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
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