A maze of brackish and freshwater ponds covers Taiwan’s coastal plain, supporting aquaculture operations that produce roughly NT $30 billion (US $920 million) worth of seafood every year. Taiwan’s government is hoping that the more than 400 square kilometers of fishponds can simultaneously produce a second harvest: solar power.

What is aquavoltaics?

That’s the impetus behind the new 42.9-megawatt aquavoltaics facility in the southern city of Tainan. To build it, Taipei-based Hongde Renewable Energy bought 57.6 hectares of abandoned land in Tainan’s fishpond-rich Qigu district, created earthen berms to delineate the two dozen ponds, and installed solar panels along the berms and over six reservoir ponds.

Tony Chang, general manager of the Hongde subsidiary Star Aquaculture, says 18 of the ponds are stocked with mullet (prized for their roe) and shrimp, while milkfish help clean the water in the reservoir ponds. In 2023, the first full year of operation, Chang says his team harvested over 100,000 kilograms of seafood. This August, they began stocking a cavernous indoor facility, also festooned with photovoltaics, to cultivate white-legged shrimp.

A number of other countries have been experimenting with aquavoltaics, including China, Chile, Bangladesh, and Norway, extending the concept to large solar arrays floating on rivers and bays. But nowhere else is the pairing of aquaculture and solar power seen as so crucial to the economy. Taiwan is striving to massively expand renewable generation to sustain its semiconductor fabs, and solar is expected to play a large role. But on this densely populated island—slightly larger than Maryland, smaller than the Netherlands—there’s not a lot of open space to install solar panels. The fishponds are hard to ignore. By the end of 2025, the government is looking to install 4.4 gigawatts of aquavoltaics to help meet its goal of 20 GW of solar generation.

Is Taiwan’s aquavoltaics plan unrealistic?

Meanwhile, though, solar developers are struggling to deliver on Taiwan’s ambitious goals, even as some projections suggest Taiwan will need over eight times more solar by 2050. And aquavoltaics in particular have come under scrutiny from environmental groups. In 2020, for example, reporter Cai Jiashan visited 100 solar plants built on agricultural land, including fishponds, and found dozens of cases where solar developers built more solar capacity than the law intended, or secured permits based on promises of continued farming that weren’t kept.

Star Aquaculture grows milkfish to help clean water for its breeding ponds.HDRenewables

On 7 July 2020, Taiwan’s Ministry of Agriculture responded by restricting solar development on farmland, in what the solar industry called the “Double-Seven Incident.” Many aquavoltaic projects were canceled while others were delayed. The latter included a 10-MW facility in Tainan that Google had announced to great fanfare in 2019 as its first renewable-energy investment in Asia, to supply power for the company’s Taiwan data centers. The array finally started up in 2023, three years behind schedule.

Critics of Taiwan’s renewed aquavoltaic plans thus see the government’s goal as unrealistic. Yuping Chen, executive director of the Taiwan Environment and Planning Association, a Taipei-based nonprofit dedicated to resolving conflicts between solar energy and agriculture, says of aquavoltaics, “It is claimed to be crucial by the government, but it’s impossible to realize.”

How aquavoltaics could revive fishing, boost revenue

Solar developers and government officials who endorse aquavoltaics argue that such projects could revive the island’s traditional fishing community. Taiwan’s fishing villages are aging and shrinking as younger people take city jobs. Climate change has also taken a toll. Severe storms damage fishpond embankments, while extreme heat and rainfall stress the fish.

4.4

Gigawatts of aquavoltaics that Taiwan wants to install by the end of 2025

Solar development could help reverse these trends. Several recent studies examining fishponds in Taiwan found that adding solar improves profitability, providing an opportunity to reinvigorate communities if agrivoltaic investors share their returns. Alan Wu, deputy director of the Green Energy Initiative at Taiwan’s Industrial Technology Research Institute, says the Hsinchu-based lab has opened a research station in Tainan to connect solar and aquaculture firms. ITRI is helping aquavoltaics facilities boost their revenues by figuring out how they can raise “species of high economic value that are normally more difficult to raise,” Wu says.

Such high-value products include the 27,000 pieces of sun-dried mullet roe that Hongde Renewable Energy’s Tainan site produced last year. The new indoor facility, meanwhile, should boost yields of the relatively pricey whiteleg shrimp. Chang expects the indoor harvests to fetch $500,000 to $600,000 annually, compared to $800,000 to $900,000 from the larger outdoor ponds.

The solar roof over the 100,000-liter indoor growth tanks protects the 2.7 million shrimp against weather and bird droppings. Chang says a patent-pending drain mechanically removes waste from each tank, and also sucks out the shrimp when they’re ready for harvest.

