The Sun is a source of energy and almost inexhaustible light, it is a shame not to take advantage. It is far to be able to tame the fury of the Sun, I must say it's far, and that closer, it becomes unbearable ^^ Nevertheless, we recover a small part of this energy through solar panels. It is far from the 80-100%, but if I'm not mistaken, you can reach 25%. Note, this isn't 25% of what we sent the Sun, between what he sent us, there is just a small 149, 6millions of km, the atmosphere and clouds… In short, solar power as an alternative energy source, it will not immediately, as it doesn't work… in day… and no night! ^^ I had already tested a solar panel of 15W, which was not bad and that worked pretty well. This time, it's a 21W solar panel, the PB Aukey – P4. 
Features
- Effectiveness of Transition: 23.5%
- 2 USB ports
- 1 output: 5V / 2A (Max)
- Exit 2: 5V / 2A (Max)
- Total power: 21W
- Weight: 895g
- Panels open: 500x305x5mm
- Panels closed: 175 * 305 * 33 mm
The test
The solar panel of Aukey PB – P4 is the portable type: folded, he is about the size of an A4 sheet. Unfolded, 3 solar panels can be discovered, but well protected. 
Beside your 3 solar panels are a Pocket no hermetic containing 2 USB ports that can charge at 2A max. You also have slots to hang your carabiners if you wish to bring your solar panels in hikes and attach it on top of your bag back so that he can charge your devices in your markets. 4 carabiners are also provided. 4 holes for carabiners are strong enough, the holes are set of metal rings. Located on the front face, so 3 solar panels + USB ports. On the back side, and that's what got me interested in the more to the point in addition to the power of solar panels, are 2 mini fastened panels that are used to hold your solar panels at an angle of about 45 °. Ideal position to deal with the Sun! In addition, 2 mini-positioning Panel may be required by a strip that prevents that the mini panels slide and to drop the solar panels! Excel
l
ent! Charging level, depends (sadly) the situation of the sky… It is pretty hard to tell the difference between 15W or 21W solar panels: you can put solar panels exactly in the same place and at the same time, to have the test, a difference of one millimeter can change everything! And the time (duration), changes the position of the Sun… But as long as it is actually of 21W, it should be faster to charge your devices from the 15W, under the same conditions. And personally from my tests, I did notice any drop in intensity compared to the 15W. 
Conclusion
These solar panels of Aukey are excellent: good, solid performance, portable, not too heavy, Folding/Foldable, compact, 2 USB ports, provided carabiners. But also well thought: 2 mini Panel allowing to position the solar panels facing the Sun. Link: https://www.amazon.fr/gp/product/B01BZL62LI/ Promo of the moment: use the code 8CK2OLO3 on Amazon to get a discount of 8 euros! 