Could electric bikes ever recharge themselves while you’re riding? Well, it seems preposterous or is it.

E-bike basics

Let’s take a look at the basics of an e-bike and see why this either would or wouldn’t work. The energy needed to propel the bike is stored in the battery, which then goes to a motor controller, which is usually tucked inside the bike hidden somewhere. It’s kind of like the brains of the operation. Are you pondering what I’m pondering, Which allows you to control how much power you’re feeding to the motor, the motor then spins the wheel on the bike, which propels you forward.

Use a generator?

Every once in a while, I still see these comments online about, why don’t you put a generator on the bike? Alternator on the bike that recaptures energy while you’re riding and feeds it back into the battery. And we already know that won’t work. I think that misconception comes from Our daily drivers, our gas vehicles, because most of them have an alternator, running a belt off the engine to produce some Electrical power, to keep the battery topped off, run your air conditioning, your radio, everything electric on your car. I think what most people don’t realize is that that energy is not Free. You have to use gas to produce that Electrical energy. And in the case of an electric bike, that energy is going to be robbed from the motor and battery that are already on it. And it’s going to result in a net loss, but how much of a loss?

Geared hub motor and Direct drive hub motor

A geared hub motor has no ability to recapture any energy. However a direct drive hub motor, There’s no gear reduction and the motor is completely fixed to the rim. There’s no freewheeling, but one of the things these can do that a typical geared hub motor cannot is regenerative braking. The axle is completely fixed to the copper coils. And then the magnets are fixed to the case of the motor, which is directly laced to the rim. This means that the motor is always spinning whenever the bike is moving, there’s no other option either you’re using power to rotate the motor and propel you forward. Or if let’s say you’re coasting down a hill, you are forcing the motor to turn over and you can use some of that power from coasting down a hill to put it back through the motor controller and back into your battery. I’ve seen people claim as high as 10% increases In range from regenerative braking. Don’t think you’re going to get twice as much range or even 50% more, maybe a small boost if you have regenerative braking, but it’s not as much as you might think.

Dynamo hub

What if we want to take this a step further and say, well, a motorist designed to propel the bike forward. It’s really not designed to be like a generator and recapture energy. What if we designed a device that all it did was recapture energy and it was extremely efficient at doing so. And we put it on the front wheel, then couldn’t we gain some more appreciable energy back? And the answer again is no, that would be even worse than the direct drive hub motor using regenerative braking.

This of course is a standard hub. It just spins. There’s no motor, there’s no nothing built in, but for decades there have been devices called dynamo hubs. It’s actually a bicycle hub that generates electricity as you ride. Usually people will use them for touring or if they do a lot of commuting, what you can do is have a dynamo hub that whenever the wheel is spinning, it’s generating a very small amount of electricity and it can charge your lights on your bike. So you never have to worry about charging them or keeping a battery on the bike. You basically have a small six volt output, usually somewhere in the neighborhood of three Watts or so.

So what would happen if we put a dynamo hub on the front of the electric bike. Wouldn’t we be propelling the bike forward and recapturing a few Watts, which we could feed back into the battery. That’s actively using less power. Again, the answer is a definite no, the power has to come from somewhere, which is the rear motor that’s what’s propelling the dynamo hub in the first place. And if we look at the efficiency numbers, it doesn’t pencil out very well. Some of the best dynamo hubs on the market have an efficiency of around 57%. So let’s say the hub can generate three Watts when moving that we could hook up to the battery and feed the three Watts in. The problem with that is that 57% efficient, let’s just call it 50% efficient for easy math. That means it would actually take six Watts from the rear motor to power. The three Watts, we get back into the battery. So we would automatically lose three Watts of power and we’d get less range than before. And if you scale this up, no one makes a dynamo hub this big. But if we assumed we had a 500 watt motor on the back, a 500 watt hub that is generating power on the front. And we account for that 57% loss, if this bike had a battery big enough to go a hundred miles. And we tried putting a hub on the front to recapture energy and put it back in. The energy losses means that the bike would not go more than a hundred miles. In fact, it would only be able to go 57 miles. We would actually lose almost half of our range, but it actually doesn’t stop there because motors like this are not 100% efficient, either some of the best at peak efficiencies might be a little over 80%, which means you’re going to cut your range down from 57 miles down to 45 miles. You would lose more than half of your range by trying to recapture energy. It’s a net loss. It’s not going to work.

Recharge while pedaling?

So what other ways could we potentially use to recharge the battery while riding? Well, we are putting in some effort by pedaling and I see this question fairly often, do e-bikes recharge while pedaling. And the answer is again, no. Technically it’s possible using a direct drive motor that you’d never want to do it. This also goes back to efficiency problems. For this, we need to look at the drive train of the bike, the peddling action that you put in through the chain, through the derailleur, through your gears is eventually going to result in that wheel moving forward. And that is actually really efficient. Single speed setups can be as high as 97%. There’s a new company called ceramic speed. That’s developing a new drive train that is supposedly 99% efficient. Meaning that 99% of the effort you put in is going to propel the bike forward. So what would happen if we took the pedaling action and instead of propelled us forward, we used that to power a small generator to feed power into the battery, which then we use the motor to propel us forward. The generators are never going to be as efficient as a drive train. So if you use your peddling power to propel you forward, you’re always going to get further than if you tried to use the peddling power to power battery, that to then power motor controller, and then a motor to then propel you forward. It’s just not as efficient. And there are two things that could be done. Number one has nothing to do with any of the mechanical components on the bike. And that is solar now for a standard e-bike, it doesn’t make any sense.

Solar power

If you put a solar panel on the rear rack, maybe you’d be able to fit something like 10 Watts, or even if it was hanging down the sides, maybe even 20 Watts of power. But when you’re using 500 Watts, it’s a small trickle charge at best. If you want to stop and say unfold, a solar panel that is stored on your bike and charge as if you were plugged into the wall, that is definitely possible. The technology is actually coming along really well for that. Don’t be surprised if you see more on that from us in the future. The only way that I can calculate out to make solar work right now on an electric bicycle is if you use a Velomobile, that is a very aerodynamic bicycle with a shell. And by cutting the wind resistance down, we don’t need as much power to operate. But on top of that, a Velomobile has a much larger surface area on which we can place solar panels. So in theory, we should be able to cover a Velomobile completely with solar panels, and it would have an infinite range by solar power alone. Those are expensive. They’re a little bit weird and quirky and not everybody’s going to do that. We could recapture some energy, it’s not going to be recharging while riding, but it would certainly boost our range. And that is with a whole new type of regenerative braking system.

Is there anywhere on an e-bike where energy is just being lost?

Is there anywhere on a bicycle where energy is just being lost in the form of heat or something else? The answer to that is yes. Our breaks. Anytime you break, when you apply pressure to the rotor, it gets hot, hot enough. After a long downhill that you could actually burn yourself on the rotor. That means we have wasted energy. We could capture, unfortunately, a regenerative system that involves only the brakes doesn’t exist yet.

Will e-bikes ever be able to recharge themselves? I don’t know. You let me know what you think in the comments below. If this technology existed, we could actually ride around the 130 mile loop.