An NPR listener (with what may be the best Twitter handle ever — Booky McReaderpants) inquired whether a home can be powered by bicycle-powered generator.
It's an interesting issue about energy and the modern world. And the short answer comes from just running the numbers.
A typical house in the U.S. uses about 1,000 kilowatt-hours of energy in a month. So — to Booky McReaderpants' question — could you generate that much power all by yourself on stationary bike?
Not even close.
Pedaling a bike at a reasonable pace generates about 100 watts of power. That's the same energy-per-time used by a 100-watt lightbulb. So if you pedaled eight hours every day for 30 days (no weekends off), then doing the math, you'd generate 24 kilowatt-hours (kWh) of energy. Note that I'm not worrying about the efficiency in the electrical systems involved, which would drop the number closer to 16 kWh.
That's only 2.4 percent of the energy your house sucks up each month via the lights, the dishwasher, running the AC and playing video games on your PS4 (like Deus Ex: Mankind Divided).
Now stop and really think about that.
Biking, full time, every day, no weekends, for four weeks gets you to just a few percent of your monthly energy use. The discrepancy between what you personally can generate and what you personally use says a lot about what's happened with civilization and the planet over the past couple of centuries.
Consider this. For all of human history the amount of power the average person had to expend across each day was, well, one person-power's worth.
And how much was that in terms of energy? Well, our little bike example gives us a good estimate: Eight hours of biking per day yields 800 Wh (0.8 kWh). So since the dawn of our species 300,000 years ago, 0.8 kWh was pretty much the energy available to pretty much everybody each day. If you personally wanted more energy you would need to buy someone else's person-power in the form of servants or, worse, enslaved populations.
But the discovery of fossil fuels did something amazing. If we look at our house example, we see that the energy running into our homes from some distant power stations is the equivalent to having about 40 people pedaling bicycles for us. Those little sockets in the wall that we plug our stuff into give us the power of 40 servants. (If I included the electrical inefficiencies, that number goes up to about 50 servants.)
We are all, literally, living like kings.
But, as we know, using that much energy has consequences for the planet in the form of climate change. The trick now is to figure how to keep a reasonable level of power available to everyone by using energy sources that have less planetary blowback.
Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester, a book author and a self-described "evangelist of science." You can keep up with more of what Adam is thinking on Facebook and Twitter: @adamfrank4
ARI SHAPIRO, HOST:
Time now for short answers to big questions - questions from you about physics, astronomy or science, in general. And to provide the answers, our astrophysicist and NPR blogger Adam Frank joins us. Hey, Adam.
ADAM FRANK, BYLINE: Hey, how's it going?
SHAPIRO: Good. So we got a question on Twitter that was - why can't I power my home using a bicycle-powered generator? Adam, I ride my bike to and from work every day. Can I power my home with it?
FRANK: OK. So on average, the typical house is using 1,000 kilowatt hours per month, and so that's kind of the target that we'll look at. And kilowatt hours - that's a weird unit. You know, kilowatts is power, hours this time. So you multiply power times time, and you get energy. So 1,000 kilowatt hours is the amount of energy your house sucks up per month.
SHAPIRO: OK, and how much energy can a person generally create by pedaling a bicycle?
FRANK: Yeah, now that's an interesting question. So it depends on whether or not you're an elite bicyclist or not.
FRANK: But, you know, for, you know, most of us, about .1 kilowatt. So that's power. That's how much you can generate when you're on your bike, so, you know, that's not a huge amount of power that you're generating. So...
SHAPIRO: So to power a house, how many people would have ride bicycles for how many hours?
FRANK: Pretty much let's just take one person on a bike biking eight hours a day for 30 days, right?
FRANK: So it turns out that if you, you know, take the average power that a person can generate, and you multiply it by eight hours a day and multiply that by 30 days, you end up with around - these are rough numbers - 24 kilowatt hours, right? Now, remember...
SHAPIRO: Out of the 1,000 it takes to power a typical house.
FRANK: Out of the 1,000 - right - the 1,000 kilowatt hours. So that means that basically the number of bicyclists you need to power a home is 41. You'd have to have 41 people in your house biking 8 hours a day for 30 days in order to power your home. And - do you know? - that actually illustrates really the kind of the mess we're in in some sense.
SHAPIRO: You mean, the challenge of creating clean energy on a scale large enough to actually power the world.
FRANK: Right, 'cause when you think about it, for the entire span of human history, every person really had one person power per day, right? That's pretty much what you got, you know? You had - you know, you had as much energy as you could lift up and, you know, put - you know, put things in different places. But of course with oil - right? - and coal, we suddenly got this enormous multiplier effect. So much so that, yeah, now each one of us has the equivalent of 40 servants, right? And so, you know, we're all living like kings. And so if you actually think about it, if everybody needs 40 - if everybody was living the kind of life that Americans are, you would have to multiply the 7 billion people times the 41 servants. You'd end up with the equivalent of 280 billion people on the planet.
SHAPIRO: You're saying my lifestyle is not sustainable.
FRANK: Your lifestyle is not sustainable. Now I think we can figure out ways to do this, but this number really just points out about the enormous amount of energy that each one of us has at our fingertips. And the question is - how do we build a sustainable society that is at - somewhere at that level, but where all that energy is not - that's being used is not feeding back on the planet in a way that is detrimental to civilization?
SHAPIRO: Adam Frank teaches physics at the University of Rochester. And if you have a question about physics, astronomy, science, in general, send us a note. The show is on Twitter at @npratc, and you can also find us on Facebook. Adam, thanks as always.
FRANK: Always great pleasure, Ari.
SHAPIRO: And if you would like to see Adam Frank and NPR reporter Adam Cole attempt to power a house with a bicycle - and trust me, this is worth it - it includes something called the Rochester garbage plate - well, you can find the video at our science YouTube channel, Skunk Bear. Transcript provided by NPR, Copyright NPR.