OutdoorGearLab

Year after year, the Anker PowerPort 21W continues to be a high scorer. It has all the same attributes as the 15W but with 6W more power. It has a fast-charging speed: 3 hours and 40 minutes to charge a 6,000 mAh external battery in full sun, one of the faster in our review. It was also excellent at charging multiple devices at once, and it handled charge interruption as well as you could expect. 
It's not the lightest model that we tested, but it does pretty well for its size &#40;over 20 watts&#41;. Its tri-folding design is about the size of a magazine and is easy to store. This contender was hard to beat when it came to charging capabilities, weight, and price.

Portable Solar Charger Comparison