Re: Space Based Solar - was Re: useful analogy

From: william mook (william.mook_at_mokindustries.com)
Date: 09/10/04 

Date: 10 Sep 2004 10:40:07 -0700

[snip!]

I answered the stuff above earlier, was called to a meeting and just
had time to get back now.

> I have some questions.
>
> Average power delivey of 600w, peak 1kW, seems inadequate. It may be
> posible to live on that, but no-one will choose to when there are
> other options. At present in UK houses use 1kW averaged, (I mean
> electricity only) with peak delivery closer to 10kW. Some houses use
> upto 25kW. The old 10kW rated services are considered inadequate -
> even though IRL theyre still performing satisfactorily.

The DOE EIA shows that 750 Watts per household is the AVERAGE usage
rate. Clearly being able to deliver 1,000 watts throughout the day is
sufficient to provide this. You are speaking of peak power ratings-
required for starting and stopping motors, and other short term
requirements. These can be provided by a small -very small if you
have constant access to satellite beamed power- energy storage, a
combination of capacitor and low-cost battery system that can deliver
25kW or more in short bursts or brief periods of time.
 
> There are also gas supplies for heating, again multiple kilowatt,
> typically mean 3kW averaged over the whole year, so more than that in
> winter.

I'd like to see the figures on that. I'm not doubting it. Even so,
replacing the electrical requirements for a household is sufficient to
get into business. If you want to replace the heating oil and natural
gas supplies you have to sell power at around $0.02 per kWh. Which is
doable if you have sufficient satellites and have surplus capacity
after you sell all you can at $0.08 per kWh. The whole business model
becomes similar to a movie owner who sells regular tickets and then
tickets for students and seniors. He has two price points to maximize
return on his seats - depending on theater size and venue.

If we were in the satellite power business as the 'theater' of
satellites grows, we'd pick up second tier pricing to continue revenue
growth. No problem. Since we can beam power anywhere any time the
sky is clear, we can cherry pick the most valuable markets first and
then adopt second tier pricing as we fill demand at the higher price.
  
> What the conversion efficiency is for various apps I dont know, but it
> wont be 100%, so your power figures seem a fair bit out.

We're looking at overall cycle efficiency of 40% sunlight to device.
The stage efficiencies I quoted are high. Laser energy to heat on a
black body is nearly perfect. Laser energy to band-gap matched
photocell ditto. Laser energy to a mix of light by dye pumping - more
efficient than light bulbs!
 
> A 10kW peak beam would be adequate for most domestic properties, if
> not used for heating. Add heating and you'd need to something like
> double it.

You are confusing average rates with peak rates. Think of a hybrid
car. You have a constant power primary source and a variable power
secondary source. This is the way I see it happening. That's because
you'll have periodic primary interruptions throughout the day.

>
> I guess you modulate the beam power according to demand, which gives
> you the diversity factor. But I think youre going to need to allow
> more like 3kW for domestic properties as an absolute minimum, and one
> that would not be accepted today, and 10kW+ where you supply heating
> power too. To gain acceptance today you'd need to provide more like
> 10kW peak, with, guessing here, an average of maybe 6kW if youre
> covering heating as well.

You just put out more receivers. That's all. The big issue is the
price point for the second teir market. You enter the market at $0.08
per kWh and once that's fully populated you come out with a second
tier product at $0.02 per kWh for heating. I agree, you might have to
have a two or three beam system ganged together for greater power
delivery - more for larger users. Industrial facilities may even have
an array of receiver on their roof. No big deal. We'll market them
in 1 kW increments though.

>
>
> Now, you have a beam providing upto 1kW or 10kW, with guard beams.
> What happens to the eyes of bystanders when a tiny speck of something
> metallic drifts through the air, and while the guard beam is no longer
> interrupted it gets into the power beam?

Depends on the details.

http://www.defra.gov.uk/environment/airquality/aqs/air_measure/pdf/05.pdf

According to research airborne metals usually occur around smelters
and nowhere else. Further, roof mounted receivers are usually not
visible in the building or on the ground. So, we're talking about
airborne metal particles that are in a beam well removed from the
receiving point - several dozens if not hundreds of meters up or more.

Now, whats the size. According to the reference above 15 um to 2.5 um
- so, assuming a spherical particle we have a projected area of 177
square micrometers. The albedo of these particles is usually 70% or
less. Being spherical they reflect light in all directions from
across their projected surface;

http://cmp.felk.cvut.cz/~svoboda/Demos/Omnivis/SphereChr/sphere.html

Now, if we are projecting 100 million micro-watts per square cm in our
power beam, and there are 100 million sq um per square cm - that's one
micro-watt per square micrometer. So, we're talking about 123
microwatts from the largest particle of metal listed in the reference.
 This 123 microwatts is dispersed like the image in a panoramic
camera. The spherical area which the total energy spreads across
increases as the square of the distance from the particle, so, 1 meter
from the small 2 cm diameter beam, we have 1/102 billionth of the
power per unit area.

http://members.misty.com/don/lasersaf.htm

Laser safety limits are in the milliwatt range. If you cannot point
the laser at anything but a receiver - which conjugate mirrors
gaurantee - then the only problems you cannot overcome is something
reflective in the beam. An airborne particle won't reflect enough
energy even if its shiny because anything big enough to stay in the
beam is too small to reflect much energy. Anything big enough and
shiny enough to cause problems will fall out of the beam, or shut the
beam off, or cause the beam not to illuminate it. Remember the
particle casts a shadow in the pilot beam too - and that means that
area is removed from the returning power beam. So, the Rayleigh limit
of the projected area for the beam forming window on the satellite
gives a lower limit for that.

In any case its difficult to imagine a scenario where a well regulated
beam would cause a problem - even round a metal smelter that didn't
control their emissions.

> Also there is the cost of the ground based conversion and control
> equipment. And the many business runing costs to factor in too.

When you put a lot of intelligence in the holographic beam steering
device, the ground based equipment can be rather simple. Which is the
whole point. Sort of like the cost of radios versus the cost of radio
stations.
 
>
> > This is enough to sustain growth until market saturation. Also to
> > sustain some research into ways of expanding laser energy use,
> > resulting ultimately in personal laser rocket driven vehicles and
> > laser powered homes, as well as laser powered package delivery.
> >
> > At this point the numbers are just silly, because the economic growth
> > spurred by these developments create fantastic growth. Comparing what
> > might be possible is akin to comparing horsedrawn carriages and
> > gaslight era industry to modern fuel injected autos and electric
> > utilities - there is scant recognition of similarities. So, speaking
> > of it in any useful terms paints one as a mad man.
> >
> > So, I've learned to be quiet. :)
>
>
> I think you need to address many questions yet.

Why should I give others a road map?

> I'm not saying you
> havent, but people dont buy these ideas unlses you can explain it all
> to them.

Or demonstrate a working system.

> We need a site that explains every aspect, provides realistic
> figures with full costings, and most importantly explains the numerous
> questions people have.

That's one way - you would still have objections - and it would hurt
our efforts to build a terrestrial solar business built around far
simpler concepts of focusing sunlight.

> What you propose is a very big leap indeed,

Yes.

> and would only be
> considered by people if you can answer all their questions. It is when
> people cant answer the relevant questions but insist that it will work
> that a reputation problem occurs.

I've been able to answer all questions since very few of thought of
things I haven't considered. Further, all conferences I have attended
I have faired well. So, I have no problem there. Even so, I am
speaking now of the business community, not the technical or
scientific community - if one spends money on far out things they're
not considered 'practical' which is a death knell for any serious
business management career.

>
> Regards, NT

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