Land that Star Aquaculture set aside for wildlife now attracts endangered birds like the black-faced spoonbill [left] and the oriental stork [right].iStock (2)

The company has also set aside 9 percent of the site for wildlife, in response to concerns from conservationists. “Egrets, endangered oriental storks, and black-faced spoonbills continue to use the site,” Chang says. “If it was all covered with PV, it could impact their habitat.”

Such measures may not satisfy environmentalists, though. In a review published last month, researchers at Fudan University in Shanghai and two Chinese power firms concluded that China’s floating aquavoltaic installations—some of which already span 5 square kilometers—will “inevitably” alter the marine environment.

Aquavoltaic facilities that are entirely indoors may be an even harder sell as they scale up. Toshiba is backing such a plant in Tainan, to generate 120 MW for an unspecified “semiconductor manufacturer,” with plans for a 360-MW expansion. The resulting buildings could exclude wildlife from 5 square kilometers of habitat. Indoor projects could compensate by protecting land elsewhere. But, as Chen of the Taiwan Environment and Planning Association notes, developers of such sites may not take such measures unless they’re required by law to do so.

Robert F. Kennedy Jr. won applause at the Libertarian National Convention by criticizing government lockdowns and deficit spending, and saying America shouldn't police the world.

It made me want to interview him. This month, I did.

He said intelligent things about America's growing debt:

"President Trump said that he was going to balance the budget and instead he (increased the debt more) than every president in United States history—$8 trillion. President Biden is on track now to beat him."

It's good to hear a candidate actually talk about our debt.

"When the debt is this large…you have to cut dramatically, and I'm going to do that," he says.

But looking at his campaign promises, I don't see it.

He promises "affordable" housing via a federal program backing 3 percent mortgages.

"Imagine that you had a rich uncle who was willing to cosign your mortgage!" gushes his campaign ad. "I'm going to make Uncle Sam that rich uncle!"

I point out that such giveaways won't reduce our debt.

"That's not a giveaway," Kennedy replies. "Every dollar that I spend as president is going to go toward building our economy."

That's big government nonsense, like his other claim: "Every million dollars we spend on child care creates 22 jobs!"

Give me a break.

When I pressed him about specific cuts, Kennedy says, "I'll cut the military in half…cut it to about $500 billion….We are not the policemen of the world."

"Stop giving any money to Ukraine?" I ask.

"Negotiate a peace," Kennedy replies. "Biden has never talked to Putin about this, and it's criminal."

He never answered whether he'd give money to Ukraine. He did answer about Israel.

"Yes, of course we should,"

"[Since] you don't want to cut this spending, what would you cut?"

"Israel spending is rather minor," he responds. "I'm going to pick the most wasteful programs, put them all in one bill, and send them to Congress with an up and down vote."

Of course, Congress would just vote it down.

Kennedy's proposed cuts would hardly slow down our path to bankruptcy. Especially since he also wants new spending that activists pretend will reduce climate change.

At a concert years ago, he smeared "crisis" skeptics like me, who believe we can adjust to climate change, screaming at the audience, "Next time you see John Stossel and [others]… these flat-earthers, these corporate toadies—lying to you. This is treason, and we need to start treating them now as traitors!"

Now, sitting with him, I ask, "You want to have me executed for treason?"

"That statement," he replies, "it's not a statement that I would make today….Climate is existential. I think it's human-caused climate change. But I don't insist other people believe that. I'm arguing for free markets and then the lowest cost providers should prevail in the marketplace….We should end all subsidies and let the market dictate."

That sounds good: "Let the market dictate."

But wait, Kennedy makes money from solar farms backed by government guaranteed loans. He "leaned on his contacts in the Obama administration to secure a $1.6 billion loan guarantee," wrote The New York Times.

"Why should you get a government subsidy?" I ask.

"If you're creating a new industry," he replies, "you're competing with the Chinese. You want the United States to own pieces of that industry."

I suppose that means his government would subsidize every industry leftists like.

Yet when a wind farm company proposed building one near his family's home, he opposed it.

"Seems hypocritical," I say.

"We're exterminating the right whale in the North Atlantic through these wind farms!" he replies.

I think he was more honest years ago, when he complained that "turbines…would be seen from Cape Cod, Martha's Vineyard… Nantucket….[They] will steal the stars and nighttime views."

Kennedy was once a Democrat, but now Democrats sue to keep him off ballots. Former Clinton Labor Secretary Robert Reich calls him a "dangerous nutcase."

Kennedy complains that Reich won't debate him.

