"Dude, that sucker was Nuclear-powered (BTTF reference and 6M$ reference, all in one! Geek Joy!)"
Actually, that sucker was electrical. Doc Brown only needed the nuclear reaction to produce the 1.21 gigawatts he needed
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"The Matrix idea about humans as batteries is very stupid. Such battery would be highly inefficient. "
A power plant with a bicycle driving an alternator might not be a great way to power a whole lot-- but if you had a billion bicycles, with six billion people 'taking turns', I think you'd do quite alright ... I'm coming up with something in the neighborhood of 50-100x the power of the Hoover Dam and the five power plants at Niagara Falls combined...
The Hoover Dam produces 4 billion KWh per year.
1 bicycle = atleast 50 watts per hour on average [including downtime for repairs and maintenance], times 24 hours times 365 days equals 438 KWh.
So a billion bikes gets you to almost 110x of the Hoover Dam