Beamed Space Based Solar Power Demonstration Progress

The Space-based Solar Power Project (SSPP) at Caltech 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—including to places that currently have no access to reliable power.

Over a period of two years, they have built and demonstrated two prototype tiles. This is the key modular element that captures the sunlight and transmits the power. Through that process, they learned many things about how to design highly integrated and ultralight systems of this sort. The second space based solar power prototype tile is 33 percent lighter than the first.

The modular tiles are scaled into a larger array. They 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.

Caltech is working on three or four technology breakthroughs that, in combination, would transform the way space solar power.

Above – An array of small solar panels that are part of the Space Solar Power Project integrate photovoltaics, power transfer circuitry, and incorporate beam steering.
Credit: Caltech

By using novel folding techniques, inspired by origami, they 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.

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.

* BPellegrino’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.

37 thoughts on “Beamed Space Based Solar Power Demonstration Progress”

  1. Ultra light, huge area maximized towards the sun…
    This sounds like a solar sail and will be a problem to maintain in orbit without expending reaction mass.
    We don’t want the entire power plant to make an involuntary relativistic fly-by of Alpha Centauri.

    Or, maybe we do?

  2. The main issue with solar energy harvested from space and beamed to earth is that this ki d of solar Does increas global warming because it effectively increases the effective surface of earth, while solar panels on earth simply exploit energy that would still hit the planet.

    • Apparently, if the beamed energy is sufficiently diffuse, you could paint the ground beneath the rectenna white and it would reflect more energy back to space than the rectenna absorbs. I haven’t done the calculations myself, so I can only rate this as a plausible hypothesis.

      • How about a large constellation of mirrors in space that can concentrate sunlight onto an enormous terrestrial boiler to generate steam … or wipe a suburb.

        • This has been tested… sort of.
          The idea was to have an orbital mirror and use it to illuminate a city or a small geographic area. This would offload the electricity used for nightly street lights etc. in that area, which would make the light worth a lot without the complexity of power beaming and conversion.

          The russians tested this with a small LEO mirror a long time ago. The reflection from the mirror moved rapidly over the landscape because it was at low altitude but the concept worked. GEO is too high for such a mirror. One would want it to follow the day and night patterns across the planet to illuminate big cities with a lot of artificial lights in the evenings and early nights probably.

          This is probably the lowest hanging fruit when it comes to power beaming and it can be done easily with current tech. Lightweight mirrors and small thrusters are all that´s needed.

          • I doubt the idea of using a space-based mirror to provide a substitute for streetlights, or anything similar to such an idea, would pass environmental regulations. It would mess up circadian rhythms of all the wildlife in sight.

          • The problem here is actually basic optics. The spot size will be enormous unless the mirror is in a low orbit, but if the mirror is in a low orbit it is moving rapidly relative to the ground, and will mostly be in the Earth’s shadow when passing over at night.

            So you either need an enormous mirror in high orbit that lights up a huge area, (By huge, I mean the size of a state, or whole country in Europe.) or you need a lot of smaller mirrors in low orbit that can only extend the day a little on each end, and are in the wrong place most of the time.

    • Not really as human energy use is much less than the radiative forcing from carbon dioxide. All 20 TW of human power release is equivalent to 0.04 W per square metre, while the excess radiative forcing is 4 W per square metre. Even if every human used 10 kW like a North American, at population peak of 10 billion we dissipate 100 GW – still only 0.2 W per square metre.

    • In principle you could build a really large SPS at the Earth-Sun L1 point, it would shade the Earth at the same time it sent Earth power.

      The downside relative to Geo SPS is that it doesn’t “see” the same point on Earth all the time, so you’d need an orbital redirection system.

      But, really, the amount of energy we’re talking is minute relative to Earth’s energy budget, so it’s hardly a real issue.

      • Maybe it does not need to see the whole planet. Daytime is peak demand time for everywhere except the coldest places during the coldest part of the year.

        The Lagrangian power sat could supplement garden variety plants in GEO during peak. Free air conditioning!