"Nobody will," he says. "They won't have me on any of their networks."

Well, obviously, I will.

I especially wanted to confront him about vaccines.

In a future column, Stossel TV will post more from our hourlong discussion.

COPYRIGHT 2024 BY JFS PRODUCTIONS INC.

The post RFK Jr. Pays Lip Service to the Debt While Pushing Policies That Would Increase It appeared first on Reason.com.

Enlarge / Some solar panels, along with a diagram of a perovskite's crystal structure. (credit: Subhakitnibhat Kewiko)

As the price of silicon panels has continued to come down, we've reached the point where they're a small and shrinking cost of building a solar farm. That means that it might be worth spending more to get a panel that converts more of the incoming sunlight to electricity, since it allows you to get more out of the price paid to get each panel installed. But silicon panels are already pushing up against physical limits on efficiency. Which means our best chance for a major boost in panel efficiency may be to combine silicon with an additional photovoltaic material.

Right now, most of the focus is on pairing silicon with a class of materials called perovskites. Perovskite crystals can be layered on top of silicon, creating a panel with two materials that absorb different areas of the spectrum—plus, perovskites can be made from relatively cheap raw materials. Unfortunately, it has been difficult to make perovskites that are both high-efficiency and last for the decades that the silicon portion will.

Lots of labs are attempting to change that, though. And two of them reported some progress this week, including a perovskite/silicon system that achieved 34 percent efficiency.

Read 15 remaining paragraphs | Comments

The accelerating buildout of solar farms on Earth is already hitting speed bumps, including public pushback against the large tracts of land required and a ballooning backlog of requests for new transmission lines and grid connections. Energy experts have been warning that electricity is likely to get more expensive and less reliable unless renewable power that waxes and wanes under inconstant sunlight and wind is backed up by generators that can run whenever needed. To space enthusiasts, that raises an obvious question: Why not stick solar power plants where the sun always shines?

Space-based solar power is an idea so beautiful, so tantalizing that some argue it is a wish worth fulfilling. A constellation of gigantic satellites in geosynchronous orbit (GEO) nearly 36,000 kilometers above the equator could collect sunlight unfiltered by atmosphere and uninterrupted by night (except for up to 70 minutes a day around the spring and fall equinoxes). Each megasat could then convert gigawatts of power into a microwave beam aimed precisely at a big field of receiving antennas on Earth. These rectennas would then convert the signal to usable DC electricity.

The thousands of rocket launches needed to loft and maintain these space power stations would dump lots of soot, carbon dioxide, and other pollutants into the stratosphere, with uncertain climate impacts. But that might be mitigated, in theory, if space solar displaced fossil fuels and helped the world transition to clean electricity.

The glamorous vision has inspired numerous futuristic proposals. Japan’s space agency has presented a road map to deployment. Space authorities in China aim to put a small test satellite in low Earth orbit (LEO) later this decade. Ideas to put megawatt-scale systems in GEO sometime in the 2030s have been floated but not yet funded.

The U.S. Naval Research Laboratory has already beamed more than a kilowatt of power between two ground antennas about a kilometer apart. It also launched in 2023 a satellite that used a laser to transmit about 1.5 watts, although the beam traveled less than 2 meters and the system had just 11 percent efficiency. A team at Caltech earlier this year wrapped up a mission that used a small satellite in LEO to test thin-film solar cells, flexible microwave-power circuitry, and a small collapsible deployment mechanism. The energy sent Earthward by the craft was too meager to power a lightbulb, but it was progress nonetheless.

The European Space Agency (ESA) debuted in 2022 its space-based solar-power program, called Solaris, with an inspiring (but entirely fantastical) video animation. The program’s director, Sanjay Vijendran, told IEEE Spectrum that the goal of the effort is not to develop a power station for space. Instead, the program aims to spend three years and €60 million (US $65 million) to figure out whether solar cells, DC-to-RF converters, assembly robots, beam-steering antennas, and other must-have technologies will improve drastically enough over the next 10 to 20 years to make orbital solar power feasible and competitive. Low-cost, low-mass, and space-hardy versions of these technologies would be required, but engineers trying to draw up detailed plans for such satellites today find no parts that meet the tough requirements.

