is only for your reference, I suggest you breadboard your layout first 
Whether you need the 1W or 2W panel, well that Weill really depend on the amount of sunlight you expect to have in these areas. If there is no size constraint and budget is not a problem, I would probably go with the 2W panel.
Hope this helps.
Regards,
F