The actual toast from experiment. 🙂
Steve of Canadian Energy Issues brought this CBC Podcast (Skip ahead to 00:24:45) to my attention. Ed Begley, actor and environmentalist makes toast from his pedal generator.
I know a toaster needs a lot of power so wanted to work through the numbers.
Okay, I’m making toast as I write this. My toast has been going for a minute as I type this sentence.
I found a table of appliance consumption (toasters take 800-1500 Watts so 1000 Watts seems like a good number for arguement).
03:15 Dinnnnnnnnnnnnnnnnnggg! I learned something. Toast takes about 3 minutes from cold.
Ed pedals 15m to make toast. That’s 5x longer than the 3m cook time. So he can put out 1/5th the toaster requirement. In other words it will take 18m to make the toast. Fifteen minutes of frantic pedaling (energy being stored) and then 3m to run the toaster.
So he needs to pedal at 200 Watts (1/5th of 1000 Watts) for 15m if he has an efficient electricity storage system attached to his bike.
To try and see how reasonable that is lets do some comparisons. A person can make about 1/10th horsepower over extended periods. A horsepower is about 746 Watts so 200W is about 1/4 horsepower.
1/4 hp for a short period seems plausible to me. In fact I’ve seen projects that require even more human input. The Gossamer Albotross pedal powered plane requires 0.4 hp and a human pedaled it across the English Channel in just under 3h.
Let’s put 200 Watts into some familiar terms so we can “Feel the Power”.
A horsepower is 550 foot-pounds/second (you can lift 550 pounds one foot in one second, or one pound 550 feet in one second). We need to do 1/4 of that so we’re talking 138 foot pounds per second.
Fifteen minutes of pedaling is 900 seconds which means he is doing 124,200 foot pounds of work.
I just googled Ed to see a picture of him to guess how much he weighs. I’m very scientific. 🙂 Um, okay he looks like a thin/fit guy so let’s give him 175lb. I understand he’d tall so perhaps we should kick another 15lb? Perhaps 190lb?
To “Feel the Power” we need to divide 190lb into the 124,200 foot pounds and see how high to climb stairs in 15m. That comes to 654 feet. That’s 65 floors in 15m.
So to get a feel for how much this is, it’s a matter of finding a 70 floor building and running up the stairs in about 15m. That’s 4-5 floors per minute.
So it looks plausible, but don’t be fooled into thinking it’s easy. This calculation also suggests that it would take 5 people to make toast in real time using 1/4 horsepower each.