Technology capable of collecting solar power in space and beaming it to Earth to provide a global supply of clean and affordable energy was once considered science fiction. Now it is moving closer to reality. Through the Space-based Solar Power Project (SSPP), a team of California Institute of Technology (Caltech) researchers is working to deploy a constellation of modular spacecraft that collect sunlight, transform it into electricity, then wirelessly transmit that electricity wherever it is needed. They could even send it to places that currently have no access to reliable power.
“This is an extraordinary and unprecedented project,” says Harry Atwater, an SSPP researcher and Otis Booth Leadership Chair of Caltech’s Division of Engineering and Applied Science. “It exemplifies the boldness and ambition needed to address one of the most significant challenges of our time, providing clean and affordable energy to the world.”
Atwater, who is also the Howard Hughes Professor of Applied Physics and Materials Science, leads the project jointly with two other researchers: Ali Hajimiri, Bren Professor of Electrical Engineering and co-director of SSPP; and Sergio Pellegrino, Joyce and Kent Kresa Professor of Aerospace and Civil Engineering, co-director of SSPP, and a senior research scientist at the Jet Propulsion Laboratory (JPL).
Harnessing solar power in space relies on breakthrough advances in three main areas:
- Atwater’s research group is designing ultralight high-efficiency photovoltaics (materials that convert light into electricity) that are optimized for space conditions and compatible with an integrated modular power conversion and transmission system.
- Hajimiri’s research team is developing the low-cost and lightweight technology needed to convert direct current power to radio frequency power (which is used to transmit cell phone signals, for example) and send it to Earth as microwaves. The process is safe, Hajimiri explains. Non-ionizing radiation at the surface is significantly less harmful than standing in the sun. In addition, the system could be quickly shut down in the event of damage or malfunction.
- Pellegrino’s group is inventing foldable, ultrathin, and ultralight space structures to support the photovoltaics as well as the components needed to convert, transmit, and steer radio frequency power to where it is needed.
The basic unit of the system the researchers envision is a 4-inch-by-4-inch tile that weighs less than a tenth of an ounce. Hundreds of thousands of these tiles would combine into a system of flying carpet-like satellites that, once unfurled, would create a sunlight-gathering surface that measures 3.5 square miles.
Work on the SSPP has been supported by more than $100 million in funding from Donald Bren, chairman of the Irvine Company and a life member of the Caltech community, and his wife, Brigitte Bren, a Caltech trustee. The Northrup Grumman Corporation provided funding for initial feasibility studies.
Atwater, Hajimiri, and Pellegrino discussed their progress—and the transformational potential of space-based solar power—as the project nears a significant milestone: a test launch of prototypes into space in December 2022.
Describe the vision behind the Space-based Solar Power Project. How did the project take shape?
Sergio Pellegrino: It was more than 10 years ago, in 2011, that conversations began with Donald Bren asking whether Caltech had any ideas when it came to research in the field of sustainable energy and space. We started discussing, in a group of faculty members, ways of building on our interests and what was happening in each of our areas that might lead to a very impactful research initiative. Over a period of a few months, we came up with a vision—I called it a dream—of three or four technology breakthroughs that, in combination, would transform the way space solar power had been previously approached.
Ali Hajimiri: This concept was, in the past, truly science fiction. What made it possible for us to consider taking it from the realm of science fiction to the realm of reality was the combination of developments happening in photovoltaics in Harry’s lab, in structures in Sergio’s lab, and in wireless power transfer, which is happening in my lab. We realized that we can now pursue space solar power in a way that is becoming both practical and economical.
One of the first questions that anyone asks is, “Why do you want to put photovoltaics in space?” Well, in space, where you don’t have day and night and clouds and things of that sort, you get about eight times more energy. The vision of this program is to be able to provide as much power as you need, where you need it, and when you need it.
What progress have you made toward realizing this ambitious vision?
Pellegrino: Over a period of two years, we built and demonstrated a prototype tile. This is the key modular element that captures the sunlight and transmits the power. Through that process, we learned many things about how to design highly integrated and ultralight systems of this sort. We then developed a second prototype, 33 percent lighter than the first.
