Can e-bike batteries be charged with solar panels?

Kapt Irk

New Member
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.
 

Kapt Irk

New Member
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.
 

Kapt Irk

New Member
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.

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

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lilrich

Member
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.
 

John U

New Member
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.
 

Ann M.

Well-Known Member
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.
 

Sandstone

New Member
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!
 

Mike's E-Bikes

Well-Known Member
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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3toesloth

New Member
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.
 

SOLARebike

New Member
I'm writing this for the random stranger who had a great idea, Googled "solar charge ebike battery", clicked on the first link and then read all the way to the bottom of page 2 of this thread. Congratulations fellow internet researcher. You have demonstrated perseverance and tenacity, both of which will serve you well on your quest!

About me: I have logged 50,000 miles (80,000 km) on ebikes over the past 13 years. Most of those were commuting miles without solar panels but several thousand were touring miles with solar panels for charging the bike. I have built several solar ebikes over the years and I'm pleased to report that it is indeed possible to combine these technologies. Whether or not it makes sense to do so will depend on your goals. More on that later.

To answer the OP's question, if you're only doing a couple of weekend ebike trips each year my advice would be to skip the solar panels, borrow a friend’s battery and charger in addition to your own and find electrical outlets en route. In fact, anyone who has reliable access to electrical outlets at the end of each day will find solar ebikes less convenient and more expensive. Assuming you can travel to your fishing destination on one battery charge from home and there are no outlets at your destination but you're going to spend a couple of days in the same place and you only need to top off your battery for the return trip home then you could get a 50 watt panel and be good to go but this is a very narrow use case.

However, if we're talking about serious long-distance touring in the range of hundreds or thousands of miles then solar can be both feasible and economical, especially if your route takes you away from electrical outlets.

You can use any solar panel you want but "semi flexible" panels made with Sunpower cells for boats and RVs are your best choice in terms of power per unit weight and ability to withstand rough treatment on a bike. You can find them in all kinds of sizes on your favorite shopping site for around US$2 per watt and up. Traditional glass/aluminum frame rooftop panels are too heavy and should be avoided. "Folding" panels of the "solar blanket" variety are overpriced and impractical unless your idea of touring involves only 1-2 hours of riding per day and you absolutely, positively must stow your panels while riding because you're touring Ethiopia and the local children are throwing rocks at you.

Everyone else, please stop asking "how long will it take to charge my battery?" That's your grid-based ride-charge-ride habit talking. Solar ebikes are different. On a properly configured solar ebike, most of the solar energy is used directly by the motor controller while riding without a wasteful round trip through the battery. You still need a battery to collect solar energy when you stop, for extra help up hills, when it's cloudy, for regenerative braking, etc. Ignore the YouTube videos demonstrating "no battery" solar conversions unless your intent is to ride to the end of your street and back and then brag about it on InstaGram.

The question you should be asking is "how many miles per day can I get with a 100 watt solar panel? 200 watt? 400 watt?" The answer is about 3.5 to 4 watt-hours per watt in the summer. Assuming you can manage to pack light and always pedal at a moderate effort then you can expect to consume about 15 watt-hours per mile (9 Wh/km) while averaging 14 mph (23 kph). That means the 100 watt panel will get you 23 miles per day (100*3.5/15), the 200 watt panel 46 miles per day and the 400 watt panel 93 miles per day or 37 km, 74 km and 150 km respectively. Obviously, if you're riding uphill into a headwind in the rain without pedaling then your mileage will vary. These are long-term average values. You’ll get more on a sunny day, less on a cloudy day. If you're physically unable to pedal, cut these range values in half.
  • 100 watts: you're either riding a very short distance each day or you're riding from electrical outlet to outlet, supplementing a bit with solar or maybe you just like the attention you get from having a solar panel on your bike (there's an accompanying paparazzi effect)
  • 200 watts: bare minimum for off-grid ebike touring, anything less than this and you could travel further each day by ditching the solar panel, motor and battery weight (assuming you're physically fit)
  • 400 watts: starting to get seriously heavy and unwieldy, borderline unrideable if electrical assist fails
The catch is that you must mount your solar panel so that it collects energy all day whether you are riding or not. If you cannot accept this then solar ebikes are not for you. This is the only way the weight/energy ratio makes sense. The simplest option is a bike trailer. Most trailers will fit a 100-150 watt panel easily. Beyond that, you will need to get creative. Recumbents and cargo bikes are popular in the 200-400 watt category but I've seen some awkward attempts to attach this much to a conventional upright bike.