Not so fast: The real-world efficiency of commercial, space-qualified solar cells has progressed much more slowly than records set in highly controlled research experiments, which often use exotic materials or complex designs that cannot currently be mass-produced. Points plotted here show the highest efficiency reported in five-year intervals.HENRI BARDE; DATA FROM NATIONAL RENEWABLE ENERGY LABORATORY (RESEARCH CELLS) AND FROM MANUFACTURER DATA SHEETS AND PRESENTATIONS (COMMERCIAL CELLS)

With the flurry of renewed attention, you might wonder: Has extraterrestrial solar power finally found its moment? As the recently retired head of space power systems at ESA—with more than 30 years of experience working on power generation, energy storage, and electrical systems design for dozens of missions, including evaluation of a power-beaming experiment proposed for the International Space Station—I think the answer is almost certainly no.

Despite mounting buzz around the concept, I and many of my former colleagues at ESA are deeply skeptical that these large and complex power systems could be deployed quickly enough and widely enough to make a meaningful contribution to the global energy transition. Among the many challenges on the long and formidable list of technical and societal obstacles: antennas so big that we cannot even simulate their behavior.

Here I offer a road map of the potential chasms and dead ends that could doom a premature space solar project to failure. Such a misadventure would undermine the credibility of the responsible space agency and waste capital that could be better spent improving less risky ways to shore up renewable energy, such as batteries, hydrogen, and grid improvements. Champions of space solar power could look at this road map as a wish list that must be fulfilled before orbital solar power can become truly appealing to electrical utilities.

Space Solar Power at Peak Hype—Again

For decades, enthusiasm for the possibility of drawing limitless, mostly clean power from the one fusion reactor we know works reliably—the sun—has run hot and cold. A 1974 study that NASA commissioned from the consultancy Arthur D. Little bullishly recommended a 20-year federal R&D program, expected to lead to a commercial station launching in the mid-1990s. After five years of work, the agency delivered a reference architecture for up to 60 orbiting power stations, each delivering 5 to 10 gigawatts of baseload power to major cities. But officials gave up on the idea when they realized that it would cost over $1 trillion (adjusted for inflation) and require hundreds of astronauts working in space for decades, all before the first kilowatt could be sold.

NASA did not seriously reconsider space solar until 1995, when it ordered a “fresh look” at the possibility. That two-year study generated enough interest that the U.S. Congress funded a small R&D program, which published plans to put up a megawatt-scale orbiter in the early 2010s and a full-size power plant in the early 2020s. Funding was cut off a few years later, with no satellites developed.

Because of the physics of power transmission from geosynchronous orbit, space power satellites must be enormous—hundreds of times larger than the International Space Station and even dwarfing the tallest skyscrapers—to generate electricity at a competitive price. The challenges for their engineering and assembly are equally gargantuan. Chris Philpot

Then, a decade ago, private-sector startups generated another flurry of media attention. One, Solaren, even signed a power-purchase agreement to deliver 200 megawatts to utility customers in California by 2016 and made bold predictions that space solar plants would enter mass production in the 2020s. But the contract and promises went unfulfilled.

The repeated hype cycles have ended the same way each time, with investors and governments balking at the huge investments that must be risked to build a system that cannot be guaranteed to work. Indeed, in what could presage the end of the current hype cycle, Solaris managers have had trouble drumming up interest among ESA’s 22 member states. So far only the United Kingdom has participated, and just 5 percent of the funds available have been committed to actual research work.

Even space-solar advocates have recognized that success clearly hinges on something that cannot be engineered: sustained political will to invest, and keep investing, in a multidecade R&D program that ultimately could yield machines that can’t put electricity on the grid. In that respect, beamed power from space is like nuclear fusion, except at least 25 years behind.

In the 1990s, the fusion community succeeded in tapping into national defense budgets and cobbled together the 35-nation, $25 billion megaproject ITER, which launched in 2006. The effort set records for delays and cost overruns, and yet a prototype is still years from completion. Nevertheless, dozens of startups are now testing new fusion-reactor concepts. Massive investments in space solar would likely proceed in the same way. Of course, if fusion succeeds, it would eclipse the rationale for solar-energy satellites.

Space Industry Experts Run the Numbers

The U.S. and European space agencies have recently released detailed technical analyses of several space-based solar-power proposals. [See diagrams.] These reports make for sobering reading.

SPS-ALPHA Mark-III

Proposed by: John C. Mankins, former NASA physicist

Features: Thin-film reflectors (conical array) track the sun and concentrate sunlight onto an Earth-facing energy-conversion array that has photovoltaic (PV) panels on one side, microwave antennas on the other, and power distribution and control electronics in the middle. Peripheral modules adjust the station’s orbit and orientation.

MR-SPS

Proposed by: China Academy of Space Technology

Features: Fifty PV solar arrays, each 200 meters wide and 600 meters long, track the sun and send power through rotating high-power joints and perpendicular trusses to a central microwave-conversion and transmission array that points 128,000 antenna modules at the receiving station on Earth.

