If a human being is capable of providing 0.1 HP of power and it is convertible to energy at 100% (which is impossible), then we are talking about 74.6 W of output power.
Pedaling for 20 hours will produce 1.492 KWh not KW.
Obviously 1 billion people therefore will produce 1,492 GWh (Giga Watt Hours) - which is nothing to sneeze at.
It takes a nuclear power plant to produce 1,000 MW. In fact the largest nuke plant in US is Palo Verde 2 with an output of 1,335 MW. The largest power plant in the world is ITAIPU which is a hydro plant with an output of 12,600 MW.
Thought I sort this out.
Now divide 1482 MW hours by 168 (because a power plant works 24/7/365) and you get a little over a 8800 Mega watts. Eight nuke or coal fired power plants a heck of a lot less than 20 BILLION manhours per week.
But look at it this way, all those people in China and India now have a job ;^)