[ExI] Trying for a minimum technical comment

[Keith Henson]

On Sat, Dec 15, 2012 at 4:00 AM,  Thirdeye Of Eris
<thirdeyeoferis at gmail.com> wrote:
>
> You plan to beam the power down by microwave? The slightest variation would
> send the "beam" skittering across the landscape, burning everything in it's
> path.

You could research the subject before making irresponsible pronouncements.

http://en.wikipedia.org/wiki/Space-based_solar_power#Safety

> This is why we have not sent up the satellites that have been on the
> drawing board since the 70's...

Not at all.  It's the lift cost to GEO that make them uneconomical.
Page 32 here:

http://www.sspi.gatech.edu/aiaa-2009-0462_ssp_alternatives_potter.pdf

mentions 2 orders magnitude or around $145,000/kW.  For a 6.8%
discount rate, you can compute the cents per kW by taking the dollar
cost and dividing it by 800 to get cents per /kWh.  That turns out to
be $1.80 per kWh.  There no large market for power at this cost.

> From: Adrian Tymes <atymes at gmail.com>

> On Fri, Dec 14, 2012 at 9:07 AM, Thirdeye Of Eris

BS deleted
>
> This is one of the reasons I suggested he might want to
> consider maybe possibly testing it on a small scale - say,
> with a satellite that can (if all goes well) produce barely
> measurable output at the ground - as an absolute
> requirement before putting up the big one, rather than a
> nice-to-have just because it wouldn't be part of said big
> one.

Been done.  Communication satellites produce an easily measurable
output on the ground.  Have you never set up a satellite dish?

> From: Tomasz Rola <rtomek at ceti.pl>
>
> On Fri, 14 Dec 2012, Thirdeye Of Eris wrote:
>
BS deleted
>
> I started to wonder myself and ended with some quick back of envelope
> calculations. First of all, if we try to send a beam from GEO, it's
> 35000km. Let's assume we can position a pow-sat with 1 arcsecond accuracy,
> this translates to this many radians:

Inappropriate math deleted.

Because a microwave system is diffraction limited, the appropriate math is here:

http://en.wikipedia.org/wiki/Airy_disc

Which is why for 2.45 GHz, and a transmission antenna of 1 km, the
rectenna is 10 km in diameter and the power density is relatively low
(1/4 kW/m^2).

On the other hand, the propulsion lasers needed to get the lift cost
down are also weapons.  On a clear day they will put 3-4 GW of power
on the ground at 20 MW/m^2.

> From: "Andrew Mckee" <andymck35 at gmail.com>
>
> Maybe I haven't been lurking around here long enough, but I'm having a hard time understanding why it's necessary to put a large photo-voltaic array in outer space when for far less money we could float a pair of hydrogen filled rafts in the stratosphere over each of the earth's poles.
> Not at the same time of course, but with one enjoying 6 months of 24/7 sunlight the other can be moved towards the equator and at least be on a day-night cycle.
>
> Is chasing 100% utilization really worth the expense of putting a PV array in orbit?
>
> What am I missing here?

Lots.  Particularly transmission cost and storage costs.  And just how
do you propose to move power plants from the arctic?  I know a good
deal about this topic.  http://www.theoildrum.com/node/8323

If you really want to go through the details, ask.  Though there are
precious few on this list who have the skills to go through a
technical paper or a spreadsheet model.

> From: BillK <pharos at gmail.com>
>
> Wind, solar could provide 99.9% of ALL POWER by 2030
> Even better: It could do so at the same cost as fossil fuels

snip

What they don't mention is that fossil fuel is expected to go up
several times as expensive as it is today.  If you don't mind paying
ten times as much for power, that's OK.  Of course the consequences
are a huge die off because fuel and food are tightly connected.
>
> Sounds good to me.

Too good.

Keith