Picked up a BigBlue 28W Solar Charger a few days ago from Amazon. As you can imagine, there's no shortage of USB solar chargers on the market, but most are subpar for one reason or another. I put the BigBlue 28W Solar Charger through my normal tests and I was impressed. Plenty of output from the four panels and it passed one of most important tests - the iPhone power recovery test. For all the details, read on...
Some close up shots showing the panel and USB
I connected two devices to the 2.4A ports to see if the panel could handle the load. No issue with charging a battery pack and a Nexus 5X at the same time. You can see the output results in the pictures.
Battery pack via MicroUSB is receiving ~5.865W and Nexus 5X is receiving 3.2W of output. Keep in mind that it's normally the device that's setting the limitation and not the output of the USB port itself. The cable that is used plays a role as well. Cheap cables impact output.
I then connected two USB C loads on the 2.4A ports and the output was impressive. ~7W on the battery pack and ~4.6W for the Nexus 5X.
In this configuration, I wanted to test the output of the 1A USB port. I connected the USB C cable to the battery pack and was able to draw ~6.9W (5.02V @ 1.37A). What I've found in every test I've done, the port labeled 1A will output more then 1A. It's a test I perform every time just to see if any of the manufactures limit the output to 1A and I haven't found one that does.
The next test is what I like to call the iPhone recovery test. iPhones like consistent current. If the current drops and then rises again, the iPhone typically caps the current to a much lower rate. In order to recover, a charger must "reset" or "restart" the port in order to get the iPhone to allow full current to flow again. This is where most solar chargers fail, but this was not the case with BigBlue. As you can see in the pictures above, it recovers without issue!
Final test - attach all three devices at the same time. The results were very acceptable given all of the factors involved. I couldn't measure the iPhone load, but the Nexus 5X was ~3W and the battery pack was ~3.75W and I'm assuming the iPhone was pulling about the same, so not bad at all.