h a l f b a k e r y
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
or get an account
Cover a large portion of the Sahara (or any other large
desert expanse) with solar cells. Use these to power a
microwave emitter to beam energy OUT of the
atmosphere. The frequencies used by GPS satellites are
not absorbed by atmospheric gasses (including
gasses), so the net effect
would be to cool the
atmosphere. Same idea as putting big reflectors outside
the atmosphere, but without having to boost them into
The emitter would have to be powered off (or carefully
aimed away) when GPS or other communication /
military satellite are in its path, to prevent frying them.
Primary purpose would be to offset global warming, but
if the transceiver that could be aimed (like Arecibo),
also serve for satellite and deep space communication,
well as radio astronomy.
Greenhouse effect, explained with pictures
Look closely at the graphs about 2/3 down the page, absorption spectrums [a1, Aug 16 2021]
A patent from 2002
A surface coating composition which exhibits low solar absorption and preferential emission at wavelengths corresponding to atmospheric windows in the infra-red regions
[a1, Aug 16 2021]
Bill Gates will block out the sun maybe
[xandram, Aug 16 2021]
Why the L band is used for GPS
L-band waves penetrate clouds, fog, rain, storms, and vegetation [a1, Aug 16 2021]
Effects of a large Sahara solar farm
[scad mientist, Aug 16 2021]
Supplementary material for above study.
Top of page 3 has calculations for effective albedo with solar panels [scad mientist, Aug 17 2021]
||Umm, I feel this would be a bit like opening your fridge door
to cool your house...
An energy-using system like this will have some losses, that
generally become heat.
Incoming sunlight has already passed through (and therefore
heated, if only a little bit) the atmosphere.
||[neutrinos_shadow], The atmospheric greenhouse
effect isnt just about how incoming sunlight heats
things up, its about the balance of incoming
energy, which wavelengths get absorbed and re-
emited, and how much energy gets trapped versus
escaping back into space. Water vapor, methane,
and carbon dioxide are very good at trapping most
IR wavelengths, but are largely transparent to
microwaves (which is why GPS and other satellite
systems use them) - so it will escape without
further heating the atmosphere.
||[a1]; fair enough. I'm still not convinced that the system can
emit enough energy to offset the losses (solar panels get
warm, that sort of thing). I suppose it only needs to nudge
over 50% to have a positive effect.
||So the idea is to make microwave emitters that work directly from solar panels and aim them at the sky?
||[neutrinos_shadow], of course, this is still a less
than half baked idea. I dont know if theres
enough desert and if the conversion can be
efficient enough. Im not good enough to do the
math properly, but at best I think it could send
back less than 2% of what would ordinarily be
||[Voice], yeah, pretty much. Idea evolved from
reading recently about some ultra-white surface
roof treatments that not only to reflect visible
light but also re-radiant absorbed energy in the
specific narrow IR band that will pass through the
atmospheric window. But that band is pretty
narrow and water vapor still traps some of it.
Microwave band is better but you cant get that
by passive re-radiation.
||OK, so yes, you could collect solar energy by some means
within the atmosphere, and "beam" it out again, reducing
net solar gain. Yes, if you were going to do that, you'd
want to choose an outgoing wavelength that wasn't going
to be absorbed by the atmosphere again. Microwave
probably isn't good from that point of view, because it's
strongly absorbed by water (and there's lots of that) - see
the graph for H2O in your first link. And also, fried
||And then there's the efficiency of generating and emitting
microwaves - if it's not very efficient, you do (as [netrinos
shadow] points out), just end up heating the atmosphere
locally more than you reject to space.
||And then, there's the "build more machines/energy
systems to mitigate the problems caused by too many
machines/energy systems" - kind of argument.
||I had a discussion with the scientist/inventor of the
"ultra-white" surface coating you link to - I was
considering investing, because the way it was described
had huge potential in multiple ways/for multiple
technologies. Ultimately I felt there were some issues
with the experimental method and the answers were a
little vague. So exciting potential, but risk of over-
||Yes, but what if a multi-billionaire on a space jolly got
in the way of the lethal beam of microwave radiation...?