CASSIOPeiA

Proposed by: Ian Cash, chief architect, Space Solar Group Holdings

Features: Circular thin-film reflectors track the sun and bounce light onto a helical array that includes myriad small PV cells covered by Fresnel-lens concentrators, power-conversion electronics, and microwave dipole antennas. The omnidirectional antennas must operate in sync to steer the beam as the station rotates relative to the Earth.

SPS (Solar power satellite)

Proposed by: Thales Alenia Space

Features: Nearly 8,000 flexible solar arrays, each 10 meters wide and 80 meters long, are unfurled from roll-out modules and linked together to form two wings. The solar array remains pointed at the sun, so the central transmitter must rotate and also operate with great precision as a phased-array antenna to continually steer the beam onto the ground station.

Electricity made this way, NASA reckoned in its 2024 report, would initially cost 12 to 80 times as much as power generated on the ground, and the first power station would require at least $275 billion in capital investment. Ten of the 13 crucial subsystems required to build such a satellite—including gigawatt-scale microwave beam transmission and robotic construction of kilometers-long, high-stiffness structures in space—rank as “high” or “very high” technical difficulty, according to a 2022 report to ESA by Frazer-Nash, a U.K. consultancy. Plus, there is no known way to safely dispose of such enormous structures, which would share an increasingly crowded GEO with crucial defense, navigation, and communications satellites, notes a 2023 ESA study by the French-Italian satellite maker Thales Alenia Space.

An alternative to microwave transmission would be to beam the energy down to Earth as reflected sunlight. Engineers at Arthur D. Little described the concept in a 2023 ESA study in which they proposed encircling the Earth with about 4,000 aimable mirrors in LEO. As each satellite zips overhead, it would shine an 8-km-wide spotlight onto participating solar farms, allowing the farms to operate a few extra hours each day (if skies are clear). In addition to the problems of clouds and light pollution, the report noted the thorny issue of orbital debris, estimating that each reflector would be penetrated about 75 billion times during its 10-year operating life.

My own assessment, presented at the 2023 European Space Power Conference and published by IEEE, pointed out dubious assumptions and inconsistencies in four space-solar designs that have received serious attention from government agencies. Indeed, the concepts detailed so far all seem to stand on shaky technical ground.

Massive Transmitters and Receiving Stations

The high costs and hard engineering problems that prevent us from building orbital solar-power systems today arise mainly from the enormity of these satellites and their distance from Earth, both of which are unavoidable consequences of the physics of this kind of energy transmission. Only in GEO can a satellite stay (almost) continuously connected to a single receiving station on the ground. The systems must beam down their energy at a frequency that passes relatively unimpeded through all kinds of weather and doesn’t interfere with critical radio systems on Earth. Most designs call for 2.45 or 5.8 gigahertz, within the range used for Wi-Fi. Diffraction will cause the beam to spread as it travels, by an amount that depends on the frequency.

Thales Alenia Space estimated that a transmitter in GEO must be at least 750 meters in diameter to train the bright center of a 5.8-GHz microwave beam onto a ground station of reasonable area over that tremendous distance—65 times the altitude of LEO satellites like Starlink. Even using a 750-meter transmitter, a receiver station in France or the northern United States would fill an elliptical field covering more than 34 square kilometers. That’s more than two-thirds the size of Bordeaux, France, where I live.

“Success hinges on something that cannot be engineered: sustained political will to keep investing in a multidecade R&D program that ultimately could yield machines that can’t put electricity on the grid.”

Huge components come with huge masses, which lead to exorbitant launch costs. Thales Alenia Space estimated that the transmitter alone would weigh at least 250 tonnes and cost well over a billion dollars to build, launch, and ferry to GEO. That estimate, based on ideas from the Caltech group that have yet to be tested in space, seems wildly optimistic; previous detailed transmitter designs are about 30 times heavier.

Because the transmitter has to be big and expensive, any orbiting solar project will maximize the power it sends through the beam, within acceptable safety limits. That’s why the systems evaluated by NASA, ESA, China, and Japan are all scaled to deliver 1–2 GW, the maximum output that utilities and grid operators now say they are willing to handle. It would take two or three of these giant satellites to replace one large retiring coal or nuclear power station.

Energy is lost at each step in the conversion from sunlight to DC electricity, then to microwaves, then back to DC electricity and finally to a grid-compatible AC current. It will be hard to improve much on the 11 percent end-to-end efficiency seen in recent field trials. So the solar arrays and electrical gear must be big enough to collect, convert, and distribute around 9 GW of power in space just to deliver 1 GW to the grid. No electronic switches, relays, and transformers have been designed or demonstrated for spacecraft that can handle voltages and currents anywhere near the required magnitude.

