Scientists beam solar power to Earth from space for first time ever
space.com
space.com
> Hajimiri, who led the Caltech that developed MAPLE, explained how the wireless transmission of energy through space is based on a quantum phenomenon called “interference.”
And then they go on to describe classical wave interference. I think the point they were trying to make is that the satellite uses a digital phased array antenna to direct its energy downward, but there's nothing quantum about that - it's the same technology used in Starlink terminals and new-ish wifi routers (among many other applications).
They also don't list how much power was received! That's the one figure that matters here I think. I'm curious whether it was watts, milliwatts, or kilowatts.
Although describing it as a "quantum phenomenon" does admittedly dress it up to be far more exotic than it is, since it's an effect that appears in all waves.
If a EM wave has g^(2)>1 then experiments that demonstrate quantum phenomena cannot be successfully performed with this wave. Hence, the EM wave is called classical. Only if g^(2) < 1 can you start doing quantum stuff with it.
In this case, almost certainly the waves have g^(2) > 1.
Since they're claiming to use interference, which only exists in coherent waves, I think it's safe to say in g(2)<1 for the scale they're utilizing interference at. Coherence is so inexorably linked to interference, it's measured using an interferometer.
Second order correlations directly test for the bosonic nature of photons. In quantum light, photons clump together because they are bosons, while in classical light photons are independent of each other and any clumping that happens is purely probabilistic. The g^(2) function tests this degree of clumping.
As for how much power - the team only claims to have "detected" the beam, not to have captured and utilized it, when transmitting from orbit to earth. Given that even with less than a meter between the transmitter and receiver, they only lit up a couple of LEDs, I think discussions of power are a bit premature.
https://www.energy.gov/articles/space-based-solar-power
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Microwave transmitting satellites orbit Earth in geostationary orbit (GEO), about 35,000 km above Earth’s surface. Designs for microwave transmitting satellites are massive, with solar reflectors spanning up to 3 km and weighing over 80,000 metric tons. They would be capable of generating multiple gigawatts of power, enough to power a major U.S. city.
The long wavelength of the microwave requires a long antenna, and allows power to be beamed through the Earth’s atmosphere, rain or shine, at safe, low intensity levels hardly stronger than the midday sun. Birds and planes wouldn’t notice much of anything flying across their paths.
The estimated cost of launching, assembling and operating a microwave-equipped GEO satellite is in the tens of billions of dollars. It would likely require as many as 40 launches for all necessary materials to reach space. On Earth, the rectenna used for collecting the microwave beam would be anywhere between 3 and 10 km in diameter, a huge area of land, and a challenge to purchase and develop.
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Laser transmitting satellites, as described by our friends at LLNL, orbit in low Earth orbit (LEO) at about 400 km above the Earth’s surface. Weighing in in at less than 10 metric tons, this satellite is a fraction of the weight of its microwave counterpart. This design is cheaper too; some predict that a laser-equipped SBSP satellite would cost nearly $500 million to launch and operate. It would be possible to launch the entire self-assembling satellite in a single rocket, drastically reducing the cost and time to production. Also, by using a laser transmitter, the beam will only be about 2 meters in diameter, instead of several km, a drastic and important reduction.
Probably not needed anymore with the recent breakthroughs in battery density but still a nice future we have ahead...
https://www.thedrive.com/the-war-zone/33339/x-37b-space-plan...
It also allows for power production without weather getting in the way. So in some hypothetical space solar based future, a rainy region might still be able to rely on solar by having energy beamed down to a farther out station.
Although yeah, there's so much room down here to place panels that doing it from space is probably not economically worthwhile just yet.
Obviously there are a bunch of downsides, because space.
I dread the weaponization of this tech.
In a well organised world, we'd have raised gas prices steadily to force a changeover. We only did that in patches, but luckily the cost of batteries dropped much faster than anyone expected, so we're firmly in the BEV wins quadrant.
You could do similar for space launch costs vs battery cost to map when space solar makes sense.
Launch costs have plummeted unexpectedly, but the reduction in battery costs have I think even further tipped the balance so this is less economically sensible than it was before.
The result is that you need multiple satellites to provide reliable power to any place on Earth. If they are high enough, they can provide power to other places on Earth. It may mean that still need batteries to store power during the night or when satellites aren't available.
The question is if better to have space solar with batteries or ground solar with batteries. Or multiple space solar or multiple ground solar. My guess is that ground solar will always be cheaper and has the advantage of being more reliable. Also, building long-distance transmission lines might be cheaper than launching solar into space.
To me it looks like building a sufficiently thick undersea HVDC line wrapping around the globe and connecting all the solar installations on the ground would be an easier route. The sun always shines somewhere.
How detectable is "detectable"; what power level did the experiment yield? Microwave satellite transmissions have been "detectable" and very useful for decades. I don't hold it against them if they are 6 orders of magnitude lower than would be useful (yet), but I'd like to know they are getting in the are of transmitting power vs information.
When this is scaled up, what is the energy density in the sky along the beam? Is it enough to have a detrimental effect on insects, birds, airplanes, etc., or can it be kept truly de minimus and still be useful? This is a key question related to considering whether we should just because we can.
Unlike a comm or spy satellite, it has no use except during an active "hot" conflict, so its useful life against any modern military would be pretty limited.
Could be used against forces that lack an ability to reach orbit: against guerilla groups maybe, or to burn opium and coca plantations.
Even just a cursory estimation shows it is going to be much cheaper to send things to space (even high orbit) than buy land on Earth.
And as a weapon it is essentially free. Because when you don't use it as a weapon you just beam that power to your power station. You just divert it temporarily when you need to make your enemy to a crisp. It more than pays for itself.
