
Harvesting solar power in space and sending it back to Earth - recordcore
http://scinotions.com/2013/08/harvesting-solar-power-in-space-and-sending-it-back-to-earth/
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kokotko
"Let me tell you one of my pet peeves: space solar power. Okay, the stupidest
thing ever. If anyone should like space solar power, it should be me. I got a
rocket company and a solar company. I should be really on it, ya know. But
it's like, super obviously, not going to work because, ya know, if you have
solar panels - first of all, it has to be better than having solar panels on
Earth, so then you say, okay, solar panel is on-orbit, you get twice the solar
energy - assuming that it is out of Earth's shadow - but you've gotta do a
double conversion. You've gotta convert it from photon to electron to photon,
back to electron. You've got to make this double conversion, so, okay, what's
your conversion efficiency? Hmm. All in, you're going to have a real hard time
even getting to 50%. [The solar cells are better.] It does not matter, put
that cell on Earth then. See, that's the point I'm making. Take any given
solar cell, is it better to have it on Earth, or is it better to have it on
orbit? What do you get from being in orbit? You get twice as much sun - best
case - but you've got to do a conversion. You've got to convert it the energy
to photons - well, you have incoming photons that go to electrons, but you -
you've gotta do two conversions that you don't have to do on Earth, which is
you've got to turn those electrons into photons and turn those photons back
into electrons on the ground, and that double conversion is going to get you
back to where you started, basically. So why are you bothering sending them to
bloody space. "I wish I could just stab that bloody thing through the heart."
BTW - electron to photon converters are not free and nor is sending stuff to
space. Then it obviously super doesn't work. Case closed. You'd think. You'd
think case closed, but no. I guarantee it's gunna come up another ten times. I
mean, for the love of God."

Elon Musk ([http://shitelonsays.com/transcript/elon-musk-panel-
bta-2012-...](http://shitelonsays.com/transcript/elon-musk-panel-
bta-2012-2013-01-28))

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schiffern
>solar panel is on-orbit, you get twice the solar energy - assuming that it is
out of Earth's shadow

Not quite. When compared to stationary panels (which beat trackers
economically, so they should be the baseline), space-based power harvests π
(yes, pi) times as much sunlight due to lack of cosine loss, plus there's the
bonus of reduced reflective loss. Atmospheric and weather loss is avoided
entirely. I would estimate 4-5x the energy.

The big advantage of space-based solar imo is the ability to create giant
collection areas defined by minutely pressurized helium structures. A giant
parabolic mirror on Earth needs to fight gravity, winds, and the Earth's
rotation (tracking). Similar concept: [https://tec.grc.nasa.gov/past-
projects/solar-concentrators/a...](https://tec.grc.nasa.gov/past-
projects/solar-concentrators/advanced-thin-film-inflatable-concentrators/)

Launch a 30,000 m^2 concentrating collector in a single launch? It's only 12
MW, but it's constant (unlike ground-based solar at ~18% capacity factor), and
it's deliverable anywhere in the world, or even to other satellites. What if
microsatellites could summon extra power by POSTing an ephemeris to an
endpoint? Is there a market there?

It's an interesting niche tech, but spaceflight is just so expensive that I
doubt it'll ever be viable.

~~~
Gravityloss
Concentrators have problems.

If you use them with solar panels, then your panel will heat up and its
efficiency will drop. Maybe lifetime as well. If you use a thermoelectric
generator, you then have wearing mechanical low efficiency systems on board.

In both cases you need to reject heat, which is hard in space.

They also require precise pointing.

There's also the problem of beaming the power to earth. If you're in low
orbit, there would have to be lots of receiving stations and the power would
be intermittent unless you had a big constellation. And all the problems with
inclination and the spinning earth... If you're in geostationary orbit, your
sending and receiving antennas would need to grow huge.

What about beaming between satellites? You'd need a laser for that. Maybe
they're becoming quite small and efficient with modern semiconductor
technology developed for military uses. Still the receiving end might have low
efficiency.

~~~
schiffern
Yep, after writing all that I realized that heat rejection is going to be a
problem. Dissipating 8.4 MW is no easy feat in orbit.

At that point the balance of system probably shifts to thin film PV. There
would need to be a _lot_ of advancement in that area before such a project
becomes practical.

>What about beaming between satellites? You'd need a laser for that.

I was picturing a microwave rectenna, actually.

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Gravityloss
If you use a laser, the receiving satellite wouldn't need extra hardware, it
could use its ordinary solar panels, if they were pointed in the right
direction.

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jacques_chester
Before the SimCity joke parade begins, remember that the frequencies that are
useful are the same frequencies that won't interact with biological matter.

Why?

Because if you pick a frequency that, like a microwave oven, heats up water,
then you are wasting energy. The atmosphere is well stocked with water at
varying, often unpredictable levels. Wasting beam energy on heating up passing
water molecules is kinda pointless, so the frequencies chosen pass through
without interacting.

So no. A beam going off axis will not set your city on fire.

In terms of the actual concept, the original book to read is Gerard O'Neill's
1976 _The High Frontier_. O'Neill proposed to boostrap orbital colonies at L4
and L5. These colonies would build and maintain orbital solar stations.

I think that realistically, that window has passed. If solar power stations
were built now, it'd all be done remotely. That's a pity, because as romantic
engineering visions go, O'Neill colonies were amazing:
[http://en.wikipedia.org/wiki/File:Spacecolony4.jpeg](http://en.wikipedia.org/wiki/File:Spacecolony4.jpeg)

~~~
abecedarius
Powersats as basis for space colonies never added up for me -- couldn't the
funders find work crews willing to live closer to spam-in-a-can style for
higher wages, with overall much lower cost?

But I loved the space colony vision even so, and it was sad feeling it slip
away over the decades. You can read Heppenheimer's book online:
[http://www.nss.org/settlement/ColoniesInSpace/](http://www.nss.org/settlement/ColoniesInSpace/)
(I remember it as better than O'Neill's, though of course O'Neill gets much
more credit for the ideas.)