Hajimiri: This tile is the building block, as Sergio mentioned, of the larger system. It has to be fully functional, compatible, and scalable. Although it may sound simple, it’s actually quite sophisticated. These tiles are mounted on a very flexible structure that can be folded to fit in a launch vehicle. Once deployed, the structure expands, and the tiles work in concert and in synchronization to generate energy, convert it, and transfer it exactly where you need it and nowhere else.
What can you tell us about the next phase in this project?
Atwater: It doesn’t get real until you actually go to space. As Sergio and Ali described, we demonstrated this key unit element called a tile in our labs. One of the lessons from that series of demonstrations was that the pathway we needed to follow for photovoltaics fundamentally had to change. We were working with what I’ll call conventional photovoltaic materials, which had to be designed in a form that was going to make it difficult to reach the mass-per-unit area and specific power goals, so we had to basically rethink the photovoltaic strategy completely. As a result, the classes of photovoltaic devices that we are testing in space have actually never flown in space before.
Pellegrino: Most spacecraft today have solar arrays—photovoltaic cells bonded to a carrier structure—but not with this type of material and not folded to the dimensions we’ve achieved. By using novel folding techniques, inspired by origami, we are able to significantly reduce the dimensions of a giant spacecraft for launch. The packaging is so tight as to be essentially free of any voids.
Hajimiri: Wireless power transfer of this nature has not been demonstrated in space. We are also demonstrating it with our flexible, lightweight material, not necessarily a rigid structure. That adds complexity.
If and when space solar power becomes a reality, what impact might it have on society?
Hajimiri: It is going to revolutionize the nature of energy and access to it so that it becomes ubiquitous, it becomes dispatchable energy. You can send it where you need it. This redirection of energy is done without any mechanical movements, purely through electrical means using a focusing array, which makes it extremely fast.
Atwater: I think one can say that the Brens’ vision really was to do something that, as Ali mentioned, originally emerged almost from science fiction, to do something that would become a large-scale energy source for the world.
Pellegrino: We have had JPL collaborators join our team, and that collaboration has become powerful and useful to us as we start thinking about these space demonstrations. The discussion about energy that was implicitly limited to powering the earth actually extends to space exploration also. We’re opening new chapters in the way JPL is thinking about future missions.
Speaking of collaboration, work across research areas has been integral to SSPP’s success. What has it been like to work together so intensely over the course of a long-term project?
Hajimiri: The students, the postdocs, all of us have been working very closely, and we’ve been learning a great deal about each other’s domains. This results in something that’s more than the sum of its parts, both in terms of the end result of the project as well as in terms of the training the students are getting. That training is incredibly important to the future of space technology, whether it’s for wireless power transfer, communications, space structures, or all sorts of other applications we haven’t even thought about yet.
Atwater: I had a former lifetime working in photovoltaics but never imagined in my wildest dreams that I would get involved in space until this opportunity came together. And for me, it’s been a window on a completely new world of science. That’s been tremendously exciting.
Pellegrino: Sometimes it feels like we are pushing our colleagues to do something that they clearly think is impossible but later turns out not to be impossible. That is just a wonderful feeling. It’s a different kind of research, where you are doing the best you can in your own field, but you are also leveraging the interface with other fields, a collective system that really is going to benefit society. Benefiting society is a much more elaborate thing than doing good work in your own area. It’s so much more challenging.
What environmental impact will the microwave beams have? Specifically will birds be able to fly safely through the beams? Also, will they heat the air as they pass through it?
From what I’ve read in other articles, birds, humans and everything else would be safe. Visions of such a beam incinerating the landscape if it went off course are fanciful gibberish (though by changing the wavelength and making other modifications it might be possible to weaponize this idea – but it wouldn’t be an accident). The air will not be heated (at least not to any measurable degree).
There are so many easier options for providing power. The risks and costs involved make this technology little more than a pipe dream IMO.
Marijuana is legal in California now. So this is what we get??? Absurd.
