Solar only ebike?

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patrickza   1 kW

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Solar only ebike?

Post by patrickza » Aug 20 2010 3:29am

I've had an idea for a while now of travelling through africa on an ebike, more exactly a tadpole e-trike. Ideally I'd go from my place in Johannesburg, to Cape Maclear on Lake Malawi and back. Now obviously this is a long way, about 2000km each way. I've read trip reports, and a lot of unpowered bike tourists manage about 100km per day pretty easily, so I'd be looking at 40 days worth of riding time, and I imagine about two months to complete the trip.

So what I was wondering is, how feasable is it to run an ebike directly off solar panels, removing the batteries from the equation completly. It doesn't need to be fast, nor does it need to be able to carry me up a hill on it's own, but how much pedal assist could I potentially get? I know it would be simpler with a battery pack that charges off solar, but lets say for arguments sake I don't go that route.

If I put a canopy on the bike and cover it in effecient solar panels I imagine I could get around 250w worth of power, depending on the size of canopy. I saw this trike here which works along those lines: http://www.solartrike.com/canopysolartrike.html . Now I never trust sites claims when they have a financial interest in stake, so what do you guys think is possible? Could I hook up a solar panel, directly to a controller and a small motor. I'm thinking a high wind version of the 9C to keep things simple and reliable.
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neptronix   100 GW

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Re: Solar only ebike?

Post by neptronix » Aug 20 2010 4:16am

Solar power's performance for applications like these is a joke.

For one, you would need to basically be coated in panels. We're talking 1000's of dollars worth. I've seen 250w panels, they are huge, feel like they're 75lb and only put out 12-24 volts!!
For two, the weight of all those solar panels would make pedaling the bike somewhat useless.
For three, you can spend all that money on an uber battery pack, stationary solar/wind turbine charger, and get better performance overall.

Look at that solar trike, the panel is angled in a fixed position. This means it will work well only for a certain part of the day.
It weighs 162lb. The peak power is 170 watts, most likely at 24 volts. That's peak power, so expect anywhere from 100% to 0% of that power.

Altogether you are better off pedaling. Unless you are *only* riding during peak sunlight hours... then it is like an eZip with a dying battery.. maybe you'll go 7mph on a good day with that solar power.

There is a reason why some batteries are included!

Sorry to burst your bubble. But go read around and you'll quickly realize why nobody's running things straight off of solar panels.
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dogman dan   100 GW

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Re: Solar only ebike?

Post by dogman dan » Aug 20 2010 6:00am

Lugging a 250 watt panel would be a lot to carry. And it would only put out an actual 250 watts when pointed exactly at the sun, on a perfect clear day.

It might work though, if you towed a fairly big trailer of panels, kept em adjusted to point at the sun, and had them hooked to at least some battery so you could stop occasionaly for a bit more charge. When they do this with solar car races, it's lots of sitting in the sun charging, then a run with some sun helping the batteries. They usually have a huge number of solar cells. But it would not work as good as carrying a tiny generator I bet. I've done that myself, and my small generator is just too heavy, at 100 pounds. But the new hondas are lighter, and might work quite well if hauled on a trailer.

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Re: Solar only ebike?

Post by Evoforce » Aug 20 2010 6:08am

Solar is not practical for what You desire. If it was, we would all be skipping the use of batteries. I power my home with solar and you would be surprised how much panel it takes to power your hair dryer alone!
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Re: Solar only ebike?

Post by Drunkskunk » Aug 20 2010 8:26am

Possably, if you got ahold of some very light pannels, you could carry enough to charge some batteries for 100km worth of distance.
But wind resistance would be a huge factor. The only design I could see working is a portable solar pannel you lay out during the day while you sleep, then ride through the night. it would be impracticle to try to ride with an array that large spread out.
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Dave Sloan   100 W

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Re: Solar only ebike?

Post by Dave Sloan » Aug 20 2010 9:33am

The most efficient solar panels are now 23 percent efficient - but cost is out of your range. At 200 dollars US a panel for 80w you would need six of them at two by four feet(monocrystaline) to produce a max of about 420 watts at the wheel (taking into account inefficiency). They would have to sit above your head and would weigh approximately 120 pounds. You would need some way to hold power to the wheel so some batteries would be required (another expense). To be stable the trike would have to be low to the ground and as said before wind is a BIG factor. More energy would be gained by using a sail and waiting for a windy day with wind in the right direction (indirect solar power). You would probably reach your destination quicker and cheaper using this method.
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Re: Solar only ebike?

Post by torker » Aug 20 2010 9:38am

You would have to use thin film solar and not panels. Like the solar race cars. They use batteries also. Not sure how much battery they use.http://www.worldsolarchallenge.org/photos
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Re: Solar only ebike?

