I have bought various rechargeables (18650, 16340, and 14500’s) in the past and now I only use primaries (CR123A, or AA alkaline or preferably lithium). For me and my short trips it’s not worth the hassle. Primaries may be more expensive but they are simple and reliable. Throw a solar charger into the mix and the potential for problems increases, a lot. I would consider investing in energy efficient camera gear and if recharging your batteries was required than it may be better to use primaries to charge up the rechargeable. Problem is that I don’t think there is much on the market for this so you may need a bit of tinkering with ICs and a soldering iron.

To help you out I’ll list some of the potential downsides of portable solar panels:
-poor build quality
-unreliable
-fragile
-time consuming
-over inflated specifications
-maximum wattage only in direct full high noon sun with panel perpendicular to sunlight.
-doesn’t work in the dark
-overcast or shaded areas produce significantly less wattage

I’m sure others on the the forum can offer better practical advise.

How long is extended? More than 3 weeks?

I looked a solar chargers last year and instead opted to go with an Anker PowerCore 21,600mAh power bank. Actually went with 2. Over 10 days on the river I was able to charge batteries for the GoPro (at least 2 per day), the Canon D30 waterproof point and shoot, and the Nikon DSLR and barely got into the 2nd PowerCore by the end of the trip (probably had enough charged batteries that I could have finished the trip with just the one PowerCore). 

I think I would go with the solar charger for the 3rd power source, but since I could only really use it when at camp and the output is hampered by weather, it wasn't the best option for guaranteed power. That particular trip was sub arctic, so we had 24 hour daylight but it was a river trip so there was no way I could have kept the solar charger out in the canoe, and the weather was not great. For the weight and size the PowerCores were completely reliable, smaller and I think individually similar enough in weight to the solar charger that they were definitely the right choice for me. 
 

Well, thanks for the mention of the 18 month warranty. One of my Anker powercores died recently. I already bought a replacement but I just submitted a warranty claim for the last one, since I bought it 17 months ago!

Edit: To contribute to the topic, solar chargers are only useful if you get the right weather, and have the time and location to use them. Power packs can be used anywhere, any time, and you've got a much clearer idea of how juice you have left. 

Last edited by Uppa (6/21/2019 2:21 pm)

Over 3 weeks, I think the solar charger could add up to another power bank. 

I'll also note that we had lousy weather on that trip last year and ended up with longer days on the river than originally planned, which meant I got to use the DSLR a lot less than I had been hoping. 

If you're going to be out a full 21 days, compare to the 10 days I was, you might want to hold on to the solar charger. 

Let us know how the RAV powerbank works out too. I have a couple of USB powered RAV chargers for the camera batteries that have been working well. 

While making the Mark in the Park TV show, we had a three to two day buffer from Day 1 on battery packs. Check out episode 10 to see some of what we brought.  We could have brought enough power (an additional 5kg of pack weight) for the whole trip in power banks but if we were half way through the trip and more than half way through our banks then we were going to be screwed.  At least with a panel, you can do something about your power situation if you run out on day 18 of your 21 day trip.  I strongly recommend doing tests like seeing how long it takes to charge a power bank in full sunlight and on a cloudy day.  Also what does the panel do when the sun goes behind a cloud and comes back which happens very often.  Some power banks take up to 12 hours to charge at full power so you would need 12 hours of sunlight over a few days to get up to 100%.  

I also caution you, that panel might be "waterproof" with the port covers on but when you plug something in, the electronics become exposed.  It's okay for splashes like when switching sides for paddling but don't count on it working in, or after rain (or the power bank plugged into it as well).  

All in all, solar panels are great when it's sunny and with the long days right now, you could charge your camera batteries directly from it for your whole trip, having the battery banks as backups on cloudy or rainy days.  If you have rain and cloudy skies for 21 days, that would be crazy and extremely unlucky so I believe bring the panel would be great insurance and stress relief in the event you do run out later on.

Best of luck!