[extropy-chat] Nanoengineered terrestrial solar vs. nanoengineered space solar power

[Keith Henson]

At 06:59 PM 4/7/2007 +0200, you wrote:
>On Sat, Apr 07, 2007 at 08:15:15AM -0500, Jay Dugger wrote:
>
> > Will photovoltaics degrade in-orbit and by what mechanism? Radiation?
> > Corrosion? Impact?
>
>It's a solved problem, lifetime would be counted in decades, and
>arguably the array could be constantly repaired by roving robots.

It is a problem that will take some thinking about.

> > Do you assume SPS based on photovoltaics? Is that really a good model?
> > What about using sunlight to heat a working fluid for a generator?
>
>Bad idea. With PV you have high efficiency and potential separation
>in a semiconductor,

Many of the early power sat designs, particularly the ones from Boeing, 
used heat engines, thermionic was another option.  If you bring 
extraterrestrial resources into the picture where mass isn't such a 
problem, I think heat engines may be the way to go.

They have the advantage that the high voltage sections can be kept small 
enough to insulate them in pipes, something you can't do for 100 square km 
of pv cells.  The problem with heat engines is dumping the waste 
heat.  Boeing designs had the radiators working at yellow heat to keep the 
mass down.

But if you can afford the mass, Drexler and I figured out how to build 
radiators up to rejecting the waste heat at near room temperature.  (Yeah 
they are *big*.)

>which is one step removed from reradiating this
>towards a particular space segment, where your rectenna is.

There is a geometry problem in that the transmitting antenna needs to be 
pointed toward the earth while the power creating part needs to point at 
the sun.  This makes for a bunch of problems like multi Gw slip rings.

Keith

> > More to follow, when I return from work.
>
>--
>Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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