Bests & Worsts Reviews from Amazon

I have been looking at different foldable solar panels in the 100+ watt range recently to charge portable battery boxes like the Prymax 555Wh. I initially asked a couple questions including if it had a built-in MPPT controller - the answer being no. I liked that this unit was small in comparison to others and attributed it to the high efficiency solar cells, claiming >25% efficiency. I liked the USB-C PD 20v output as well, so my mind was made up. The unit arrived and looks to be of good quality. Then I tried to test it… I was a bit disappointed with the panel’s output into the Prymax as it seemed to begin at around 54 watts and continue to drop to zero over the course of 20 minutes. After looking into it I realized that this is due to the Prymax requiring a 21v input, not 18v… The COOCHEER 120w solar panel initially puts out over 21v until the panels warm up, and it drops to around 19.4 volts. At this point I resorted to using the USB-C connection to charge the Prymax and take advantage of the 20v PD output. It worked – but it must be noted that the USB-C Power Delivery maxed out at 45 watts, not 60 watts – this is stated on the panel 20v2a max. I then decided to get a bit more technical about the panel and see if I could verify its stated output. Over the course of 2 days I measured both voltage and amperage out of the panel at different times throughout the day and relating it back to the current solar radiance. Things I have learned about this panel: • I realize that this panel must be rated at 120 watts at STC – Meaning 1000 w/m2 and 75F • I was testing in ideal conditions including days that ranged from 900-980 w/m2, at an ambient temperature between 70-78F • Therefore, I expected a bit of a reduction of 10%-15% to compensate for the panels heating up under the sun, then another reduction for being under the 1000w/m2 solar radiance. I applied 85% for PTC conditions and 90% to compensate for solar radiance. This means I should be seeing 120x0.85*0.9 = 91.8 watts of output. • Maximum output I was able to measure was 69.84 watts. This was at 21.1v and 3.31amps, with the panels at 75F. Solar Radiance at the time at the location was 904 w/m2. This means I was only generating about 75% of the calculated power – Seeming as though one of the 4 panels was not functioning. • I then measure each panel independently from the controller panel side to the opposite end and saw 0.71a at 17.7v, 0.72a at 17.7v, 0.99a at 18.0v, and 0.98a at 18.0v. Meaning each panel was outputting 12.57w, 12.74w, 17.82w, 17.64w… At this point I realized two of the panels were not performing up to par and was most likely the source of my gap in power output accounting for over 10 watts of loss. I really want to like this panel. It is at a great price point, has good features, is super small comparatively, but I don’t like the limited PD output at 45w and the fact that two of the panels are under-performing. I have requested a replacement to see about getting four fully-functional panels and will see how the second round tests out. I will update this review at that time. 4/24/20 UPDATE: The replacement panel was received today and I tested each panel again. 20.4v at 0.973a, 20.4v at 0.996a, 20.3v at 1.0a, and 20.2v at 0.893a. Much better on this panel, but panel 4 is still underperforming a bit. I compared my original 120w COOCHEER panel side by side to this one today at 4:15p, sun was around 805 w/m2. The original panel was outputting 3.39a at 19.5v, the replacement was 3.81a at 20.0v, which is a full 10 watts more than the first one I received for a total of 76.2 watts. My calculations would say that at that time I should be seeing 81.6 watts, 76.2 is very close to that. The discrepancy is most likely due to the lower amperage on panel 4, which has a wrinkle in the plastic above one of the cells... I have ordered one other brand 120w tri-fold panel to compare the outputs of each to ensure this is performing as it should. I have raised my review to 4 stars based on the replacements performance, I will update my review to 5 stars if this is comparable to the more expensive tri-fold. Update 4/30/2020: I received a competitors tri-fold 120 watt panel today. I placed these side-by-side and pulled the multimeter out. The COOCHEER was generating 21.7v at 3.37a = 73.13 watts. The other brand's 120w tri-fold was generating 21.4v at 4.96a = 106.14 watts. Therefore my mind was made up, the COOCHEER is heading back. I have reduced my review down to 2 stars as the quality control seems lacking due to the variability in the panels, and the overall output is not comparable to other 120w panels in the similar price range. I would love for this unit to have worked and put out the same level of power as stated. Keep trying!