        • There is enough solar electricity in the day time, the problem is that the peak consumption continues to the evening.
          Anyway you can’t generate a narrow enough beam from the LaGrange point to a specific reception field, so you will need to use a highly concentrated beam directed at a repeater satellite that will resend the power to earth.

  3. The only part of the problem that I see as not solvable is the power beaming. You can cheaper rocket flights, less mass per kW, etc, but if you cannot beam back the power, it doesn’t matter.

    Last time I looked, while in a discussion with he-who-should-not-be-stirred, it just did not seem possible and there was no demonstration that was even a couple of orders of magnitude within the required beam sharpness.

    • But that’s the least speculative part of the technology, really. It’s just a really big phased array antenna, nothing more.

      • When you do the numbers you will see that the requirements on phase become completely unreasonable and thus technically impossible. That is why all demonstrated beam centre angles are off by 2-3 orders of magnitude. At least the scarce data that I could find..

        And the proponents of space based solar themselves cannot quote a single experimental data point of beam centre angle….

        • The only feasible way to do it is for each section of the array to work off a remote phase reference, rather than locally controlling the phase. But nobody has done this work yet.

          • Even so.

            If you use a remote reference (from the target), you local transmitter has to follow that phase by some accuracy and have at most a certain amount of jitter. Any jitter on the individual tiles in the array will result in a broadening of the aggregate beam.

            So what are the maximum allowed phase error and what is the maximum allowed jitter? These are very basic questions, but curiously this low level question is not answered anywhere….You would think that every article about power beaming would have that information in the introduction. But no.

            I think that the people doing this as a research project have these numbers, but they say: “Ooops… let’s not talk about this any more”. So the cash keeps flowing. Otherwise, they would have to admit that RF amplifiers and circuitry has to advance by X orders of magnitude. On top of everything else.

    • For radio frequencies, beam forming is a matter of optics. With large enough transmitter and receiver aperture, you can capture the whole beam up to a certain distance. Light solar arrays are useful in their own right in space, but launching from Earth is a losing game in the long term. Bootstrapping space industry from a starter set (seed factory) can reduce launch by 50-100 times by using materials already in space. Simple items like a very large transmitter dish would vastly improve beam capture.

    • There’s no reason a rectenna can’t be vast. South Texas has plenty of room, a cattle can graze under it, and in the buffer zone around the rectenna, and south Texas has good access to the gulf coast energy complex. You could use the gulf itself, but corrosion would be a problem. I wonder how hard it would be to convert natural gas pipelines to ammonia. You’d have to remover all copper/copper alloy components.

      Perhaps each tile could transmit, or every hundred, or thousand could have their own transmitter. You could make one or more huge phased array antennas with good resolution from you tiles, that could skew around electronically to serve more than one rectenna, and to load follow. This could obviate the need for GEO. It might turn out highly polar orbits would be best so high latitude sites would not be left out. Hopefully a rectenna can be made to have good wide angle gain.

  4. Even though microwaves are non-ionizing radiation, like visible light and radio waves, if they are concentrated enough, they can heat up anything to the boiling point. I’d like to know more about the potential harm of sending microwaves 100s of miles through the atmosphere, through birds, planes, into crowded cities, etc. before this goes live. If the beam has enough energy to power a ship, does it have enough energy to cook us over time?

    • I believe the plan, at least as laid out by O’Neill, was to set up rectenna farms out in the countryside. They’re largely open to light, so you can farm under them, the space isn’t wasted.

      Then you limit the beam intensity to rather less than sunlight, relying on the fact that rectennas are very efficient and substantially cheaper than solar panels, and so don’t require a high intensity beam to be economical. This is supposed to render the beams safe to wildlife and the farmers. (Especially when they’re *under* the antenna, and thus shielded.)

    • The idea is to send microwaves at a low power density, up to about 20% of noon sunlight, and then deploy a large rectenna on the ground, as large as you need to receive the power you require. If a person or a bird passes through the beam, they won’t absorb enough power that they cannot naturally dissipate it.

      • That would require some testing to confirm. The real problem with microwave exposure isn’t the overall heat load, it’s the heat load to the eyeball, which has an extremely small blood flow relative to its size. Or other tissues that are poorly vascularized, like fat.

