Re: Interesting concultural ideas

> Date:         Sun, 9 Dec 2001 12:05:06 -0500
> From: Andreas Johansson <and_yo@...>
>
> If we could use all the solar energy reaching the earth, energy
> would[n't] become a problem until way after we've used up all the
> carbon etc of the Earth for making humans.
Hmmm, I'm not quite sure the math holds up.

The total biomass of the Earth is 1.8 million million tons. At 75 kg
per person, that could be 24 million million people.

The Earth presents an area of around 100 million square kilometers to
the sun. At 1kW/m^2, that's 100,000 million million Watt. (The total
surface area is four times that, allowing each person 16 square meters
total for living space and support equipment).

That's 4 kW per person, or 350 MJ/day, before conversion to usable
energy. You need to provide about 8 MJ of food energy content per
person per day alone, which is hard to produce efficiently, and then
there's cooling, heating, waste disposal, purification of drinking
water --- and collecting all the waste heat that used to get reflected
into space, and radiating it off somehow.

So, if my math is right: even without converting carbon dioxide and
other easily available carbon sources to make humans, just using
existing biomass, you could only just about get by with the available
solar radiation.

Lars Mathiesen (U of Copenhagen CS Dep) <thorinn@...> (Humour NOT marked)