The idea for changing radiation to clean electricity has been around for awhile but, as this article shows, the enormous problems in the way make such technology (IMHO) unfeasible. Instead, I suggest using very small amounts of plutonium-238 as nuclear radiation sources for electricity for batteries. NASA does this for their deep space missions, where the sun is too distant for solar power. My proposal involves a speculated process different from NASA’s which, if successful, could generate clean auto and house electricity. No more fillups at gas stations, no more electric lines from power stations, no more oil politics. Sure, greenhouse gasses are the main culprit, but if we don’t fix the power issues we don’t fix the changing climate. This is part of my book on Amazon, “Gaia’s Climate Challenge – Giving Humans Their Last Chance”.
Is there danger of ‘space debris’ crashing into the array, damaging it and creating even more ‘space debris’?
I expect such a large array would be “shotgunned” by tiny space debris over time. It would need to be designed to not be fragile and prone to error from such events. I’m guessing that the vast majority of such impacts would not create additional debris if only the thin panels are being perforated. But it will be good to see what happens with the prototypes, as debris is becoming a serious issue in LEO from what I understand. I’d be way more concerned with Starlink on that subject at this point.
Could the capture of additional soler energy lead to an increase in global temperatures?
Even if widely adopted I doubt the power beamed down would be enough to make more than a tiny fraction of a degree of difference. Even if that were an issue, I would suggest that additional power is more a solution than a problem. That is, providing large amounts of power would enable humans to power projects that would reduce temperature increase (such as by evaporating more water to increase the albedo of the earth and increase rainfall in drought-prone areas.)
In the 1970’s Boeing looked at the concept
I’m concerned that the shadow of the earth may periodically eclipse the solar array. Is an eclipse-free earth orbit possible, without using lots of extra energy and/or mass?
Per https://www.sciencedirect.com/topics/engineering/geosynchronous-orbit this would be an issue. I would propose that multiple solar arrays be deployed in different geosynchronous orbits, such that a power receiving station on earth could receive power from several different arrays at any given point in time. Whether this is easy, hard or impossible I can’t say. I suppose it would depend on whether the receiving station needs to be “tuned” to a sending antenna at a particular location or not, and whether power from two (or more) different antennae can send power at the same time.
The delivery of significant amounts of power to the earth over radio waves is a significant problem. If you need hundreds of kilowatts of power in a small location you will need to exceed the radiated power density SAR human safety limits of RF radiation hazard by a factor of millions. Either this is an April fool’s joke or what they’re really working on is a military weapon.
The applications for space exploration alone makes this truly worthwhile.
You mom is a pipe dream
The lack of scientific understanding in some of these comments gives me pause.
I do wonder if this announcement is a direct correlation to the Chinese moving forward with their solar power plant transmission design out of Xidian University.
I don’t understand these things but what I noticed was completely absent was any discussion of this supplying power to millions of people, much less billions. There were several references to targeting power to a specific area which while in emergencies might be good but what we need is power for our whole planet. Maybe all ways will not have that potential. But how many households are they thinking they can reach? Is this something that after billions and much work would at best involve much effort and money just for power for a tiny number?
Park it at earth-sun L1 and give the earth a (very) little shade.
This was the subject of a GCE Physics exam question for teenagers in the ’70s. Here we are, half a century later, still debating it.
SciTech is like Climbing on Stairs. Endless. Just like The Universe is Endless.
Is this a joke or something..?? NASA/Glaser published a Detailed Report on Geo-Synchronous Sattelite based Microwave Power Transmission over 50 years back.. yes probably when these authors were kids or not even born… but is being promoted as “SOMETHING NEW & SPECTACULAR”..
Who are they kidding..???
May be they did not have the gadgets/Equipment then. Probably, Now is the time to experiment, whether it works or not.
