What if you captured some of that exercising energy?

My brother, a cool guy and a road cyclist by avocation, sent me an email yesterday:

Ok, here's an idea. I want to get a trainer bike for the basement. Can you devise a way of taking my effort and storing the energy in a battery so I can reduce some of my household elec consumption off the grid. I see a future - kind of like Tina Turner running Bordertown in Return To Thunderdome on sheep s**t or whaterver.

Always thinkin,
yer brudda.

I had thought about things like this a little myself. I wrote back:

Yes, I can, Tina!

I'm working on one for myself. Despite that human effort isn't much next to the grid. But wait...

The good news is that in winter time, it's a done thing. EVERY CALORIE EXPENDED cycling indoors goes to heating your house. No kidding, no exaggeration. Even if you're not using your mechanical output as stored or delivered electrical energy, it, and your metabolic energy expenditure, are reducing heating demand in your house; you need to burn less gas in the furnace to maintain the indoor temperature! Indeed, if road cycling really takes 700 Calories/hr, or 700,000 calories, which is almost 3 MJ, that's a big help to your furnace; the rough equivalent of burning a 1000W lamp for the whole hour.

Back to the bad news: Imagine that you could capture what you can of the mechanical output from your exertions. (You still get to keep metabolic output as home heating, by the way; indeed, "waste heat" is really hard to capture for re-use for anything but heating.) A fit cycling demon like yourself can sustain about 1/3 hp, or 250W, of mechanical output for your, say, hour-long workout. Thus, assuming perfect conversion to storage, and then perfect energy conversion from storage back to electrical, you will have captured about .25 kW-hr of energy. At 7.3 cents/kW-hr, you will have saved yourself... TWO CENTS! (Almost two cents. Not quite.) You could run your toaster for about 10 minutes with that kind of effort! Neat.

Of course, that's assuming no losses. It's really about half that, because of losses converting from mechanical to electrical to chemical and back to electrical. So you could save about a penny's worth of electricity from the grid with an hour of exercise; maybe get something worth spreading butter and jam on.

But then, back to good news: the waste heat from the inefficient conversions STILL goes to heating your house. Thank goodness. Otherwise this would be really depressing, instead of just mildly depressing.

As I said, I am still going to build an energy storage device for an exercise bike because that's cool, and I am still going to heat my house partly with exercise; "being" a 1000W bulb for an hour every now and then is good support for the home-heating plant.

Hey! You just caused me to write an awesome blog entry! What a brother. Thanks!

...and I wasn't kidding.