That's not "a fit man" that's a trained and fit cyclist, good marathon runners (2h15) were measured at an average 300W over the run[0], a fit adult might reach 200W.h over an hour or two, over long periods of time (e.g. an entire workday) you won't get much more than 100W.h if even that, an average fit labourer would be around 75W.h.
And that's mechanical in all cases, not electrical, you then have to factor in conversion losses. While a large rotary generator is ridiculously efficient (98~99%) it doesn't scale down that well (you'll be at about 80~90% at the generator output) following which you still need to remove the losses from the voltage regulator, battery, and possibly AC converter.
And then you still have the issue that your base energy sources (people) is not really efficient at converting food to mechanical energy in the first place.
Frankly, you'd be better off with a team of draft animals powering a big crank/wheel (with a flywheel for regulation), the average draft horse can produce ~740W (1hp) sustained. There's a reason why they (and oxen and other beasts of burden) have been used until engines became a thing.
[0] http://running.competitor.com/2016/11/photos/understanding-r...
('Only' because you need to do 580W to gain those six seconds. 2% faster = 6% more power)
It's just pointless to generate electricity by human power. It's not pointless to ride a bike.
440 watts for a world hour record.
350 watts for one hour, once a day, would be challenging to maintain for one week.
First of all, human power releases tons of carbon dioxide just like burning fossil fuels does [0].
Second of all, modern society currently depends on burning millions of years of stored sunlight energy in a matter of centuries (i.e. fossil fuels). Human power doesn't begin to compare. Bang Goes The Theory (BBC show) did an entire episode on this. It's shocking how many bicyclists were needed to run a tiny household [1].
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[0] http://www.livestrong.com/article/402142-how-does-exercise-a...
(This is assuming you didn't use a bunch of fossil fuels to create and transport food in the first place, and you're instead using human/animal power to do that.)
Unfortunately, agriculture is a major driver of deforestation (and forests are excellent at actually sequestering carbon in the ground). It also requires trucks, boats, and planes to haul supplies to farms, work the land, move water around, and transport the produce to stores. You have processing and packaging that rely on fossil resources (paper, plastic, metal cans...)
That doesn't even touch on the impact of meat production, which is several times worse for the environment.
Food consumption is absolutely not carbon neutral. You're far better off taking public transportation to work (if available) than walking or riding a bike, if you care about the environment.
On a bike I can do around 220W for an hour, and 160W for an indefinite period (have done up to 12 hours before).
Biking is known to be 20-25% efficient from calories burned to power at the wheel, so that's ~700 kCal/h for an hour at 160W. My idle consumption is ~1600 kCal/day, or roughly 70 kCal per hour, so riding on the bike uses 10x as much; therefore I'm going to be producing 10x as much CO2 (obviously).
It takes ~140 L of oxygen to burn those ~700 calories, resulting in ~110 L of CO2.
So if I do a 4 hour ride at 160W to produce maybe 600Wh of energy after conversion inefficiencies, that's 2800 kCal just for the ride and 4400 kCal for the whole day, around 2.75x my idle consumption.
Disclaimer: I've done this quickly. Feel free to point out any errors.
> Whether a human eats the plant or it decomposes naturally, the same amount of carbon dioxide is released.
Yes, but we produce agricultural crops to meet demand. If as per the calculations above, every human suddenly started consuming 2.5x as much food, we'd have to grow more.
And yes, this is part of the carbon cycle. The problem is that we use fossil fuels and release CO2 above and beyond what's part of the normal cycle.
I was disappointed that for all its calculations, the article completely avoided the question of "How green is human power?" Instead, it just repeated "could become one of the cleanest energy forms available".
But they had to, of course - answering that would have destroyed the entire idea. Fueling humans burns a huge amount of carbon, and neither the food > muscle conversion or the muscle > electricity conversion is even passably efficient.
But it's all the other costs of owning a car that make it so much more expensive: depreciation, licensing, registration, maintenance, blah, blah.
But most people are in an unwanted caloric surplus so it's really even better than this for those people.
I choose not to drink pure canola oil because reasons. But if I did, my ride to work would be fueled by 30mL - so I could maybe just start taking a shot in the morning and a shot in the evening. Yummy.
You can just make some delicious fried or oily snack, like crisps or chips or sauteed spinach, or fried what-have-you.
...but even a shot of oil is more healthy, pleasurable and hygenic (assuming you burn it all) than filling your tank with petrol :)
It's greener in a pleasantly 'immediate' way - i.e. you could quite literally be keeping the lights, music system, etc on at the gym :-) And what's more, assuming power costs are a non-trivial overhead, it could even result in lower membership fees.
If somebody opens a gym like this, sign me up!