Some space solar designs, such as SPS-ALPHA and CASSIOPeiA, would suspend huge reflectors on kilometers-long booms to concentrate sunlight onto high-efficiency solar cells on the back side of the transmitter or intermingled with antennas. Other concepts, such as China’s MR-SPS and the design proposed by Thales Alenia Space, would send the currents through heavy, motorized rotating joints that allow the large solar arrays to face the sun while the transmitter pivots to stay fixed on the receiving station on Earth.

All space solar-power concepts that send energy to Earth via a microwave beam would need a large receiving station on the ground. An elliptical rectenna field 6 to 10 kilometers wide would be covered with antennas and electronics that rectify the microwaves into DC power. Additional inverters would then convert the electricity to grid-compatible AC current.Chris Philpot

The net result, regardless of approach, is an orbiting power station that spans several kilometers, totals many thousands of tonnes, sends gigawatts of continuous power through onboard electronics, and comprises up to a million modules that must be assembled in space—by robots. That is a gigantic leap from the largest satellite and solar array ever constructed in orbit: the 420-tonne, 109-meter International Space Station (ISS), whose 164 solar panels produce less than 100 kilowatts to power its 43 modules.

The ISS has been built and maintained by astronauts, drawing on 30 years of prior experience with the Salyut, Skylab, and Mir space stations. But there is no comparable incremental path to a robot-assembled power satellite in GEO. Successfully beaming down a few megawatts from LEO would be an impressive achievement, but it wouldn’t prove that a full-scale system is feasible, nor would the intermittent power be particularly interesting to commercial utilities.

T Minus...Decades?

NASA’s 2024 report used sensitivity analysis to look for advances, however implausible, that would enable orbital solar power to be commercially competitive with nuclear fission and other low-emissions power. To start, the price of sending a tonne of cargo to LEO on a large reusable rocket, which has fallen 36 percent over the past 10 years, would have to drop by another two-thirds, to $500,000. This assumes that all the pieces of the station could be dropped off in low orbit and then raised to GEO over a period of months by space tugs propelled by electrical ion thrusters rather than conventional rockets. The approach would slow the pace of construction and add to the overall mass and cost. New tugs would have to be developed that could tow up to 100 times as much cargo as the biggest electric tugs do today. And by my calculations, the world’s annual production of xenon—the go-to propellant for ion engines—is insufficient to carry even a single solar-power satellite to GEO.

Thales Alenia Space looked at a slightly more realistic option: using a fleet of conventional rockets as big as SpaceX’s new Starship—the largest rocket ever built—to ferry loads from LEO to GEO, and then back to LEO for refueling from an orbiting fuel depot. Even if launch prices plummeted to $200,000 a tonne, they calculated, electricity from their system would be six times as expensive as NASA’s projected cost for a terrestrial solar farm outfitted with battery storage—one obvious alternative.

What else would have to go spectacularly right? In NASA’s cost-competitive scenario, the price of new, specialized spaceships that could maintain the satellite for 30 years—and then disassemble and dispose of it—would have to come down by 90 percent. The efficiency of commercially produced, space-qualified solar cells would have to soar from 32 percent today to 40 percent, while falling in cost. Yet over the past 30 years, big gains in the efficiency of research cells have not translated well to the commercial cells available at low cost [see chart, “Not So Fast”].

Is it possible for all these things to go right simultaneously? Perhaps. But wait—there’s more that can go wrong.

The Toll of Operating a Solar Plant in Space

Let’s start with temperature. Gigawatts of power coursing through the system will make heat removal essential because solar cells lose efficiency and microcircuits fry when they get too hot. A couple of dozen times a year, the satellite will pass suddenly into the utter darkness of Earth’s shadow, causing temperatures to swing by around 300 °C, well beyond the usual operating range of electronics. Thermal expansion and contraction may cause large structures on the station to warp or vibrate.

Then there’s the physical toll of operating in space. Vibrations and torques exerted by altitude-control thrusters, plus the pressure of solar radiation on the massive sail-like arrays, will continually bend and twist the station this way and that. The sprawling arrays will suffer unavoidable strikes from man-made debris and micrometeorites, perhaps even a malfunctioning construction robot. As the number of space power stations increases, we could see a rapid rise in the threat of Kessler syndrome, a runaway cascade of collisions that is every space operator’s nightmare.