Why not apply the massive increase in photovoltaic efficiency they claim to have achieved to strictly terrestrial applications? I cannot imagine their system transmitting power efficiently through the atmosphere given what little I know of RF satellite communications, that kilowatts of satellite transmissions result in femtowatts recieved on Earth. Not to mention the aforementioned comments about the extreme hazards of high energy RF focused to a point on Earth, it seems far too risky to contemplate. Nowhere is mentioned their theoretical array’s power generating numbers, nor how they would offset the development and launch costs. It’s a wonderful concept at face value yet I cannot see it being practical or economically viable, not to mention safe in any way. If anything will be a significant game changer in renewable energy, a revolutionary breakthrough in photovoltaic efficiency will be a key factor. Small scale nuclear electric batteries as mentioned above are an elegant solution yet can never be because of the fear factor. At least the Caltech research can apply to solar energy generation for on-orbit use, perhaps it can translate to new types of terrestrial solar arrays.
Elon Musk Spent $44,000 Millions on Twitter? People much of the time find 2 Roads and they jump on the Wrong Road…Endless !
Striving for Popularity & Dollars is the reason.
Many seem to be thinking like Trump. Many subvariants appeared in S.Africa and in Europe first. Are they Responsible, then? Such appear to be Mouths for Millions of Hard workers, but are only for Fools.
If only they can make Mega Batteries that can get charged safely and store the energy forever. Then, they can repeat the process once in a while, when needed. No such Batteries yet? Both Researches should go simultaneously in tandem.
If this endeavor becomes successful, What will be the next step? Digging Asteroids & Moon etc., for scarce natural resources, because energy will be dirt cheap then ! What is needed is for everyone to finally become a millionaire very fast…Not anyone Resorting to Stealing, Cheating etc., No more Prejudice. Other approaches failed since millennia.
Japan has been working on this over a decade.
Yea japan literaly stole my elemetary idea i designed this idea i was just in fifth grade i was just nine years old scroll down and read my post if you like im 29 now i was just 9 years old
This could be one significant piece in solving the daunting puzzle of clean, abundant energy for all. The “all” being key for this particular methodology, as it would be the most continuous and mobile energy source ever developed. Very exciting development of a technology proposed over half a century ago.
As per the reference to the Japanese effort into this endeavor, although they started sooner, it seems they have challenges to overcome that the Caltech program is designed to circumvent (or at least address from the start). Per the article;
“Transmitting microwaves from an altitude of 36,000 kilometers to a flat surface 3km in diameter is like threading a needle,” he says.
And to build a structure as large as the SSPS in space, Japan will need a new space transport system and sophisticated robots, requiring much more research and development.
Like nuclear power, the space solar concept is also potentially dangerous: how can you prevent unintended zapping?”
Caltech’s current designs and targets address both of these issues if feasible deployment as well as safety concerning transmission. Microwave radiation is a much safer alternative to RF at the required energy densities to make this worth while (which both projects are pursuing, although lasers were also mentioned by the Japanese).
As an after thought, it is always disheartening to see useless comments about new advancements in established scientific ideals such as, “that was already suggested!” as though the idea is dead and any further exploration is fruitless. This belief is so contrary to science at its core, and the irony is immense. Science at its foundations is about pushing the envelope of understanding and ability so to make anything possible. If everyone ascribed to such a belief, the wheel would never have been discovered. As Einstein said, imagination is more important even than intellect!
The new Tesla.
The fossil fuel cartel will do everything in their power to prevent this from happening.
Gerard K. O’Neill from Princeton described this idea in the 70’s. He wanted to build it from lunar materials and use it as a “Cash Crop” to fund space colonies. Yes the idea has been around a lot.
The power beam dispersed to be about a mile across and a safe level of energy when it reached earth.
To receive the power he described a field of “rectinnas” (Combinition rectifiers & Antinne)
So any use location would have to have this antenna array. That limits how quickly flexible it would be.
I wish they’d cover the receiver tech more. My understanding from previous incarnations of this idea from e.g. Gerard K O’Neill is that the rectenna would be like loose fabric or wires strewn on poles over a square kilometer. Not too hard to do and very diffuse so no fried birds. Is that what they’re planning.
Why not use wave pulses transmitted from the solar satellite to earth and turn those wave pulses into sound into electricity use magnets instead of beaming light from the sun to earth safer for the environment and not causing any more global warming. the beaming of sun light to earth from satellite is practically a magnifying glass and we’re the ants it has good intentions but a bad outcome if using of redirected sun light.