~~~
jacques_chester
I reckon I might have read that book too. Certainly the art rings some bells.

~~~
dredmorbius
I think Heppenheimer's book re-used much of the O'Neill art.

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jacques_chester
Some of it is distinct.

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dredmorbius
Not mutually exclusive statements ;-)

~~~
jacques_chester
Sorry, I didn't see the "much of" qualifier.

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brianmcconnell
This might make sense _if_ we had run out of real estate to plop down solar
panels, but that's not the case. You can easily cover a few acres in static
mounted solar panels, hose the dust off them every now and then, and they'll
last 30+ years. A space based power plant, that crap will break down in a few
years max.

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goombastic
No. Bad idea, while everyone is trying to disintermediate and run the brokers
out of every business, why get another centralized energy provider? This is
like the oil con.

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dredmorbius
Cost would be absolutely prohibitive.

The one benefit to space-based solar with some form of power beam (likely
microwave based, look up Heppenheimer's book it's now online) is
_reliability_. Solar presently only works when the Sun shines -- that's during
daylight, and not under cloudy conditions.

Orbital solar would be 24/7/365, with the exception of a couple of brief
outages each year at high noon on the equinox when your powersat was eclipsed
by the Earth itself. Feed-ins from another location could glide you through
this, or a reserve biomass-fed plant, or ... The point being it's an utterly
predictable downtime.

The alternative is to build out a (vastly cheaper) ground-based solar
infrastructure ... and find some viable way of storing energy for a period of
time (possibly up to a couple of weeks). A hard problem, but ultimately less
hard, I suspect, than trying to orbit megatons of material.

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icegreentea
This blog likes to crush various energy schemes with math and physics.

[http://physics.ucsd.edu/do-the-math/2012/03/space-based-
sola...](http://physics.ucsd.edu/do-the-math/2012/03/space-based-solar-power/)

Honestly, reading through his stuff is almost depressing. But as long as he
sticks to the physics stuff, it's pretty hard to argue - all the math and
sources are there.

The planned proposal claims that they can use some nifty beamforming to get
good microwave transmission. It appears that the proposed technology will
reduce the weight to diameter size of the transmitter, but Do The Math's
calculations should still more or less be in the right magnitude.

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Fortaymedia
SORRY WHAT? Send the energy back in the form of microwaves? I'm assuming this
means lining something up on the ground to receive it? What if its goes off
course or is knocked by a small meteorite? are all those waves going to just
fry us instead?

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tehwalrus
I'm reminded of Henry Tam's book "Kuan's Wonderland,"[1] where [SPOILERS] the
government blocks out the sun with a disk in space, and then sells you the
energy via a subscription. If you don't have one, you freeze to death.

[1] [http://www.amazon.co.uk/Kuans-Wonderland-
ebook/dp/B008144G9I...](http://www.amazon.co.uk/Kuans-Wonderland-
ebook/dp/B008144G9I/ref=sr_1_1_bnp_1_kin?s=books&ie=UTF8&qid=1377775573&sr=1-1&keywords=kuans+wonderland)

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k__
Would it be possible to put something like a lens in space? Geosational so
that a focuspoint would "draw" over the earth, where many solarpanels are put
down.

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ndonnellan
Keep the power in space. Use it to mine asteroids and convert water-ice to
rocket fuel. With the asteroid as a heat-sink, your efficiency will be
amazing!

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aufreak3
It would be nice if the article had some absolute minimal details on how about
10 terrawatts of power[1] is going to be beamed down, and if that's a no
brainer, over what _area_ is it going to be beamed down.

[1] Based on energy consumption figures from
[http://en.wikipedia.org/wiki/World_energy_consumption](http://en.wikipedia.org/wiki/World_energy_consumption)

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racbart
Taking aside feasibility of this, having a single source of power delivering
33% of world's energy is a terrible idea. Especially if it would not be quick
to fix or replace if it'd had been completely destroyed. Such a single point
of failure would become a single point of doom if the world suddenly would be
cut off of third of its energy for weeks or months.

~~~
XorNot
Except it's not a single source. It would be dozens of satellites, hundreds
ground stations etc. This is like claiming that "coal power" is a single point
of failure.

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racbart
“According to his calculation, one such satellite is able to supply a third of
total energy needed by humans.”

I'm just commenting on what they wrote and I see nothing about a farm of
satellites in the article. Perhaps the original source is more clear about it.
Or maybe this technology doesn't scale down well and that's the reason they're
writing about one powerful satellite?

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schiffern
Article is content free; here's the paper:
[http://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_Alph...](http://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_Alpha.pdf)

11,800 tonnes in GEO for 500 MW. At Proton-M prices, that's $295/watt for the
launch. Not great…

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whadar
They can just fill Energons and send those back to earth...
[http://tfwiki.net/wiki/Energon](http://tfwiki.net/wiki/Energon)

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alokv28
I'm confused. Is there an announcement or update of some sort associated with
this project? It's unclear from the article.

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babuskov
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AutoCorrect
why convert from photon to electron back to photon? Why not just use mirrors
to focus light on lasing material and create a laser directed to a solar
panel/s on the Earth and then convert to electrons?

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loxs
Hmm, this can be used as a weapon of mass destruction?

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shacharz
I get a 503

