Why Powering A City With Bicycles Is Impossible

One of the iconic European films of the 1990s, Emir Kusturica’s “Underground”, features a scene where a character pedals a stationary bicycle to produce electricity. The work that character did on the bike was enough to power a headlight. Is this really possible? And if so, would it be an efficient use of energy?

The idea of using bicycles to generate electricity while you work out is far from new. With climate change concern on the rise, more and more people are looking for ways to make electricity generation less emission-intensive. Back in 2009, the BBC even made a film about bicycles powering a whole household, but more on that later.

On the face of it, the idea of generating electricity while you bicycle—at home or in a special gym, perhaps since the bike would need to be connected to a battery or plugged into the grid—seems nothing short of brilliant. You work out, and not only do you reap the benefits of the workout by improved health and weight loss, you also produce power. All gains, no losses, right?

Wrong.

How it works

Here’s how electricity by bike works: Some sort of generator—a spinning magnet plus a coil of wire— is attached to a stationary bike. Now, you start pedalling. Pedalling spins the wheel to which the generator is attached, and the magnet begins to spin, generating an electric flow that goes through the wire.

This electricity can either be used immediately or—and that’s the better part—stored in a battery for later use. Basically, you get to fill your own battery pack whenever you feel like working out. Or maybe not, exactly.

People who like to work on hypothetical problems have calculated that a person pedalling a bike with a generator can produce about 100 watts of power per hour. That’s the plausible average for an adult human’s capacity to generate electricity while riding a bike in place.

Some proponents of bike-generated power note a stronger, fitter individual could produce more than 300 watts of power by pedalling, but let’s stick with the average of 100 watt for now. It makes the calculations easier. We will also ignore the issue of energy loss during generation for simplicity’s sake, though it’s worth remembering the fact that some of the power you produce while cycling does get wasted along the way.

So, if an averagely fit adult pedals a bike at home for an hour every day, they would produce 100 watts of electricity. How much is that? It’s about enough to power one 100-watt light bulb for one hour, or a 25-watt light bulb for four hours. That’s for every hour pedalled.

What if you pedal—or hire someone to pedal—for eight hours every day?

Well, if you pedal full-day for a month, you could produce as much as…24 kWh. The average American household consumes about 1,000 kWh every month. In this context, your pedalling contribution to the total seems minuscule and not really worth the effort.

Let’s say you’re a cycling enthusiast and you ambitiously pedal for two hours—and you’re fit. In this scenario you could potentially generate enough electricity to power s 200-watt TV for two hours, which would be enough to watch one movie or charge one 20-watt laptop that will last 20 hours. That’s not half bad since you produce this energy for free, right?

Wrong again.

The production of energy, put quite simply, requires the expense of energy. In this case, the input energy is expended through pedalling. While you pedal, in other words, you burn calories. While that would be music to the ears of millions of people fighting excess weight, remember that the fitter bikers produce more electricity.

These fitter bikers would need to eat to replenish their energy resources. Since food costs money, at the end of the day, that free electricity is not free at all. It may even end up being more expensive if you produce it by cycling than if you simply get it from the grid. Put bluntly, if you’re fit and you want to generate your own electricity—to power a light bulb or a TV—you will likely end up paying for it all the same, just not in utility bills, but in food.

The Power-Generating Gym

So, cycling at home to power a light bulb or charge a laptop may not be such a beneficial idea. But there are other places where people can gather to generate electricity while working out. The more people bike, the more energy they produce, after all.

This is exactly what one gym in Sacramento decided to offer its customers. The Sacramento Eco Fitness opened doors in 2016 with 15 eco-cycles that generate electricity while you pedal them. At the time, IEEE Spectrum’s Andrew Silver reported that he gym’s owner expected to recoup his investment of $26,000 for the bikes within a year, not least because of lower electricity bills thanks to the bikes.

According to its website, however, the electricity-generating bikes are still there, so they must be working.

Here’s how they work. Pedalling produces low voltage AC. This electricity is converted into a higher-voltage flow of DC, which is in turn converted into a 60-hertz AC waveform. Then it goes into the grid… but not all of it. In fact, most of the electricity produced in such a bike is used to power that bike. That’s as much as 74 percent of the power it produces. Yes, 74 percent of the power generated by pedalling on one of those bikes stays in the bike. Talk about efficiency.

The “Free Electric” Bike

There seems to be a reason why cycling for power has not yet taken off the way rooftop solar panels, for example, have. The idea sounds good, but it’s not really practical.

Take the “Free Electric” bike concept. Developed by Indian billionaire Manoj Bhargava, the stationary bike is as simple as they get. You just sit down and start pedalling. The electricity you generate goes into a battery. The aim was to bring electricity to one of the millions of people in India with no access to the grid.

In 2015, there was an article about the “Free Electric” bike, touting it as the only device that can generate enough electricity for 24 hours from just one hour of pedalling. There was even a Youtube video about it.

Then in 2016, another article appeared, praising the “Free Electric” bike as a solution to electricity troubles in rural areas in India and elsewhere. Distribution was scheduled to begin that same year.

And then again, earlier this year, another article was published, promoting the benefits of the “Free Electric” bicycle. That article linked to the website of the initiative of which the bicycle is part, but there is nothing on that website about the bike now. The Facebook page for the bike was last updated in 2017. It seems the “Free Electric”, for all its promise, has not really taken off.

Why it Can’t Work

Forget about powering a whole city by cycling. Not only can it not be done while cycling to work and back because you can’t strap a portable generator to your bike, but it can’t be done at home, either. It’s simply too expensive to produce your own electricity by cycling. As for the idea about some sort of huge gyms when people gather to cycle and generate electricity, there is really a whiff of Black Mirror around such an idea, and that’s besides questions such as available space and cost efficiency.

In case you still have doubts, here’s an excerpt from that film the BBC made to see if cyclists can power a single household. Sure, they can. All 80 of them.