I cant believe this people taking our idea and not giving us no credit for this when we were in elementary we brainstormed and designed this idea and we not given anything in return our idea were simply stolen we designed this and we were in 5th grade we took our ideas and gave it to idk who the (beep) we were having trouble with our city bills light, water you name it our city taxes were too much mostly water and we invented the solar switch were u put your hands and turned on took your hands off and the water would stop the water faucet were broken and water would keep running loosing alot of clean water and having a great bill in our city thanks to broken faucets but we changed that we also created the predator drone for our miltary that didnt need an engine only solar power and where we put a special camera that can zoom in from miles and miles away also putting info red lenses and missles for our troops not get killed and make it home safe to there family this project was for counter-terrorism which helped out alot killing all those terrorist even the one trump killed saving us from future terrorist anyways back to my point our school nor anyone ever mentioned our names nor given a job i suffer from mental illness since i was a baby and i died for a couple of minutes 3minutes falling in my head while i was given to one of my family members getting 12 seizures one after another non stop doctor said i was a miracle baby suviving and only bein a newborn and later again dying of hypothermia turning blue having convolutions and seizures again my point is im sharing this becsuse of illegal abortions we should not be having abortions of course only for victims of abuse look what we help create due not dying while a baby we can change the future together i will always remain prolife we made a huge change and we need to stop abortions its changes the whole ball game i will now let you sink in that we created our solar panels to have futher help with this idea and evolving our solar panels idea never ending enegry was our way to help the future openening doors at the hospitals with senors we used to open the door thanks to me and my elementary team this was never out there til we made it happened in my elementary school and at the same time im glad these i dont want to offend noone by name calling thats not me just real sus that they get credited while they making it seem they were the ones that created it since i was in school ive been waiting for someone to help me and my elementary team build this thank you for not giving up on us and restore life as we know it hard to not be able to join the milatary nor other jobs due to my mental illness i hallucinate thats what the doctors call it but i dont i can speak to the dead am a medium and its hard to people think your crazy and want to put u to sleep all day with medicine and scoot you to the side not credit your school and just for you guys to understsnd where im comming from and not lying my son was born healthy as shown me he can also see the dead as well he was scared at first until i taught him what a gaurdian angel was and he didnt fear nothing anymore he would tell me papi look guardian angel and he would be looking at the ceiling saying hi and bye to them he was would also say stop im seein a movie shooo go away and i would tell him be nice he taking care of me and you hes god angel and he say sorry and follow the angel saying sorry come back please dont leave come back sorry and he was only 3 years old so his docotr said he was born normal nothing was wrong so why call me crazy and give me medicine and try to put me in a mental hospital when i changed the future and helped with this life changing ideas we need more people to help and support people with mental illness is what they call it we are also like you guys… please dont scoot me and my son to the side and call us crazy when i can see the world like you do….i just happened to make door that open with sensors and solar panels to make ater come out i am proud to be one special dad and an inventor
P.s sorry if i mispelled something ohhh by the way i always wated to join the military to help clean water and drink clean water for our troops not have a gun and kill i was also taken my name away im the real bobby booshay
Giant microwaves pointing at the Earth.
What could go wrong? Lol.
But the real question is will it cause global warming.
I read about it a while back in the Caltech News, IIRC they got a $100 million donation for that, really a very unusual kind of donation, both in size and purpose. Was wondering what happened with that.
But I agree with Elon that that SPS are not likely to be worth it. We already have a huge amount of energy getting beamed to Earth every day for free. Of course, as with any new technology, if it does take hold, it will likely start with niche applications. The military has shown at least a little interest.
I guess if you had a difficult to access place that needed a lot of energy, maybe SPS would be a candidate, as long as it’s not too far from the equator. But even if this never pans out as envisioned, developing the tiles and other technologies might still be very worthwhile in the long run, because we’re still gonna need power in space, too. 😁
I’d like to hear more about the conversion efficiencies in CalTech’s system, particularly DC-to-RF, beam collection efficiency and RF-to-DC rectification efficiency. The X-band system they’re proposing will also suffer from attenuation losses during wet weather. Why choose this frequency band?