||this doesnt sound any worse than Bill Gates
wanting to block out the sun.(see link)
||//Microwave probably isn't good from that point of view,
because it's strongly absorbed by water //
||Not the entire range of microwave frequenciess. There's
more than one choice but look specifically at the
absorption spectrum of L-band used by GPS (link).
||// you just end up heating the atmosphere locally more
than you reject to space. //
||Net zero in that case, as it's still energy that's come in from
outside of the atmosphere. Even if you don't beam it back
it's not like you have any EXTRA to deal with.
||//what if a multi-billionaire on a space jolly got in the way
of the lethal beam of microwave radiation...? //
||Well, the original idea was to carefully aim and power cycle it
to avoid mishaps, but ... hmmm. "Nice private space
yacht you got there mate. Be a shape if anything ...
happened to it."
||Could finance the whole program.
||I thought you could finance it by using the powerful
microwave beam to burn the moon's surface in the shape of
various corporate logos, for which you could charge big
||// finance it by using the powerful microwave beam to burn
the moon's surface in the shape of various corporate logos //
||There are a lot of possible ways to mark up the Moon - but its
apparent diameter from Earth is too small for an effective
||Yet another reason to bring the moon closer
||Do as you will, but try to stay above the Roche limit.
||Interesting idea for some future time. If we could
magically fund this now, just build the solar panels and use
the generated electricity to offset energy technologies
such as nuclear and fossil fuel that generate heat, but
maybe someday when all heat producing energy generation
is replaced, if the earth is still too hot, I guess beaming the
energy away is a theoretical solution.
||As to covering the Sahara with solar panels to cool the
earth, the desert has a fairly high albedo and reflects about
40% of the solar energy back into space. Solar panels are
black and reflect very little energy back into space. Lets
say they reflect 5% (probably much less) back to space and
convert 20% to electricity. That means that 75% of the
sunlight is being turned to heat instead of 60%. If you can
beam the energy back out with 75% efficiency, then you
can just break even.
||I hit an interesting article about the side effects of turning
the Sahara into a solar farm. [link]
||Note that if you use solar panels to replace some heat
producing electricity generation, you actually do come out
ahead. Nuclear plants apparently have a thermal efficiency
||On the other hand, a combined cycle natural gas plant can
apparently be as efficient as 60%. So, using the numbers I
said before, if you put solar panels on a desert, 35% more
of the incoming solar energy is absorbed and 20% is
converted to electricity, giving it a thermal efficiency of
20/35 = 57%. So a best in class natural gas generator may
produce less thermal pollution than a solar panel added to
the desert (assuming my numbers are close). Of course
that doesn't take into account the CO2 released by the
generator, but it does highlight why we should pay
attention to where we install the solar panels. Solar
panels placed above existing asphalt roads for example
would have great thermal efficiency.
||Good article on the desert to solar farm consequences, thanks.
||// produce less thermal pollution than a solar
||But solar panels cannot "produce" thermal
pollution (even if
they might locally heat up an area that you rather
Whether it heats up the air, ocean, desert sand - or
your Tesla - incoming sunlight is already part of the
thermal budget. And it stays until/unless it
radiates back out into space as EM in some form
through the atmospheric window.
||And if humanity ever taps hydrogen fusion or other
of "limitless" power here on Earth (quantum
fluctuations, anyone?), we'll be in
even more hot water than we are now. All the
worries about greenhouse / global warming will
||[Frankx]; //over- hype/under-deliver//
There's a lot of that these days. One that sticks in my mind
is super-sonic air travel. So many companies have popped up
with promises & pretty graphics, never to be seen again.
||//Do as you will, but try to stay above the Roche limit.// I don't think extra, extra high tides would be pleasant. Or earthquakes.
