Re: Interesting concultural ideas

Lars Henrik Mathiesen wrote:
> > 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.
Ok, I admit I didn't check the numbers before I wrote. However, likely it
isn't carbon but "etc" (=other essential elements) that'll  set the limit.

                                       Andreas

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