The size of your battery has some bearing on the efficiency of your system but does not determine your range in an off-grid situation. Assuming you're trying to maximize distance traveled in a day, a bigger battery means you can take longer breaks before you battery hits 4.2V/cell at which point you have to choose between getting back on the road or wasting potential solar energy because it has nowhere to go. That's right, longer charge times are actually a feature. Conversely, an undersized battery (300-400 Wh) coupled with a large solar panel may run into problems with too much charging current for the battery cells or the BMS to handle. In that case, you’ll need to explore getting a bigger battery or using multiple batteries with multiple charge controllers.

Speaking of which, how do you connect your solar panels to your battery? You’ll need a "boost solar charge controller." Just copy and paste those words into your favorite shopping site. You should find a couple of inexpensive Chinese models with MPPT for around US$30-45. The output can be programmed for 36V, 48V or 52V lithium packs. If you have the budget, you should get a Genasun boost controller for US$205. These are not programmable but are available in fixed output voltages and are fully potted and waterproof instead of having loud cooling fans which suck in dust and moisture like some of the cheaper models.

These controllers have PV input ranges which will work with most solar panels -- just make sure that the open circuit voltage of your panel ("Voc") is less than your battery voltage when empty (around 3.3V per cell) or you may find that you are not able to charge when the input voltage is higher than the output voltage under some conditions (low battery on a cold day). You may be able to connect two small panels in parallel but with larger panels that will likely exceed the maximum input current so you may need multiple charge controllers. A higher input voltage will result in better controller efficiency than a lower input voltage but connecting panels in parallel gives you better partial shading mitigation so there are trade-offs to be made. Read the specifications. I mean it.

If you have a Bosch, Yamaha or Shimano battery... I offer you my condolences. These closed, proprietary systems make it much more difficult to modify and enjoy your bike as you see fit. They’re well-engineered systems designed to maximize corporate shareholder value and minimize liability and warranty claims. They have no interest in helping you with your wacky solar modification project or supporting inter-operability with equipment from other vendors. If you're doing pre-purchase research and solar charging is important to you then brands which reject open standards do not belong on your short list.

I’ve read that you can trick the Bosch batteries into accepting a charge from a non-Bosch source by applying +5V to the signal pin and keeping charge current at 4A or less. If anyone knows a similar trick that will work with Yamaha or Shimano, please share with the rest of us? I know several solar ebike enthusiasts who charge using AC inverters on the bike but these workarounds are heavy and inefficient. They should only be considered as an option of last resort.

I have written extensively about my solar conversions. I mention this as proof of real world experience in this subject matter and not as an example of a low cost beginner project. Hopefully, my build will provide some inspiration for those of you who managed to read past the negative "it can't be done" posts above. You can do it. Start small and keep it simple. Add more later after you've had your first success. It’s not rocket science. If budget is an issue, you may find used solar panels on eBay, craigslist or your local equivalent. Or reach out to local solar installers or RV/boat supply shops and ask if they have any returned, blemished or damaged panels they're willing to donate to you. Most of all, stop "thinking about it" and get out there and start doing something about it.

My current build has a 315 watt solar array good for around 80 miles (130km) per day. Just for fun, I recently did a 207 mile (333km) single-day ride using 784 Wh from grid-charged batteries and generating 2266 solar Wh. Here's some video.


If you want to learn more, I recommend watching the following presentation from someone who is far more knowledgeable than I.


Happy solar biking.
 
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webcurl

Active Member
In fact, they sell the Bosch connector separately so you could buy just the connector, wire it to a boost solar charge controller, supply +5V to the interlock pin and you've got DC-DC solar charging without any silly AC conversion nonsense. I'm almost tempted to make a few of these and put them up on eBay. Parts, shipping and labor would mean I would need to charge at least US$200.
There seems to be a distinct lack of reliable information worldwide on this "+5VDC on CAN bus line trick", the discontinued 12V Bosch Travel charger & powerbutler.de in regards to newer Bosch batteries & Y-Cables (dual battery setup).
 

FlatSix911

Well-Known Member
I'm writing this for the random stranger who had a great idea, Googled "solar charge ebike battery", clicked on the first link and then read all the way to the bottom of page 2 of this thread. Congratulations fellow internet researcher. You have demonstrated perseverance and tenacity, both of which will serve you well on your quest!

About me: I have logged 50,000 miles (80,000 km) on ebikes over the past 13 years. Most of those were commuting miles without solar panels but several thousand were touring miles with solar panels for charging the bike. I have built several solar ebikes over the years and I'm pleased to report that it is indeed possible to combine these technologies. Whether or not it makes sense to do so will depend on your goals. More on that later.

