What's wrong with this idea?

Hi folks,
Just a few comments on the SPS idea being bounced between Bobunf and
Tango...

>
>Message: 3
> Date: Tue, 24 Sep 2002 05:02:11 -0000
> From: "victoriatangoman"
>Subject: Re: What's wrong with this idea?
>
>--- In spacesettlers@y..., "bobunf" wrote:
>
>>Electricity produced from solar on Earth is much more expensive
>>than electricity produced from coal, nuclear, oil, gas, hydro or even
>>wind. Producing electricity in space will cost more than
>>producing it on Earth. The principal advantage to space is that solar
>>insolation is about three times what it would be at any point on
>>the Earth's surface.
>>
I don't think I agree with this; the way I have always seen the case
for space presented is that the biggest advantages have to do with
plentiful, inexpensive resources (including insolation, true) and low
transport costs. These considerable advantages must be weighed (no pun
intended) against the costs of getting out of our gravity-well.

>>But the cost of delivering, assembling and maintaining electric
>>generating equipment to and in orbit much exceed the cost of the
>>same tasks performed on Earth by orders of magnitude.
>>
Actually, the same tasks cannot be performed on Earth - unless you'd
care to take a stab at building a self supporting thin-film mirror about
3 km across. Also, if your objection here centers on the launch costs,
what effects would fabricating the equipment on-orbit from space
resources have on your projected pricing?

>> But even if
>>constructing this facility in orbit cost the same as on Earth (a
>>ridiculous assumption within the range of any foreseeable
>>technology), there would still be three show stoppers:
>>
>>1. The losses inherent in converting electricity to some form of
>>beamable energy which must be at least 50% and probably higher.
>>
>Why must it be? Is this new research that you're quoting? Could you
>post a citation for us? The body of research that underlies the
>discussion on this group has been performed by scientists, published
>in peer-reviewed journals and their results have been duplicateable.
>Unless you can provide us with some support for your claim that the
>losses must be >50%, then I think I'll rely on the proven numbers
>thus far, which show a conversion efficiency of 85% from DC to radio
>frequency. In the SSI list, Charles Radley was able to provide some
>data which was summerized by William Mook, that breaks the whole
>process down as follows.
>
>DC to RF 0.85. . . . . . .Conversion at the SPS
>Antenna 0.98 . . . . . . .Power sent from SPS
>Atmosphere 0.98. . . . . .Atmospheric attneuation
>Energy Collection 0.88 . .Earth Rectenna Efficiency
>RF to DC 0.89. . . . . . .Conversion at the Rectenna
>Grid .97 . . . . . . . . .Convert DC to AC with Inverter
>
>Thus, .85*.98*.98*.88*.89*.97 = 62.02% overall efficiency delivered
>into the grid.
>
Hi Tango - I notice you got some better numbers than I could supply,
but I also notice that you don't list a solar to DC efficiency. If I
may ask, what sort of technology is assumed, and at what efficiency? It
occurs to me that I have assumed PV, and that the 35% efficiency I gave
them in my example was very generous, but Bobunfs' idea of a steam
turbine is actually quite good - I got to looking through one of my
ancient college physics texts and the Carnot efficency of steam turbines
can be very good in space.

>>And there will additional losses in the energy beam--aiming and
>>focussing will not be 100% perfect all the time, and there will be
>>atmospheric losses.
>>
>>2. Converting this beamed energy back into electricity is not a
>>trivial problem. The best technology for doing this currently
>>would be using a steam turbine generator at less than 40% efficiency.
>>
>How did you come up with the conclusion that a steam turbine
>generator is the best option? You really should dig deeper into the
>research on the matter of SPS and associated technologies!
>
Ok, here the idea of a steam turbine is actually quite bad - a
rectenna can convert microwaves into DC much more efficiently than this.

>>3. The solar energy which is not converted into electricity will
>>be deposited as heat onto the power satellite. With photovoltic
>>there is a theoretical maximum efficiency of 37%. If there's not enough
>>energy in the photon to flip the electron, all the energy of the
>>photon is deposited as heat. If the photon carries excess energy,
>>that excess is deposited as heat. The best commercially available
>>PV cells today opearate at less than 20% efficiency, and they are
>>very expensive.
>>
>>At least 63% of the solar energy must be deposited as heat,
>>probably closer to 80% with current off-the-shelf technology. In addition,
>>the energy lost in converting electricity to beamable energy will
>>also be deposited as heat. More than 80% of the energy received
>>from the sun will be used to heat the power satellite, and convention
>>is not available in a vacuum.
>>
All good points, and quite true as far as I can tell - but don't
limit your thinking to PV. Also, as misirable as PV looks to you right
now, consider that it actually is the energy source of choice on-orbit
with todays technology; the ISS consumes somewhere near 100 Kw, and
supplys all of its needs with PV without boiling the crew.

>>Using current technology I calculate the electricity delivered
>>from a satellite would cost about 15,000 times more than today's
>>conventionally supplied electricity. A $100 electric bill would
>>rise to $1.5 million.
>>
>Please show us how you calculate your 15,000X factor. I really want
>to understand your argument, but all of your conclusions are
>unsupported, so basically, I'm left with you presenting no argument
>other than wild assertions.
>
>If it comes down to having to compare your unsupported asertions
>against those of others who have actually done published research
>and show that SPS, less lift costs and space development costs, is
>more than economically competitive against any earth based power
>solution, then hands down I'll support those who actually present
>evidence to supoort their conclusions.
>
>And a last thought, do any of the earth based solutions have to
>completely support the infrastructure they use on earth, e.g.
>housing for workers, food they eat, transportation network,
>vehicles, and development.
>
I'd like to see the calculations on the "15000 times" figure as
well. I also agree the playing feild isn't remotely level - but perhaps
we're just going to have to deal with the idea that it never will be;
the inherent differences in how the infrastructure is built, shared, and
maintained might be the one advantage that planets have. What needs to
be done is to make space competitive in spite of the seeming unfairness
of the current market.