||[a1] Except that total solar energy gain of the earth is 1.5
||Total human energy use is 160 PWh/year. Incoming solar
outweighs that by a factor of 10^4. So if the reduction in
greenhouse gasses allows .01% more of incoming solar
energy to escape, it's balanced.
||And much of that current energy use is, for human time
scales, producing energy just as much as any sort of
matter conversion type generation would.
||[scad] Sand reflects about 40% of incoming energy back
outwards, at surface level. But some of that will be
absorbed by the atmosphere on the way back out (yes, what
hits ground is heavily weighted to wavelengths the
atmosphere doesn't absorb well, but "well" is not the same
as "at all". I can't actually find numbers for net energy
balance of sand, round trip.
||// Total human energy use is 160 PWh year //
||For now. You just wait until everybody has a Mr. Fusion in
house and car.
||If you want a good conspiracy theory, imagine TPTB already
have this capability, and are withholding it from the masses.
Why? Because of what would happen if "they" let every
person on the planet have a few free gigawatts to play with.
We'll be the frogs in
the pot of boiling water, turning up the burner on our own.
||// Sand reflects about 40% of incoming energy back
outwards, at surface level. But some of that will be
absorbed by the atmosphere on the way back out //
||I was under the impression that the definition of albedo
was the fraction of of solar energy reflected back to space,
so the 0.4 number quoted for deserts already accounted
for atmospheric absorption. However I can't seem to find a
link that says that definitively. Wikipedia attributed the
0.4 number to a 1983 paper, but I could only find the
abstract online. The article I linked to links to a study. In
the study they say a 15% efficient panel will decrease the
albedo of the Sahara dessert and that a 30% efficient panel
will not affect albedo, with a footnote (30) saying
"Materials and methods are available as supplementary
materials." I found a link on that page to the
supplementary materials [link], and it appears that they are
using calculations similar to mine (top of page 3) except
they say the solar panel reflects 10% of the light compared
to my guess of 5%, and they assume efficiency of 15%, not
20%. They use 0.4 for Sahara albedo. However they don't
specify whether or not these number take into account
||// But solar panels cannot "produce" thermal pollution //
Sorry I was using the term "produce" loosely. If you
compare the air/ground temperature in the dessert before
installing solar panels, to the temperature after installing
them, and it shows an increase, I am saying that increase
in temperature was produced by the panel. A nuclear
reactor sitting somewhere will actually produce heat. Both
solar and nuclear will also produce electricity that will in
most cases also be turned into heat elsewhere, but I'm not
counting that as heat because as discussed in this idea,
maybe we're beaming that energy off-planet, or as I
discussed, offsetting electricity produced some other way.
||How much pollution to make a solar panel these
||If you're going to beam the energy away, use it to lift
a satellite or something to orbit.
||Or target some space junk with it.
||// target some space junk with it //
||Someone already suggested billionaire "accidentally"
bumping off some spoiled Bozos personal space yacht -
would that count?
||For now I'm only suggesting this to re-radiate incoming solar
energy to balance the atmosphere's thermal budget. If/when
non-fossil, non-solar power sources account for enough of
that thermal load, we can look at that.
||I wouldn't worry about it until the lizard people let us have
access to that technology though. Which they probably
won't, unless we can show how we would solve little
problems like this one.
||//imagine TPTB already have this capability, and are withholding it from the masses. Why? Because of what would happen if "they" let every person on the planet have a few free gigawatts to play with//
||With enormous amounts of cheap energy comes the ability to build all sorts of thing that can reduce the total energy in our atmosphere and water. We could bake calcium and dump it into the water. We could paint all the roofs white. We could build a giant refrigerator for the ocean and send the heat upwards. We could stop burning oil for energy. We could extract CO2 from the atmosphere, break it apart into C and O and use the C to make cool space ships and swords.
||//the air/ground temperature in the dessert before installing solar panels//
||By the time you have finished the installation, your pudding will be cold, so it's a moot point anyway.