🚀 go-pugleaf

In article <01bcc7b3$47e9a860$0400a8c0@bahn>,
William L. Bahn <bahn@pcisys.net> wrote:
>
>
>Karl Denninger <karl@MCS.COM> wrote in article
><6069ok$lbl$1@Jupiter.Mcs.Net>...
>> In article <01bcc779$f78bdd40$0400a8c0@bahn>,
>> You're doing this the hard way.
>> 
>> Try mirrors (yes, mirrors).  Use an array of them and focus the sun's
>energy
>> from a large area (ie: a few acres) onto a water tank on top of a tower.
>> 
>> Now use the energy you just concentrated to boil water (aka: steam).
>> 
>> Use the superheated steam produced to drive a conventional turbine and 
>> produce electricity.
>> 
>> Anyone who has ever used a magnifying glass of parabolic mirror during
>the
>> daytime to ignite combustable material knows damn well what kind of power
>is
>> available from even a *small* area illuminated by the sun.
>
>Actually, what you learn by smoking ants is what kind of energy density can
>be achieved by focusing a modest amount of energy into a very small area.
>But it is total energy that counts. Just as some 10MW lasers can be run
>quite handily from a 110VAC outlet because the concentrate a small amount
>of energy into a very short duration pulse - and put out nothing the rest
>of the time.

Correct.  But the point is that if you look at the area which you started
with (the aperature of the lens) and the area onto which you focused the
beam, you get a pretty good idea of what we're looking at here.

This is continuous output, of course.  The pulse-laser isn't, which is why
you can run it off 110V.  But try to run a high-powered emitter of any kind
off line power that runs *continuously* and you run into interesting
problems "feeding" it.

>You don't need a refractive medium to get focusing with reflectors - you
>could use polished metal or aluminized mylar. 

Yes, but both polished metal and mylar have rigidity problems, as you noted,
and both also pit and "tarnish" something awful.  Glass has the advantage 
here, even if its not real thick and you take the breakage that you end up 
with as an operating cost.

Over time you're going to see efficiency drop, yes, and maintenance cost will
have to be factored in to keep it from getting out of hand.  But mirrors can
be replaced while the system is online; there's no high power running around
out by the collectors, as there would be with photovoltatics, and in fact at
"ground level" the concentration of energy is zero -- so its completely
safe to send a crew out to the mirror farm while you're in production.  This
is not necessarily true for solar cell arrays; the current levels running
around in the interconnect area would be substantial.  

Then you get into the whole AC/DC thing.  Photovoltatics will require a
motor-generator setup to convert to traditional A/C, or its electronic
equivalent.  This sucks, and is going to drain efficiency (or money) 
big-time -- which makes the system even more expensive.  A reflector array 
system drives a standard turbine which produces AC right at the outset.  
That's a big advantage.

>I don't know that it's all that much cheaper to build. You still have the
>support structures and you will still have to track the sun for maximum
>output. I think the lion's share of the cost is going to be here. 

The tracking mechanisms are going to cost real money.  But remember that you
don't need to hit this thing *SPOT ON* - the "boiler" on top of the tower is
going to be of considerable size, and as such you need to hit the target
from each reflector within whatever that size is.  Consider that the tank is
going to *have to* be sizeable, otherwise it would melt into slag instantly 
when this thing was powered up -- enclosed water or not.  The energy 
concentrations which will be reflected onto this thing will be absolutely
phenomenal.  

I'd love to run some numbers on this thing, just to see what the total power
available is and then apply some rational deratings to it to try to figure
out what the real expectation of total energy available might be.  I bet it
would surprise both of us.

> It's true
>you don't have the thousands of kilometers of interconnect wiring and your
>maintenance costs would be a lot lower - these are significant advantages.

Yep.  Very significant.  Solar energy's biggest problem in the typical
photovoltatic system is the cost of the frigging collectors.  Those cells
are EXPENSIVE.  Especially when you start talking about larger cells and
arrays, its big bucks. Glass is cheap, even back-coated to produce a
mirror.  Mass-produced to a specific size for this kind of thing in
"cookie-cutter" fashion it would be even cheaper.

>The same is true of photovoltaics - though there is probably more pollution
>involved in the production of the solar cells than in the production of the
>mirrors.

This is true.

--
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Karl Denninger (karl@MCS.Net)| MCSNet - Serving Chicagoland and Wisconsin
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