A bare panel is not a power supply. Match panel voltage to a solar power manager or charger first, then size wattage for the battery and load you actually run.
Solar panels from 1.5V 250mA flexible film to 18V 10W polysilicon, MPPT solar power managers (DFRobot 5V and 9V/12V/18V, Waveshare 6V–24V), bq25185 charger boards and LTC3588 energy-harvesting breakouts.