Question about Xtorm Xtreme Series

To fully charge a 20000 mAh power bank with a 28 W solar panel, we need to calculate the charging time. The power bank needs about 20000 mAh / 5 V = 4000 mWh of energy. The solar panel supplies 28 W. With full sunlight, charging takes around 4000 mWh / 28 W = 142.86 minutes or around 2.38 hours. This assumes that the sun shines constantly and there are no losses. In practice, the charging time can be longer, as solar radiation can vary.