Post by John in CR » Aug 20 2010 10:31am

Wow, the negativity is surprising. Panels are built for static installations where weight is all but irrelevant. You'd need to do your own panels, just like the solar racers have done for decades. Thin film would be great if you can source it, but people have used the crystal based cells for decades, and you can get them right on Ebay for about 50 cents per watt for 16-17% efficiency cells. That means just 1 square meter of cells would provide more power than your legs could for most of the day. I don't know about you but I think I'd want a bit more shade than that.

I'm going to be putting some cells on a bike, but as a charger, since the bike sits most of the day. I'll probably be able to get away with less than 100W.

John

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Re: Solar only ebike?

Post by veloman » Aug 20 2010 11:52am

The cheap cells on ebay weigh 6 grams each, which came out to just about a pound for 120watts. Now, of course you need to build a panel with them, and that is up to you how you do it. But is it possible to build an effective, sturdy panel of 120watts for a total weight of say 10lbs? Maybe 15lbs? Add in some controls and I think it's possible, to do the whole 120watt setup with less than 20lbs realistically, maybe even closer to 12lbs. 12lbs would only require an additional 25watts during a high pace, steep climb. On the flats, there wouldn't be much frontal area if you designed the panels properly, and still only require <20watts additional at 20mph. We aren't racing down a highway at 50mph here.
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dogman dan   100 GW

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Re: Solar only ebike?

Post by dogman dan » Aug 20 2010 2:24pm

It takes a lot of panel. One of those posts above talks about riding around with a panel 4' wide and 12' long over your head. yeah right.

It might work well enough though, to do something along the lines of flexible panels that roll out to charge when you stop, combined with something smaller that still collects while you ride.

Sorry, but I still just can't think of any solar setup that could provide the same power at the same weight as a small generator. Listening to it and smelling its fumes though, uggh. And if you carried that much weight in good battery, you'd have lots of range to get between pretty distant plugs.

Back to solar, I just don't see solar without a battery being much of a practical way to go. But maybe you could haul a trailer with two or three of those 80 watt panels, and spend the middle of the day parked with them pointed 90 degrees to the sun. It could certainly make a range extender if nothing else.

It's going to be some kind of compromise, unless you build a full on solar car or trike, with a roof 8' wide and 16' long covered with cells.

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Re: Solar only ebike?

Post by torker » Aug 20 2010 3:13pm

John in CR wrote:Wow, the negativity is surprising. Panels are built for static installations where weight is all but irrelevant. You'd need to do your own panels, just like the solar racers have done for decades. Thin film would be great if you can source it, but people have used the crystal based cells for decades, and you can get them right on Ebay for about 50 cents per watt for 16-17% efficiency cells. That means just 1 square meter of cells would provide more power than your legs could for most of the day. I don't know about you but I think I'd want a bit more shade than that.

I'm going to be putting some cells on a bike, but as a charger, since the bike sits most of the day. I'll probably be able to get away with less than 100W.

John

I think one square meter would only make like40 watts at 36 volts. Less on 48 maybe 30 watts. Not much. That is why the solar racers cars are designed the way they are and covered with cells. And I'm pretty sure they run less volts than most of us,maybe
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Re: Solar only ebike?

Post by dogman dan » Aug 20 2010 3:18pm

I forgot about that too. Those 12v 80 watt panels would take three of em to make 80 watts of 36v. And you'd only get half that most of the day, unless you stopped to point em at the sun perfect. So a six foot by 4 foot panel would get you 40 watts. Woo hoo!

Still, it's not impossible, just awkward. You could charge from sunup till the battery got full, or sundown. Fold up the panels to a 2'x4' package and carry on a trailer as far as a 36v 20 ah battery can go on it. Also charge at all avaliable plugs. Fine if you got time.

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Re: Solar only ebike?

Post by AmpEater » Aug 20 2010 3:55pm

dogman wrote:I forgot about that too. Those 12v 80 watt panels would take three of em to make 80 watts of 36v.
That's not how it works

You need a grasp of watts, volts, amps, to hang with this pack

Watts = volts x amps

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Re: Solar only ebike?

Post by swbluto » Aug 20 2010 4:06pm

You'll be wishing for at least a small battery. When a big cloud comes by or you go under a swath of trees (And *gasp*, up a hill at the same time!)... :)

But, yeah, even 200 watts would be good to have. That's like 13-14 mph unassisted on a regular standup bike on flat land. It's peanuts without appropriate gearing on hills.

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Re: Solar only ebike?

Post by torker » Aug 20 2010 4:44pm

Yea to get anywhere near that would take a few meters of realestate and if it was part of the body it all wouldn't be at the right angle to the sun at any one time. So you would need extra to cover that loss.
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Re: Solar only ebike?

