Over my 52 years I have tried to stay fit. Years ago, I got into yoga, then hot yoga—that is a challenge, especially when done in a really hot room. You essentially give your body a dual challenge: do strenuous, mentally taxing exercise while maintaining a core body temperature of 37 degrees. That dual effort produces an intense physical, and sometimes emotional, experience. I recommend it, provided you ease into it and are already familiar with yoga.
Lately I have gotten into Crossfit, which is constantly varied functional and “old fashioned” exercises like pushups, burpees, kettleball swings, box jumps, lots of weightlifting, and lots of gymnastic-type stuff that I was no good at during grade-school and that I am still no good at. You do a Crossfit workout at high intensity, i.e. at a sprint, all-out pace. It is brutal, and addictive. The only good news is, it is short: often less than ten minutes and rarely more than 20 minutes. It is also very effective.
At the peak of a hot yoga class (i.e., the standing posture portion, which lasts usually around five to ten minutes), or all through a Crossfit Workout of the Day (WOD), you are cranking out more or less peak energy. In a normal male human, that amounts to a work output of between 300 and 400 watts. Chris Horner, a Tour de France rider, is reported as having output 422 watts during one ten-minute uphill stretch. Catalyst Athletics has a great online calculator that might help you roughly calculate your output in a Crossfit WOD.
If during your hot yoga or Crossfit session you could somehow convert your physical energy into electricity, you might, if you really go for broke, do enough work to power one 100-watt light bulb. When the session was finished, ten to twenty minutes later, you would be gasping for air, lying in a puddle of sweat and drool. The lightbulb would be dark.
If you have never tried either hot yoga or Crossfit, I urge you to at least give it a try. It is a sobering, humbling experience. Especially when you realize how much work it takes to power one lousy 100-watt lightbulb. I mean, you go all out, to the point of serious exhaustion, and you can keep it lit for maybe 20 minutes at most. You might be ready for another 20-minute session four or five hours later. And that is it for the day.
Think about that, and then think about how much sheer energy it takes to produce enough electricity to run a city. You may have noticed that I said your 300-to-400-watt effort might, while that effort is underway, translate into enough energy to light a single 100-watt lightbulb. That is because you cannot convert mechanical energy into electricity, a higher form of energy, with perfect efficiency. That conversion is inherently inefficient: to make one unit of electrical power, you have to put in at least three units of mechanical power.
How many fit humans, working at a hot yoga or Crossfit pace, would it take to power your house, let alone the city you live in? Too many. That is why we have the grid.
The Ontario grid has not experienced a single general failure since August 14 2003. In the 3,541 days since then, Ontario’s power generation fleet has provided indispensable electricity to every man, woman, and child every second of every hour, 24 hours a day, without letup. There is no possible way humans could have done that work. Again: try hot yoga or crossfit. Then imagine working at that pace for even one hour, forget about 24 hours straight.
Most Ontario electricity comes from three relatively tiny locations which host nuclear plants. Have a look at Tables 1 and 2 in the upper left sidebar. Imagine how much energy it takes to clock those kinds of numbers, second after second, minute after minute, hour after hour.
I’d rather machines do that work than humans. So, to the humans that run these machines, a big shout out. Too few people know what you do, and fewer appreciate it.
Steve, I like the comparison overall, but I think you have misrepresented thermal efficiency a bit. Transferring heat energy at the roughly 600 degrees Fahrenheit of most PWRs’ reactor coolant to mechanical energy and then to electricity is what is only about 33% efficient. Going from mechanical rotational energy to electricity would probably be upwards of 90% efficient (I don’t know the actual number off hand), so a person could light about 3+ 100-Watt incandescent bulbs.
Overall, still a good comparison though.
Joel, thanks. I guess it depends on initial assumptions. I assumed a functional device, say a bicycle, and worked from there. Further, I took the Ed Begley Jr. example: he said he can make toast from electricity made on his bike. Since a toaster runs at upwards of a kilowatt, Ed would have to be a true Olympic super-athlete freak to be able to go at 1000 watts for the two minutes it takes to make toast. So I guess he stores electricity from many workouts in a battery (or series of batteries). Which involves all sorts of losses and inefficiency.
To make useful electricity you have to store it. You can’t always make when you need it. That’s what’s wrong with solar and wind in general.
So it’s fair game to include losses from storage when looking at pedal electricity or something along those lines.
The actual efficiency of a reactor I don’t know off hand but it’s the same problem you have with solar (the actual amount of energy harvested may not be perfect). I think solar is around 20 percent. There’s a carnot limit on these systems so it’s very hard to make them highly efficient.
Steve – thanks for the post. I came across a great story on the SkeptEco blog, Earth Hour: We will Never Give up our Energy Slaves that led to a real world trial of bicycle power. The post includes an excerpt from a BBC TV program, Bang Goes the Theory, in which the producers run a typical UK home for 12 hours using a bank of pedal powered dynamos.
The 3:16 clip, Human Power Shower – Bang Goes The Theory – BBC One, gives the flavor of the show. The complete episode, Bang Goes the Theory – S01E11 – Human power station Special is well worth watching.
” In a normal male human, that amounts to a work output of between 300 and 400 watts…”
Normal?…don’t think so. That’s roughly 1/2 HP. That’s probably a well conditioned athlete. Or a feel-good power monitor…like, for golfers,todays 9 iron which is really about a 7 1/2 iron of yesteryear.
While your basic point stands, I think you’re underrating the power level people can reach. I’m nowhere near being able to compete in the Tour De France, but I’ve often put out 200 W for half an hour on my bike. And I could have gone longer, but I’d run out of hill to climb. Doing half that for several hours doesn’t seem implausible.