# Completely solar powered bike?

Discussion in 'Electric Bicycles' started by gameshark39, Mar 25, 2008.

1. ### gameshark39New Member

Is it possible to create an e-bike with a thin solar array attached to the back that is always charging the battery? Has anyone done this or something similar? I just was curious to know if it was possible and if so how much it would cost approximately.

2. ### gameshark39New Member

also has any company been able to create an electric bike which has the battery charged by pedaling?

What would be the point?

4. ### codi79Member

Good thinking, and good luck to you. Collect your solar calculators!

5. ### gameshark39New Member

dur the points would be to have the motor assist u when ur tired, and when u do pedal without it, it charges the motor again. i thought that much was obvious 0.o

6. ### motoredhobartNew Member

There wouldn't be much point charging from the pedals, converting the energy to electricity and back again you'd probably only end up with half of what you started with. The extra resistance any charging device would have would be hindering you from getting from point A to B as well. Just some basic physics..

7. ### loquinActive Member

Correct. Losses in the generator used to provide power to the battery recharge circuit make this a losing situation. With the intermediate generator, you would always be putting more power into the system than you can possibly take out.

Now, re the original question. There is currently no solar cells with an efficiency great enough to make driving the bike practical. The BEST you're going to get is about 20% conversion of light into electricity. A 3 foot by 3 foot solar panel at 20% efficiency would net you about 224 watts. Which could push you, very slowly, I would guess.

A better approach would be to have a smaller panel which could recharge your batteries during the day while you're at work. Suppose you have a 500 watt motor, and a 30 minute ride. a half hour ride at 500 watts is 250 watt-hours. This means that during the 8 hours (approximately) that you're at work, you would need 250 watt-hours of charge (plus the efficiency lossses in charging the battery.) If we assume 80% efficiency, that would mean 312 watt-hours total, or, an average hourly charge of 39 watts, which is a charging current of approximately 1.1 Amps at 36 volts. Since most of the 12 volt trickle chargers are on the order of half an amp, you would need at least 6 of these panels to recharge the battery while you work.

Last edited: Mar 31, 2008
8. ### StrykerGuest

why would anyone want it? uh to increase the range of your bike?

and yes they have it. The BionX set ups allow charging from pedaling. Since they are mostly a pedal assist bike, (although they do offer a thumb throttle for instant on), they have a 1-4 setting on the controller that allows for a regenerative setting, 4 being the hardest to pedal. This comes in handy when you are going down hill. This increases the bikes range. They also use regenerative braking, which does not replace braking but does help a lot, and again recharges the battery, Amazing stuff.
http://jvbike.com/eps_kit.htm
Scroll down and it will explain the system

Last edited by a moderator: Apr 7, 2008
9. ### loquinActive Member

The losses involved in putting power into a generator by peddling, and then moving that power to a battery, and then taking the poser from the battery to the motor make the work involved MORE than if you were peddling. Think about it. There are actually four energy changes taking place, and NONE of them are 100% efficient. The first involves converting mechanical energy to electrical with the generator. The second is converting electrical energy to Chemical in the battery when charging it. The third is converting chemical energy back to electrical when you want a boost, and the fourth is when you convert electrical energy back to mechancal with the motor.

A generator is (optimistically) about 75-80 percent efficient. Charging a battery and then retrieving the electricity is about 80 percent efficient. The electric motor is about 80 percent efficient. So, in order to provide 500 watt hours to the bike motor, you would have to peddle 500WH / (.75*.8*.8) or, approximately 1042 watts-hours. It's a LOT more efficient to just peddle the bike!

Now, as far as regenerative braking. That idea's been around for a long time. I read an article in the mid-70's in "The Mother Earth News," discussing building a hybrid car, using regenerative braking to help boost efficiency. And, it does help in extending the range of an electric hybrid. (an electric bike is a form of a hybrid. But, for that matter, so is a gasoline powered bike...)

10. ### StrykerGuest

You don't pedal the bike to charge the entire battery. Thats why there is a battery charger. Its there just to increase battery life when your headed down hill.That is why you can turn the pedal charge off. I have heard that there is up to a 3 to 1 exchange, 3 mile of pedaling earns you 1 mile of free ride. I read that on another forum so that is not from the manufacturer. There is some obvious benefit to the technology, or why would they put it on the unit. I am guessing there are engineers with a little more knowledge than I have creating it. The funny part is that they also made this part of the alarm. If someone moves your bike without entering the code, an alarm goes off and the controller sets to regen level 4 so its really hard to pedal. At that point the thief just picks up the bike and runs away, good effort though.
and yes I know regenerative braking has been around for a while, as has pedaling to create electricity. I have a hamster wheel that runs my air conditioner, (not really)

11. ### loquinActive Member

LOL. By the time I get to the top of a hill, I'm ready to coast. Regen braking would put some of the power expended back into the battery. But, it would have to be a LONG hill for me to be peddling on the way down!

12. ### billvonGuest

Yes. For thin film arrays you can get about 5 watts per square foot. Crystalline panels can get closer to 10 watts per square foot. Figure you can get 9 square feet on the back of a bike (3' x 3') so you'd be looking at 90 watts max. (Naturally that's when it's 50F out, with sun directly overhead and the panels completely unshaded.)

13. ### DrunkskunkMember

Loquin hit on what others have found on other forums. Over on Endless Sphere, The question of pedal generators comes up often. Its been calculated to be only 50% as efficent as just pedaling the bike at best, and many applications are going to be worse. meaning if you could go 20 miles on your bike by pedaling, by using a generator to charge a battery and run a motor, you have reduced your range to 10 miles.

"But wait! I didn't mean charging the battery exclusivly, I only ment using the generator to extend my range. I'd charge the batteries at home!"

Right. Same principle. If you could normaly go 20 miles on battery alone. and you also have the fitness level to pedal 20 miles, by using the pedals to generate power, you could extend your range to at best 30 miles. HOWEVER, if you skipped the whole generator mess, and just pedaled along with the motor, you would extend your range to 40 miles.

As for the solar charger, Ypedal hits upon the best solution in another thread. it just isn't practicle to carry a pannel big enough to charge the battery during the day. Solar panels just don't have that much output for there size. But a home base pannel, charging up some car batteries all day long, could be used to recharge your bike over night. Such a system could also be used for emergancy power around the house, so it has added benifits.

14. ### loquinActive Member

You could also ride the bike to work on the battery, unfold your solar panel array, and have it charge your bike's batteries all day long directly, at the 90 wH rate. 8.5 hours * 90 wH = 765 wH. (minus the charging losses) Then, ride home on the batteries & plug into the wall there.

15. ### fastboy9Member

Anybody who does fancy this idea then I've found a link with instructions on how to build one. http://www.instructables.com/id/Solar-Powered-Trike/
If your not familiar with the website then it is well worth a look! Some fantastic project ideas on absolutely everything. There is a section all about bicycle related mods and projects too.