Can e-bike batteries be charged with solar panels?

Of course there are variables with solar, but not sure why you say it would take 2 days to recharge the battery. My Rad Power charger is only 2 amps @ 48 volts. The specs in the owner's manual indicates a nearly depleted 48 volt 14Ah battery takes 5.5 hours to recharge with the supplied 2 amp charger.

My suggestion for the 20 watt panels is that they're fairly small, since one would need 4 of them to create 48+ volts. Assuming one's battery is not fully discharged, a few hours of good sunlight will still help, without the need to haul around a monstrous array.
Of course, there are variables to consider with solar charging (seasons, terrain, shade, etc.).

My suggestion for 4x 20 watt panels is that they aren't very large and could be built into a 48 volt array without taking up a large amount of space on a bike, without towing a big box behind you. One could be charging a spare battery whilst riding or camping out for the day. Even though it may not provide a full charge during that particular day, at least it would be providing a fairly good charge.

The charger that came with my Rad bike is 48 volt @ 2 amps. The operator's manual indicates that the 14Ah battery that came with would fully charge from a deep discharge in 5.5 hours with that charger.

Yes, a larger array (more wattage/current) would be more effective. Quality 30 watt panels would increase the current to 1.7 amps ... 40 watt panel is capable of approx 2.5 amps.
Sorry for the double post. I didn't see my first reply when I checked back in, so re-posted.

I've been working with solar, fixed and mobile, for quite a few years. I have a 4kW system that I engineered and installed at my CA home in 2001, and more recently, a small 1K system at my AZ vacation home.

1. My '84 Vanagon (200 watts)
2. My '96 Tacoma (80 watts)
3. Building the AZ array 2016


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As I answer the folks at the Midwest Renewable Energy Association at their fair each year "electricity is not prejudice it does not care how you produce it". If I plug into the grid, the bike is solar, wind, gas, coal and nuclear powered. How you charge up your battery is not dependent on the source of electricity. Charge rates and times will vary dependent on voltage and amps but source is not a factor. Always design your charging system to maintain safe charge rates and levels especially with lithium based chemistries.
I just bought a Yeti 400 (400 watt hour) "generator" battery with a Boulder 100 solar panel (100 watts) solar panel. This combo works to charge my Bosch-based ebikes. Exciting stuff for camping and maybe for a charge-as-you-go bike trailer.
For those of you who are curious about the Leos bikes, including that design award winning (2015) Carbon Fiber bike with the imbedded solar panels, there's a lot of interesting info about the general frame design and integrated battery on the Leos website. Not too sure that technology is ready for prime time; they claim at middle power use, the rider gets about 15km; that's a little over 9 miles and doesn't account for wind or hills or bigger riders. I think as our solar technology improves with higher power density and higher conversion rates from panels, paints and the like we'll start to see more practical versions of ebikes with solar integrated.
I have been wondering about what is likely an easier to solve version of this problem, in that I have a small motorhome with 200W portable solar panels already. I usually camp off the grid and would like to take our two 48V mountain bikes out in the boonies when we camp. So if I was using the bikes part of the day and needing to charge the batteries when I got back to camp, rather than use my standard 110V charger plugged into an invertor on the two deep cycle 6V batteries charged by either the solar panel set-up I already have, or (worse yet) running the bloody generator for hours, I sure would like to have a charger that would take the variable DC output of the solar panels, or for that matter, the RV alternator while travelling, and charge the bike batteries directly DC to DC, which as previously mentioned should be a lot more efficient than going from DC to AC to DC!
Sorry folks, but you are not going to get around the issue of having a storage battery in between the solar panel, and your charger, and also needing an invertor. The chargers are designed specifically for the ebike batteries. They are AC, and draw about 95 watts. Some a little less, some a little more.

Like someone else here in this thread found, you can utilize a Yeti 400, which has the battery and invertor built in. Plus at least 100 watt solar panel. 200 watts charge the battery faster on the Yeti, but it wont change the charge rate of your ebike battery.

I built my own for other reasons, and with a 100 Amphour Sealed AGM Battery, and Invertor, you can definitely charge your ebike battery. But its going to be slower. First you have to put the 100 watt power on for long enough to charge up the 100 AH battery. (The 100 AH AGM battery is going to have a much longer life than the crap in the Yeti.) Then using that with the invertor, you can plug in your existing charger. (I also have the Yeti 400 too. I got it 'free' using bank card points. Its frankly junk.)

That operation is going to go slower than plugging into a wall outlet. I've tried it. Its not worth it. You'll pay $800 to $1000 to put together a SAFE and reliable DIY package. Versus 8 cents per charge from the outlet. Um, thats 12,500 charges to break even. If you want to use this for camping or off grid, so be it. But you are still better off buying a propane, or gas generator, with a quality invertor.

If someone says they can do it cheaper, or charge it faster using solar, they are lying.

p.s. the charge and discharge characteristics of a lead acid battery, are such that, if you are using 12 volts, you are going to want/need a 100 AH worth of capacity. If you don't, you are going to go through smaller lead acid batteries in no time. they wont last 2 seasons. Sure you could buy a lithium 100 AH battery for storage, but that will cost you and an arm and two legs. Don't confuse the fact that your ebike battery is only 14 or 17 AH, and 48 volts versus the sizing of the intermediate storage battery at 100 AH. You need to understand the math, and the conversions, power draw from the charger at AC, etc. If you do, then you will know that I am right about the sizing choice of the 100 AH capacity battery for storage and semi practical functioning. The entire package is a b*tch to haul around. Very heavy.

Attached are some photos of a package i built, using a 100 watt solar panel. Mounted it all on a trailer, that could also tow ebikes.


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Sorry folks, but you are not going to get around the issue of having a storage battery in between the solar panel, and your charger, and also needing an invertor. The chargers are designed specifically for the ebike batteries. They are AC, and draw about 95 watts. Some a little less, some a little more.
Why use the original AC charger? There are tons of DC/DC chargers available, and a few example builds on the first page of the thread.