Post by FMB42 » Aug 20 2010 5:18pm

Ampeater wrote:

"That's not how it works"

Three 12volt 80watt solar panels wired in series would give you 36volts @ 80watts.

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Re: Solar only ebike?

Post by John in CR » Aug 20 2010 6:11pm

An the negativity continues. The sun shines at 1000 watts per meter (good enough for an average). A panel made of 15-17% efficient cells would theoretically put out 150+ watts, so 100 watts output for hours either side of midday isn't unreasonable. The original poster is talking about maybe doing this trek pedal only, so no doubt 100 watts would be a welcome assist, and with DIY'd panels the form could easily enhance aerodynamics and maybe get some shade out of the deal too.

I too would want a battery aboard. Then the solar panel output isn't lost while stopped (it is supposed to be a fun sightseeing ride, not just non-stop pedal torture from dawn till dusk right?). Also, it would provide power for some nice LED lighting at night. Then once the sun is up in the morning the panel output starts charging the battery right away, even if the output is too low to actually power the bike significantly. The stop for lunch during the hottest part of the day would be prime time for the panel that would go to waste with no battery to charge. Even a 5kg lithium battery would come in really handy.

BTW, three 12V 80 watt panels would be 240 watts. In series they'd be 36V with the same current as one (6.7A rated) and in parallel they'd be 12V with 20A. I think PV panels are rated at peak output, so to get a real 100W for much of the day you'd probably need 2 80W panels, but they're not really made for mobile installations. A a much more aerodynamic and lightweight DIY job has the potential to be drastically better, just like they do for those solar racers.

John

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Re: Solar only ebike?

Post by Evoforce » Aug 20 2010 6:59pm

Again I say, not trying to be negative, it is not pratical. All things considered. If it were, I would already be doing it. Now to give your batteries a little trickle charge (maybe) to extend milage or opportunity charge, I say yes, go for it! To replace your batteries, no, not a wise decision. You have not stated what voltage you desire to run your ebike. Several have pointed out very important drawbacks. WIND, lack of enough surface area on bike, position of panels in relation to sun, the need for batteries anyway, the cost of solar, the weight of solar, the need for specialized vehicle/bike and/or panels and/or trailer, etc... Yes you could attach a small solar panel and a small motor without a battery and pedal all the way. Claim that you used solar power to get you from point A to point B (technically true). In the end you would have had very little actual benefit, especially not cost wise. Sorry for my cold north wind. I really wish I could tell you what you wanted to hear. :wink:
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Re: Solar only ebike?

Post by John in CR » Aug 20 2010 7:20pm

Evoforce,

Did you miss that it's a tadpole trike, so properly done solar panels could easily enhance aerodynamics, and over a meter of surface area is quite possible? I definitely agree though that with a battery makes more sense than without, but you seem to be stuck on store bought panels when DIY panels could weigh a fraction, cost a fraction, and increase aerodynamics. Just 100W of average assist through much of the day would make a 4000km journey there and back an enjoyable ride verses a potentially grueling trek.

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Re: Solar only ebike?

Post by AmpEater » Aug 20 2010 7:35pm

FMB42 wrote:Ampeater wrote:

"That's not how it works"

Three 12volt 80watt solar panels wired in series would give you 36volts @ 80watts.
No, that still isn't how it works guys. Really?

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Re: Solar only ebike?

Post by AmpEater » Aug 20 2010 7:38pm

John in CR wrote:An the negativity continues. The sun shines at 1000 watts per meter (good enough for an average). A panel made of 15-17% efficient cells would theoretically put out 150+ watts, so 100 watts output for hours either side of midday isn't unreasonable. The original poster is talking about maybe doing this trek pedal only, so no doubt 100 watts would be a welcome assist, and with DIY'd panels the form could easily enhance aerodynamics and maybe get some shade out of the deal too.

BTW, three 12V 80 watt panels would be 240 watts. In series they'd be 36V with the same current as one (6.7A rated) and in parallel they'd be 12V with 20A.

John
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Re: Solar only ebike?

Post by dodjob » Aug 20 2010 7:44pm

I second that, The 15%-17% efficiency are only available when the sun is hitting the cells with the right angle (90°) just forget what you can get if you only deviate from 10 or more degres from this. Then this is an output at the pannels, then you will have your solar controller (absolutely necesary to reach the Pmax of the pannels), the bike controller and motor efficiency... the results will be quite disapointing at the wheel :-(
As it as been mentionned, increase your range is the only thing you will rich with solar pannels. There is a guy from Switzerland which has made a trip around the world with such configuration (solar+batteries) in a "car" and it has worked :-)
This post is nothing like negativism. Only a objective view of the actual limits of this technology. 80W pannels are already really uge (nearly 1m²), three of them would be way to much weight for the power you will get. Finally will have to add the weight of the 2 axis tracking system to try to keep your "official" 15% during your drive ;-)
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Re: Solar only ebike?