To answer the OP's question, if you're only doing a couple of weekend ebike trips each year my advice would be to skip the solar panels, borrow a friend’s battery and charger in addition to your own and find electrical outlets en route. In fact, anyone who has reliable access to electrical outlets at the end of each day will find solar ebikes less convenient and more expensive. Assuming you can travel to your fishing destination on one battery charge from home and there are no outlets at your destination but you're going to spend a couple of days in the same place and you only need to top off your battery for the return trip home then you could get a 50 watt panel and be good to go but this is a very narrow use case.

However, if we're talking about serious long-distance touring in the range of hundreds or thousands of miles then solar can be both feasible and economical, especially if your route takes you away from electrical outlets.

You can use any solar panel you want but "semi flexible" panels made with Sunpower cells for boats and RVs are your best choice in terms of power per unit weight and ability to withstand rough treatment on a bike. You can find them in all kinds of sizes on your favorite shopping site for around US$2 per watt and up. Traditional glass/aluminum frame rooftop panels are too heavy and should be avoided. "Folding" panels of the "solar blanket" variety are overpriced and impractical unless your idea of touring involves only 1-2 hours of riding per day and you absolutely, positively must stow your panels while riding because you're touring Ethiopia and the local children are throwing rocks at you.

Everyone else, please stop asking "how long will it take to charge my battery?" That's your grid-based ride-charge-ride habit talking. Solar ebikes are different. On a properly configured solar ebike, most of the solar energy is used directly by the motor controller while riding without a wasteful round trip through the battery. You still need a battery to collect solar energy when you stop, for extra help up hills, when it's cloudy, for regenerative braking, etc. Ignore the YouTube videos demonstrating "no battery" solar conversions unless your intent is to ride to the end of your street and back and then brag about it on InstaGram.

The question you should be asking is "how many miles per day can I get with a 100 watt solar panel? 200 watt? 400 watt?" The answer is about 3.5 to 4 watt-hours per watt in the summer. Assuming you can manage to pack light and always pedal at a moderate effort then you can expect to consume about 15 watt-hours per mile (9 Wh/km) while averaging 14 mph (23 kph). That means the 100 watt panel will get you 23 miles per day (100*3.5/15), the 200 watt panel 46 miles per day and the 400 watt panel 93 miles per day or 37 km, 74 km and 150 km respectively. Obviously, if you're riding uphill into a headwind in the rain without pedaling then your mileage will vary. These are long-term average values. You’ll get more on a sunny day, less on a cloudy day. If you're physically unable to pedal, cut these range values in half.
  • 100 watts: you're either riding a very short distance each day or you're riding from electrical outlet to outlet, supplementing a bit with solar or maybe you just like the attention you get from having a solar panel on your bike (there's an accompanying paparazzi effect)
  • 200 watts: bare minimum for off-grid ebike touring, anything less than this and you could travel further each day by ditching the solar panel, motor and battery weight (assuming you're physically fit)
  • 400 watts: starting to get seriously heavy and unwieldy, borderline unrideable if electrical assist fails
The catch is that you must mount your solar panel so that it collects energy all day whether you are riding or not. If you cannot accept this then solar ebikes are not for you. This is the only way the weight/energy ratio makes sense. The simplest option is a bike trailer. Most trailers will fit a 100-150 watt panel easily. Beyond that, you will need to get creative. Recumbents and cargo bikes are popular in the 200-400 watt category but I've seen some awkward attempts to attach this much to a conventional upright bike.

The size of your battery has some bearing on the efficiency of your system but does not determine your range in an off-grid situation. Assuming you're trying to maximize distance traveled in a day, a bigger battery means you can take longer breaks before you battery hits 4.2V/cell at which point you have to choose between getting back on the road or wasting potential solar energy because it has nowhere to go. That's right, longer charge times are actually a feature. Conversely, an undersized battery (300-400 Wh) coupled with a large solar panel may run into problems with too much charging current for the battery cells or the BMS to handle. In that case, you’ll need to explore getting a bigger battery or using multiple batteries with multiple charge controllers.

Speaking of which, how do you connect your solar panels to your battery? You’ll need a "boost solar charge controller." Just copy and paste those words into your favorite shopping site. You should find a couple of inexpensive Chinese models with MPPT for around US$30-45. The output can be programmed for 36V, 48V or 52V lithium packs. If you have the budget, you should get a Genasun boost controller for US$205. These are not programmable but are available in fixed output voltages and are fully potted and waterproof instead of having loud cooling fans which suck in dust and moisture like some of the cheaper models.