I wonder if it would ever make sense to beam power from Earth to space? For example there are places on Earth that would be great for large solar farms but don't have sufficient transmission lines to get that power to where it is needed.
Perhaps power from those Earth-based solar farms could be beamed to relays in space that would them beam it down to receivers on Earth that can get the power to where it is needed.
A re-run of the Berlin Wall might do it, but only if the city to which that is an apt analogy is OK with totally enclosing it's entire land area in antenna.
1) Will this heat the atmosphere from the contact with water vapour in clouds?
2) Could a plane passing underneath inadvertently reflect or absorb some of this power, if it's banking and it enters a window, turn into a microwave oven?
3) Really it's a weapon in disguise isn't it, like James Bond villain, or the failed Star Wars programme of the US gov?
4) For the levels of power needed, this is going to add many more satellites around Earth, why is this not being considered even compared to fusion or improving existing processes?
Why do all these various energy transformations (and transfer it then 'wirelessly', LOL) and not just make some sort of lens / mirrors and focus it on specific point on Earth, that would collect it efficiently? Or does atmosphere do too much dispersion/absorption for it to be effective, compared to microwaves?
Exactly. Water vapor attenuates visible light more than microwaves. One way to think about SBSP is as an orbital lens converting sunlight into a form that better penetrates the atmosphere.
The current plan for solar power stations entail using mirrors to focus it to one spot anyway, so the evolution of that might be space mirrors that convert it to a single frequency before beaming it down to a focal point.
Also, the panels/mirrors can be sun-synchronous to receive sun all the time, reducing the amount of them needed (surface panels would not get peak sunlight all the time, and half the time will be shadowed by earth).
I had no idea geostationary satellites were so far away! (Per Google, 36,000 km -- about 6 times the radius of the Earth.)
There are a few more "advantages" (if one wants to frame it that way) over collecting sunlight on the surface, for one the sun always shines in space and depending on the satellite's orbit it could collect energy almost 24/7. It could also be sent to different ground stations depending on demand. In theory, if it ever became viable.
That's because they're on a completely different scale. The Sun is constantly producing absolutely gargantuan amounts of energy, on the order of 173,000 terawatts hitting the Earth constantly.
Comparatively, the entire world population uses about 15 terawatts. Even if the entire Earth switched to microwave beam power, it would be miniscule in comparison.
If it didn't matter to introduce new energy into the system, we could burn all the oil we want since all it does is increase the greenhouse effect, i.e. capture more solar energy and trap it below the stratosphere. Which is exactly what you're doing when you collect energy in space and convert it to a wavelength that can pass more unhindered through the atmosphere.
The number I quoted isn't the wattage that the sun produces. It's just the amount that hits the Earth.
The greenhouse effect isn't the kind of thermodynamics that people are used to in a straight "energy in versus energy out" scenario. The issue with "burning all the oil we want" isn't that we're adding energy to the system, it's that it reduces the energy that can escape. The Sun's energy is the absolute operative factor here, not whatever pittance we generate on the surface.
Technically, haven't the anti-satellite weapons tests that the US, Russia, China, and India have conducted involved wireless energy transfer in space? It was kinetic energy and destroyed the receiver but it was energy transfer. :-)
I thought that this is what the first communication satellite did.
Solar panels are now so cheap that the expensive part is mounting them. There are more efficient panels but they aren't worth the cost. The result is that can put panels on a much larger area.
Perhaps a way to minimize cable tension if at right height + assisted by some space craft?
This isn't a "no": if you're building a space elevator anyway you probably do want to put solar on the top. It's just you don't want to build one only for the solar on the top.
You thought windmills were bad?
Hold my beer.
Because it's a single wavelength, ground stations can be much more efficient than solar; this means 80-90% for the relevant frequencies rather than 20-45% for typical solar PV.
Given the size of the ground stations are necessarily enormous, the energy can be quite dilute and still "interesting" power output.
I don't think it'll pass the geopolitics test, as you need to prove to your enemies that it can't be abused; and I have yet to hear any proponents seriously consider what can go wrong if there's more than one over the horizon at any one time (that reminds me, I do need to write this up properly…), but if there's only one then the maths says it's probably safe.
Unfortunately, the very thing that makes it safe is another reason for pessimism (on Earth): a back-of-the envelope calculation suggests the ground stations have to use about 50,000 tons of aluminium given the size constraints are based on wavelengths, regardless of the power going through them. That's not much for one, but if you need four thousand of them then it's comparable to a 2 TW antipodal power grid which would make space beaming redundant anyway.
I can easily see this being used on a Mars colony to get past the global dust storms, but I don't really see it becoming a major player on Earth thanks to the political issues and the alternatives.
I could see it becoming analogous to current-day satellite phones. Some very specific uses in remote areas, but not the standard for everyone.
Humanity will probably create an Earth-orbiting swarm first, to prove the concept.
And also, we could move large parts of our industry to outside our biosphere.
So 4 mW received. Without saying how much they transmitted does not tell much.
If space debris hits it's the same as any other satellite
MAPLE "radiates microwave energy at 9.884 GHz" [1]. At this frequency, water vapor attenuates, but by less than dry air [2].
> What if some space debris hits it
It breaks.
[1] https://www.its.caltech.edu/~sslab/PUBLICATIONS/2022%20IEEE%...
[2] https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.676-9-201... Figure 5
The instrument then beamed energy from a tiny window installed in the unit to the roof of Gordon and Betty Moore Laboratory of Engineering on Caltech’s campus in Pasadena.