Reddit reviews Portable Solar Chargers X-DRAGON 20W SunPower Solar Panel Waterproof Foldable Camping Battery Charger with Dual USB Ports & SolarIQ Technology for iPhone, iPad Mini, Samsung, Other Cell Phones

you will need at least a 10 watt panel to charge a normal battery bank. Probably 20, given that you wont get perfect conditions for use.

https://www.amazon.com/X-DRAGON-Efficency-Technology-Smartphones-Foldable/dp/B00NGKPX4Y/ref=sr_1_3?ie=UTF8&qid=1473595315&sr=8-3&keywords=x+dragon+solar+charger

Thats one of the cheapest portable panels and its over $40. 14 watts is $35, so you will be paying at least 25 for the minimum panel required. An 8 cell 18650 battery bank should provide ~15 Ah for around 20 bucks. You just need to make sure the battery isn't in the sun when charging to ensure the lifespan of the batteries.

Thats probably your best bet for a solution that will actually work. You should get 2-3 charges of a phone per day.

Maybe you'd like to charge your phone with the sun?

http://www.amazon.com/gp/aw/d/B00NGKPX4Y/ref=mp_s_a_1_4?qid=1427551387&sr=8-4&pi=AC_SX110_SY165_QL70&keywords=portable+solar+charger&dpPl=1&dpID=41AwgKykXnL&ref=plSrch

I got one of these last summer for my birthday and love it:

http://www.amazon.com/X-DRAGON-Efficency-Technology-Smartphones-Foldable/dp/B00NGKPX4Y/ref=sr_1_2?ie=UTF8&qid=1449512304&sr=8-2&keywords=dragon+x

It's certainly not cheap, but I have a fold-out solar charger that I attach to a 22000 mAh battery:

Charger: http://smile.amazon.com/dp/B00NGKPX4Y
Battery: http://smile.amazon.com/dp/B00FDK2G2C

That way I charge the battery while I have the solar panel in the sun, and the charger then can be used to power anything USB that I might need. It's not particularly cost effective, but it's a sub-100 dollar portable solution that has worked really well for me so far on all of my trips.

Tesla should make a solar sun shade to go in your front window too. Something like this could be patched together for foldable solar energy that will keep your car cool and charged.

You could even keep it self-contained so you can use it without needing the car. Traveling somewhere in your Tesla? Well now you're bringing some solar power with you.

I have something like this: http://amzn.to/1FwjMrX. I use it to charge a battery pack like this: http://amzn.to/1GRSb2X. It is sufficient for phones and cameras and the like.

Non-mobile: http://www.amazon.com/dp/B00NGKPX4Y/ref=mp_s_a_1_4?qid=1427551387&sr=8-4&pi=AC_SX110_SY165_QL70&keywords=portable+solar+charger&dpPl=1&dpID=41AwgKykXnL&ref=plSrch

^That's ^why ^I'm ^here, ^I ^don't ^judge ^you. ^PM ^/u/xl0 ^if ^I'm ^causing ^any ^trouble. ^WUT?

Buy one worth using:

http://www.amazon.com/gp/product/B012YUJJM8

http://www.amazon.com/X-DRAGON-Efficency-Technology-Smartphones-Foldable/dp/B00NGKPX4Y

It's got USB ports for charging typical mobile devices.

Get this charger, which has both USB in (for charging batteries) and USB out (for using the device as a power-pack)...
http://www.amazon.ca/gp/product/B00WFXWUOE

It charges NiCad, NiMH, and Li-Ion cells, and comes with an 18650 which is kind of universal and can be used to power other devices.

See also:

/r/18650masterrace/

As other mentioned - solar chargers aren't all rosy when it comes to bicycle touring:

• Power generation varies tremendously depending on conditions - it is much more viable in sunny areas with little cover. Traveling though forests in overcast weather will heavily cut into energy production. This means that you probably want a large power bank anyway - to use it as a buffer.
  
• To get some decent amount of power going throughout an average day you need something much bigger than map case. Like several times the size. It probably should cover the tops of both your rear panniers.
  
• Solar panel of that size despite being just a thin folding piece does weight around half kilo - which is about as much as a very big powerbank that is independent from weather and can be stowed away in whatever corner of your panniers.
  
• Avoid powerbanks with integrated solar panel on the top. Solar panel of that size is basically useless.
  
  That said there are conditions that make using them a less of a bad idea:
  
  
• Your power consumption is actually very low, because you are using the phone only occasionally and it lasts several days on its battery.
  
• You expect lots of sun all around.
  
• You will be traveling for a long time in largely uninhabited area.
  
  Alternatives would be:
  
  
• A big power bank or two. Especially on shorter trips this is probably the best option.
  
• Top up your reserves in electric outlets along the way. For example some campsites might have them available.
  
• Dynamo hub with USB charger. Might be viable as long as your power needs are moderate. I have mixed feelings about it since even if you already have a dynamo hub the rest of USB setup can be surprisingly expensive. Its biggest advantage is that it works all the time you are riding regardless of weather. And its biggest disadvantage is that it only works when you are riding.