Solar Panel to charge a smart phone?
 

Not interested in spending a great deal, mostly because it won't hurt as much that way if it gets taken. Doesn't have to plug direct into the phone, charging a battery which is then used to charge the phone would be fine. In a perfect world it would just sit on a rack or on top of a pannier and do it's thing. Not anticipating a great deal of after-hours phone use, but nowadays folks get worried if you don't check in.

Charging a battery is best about 80% efficient. Charging a phone battery is best 80% efficient. .8x.8=.64 So 64% efficiency if you charge a brick to charge your phone.

Direct solar panel to phone will be best. Panels you can daisy chain will help on not so sunny days.

Goal Zero panels work good, plug directly in to your phone, have attach points for bungie cords/carabeeners/etc...are waterproof, & can be daisy chained. They fold up to protect the panels when stuffed in a pannier. They also have a pocket to stuff your phone in, so it doesn't go anywhere while bungied to your bike for charging.

sharp, every time I see this type of panels in outdoor stores, I always wonder how they actually work and actually last in real world conditions.
I imagine there are better ones out there, and hopefully you can find some reliable reviews, long term ones ideally, that can show which ones are worth the money and which ones keep working over time.

if it were me, I would start looking at established outdoor stores as a reference for what they stock, as one would hope and imagine that as well established places (Im thinking MEC in Canada, REI etc in the states) that they would have done the research and stock sell stuff that is well made and reliable over time (but never assume that!)

good luck and hope that experienced folks can chime in here

Size Matters , bigger area more power..(less charge time)

and best efficiency is when it tracks the sun to be at a right angle to it, So, not favoring recharging on the road.

I might carry a panel on a kayak or canoe trip, on those trips I am more inclined to spend a day on occasion in a sunny campsite. But biking I have never used a solar panel, photo below is from a kayak trip where I was charging up AA batteries for my GPS. That panel is no longer sold.

https://cimg9.ibsrv.net/gimg/bikefor...a2ec6eb11a.jpg

I got an older version of one of these back in 2015.
https://www.amazon.de/dp/B00PW4I9M0/ref=dp_prsubs_1

I have had no problems with mine. It's robust enough to be strapped on the back rack. Has a pocket for holding a phone/battery.
I bought a powerbank from the same company at the same time and when that failed within a year I was sent a newer, bigger version.

In practise, this works best when in direct sunlight, so is far from optimum when strapped on a bike, but it will charge. I prefer to use a battery when it's in use on the bike because the changing light can mean that my phone is switching on & off and therefore losing a lot of the charge.
Set up at camp it'll charge my phone very quickly.

I upgraded to a Dynohub and charger so now the panel only gets used when I'm not moving on the bike.

My verdict - cheap, robust and does the job.

Have used this: https://www.amazon.com/gp/product/B012YUJJM8/

Used it to best effect when sitting still, but it has worked when just hung over my handlebar bag. I have found that charging my phone with an inconstant power source was not easy. The screen would come on with any change in power, and the screen coming on would draw power. Charging a second battery and using that batter to charge the phone overnight worked best for me.

On my past several tours I successfully used an Anker 21 watt solar panel bungeed to my rear rack and panniers. I used it to charge a power bank during the day, then charged my phone at night. If you have your phone on while charging variations in sunlight will cause the charge to start and stop. Your phone will then light up the screen which is inefficient. Works fine if your phone is off. Paid $60 a few years ago on Amazon but they no longer carry it. Can find them on eBay for the same price though.

mike

On a supported ride across Africa, I brought a Goal Zero 7 panel and it worked fine. In that case, I used after we arrived at camp rather than carrying on my bike.

I haven't really used it on tours since then. Instead I've stayed in lodging often enough and also carry a battery pack. I charge the battery pack + phone at those opportunities. I typically update something on the internet rather than calling. The "something" has varied:
- one trip, the twitter messages had coded GPS coordinates and my father updated a website with pins in a map
- one another trip I used a "wordpress for android" app to make a quick update
- on another trip, I used a wordpress plugin that took messages from twitter to post

Separate from that I've been careful to manage expectations on the "checkin" aspect. On occasions when I've posted, I've sometimes noted "wifi connection problems" or "no cell service" but "finally was able to post something"... so folks get more of the idea that these can be unreliable. I also post fairly often but also explicitly set expectations that sometimes it might not be reliable...I've also occasionally noted that I am coming up to areas with limited connections.

A test of my expectation setting came in Peru when I was climbing up on the Altiplano. I had noted that it could be 5-7 days before I was in a town with connectivity again. Some of my co-workers had gotten antsy since they hadn't seen a post for 4 days when previously they seemed to show up every day or two... Not sure how they got the name but somehow someone contacted my brother and relayed the concern. My brother and parents pointed out - that this wasn't really unexpected since I had identified the gap previously... I was happy my parents had reached that level of progression with dealing with these inevitable gaps ;)

I've used this set up for two month-long rides and several shorter day or two trips so far. It's been enough to keep my Samsung Galaxy S5 smartphone and my 50-lumen rear blinky charged without ever needing a wall socket.

The CHOETECH 19 watt solar panel is a tri-fold design and was easy to tie across my rear rack. I chose it tested and reviewed good on youtube and elsewhere. It charges a 10000mAh brick battery 75 to 100 percent during a day's ride with good sun. (10,000 mAh will charge my phone about 3 times). I chose the Anker PowerCore battery because it claimed to be one of the lightest.

Looks like the price of the solar panel has gone up since I bought mine a couple years ago for around $40. Looks like it's 50 now. Still, I'd recommended it. Mine has seen a lot of use; just short of 3k miles on the bike -and it's as good as new as far as I can tell.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I "suspect" that about 50% of the reason this set up worked for you for a 2 month never plugged into a wall plug is because you had the phone turned off most of the time... JMO... ;)

Nope. You're opinion isn't accurate. As I wrote in my earlier post, the solar panel produced enough electricity for the battery pack to charge my phone 2.5 to 3x a day, so I could afford to use it. My phone was my only source of navigation for the first month-long, and a primary navigation tool on the second. Plus it was my only camera, mp3 player, internet access, etc. It's math and science. Someone could work out the numbers if they wanted to. All the specs are available. Which is actually a good way to go about it. Work backwards from how much electricity you think you'll need per day and buy equipment that will produce that much.

But I had good luck with weather. The thing about solar, of course, is that you don't get much power when it's cloudy, so it's unreliable in that manner.

I have a similar solar panel, and it's been pretty reliable, weather permitting, in terms of keeping me charged. I also had a dynamo solution that is now non-functional. I want to replace it, but if memory serves, I got more juice out of the solar panel under optimal conditions, but the dynamo would work regardless of weather. But then if there's no sun, that's often a time when you want to use your headlight, so the dynamo is otherwise occupied, so solar has been a good way to go.

I used a Goal Zero solar panel that I bought in Cairns last year for a while. I found it pretty slow to charge my phone if I'm honest. Eventually I lost it somewhere near Townsville when I didn't tie it securely enough (I was trying to charge the phone while riding -- probably a sign it was too slow to charge. Probably lucky not to use the phone with it). I'm in two minds about whether or not I'll bother with a replacement.