Re: Understanding nanotech

Robert J. Bradbury (
Tue, 31 Aug 1999 07:04:04 -0700 (PDT)

On Tue, 31 Aug 1999 wrote:

> A technicality: Houses in the US are normally fed with 240 volts single
> phase center-tapped, on three wires. One wire is the neutral or ground,
> and the other two wires each carry 120 volts relative to ground, with 240
> volts between the two live wires. The 240 is used for running heat
> pumps, air conditioners, and some clothes dryers and water heaters. The
> 120 is used for most everything else. So when the two live wires are
> each carrying 200 amps, which is what the 200 amp rating means, the total
> power is 240 volts x 200 amps, or nominally 48 KW, assuming unity power
> factor.

Eeek, someone who really understands how the system works. I stand corrected on the total possible power. I'd stick by my belief that most homes don't come close to using this (I suppose I could figure it out from my electric bill).

> On Mon, 30 Aug 1999 23:15:56 -0500 "Billy Brown"
> <> writes:

> > Something is seriously wrong with these numbers. My handy reference
> > lists the solar constant at 1340 W/m^2,

My table says 1374, so either one is probably correct. You do get somewhat less at the surface due to scattering and dispersion in the atmosphere. You might get close to that at noon at the equator. Perhaps mine is the above the atmosphere #, and yours is the noontime equatorial #.

> Earth is 6.37x10^6 m.

Yep, 6,378 km.

> > Multiply that out, divide by 3 billion people, and you
> > get an approximate natural energy budget of 5.6x10^4 KW per person.

> > We should be able to use whatever fraction of that we care to actually
> > harvest without fear of creating a global heat problem.

Not without distorting the weather or killing plants and animals (and whatever humans choose to live "off of" them).

> Those numbers work out to 5.7x10^4 KW per person, modeling the earth as a
> disk of the given radius, facing the sun. But the earth's population is
> now reported to be 6 billion rather than 3 billion.

We must be using different calculators because when I take

Insolation*Pi*R_earth^2 / 6*10^9
I get 2.93*10^7.

That is what Hal has been complaining about, he wants the difference between the NM limit of ~10^4 W (10kg of nanobots) and ~10^7 W. Those 3 orders of magnitude let him build that mansion much faster. [Of course if he gets the entire power budget, we don't have any plants and very few animals left.]

I would generally agree with Hal, in that I think we can get almost an order of magnitude more power without too much trouble. More than that and it is going to start creating problems until we have a lot of computer power to simulate the potential effects.

But I suspect you can get probably 2-4 orders of magnitude better by doing more efficient assembly (i.e. chemical reactions that utilize/reuse the free energy effectively), reusing building blocks (so once you have invested in building them, you don't rebuild them) and going to more efficient nanodesigns. So we are probably wasting mental energy on the wrong side of the problem.