This is a provisional review because I've had the 40W panel only a few hours, but it was already worth mentioning something fall / winter-related for those who are curious, like I was, whether or not this could do anything with a cloudy day in the northern half of the US. Apparently it can: It trickle-charged, at around 200 milliamps @ 12V (voltage controlled separately), a mostly-charged 12V 18Ah AGM battery I had lying around as a test.

I know the instructions mention charging 12V batteries, but I used a small separate battery charge controller with this panel to make sure the voltage was appropriate for the battery. No comment yet on what the built-in controller does, but the instructions say it'll detect the device and deliver the proper voltage. Will test that out later.

That trickle-charge took only a couple of hours, but the battery was nearly full already. The point being, this is apparently big enough to supply a little sip of juice for that kind of application even on a cloudy, wintry day. Which is what I was hoping. In cloudy parts of the US, this is the best time of year to put something like this to the test"”if it can do this on a cloudy day while sitting on a table inside a dwelling by a window (no trees or other buildings obscuring most of the sky view), then it'll probably be just fine in full sun.

It's also over two pounds, if that matters to you, but I suspect this will be useful enough for that to be worth it. Just keep it in mind. It's substantial.

Will update after more testing. Five stars until it gives me a reason to dock any.

This is a very good battery charger for urban survival. Not only does it recharge with the Sun but it also has a compass, decently bright light, and an electric cigarette lighter. Also there is a digital readout instead of four little dots to tell me what the power remaining is. Overall this is my new charger that stays with me. The only thing that can make it better would be a larger capacity.

I purchased the X-Dragon charger for the 18 VDC output to charge speakers. I checked the voltage output from the panels in direct sunlight and they were putting out 26-30 VDC. This is a big problem and could damage devices rated for 18-20 VDC input. There does not seem to be any effective voltage regulation built into the 18 VDC circuit. I have written an email to the X-Dragon tech support and will update this posting with the response. Reserving judgment.

I have tried an x-dragon 40w and allpowers 80w solar panel, both claim they can charge a laptop. I have a netbook that has a power brick of 20v 2a. The 40w and 80w panels both have a plug that fits and claim 18v 3a output. For a second when plugging into the netbook it flashes that it's charging, about 10 seconds later it comes off. After leaving plugged in all day, no % increase, rather a decrease (slight due to turning on/off). I also tried to charge a guggha battery bank that has 2 inputs. Micro USB and DC (varying). With the micro usb it will charge at 2a or about 8.5-9.5w varying as shown on its lcd screen. When plugging the DC in, it does not charge at all, the backlight of the power bank flashes on and off, and the charge indicator on the screen goes on and off, and the wattage indicator never comes on to show any incoming amperage/wattage.

In short, beyond getting a 20-30w rated USB only panel, solar is quite worthless unless you get 100w panels and hook up to a large heavy battery. I now have a few 21w solar panels with dual USB and those work just fine for charging power banks and cell phones at 5v 2a speeds. The 21w panels were around $29. Anything larger is just throwing money away.

Hope this helps other people new to looking into solar like I was. My next step past the cheaper 21-28w panels (5v usb x2) is to go with a minimum of multiple 100w panels for ~$1 per watt.

This solar panel impresses me a great deal. I first started thinking about solar technology after Hurricane Sandy, I was stuck for 5 days with a dying cell phone battery which I kept off and charged off my laptop's battery. It worked fairly well but after that I never wanted to be stuck like that again. I also wanted something for when I'm on the go. I've looked at many options and finally settled on this panel, mainly because it was on sale. I feel like it far exceeds the value of the $30 I spent on it. It is a little big, but still small enough to fit in my backpack. The dual chargers are very nice too. I have a dual charger USB battery box and a smaller Duracell USB battery box. Both fit snugly in the mesh netted sack which has the USB adapter. And both charge fairly quickly from 0% if left outside.

The ONLY reason this isn't 5 stars is because of that mesh sack & flap covering. I wish it was larger and waterproof, it seems like they could have made the flap that goes over the sack into a pocket to keep the internal components more secure. My main concern is I don't want moisture getting in there by accident and corroding anything. And that open design doesn't prevent that. I'll probably end up modifying this soon.