        Historically the first problem seen in humans with microwave exposure was the development of cataracts due to the heat buildup in the eye cooking the lens. This was seen in radar technicians at the beginning of radar, when they’d actually stand in front of the dish on cold days to take advantage of the warmth. On average they were fine, but too much heat built up inside their eyeballs, and after a while cataracts resulted.

        Current research suggests that microwaves are safe below 1mw/cm2, which is only 10 watts per square meter, way too low for a practical system. You’d be safe under the rectenna, of course, because it’s built to absorb the microwaves. Birds flying over the antenna could be an issue.

        I’d expect the safe exposure for birds would be somewhat higher than for humans, because we have relatively large eyeballs with correspondingly poor heat rejection. And that 1mw limit was conservative. But testing would be required.

        • Possibly. The figure I read quoted was assuming “noon sunlight” would be 1 kW/m² (midday at summer with no clouds in the sky), so about 200 W/m². I have not studied the economics of this so I have no opinion on where is the financial viability point.

          As for studying those effects, what we need right now is a sense by the public that the technology *can* be achieved, which is what those space transmission tests are doing. After these are proven to be workable, I’m sure the EPA will come around with all sorts of novel objections we will have to test and control for. But while the whole idea is considered niche, no one will fund the studies.

          • I wouldn’t think that this would be particularly expensive research. You could even eat the chickens afterwards. OTOH, it’s the sort of research that would have animal rights activists going nuts.

    • I don’t know about powering a ship, but power densities much lower than that used by military radar would do for land based static rectennas.

  5. I’d try a folded framework, with tiny crawlers that would deploy tiles, and would replaced malfunctioning tiles. One starship for the largest frame that could make it to the required orbit, and likely several to carry tiles, and drop them of at the hub(s).

    As big, and as light as this thing would be, you’d want to open it up in a high orbit with few occupied orbits crossing. Geosynchronous would be nice. Maybe it could act as a solar sail until on station. Might be a good mission for a tug using part of the tiles, and a vasimr thruster. One tug, many deliveries from a lower orbit to GEO.

  6. I wonder if using Tesla coils and towers is feasible here, it may be a much more efficient solution for transfering energy to earth than beaming.

  7. Can they power ships? Competing with coal is a losing bet.

    Competing against marine fuels might be attractive for some customers.

    • It’s not like wind can compete with coal, and here we are building more, not less, every year. If space solar can outcompete wind it might have a decent slab of the green energy market.

    • The main problem of solar power is that you want to limit the power density of the beam to protect humans and animals. Usually proposals are around 200W/M^2.
      Large containers ships use to much power then can be generated with this concentration.
      However if the ships are autonomous without any human crew and in deep seas far from land, then you can increase the concentration to get enough power.

  8. It’s interesting that previous skeptics of SPS are changing their tune recently. With Starship availability on the imminent horizon, the updated SPS studies around costing say we are getting closer to a business case that closes. ESA is hedging their bets enough to start funding some fundamental work now (they are paying Emrod to work on their psuedo-nearfield tech, but that seems to be for niche applications, because it’s hard to believe that can be cheaper than a bulk mesh rectenna). ESA is even funding a heavy lifter study (PROTEIN/EHLL) to launch 10,000 tons a year in support of SPS deployment.

    This recent work at Caltech was secretly funded in 2013 by Bren, only recently was the donation announced.

    • It would be nice to retire in an O Neill colony…if you can get over the sight of people living on the “ceilings” 😉

    • O’Neil’s work in the 1970s was based on the promise of the Space Shuttle being cheap to fly. That never happened, so the idea has sat on the shelf. Now that the SpaceX Starship is finally promising cheap space launches, people are digging up old ideas again, and updating them with 50 years of progress in other technologies.

      • Musk isn’t very keen on SPS, perhaps because he makes some of his money off ground based solar and batteries. But I have no doubt that he’d gladly take the money of anybody who wanted to launch an SPS anyway.

        He really should consider an SPS for his Mars colony. Ground based solar has problems with dust storms there, and SPS are more practical for Mars, as the synchronous orbit is so much lower. And you could get one there gradually using the power for ion propulsion.

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