These controllers have PV input ranges which will work with most solar panels -- just make sure that the open circuit voltage of your panel ("Voc") is less than your battery voltage when empty (around 3.3V per cell) or you may find that you are not able to charge when the input voltage is higher than the output voltage under some conditions (low battery on a cold day). You may be able to connect two small panels in parallel but with larger panels that will likely exceed the maximum input current so you may need multiple charge controllers. A higher input voltage will result in better controller efficiency than a lower input voltage but connecting panels in parallel gives you better partial shading mitigation so there are trade-offs to be made. Read the specifications. I mean it.

If you have a Bosch, Yamaha or Shimano battery... I offer you my condolences. These closed, proprietary systems make it much more difficult to modify and enjoy your bike as you see fit. They’re well-engineered systems designed to maximize corporate shareholder value and minimize liability and warranty claims. They have no interest in helping you with your wacky solar modification project or supporting inter-operability with equipment from other vendors. If you're doing pre-purchase research and solar charging is important to you then brands which reject open standards do not belong on your short list.

I’ve read that you can trick the Bosch batteries into accepting a charge from a non-Bosch source by applying +5V to the signal pin and keeping charge current at 4A or less. If anyone knows a similar trick that will work with Yamaha or Shimano, please share with the rest of us? I know several solar ebike enthusiasts who charge using AC inverters on the bike but these workarounds are heavy and inefficient. They should only be considered as an option of last resort.

I have written extensively about my solar conversions. I mention this as proof of real world experience in this subject matter and not as an example of a low cost beginner project. Hopefully, my build will provide some inspiration for those of you who managed to read past the negative "it can't be done" posts above. You can do it. Start small and keep it simple. Add more later after you've had your first success. It’s not rocket science. If budget is an issue, you may find used solar panels on eBay, craigslist or your local equivalent. Or reach out to local solar installers or RV/boat supply shops and ask if they have any returned, blemished or damaged panels they're willing to donate to you. Most of all, stop "thinking about it" and get out there and start doing something about it.

My current build has a 315 watt solar array good for around 80 miles (130km) per day. Just for fun, I recently did a 207 mile (333km) single-day ride using 784 Wh from grid-charged batteries and generating 2266 solar Wh. Here's some video.


If you want to learn more, I recommend watching the following presentation from someone who is far more knowledgeable than I.


Happy solar biking.
Welcome to EBR and thanks for posting!
 

SOLARebike

New Member
There seems to be a distinct lack of reliable information worldwide on this "+5VDC on CAN bus line trick", the discontinued 12V Bosch Travel charger & powerbutler.de in regards to newer Bosch batteries & Y-Cables (dual battery setup).
Upon closer investigation, PowerButler looks like they weren't shipping outside Europe and the dead YouTube channel with the unanswered comments looks like they're not in business any more. I've deleted the post to avoid wasting anyone's time with them. I'd love to test some Bosch batteries but sadly all of my batteries are free of proprietary encumbrances and I don't know anyone who would be willing to let me play with theirs.

What i like most about this is: "Operating Temperature: 40-85 degrees" !
And secondly "Maximum Power (pm)" :)
Oh, and thirdly "Power Tolerance: -5%" :)
The first two are just lazy typos while the -5% power tolerance is incomplete but not surprising. PV modules are commonly rated with power tolerances with -5w/+5w (US, a few years ago) or 0/+5w (Europe, due to different laws and US now as well) as the PV cells have manufacturing variances and the PV modules have cell mismatch so all manufacturers have to bin the power ratings this way. This is why you typically see PV module datasheets for the same module but listing, say "355w, 360w, 365w, 370w" variants of the same module. They all come off the same assembly line and they just put a different sticker on them depending on how they test when done.

I'm more offended by the price. $900 for 205 watts? That's $4.39/watt! Unless these Rambos are adding value to what they're selling, you can and should get the same quality from the usual scumbags (AliExpress, Alibaba, eBay, Amazon) for $1 to $2 per watt. Given the lack of attention to detail in spelling out the product specs, I wouldn't hold my breath.

And what's the deal with photographing the product on a cloudy day? It's a notch above the hatchet-job PhotoShop abominations I keep seeing in so many other folding solar panel product postings but come on, you're selling a solar panel. At least pretend you know how to use it.

I've been looking into these folding panels made with Sunpower cells and overall, I'm impressed. My neighbor got this Jackery-branded 60W model and he likes it for his non-ebike charging needs. The good news is that this 2x3 cell form factor fits easily in a 40L Ortlieb pannier. The bad news is that it's kinda heavy... significantly heavier than and equal size boat/RV-grade semi-flex module because they use a thick sheet of fiberglass as the backing plate to make them more robust. I like the added stiffness but they prioritized low cost over low weight which is unfortunate if you're stuffing these into a bike bag.

Jackery-60W.jpg
 
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Handlebars

Well-Known Member