Good news. Even at cloudy sky (no shadow) the solar panel produces abt. the same charging current as a 5V USB charging adapter. The idle voltage seems to be limited to abt. 5.1V (might be to protect smartphones, thus at bright sunshine the charging current is therefore not much higher. Conclusion: It takes about the same time to fully charge a smartphone or iPad as with a 5V charging adaptor. The 2 solar panels are well protected against scratches and the unit can easy be fixed onto a backpack. Overall a good product, fulfil its purpose well and the price is good. Can recommend it to everybody who wish to be independent from mains.