Post by John in CR » Aug 20 2010 8:12pm

Dodjob,

You have a valid point, but a big flat panel seems dangerous to me on such a lightweight vehicle. Instead, I'd go with about 300W worth of cells at different angles in an aerodynamic form on the trike oriented at different angles, including a gently curved shade over my head so I could reasonably expect 100W while the sun is shining good. Ultra cheap solar cells enable this, and it's exactly what I plan with my lower powered built in solar bike charger. ie I will have more cells on the sides than I do with good angles to the midday sun, but my goal is just 50 watts or so but mine is a bike, so I don't have nearly the surface area presented to a midday sun that a trike could have without negatively affecting aerodynamics.

To give you guys an idea of what may be possible, here's the one 6"x6" cell that I've fooled with and broke. That's a curve to less than a 1ft radius. Using 3"x6" cells you could also keep individual cells flat to form a curve. I plan to go with a much gentler curve with my cells because I don't want them be under that much stress long term, but if you look closely at the solar competition cars, some curve is absolutely possible, and it will add significant structural rigidity to the DIY panel. Add in some backside support of the curve with fiberglass plus epoxy (or vinyl ester resin for higher thermal limits), and it's easy to see how light, strong, rigid, aerodynamic panels are possible. Think cells DIY'd into a panel, not a heavy rectangular box that is already a panel, but has no place on any vehicle, except maybe on the moon that doesn't have an atmosphere.
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Re: Solar only ebike?

Post by Evoforce » Aug 21 2010 1:53am

I have plenty of experience with solar. I wish it were truly a viable thing to do at a reasonable expense. Sure if you could afford the solar cells that could harness the full spectrum of light similar to the ones they send into outerspace it might bring it closer to reality. Problem 1: The OP said they did not want to use a battery. Pretty much unless that idea is changed everything else is mute. Problem 2: Wind resistance and aerodynamics. Problem 3: shear size of surface area needed to produce enough electricity. Problem 4: Weight of whole vehicle (using flexible panels). Problem 5: Cost of producing a vehicle that even comes close to viable is expensive. Problem 6: Inefficient ability to harness sun due to moving platform. Problem 7: If the sun wasn't shining, you would not want to pedal this beast. I could go on... I have experimented with this stuff and have a deep desire to wish it were truly doable at the normal human level (no outerspace budget here). But at least 1 of you here is going to try for yourself. I think that is excellent! I found out for myself too. It is fun to experiment. I just love solar. A better experiment is to start adding solar to your house. Good luck! P.S. I charge my ebikes with solar. :mrgreen:
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                                                                                   Several 5403 motors, Phoenix Racer(5403) crystalyte suspension mtn bike LiFepo4 72/20.  (409) crystalyte 48 volt hardtail.   Phoenix Cruiser(5304)  LiFePo4 48/20.  First electric bike a 2009 XB 502-700 style, 36/20 sla scooter bike.  2) 2011 Nissan Leaf's in the mix.  Tesla Model S.  And solar!

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Re: Solar only ebike?

Post by dogman dan » Aug 21 2010 6:31am

Hey, I'm wrong when I write here all the time. Thanks for the slapdown. But I do belive I do understand at least one of the ways solar "works"

I live where the sun shines harder than just about anywhere in the US. But because of clouds, dirt on the panels, etc etc etc etc, even here the average is 6 hours of insolation per day. Most places in the world are much worse. You aint gonna get 16 hours of 80 watts out of any panel in a 16 hour day. That my freind is a fact that's been known since the 60's if not earlier. So even here in a best possible place for solar, you cut the rated wattage of the panel just about in half to know the average amount you are going to really get.

That's where I got the idea that an 80 watt panel is going to put out 40 watts on average. That will improve some of course, if you spend all day keeping that panel 90 degrees to the sun. At some point in the day, output may exceed 80 watts. Most of the day it will be less. Most of those solar cars spend a significant part of the day tilted into the sun to get a start in the morning with as full a charge as possible. They can run on just the panels when the sun is high, but mornings and late afternoons their output drops a lot.

I still think it could work as a range extender in a place with no power at a plug, but at times you'd end up mostly pedaling the weight around, or ending up with a pretty short daily range. But using the motor at 200 watt levels, you could go a long way on little as long as grades weren't too dang steep. Stripping down stock panels to the lightest possible weight would be a key to succeding with this, as John points out. Perhaps they could be carried in an areo configuration part of the day, and folded out flat for noon?

Practical or not, it would be a fun thing to play with, and see just what is actually possible.

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