Probably the toughest technical obstacle blocking space solar power is a basic one: shaping and aiming the beam. The transmitter is not a dish, like a radio telescope in reverse. It’s a phased array, a collection of millions of little antennas that must work in near-perfect synchrony, each contributing its piece to a collective waveform aimed at the ground station.

Like people in a stadium crowd raising their arms on cue to do “the wave,” coordination of a phased array is essential. It will work properly only if every element on the emitter syncs the phase of its transmission to align precisely with the transmission of its neighbors and with an incoming beacon signal sent from the ground station. Phase errors measured in picoseconds can cause the microwave beam to blur or drift off its target. How can the system synchronize elements separated by as much as a kilometer with such incredible accuracy? If you have the answer, please patent and publish it, because this problem currently has engineers stumped.

There is no denying the beauty of the idea of turning to deep space for inexhaustible electricity. But nature gets a vote. As Lao Tzu observed long ago in the Tao Te Ching, “The truth is not always beautiful, nor beautiful words the truth.”

Solar panels are built to last 25 years or more in all kinds of weather. Key to this longevity is a tight seal of the photovoltaic materials. Manufacturers achieve the seal by laminating a panel’s silicon cells with polymer sheets between glass panes. But the sticky polymer is hard to separate from the silicon cells at the end of a solar panel’s life, making recycling the materials more difficult.

Researchers at the U.S. National Renewable Energy Lab (NREL) in Golden, Colo., say they’ve found a better way to seal solar modules. Using a femtosecond laser, the researchers welded together solar panel glass without the use of polymers such as ethylene vinyl acetate. These glass-to-glass precision welds are strong enough for outdoor solar panels, and are better at keeping out corrosive moisture, the researchers say.

A femtosecond laser welds a small piece of test glass.NREL

“Solar panels are not easily recycled,” says David Young, a senior scientist at NREL. “There are companies that are doing it now, but it’s a tricky play between cost and benefit, and most of the problem is with the polymers.” With no adhesive polymers involved, recycling facilities can more easily separate and reuse the valuable materials in solar panels such as silicon, silver, copper, and glass.

Because of the polymer problem, many recycling facilities just trash the polymer-covered silicon cells and recover only the aluminum frames and glass encasements, says Silvana Ovaitt, a photovoltaic (PV) analyst at NREL. This partial recycling wastes the most valuable materials in the modules.

“At some point there’s going to be a huge amount of spent panels out there, and we want to get it right, and make it easy to recycle.” —David Young, NREL

Finding cost-effective ways to recycle all the materials in solar panels will become increasingly important. Manufacturers globally are deploying enough solar panels to produce an additional 240 gigawatts each year. That rate is projected to increase to 3 terawatts by 2030, Ovaitt says. By 2050, anywhere from 54 to 160 million tonnes of PV panels will have reached the end of their life-spans, she says.

“At some point there’s going to be a huge amount of spent panels out there, and we want to get it right, and make it easy to recycle,” says Young. “There’s no reason not to.” A change in manufacturing could help alleviate the problem—although not for at least another 25 years, when panels constructed with the new technique would be due to be retired.

In NREL’s technique, the glass that encases the solar cells in a PV panel is welded together by precision melting. The precision melting is accomplished with femtosecond lasers, which pack a tremendous number of photons into a very short time scale--about 1 millionth of 1 billionth of a second. The number of photons emitted per second from the laser is so intense that it changes the optical absorption process in the glass, says Young. The process changes from linear (normal absorption) to nonlinear, which allows the glass to absorb energy from the photons that it would normally not absorb, he says.

The intense beam, focused near the interface of the two sheets of glass, generates a small plasma of ionized glass atoms. This plasma allows the glass to absorb most of the photons from the laser and locally melt the two glass sheets to form a weld. Because there’s no open surface, there is no evaporation of the molten glass during the welding process. The lack of evaporation from the molten pool allows the glass to cool in a stress-free state, leaving a very strong weld.

A femtosecond laser creates precision welds between two glass plates.David Young/NREL

In stress tests conducted by the NREL group, the welds proved almost as strong as the glass itself, as if there were no weld at all. Young and his colleagues described their proof-of-concept technique in a paper published 21 February in the IEEE Journal of Photovoltaics.

This is the first time a femtosecond laser has been used to test glass-to-glass welds for solar modules, the authors say. The cost of such lasers has declined over the last few years, so researchers are finding uses for them in a wide range of applications. For example, femtosecond lasers have been used to create 3D midair plasma displays and to turn tellurite glass into a semiconductor crystal. They’ve also been used to weld glass in medical devices.

