The BioLite SolarPanel 10+ uses two foldable solar panels to create a 10-watt panel. If you set it in the sun, it can charge your phone or mobile device directly. In addition, it has a built-in 3,000 mAh battery. This means you can charge the on-board battery during the day, and then, when the weather is cloudy or the sun goes down, you can use the battery to charge your devices.