Charging eBike Battery with Solar I need some advice / info on solar charging an eBike battery. We have two RadRovers from Rad Power Bikes. They are powered with a Panasonic Dolphin 48V, 11.6Ah Lithium-Ion battery https://www.radpowerbikes.com/collections/replacement-parts/products/radrover-battery-pack.

We are planing a road trip from the North West US down south and would like to extend the range of the bikes. The specs say that the range is between 20 and 40 miles depending on how you ride. We are planning on using the low pedal-assist setting as much as possible, so we should be able to get to 40 miles or above.

We are bringing a second battery so we should be able to count on 70 to 80 miles a day. With that said, I’d like to rig up a solar set up to extend our range even further. Ideally, we’d have it set up so that the solar panel is plugged directly into the battery being used to extend the range.

I have found these 100w folding solar panel that will work for us https://www.amazon.com/dp/B071YP7X4F/ref=psdc_2236628011_t3_B01M28W7KR.

We can attach this to the rear of the bike with a frame. However, the panel will be fixed in a flat horizontal position, and will not always be in direct sunlight, but it’ll still be better than nothing I figure. If we can get just a little extra boost in between plugging in for a recharge, its worth it. My question is, is it possible for us to plug directly into the battery that is currently powering the bike? If not I’ll just charge the spare battery while in transit, but the first option is preferred. Also, what additional equipment do I need to achieve this? I know I need a controller, but I am not familiar with how this works exactly. A link to an ideal controller would be much appreciated.

Finally, if I then want to change the solar charger over to this laptop battery to charge it on occasion https://www.voltaicsystems.com/v72, would this same controller be used? How would this work.

I really appreciate any advice and info you can give us.
A 100 watt solar panel is nominal watts under ideal situations. You'll be lucky to get 25 watts/hr tied to the back of your bike - and this would be only for a few hours of the day, from 11a to 3p. 

Given that your bike is likely using at least 100-200 watts/hr even on low pedal assist, you're only going to gain 5-10% more range over the entire day. From experience, even with low pedal assist, its highly unlikely you'll get anywhere near the maximum (or even middle) advertised range of the ebike. 

There is a further complication that  your battery management system won't allow you to charge while biking. Many if not most don't.  So you can only charge the spare pack and you'll have to figure out how to convert the solar panel to the right D.C. voltage and amperage for your charger. If you overcharge or overvolt, a poorly design lithium pack can go up in flames.   

It'd be much easier and safer logistically to just bring another spare battery pack or two. I assume you'll be pulling trailers and as a result your mileage will be even further reduced but it means you can carry more. Just load up your trailer with spare packs and bring multiple chargers. Forget solar, it's not worth the hassle. The one exception would be to use solar to charge your iPhone/iPad and other electronic devices -- it's relatively easy to find small solar chargers that have USB leads.