Prior to femtosecond lasers, research groups attempted to weld solar panel glass with nanosecond lasers. But those lasers, with pulses a million times as long as those of a femtosecond laser, couldn’t create a glass-to-glass weld. Researchers tried using a filler material called glass frit in the weld, but the bonds of the dissimilar materials proved too brittle and weak for outdoor solar panel designs, Young says.

In addition to making recycling easier, NREL’s design may make solar panels last longer. Polymers are poor barriers to moisture compared with glass, and the material degrades over time. This lets moisture into the solar cells, and eventually leads to corrosion. “Current solar modules aren’t watertight,” says Young. That will be a problem for perovskite cells, a leading next-generation solar technology that is extremely sensitive to moisture and oxygen.

“If we can provide a different kind of seal where we can eliminate the polymers, not only do we get a better module that lasts longer, but also one that is much easier to recycle,” says Young.

The idea of powering civilization from gigantic solar plants in orbit is older than any space program, but despite seven decades of rocket science, the concept—to gather near-constant sunlight tens of thousands of kilometers above the equator, beam it to Earth as microwaves, and convert it to electricity—still remains tantalizingly over the horizon. Several recently published deep-dive analyses commissioned by NASA and the European Space Agency have thrown cold water on the hope that space solar power could affordably generate many gigawatts of clean energy in the near future. And yet the dream lives on.

The dream achieved a kind of lift-off in January 2023. That’s when SSPD-1, a solar space-power demonstrator satellite carrying a bevy of new technologies designed at the California Institute of Technology, blasted into low Earth orbit for a year-long mission. Mindful of concerns about the technical feasibility of robotic in-space assembly of satellites, each an order of magnitude larger than the International Space Station, the Caltech team has been looking at very different approaches to space solar power.

For an update on what the SSPD-1 mission achieved and how it will shape future concepts for space solar-power satellites, IEEE Spectrum spoke with Ali Hajimiri, an IEEE Fellow, professor of electrical engineering at Caltech, and codirector of the school’s space-based solar power project. The interview has been condensed and edited for length and clarity.

SSPD-1 flew with several different testbeds. Let’s start with the MAPLE (Microwave Array for Power-transfer Low-orbit Experiment) testbed for wireless power transmission: When you and your team went up on the roof of your building on campus in May 2023 and aimed your antennas to where the satellite was passing over, did your equipment pick up actual power being beamed down or just a diagnostic signal?

Ali Hajimiri is the codirector of Caltech’s space-based solar power project.Caltech

Ali Hajimiri: I would call it a detection. The primary purpose of the MAPLE experiment was to demonstrate wireless energy transfer in space using flexible, lightweight structures and also standard CMOS integrated circuits. On one side are the antennas that transmit the power, and on the flip side are our custom CMOS chips that are part of the power-transfer electronics. The point of these things is to be very lightweight, to reduce the cost of launch into space, and to be very flexible for storage and deployment, because we want to wrap it and unwrap it like a sail.

I see—wrap them up to fit inside a rocket and then unwrap and stretch them flat once they are released into orbit.

Hajimiri: MAPLE’s primary objective was to demonstrate that these flimsy-looking arrays and CMOS integrated circuits can operate in space. And not only that, but that they can steer wireless energy transfer to different targets in space, different receivers. And by energy transfer I mean net power out at the receiver side. We did demonstrate power transfer in space, and we made a lot of measurements. We are writing up the details now and will publish those results.

The second part of this experiment—really a stretch goal—was to demonstrate that ability to point the beam to the right place on Earth and see whether we picked up the expected power levels. Now, the larger the transmission array is in space, the greater the ability to focus the energy to a smaller spot on the ground.

Right, because diffraction of the beam limits the size of the spot, as a function of the transmitter size and the frequency of the microwaves.

Hajimiri: Yes. The array we had in space for MAPLE was very small. As a result, the transmitter spread the power over a very large area. So we captured a very small fraction of the energy—that’s why I call it a detection; it was not net positive power. But we measured it. We wanted to see: Do we get what we predict from our calculations? And we found it was in the right range of power levels we expected from an experiment like that.

So, comparable in power to the signals that come down in standard communication satellite operations.

Hajimiri: But done using this flexible, lightweight system—that’s what makes it better. You can imagine developing the next generation of communication satellites or space-based sensors being built with these to make the system significantly cheaper and lighter and easier to deploy. The satellites used now for Starlink and Kuiper—they work great, but they are bulky and heavy. With this technology for the next generation, you could deploy hundreds of them with a very small and much cheaper launch. It could lead to a much more effective Internet in the sky.

Tell me about ALBA, the experiment on the mission that tested 32 different and novel kinds of photovoltaic solar cells to see how they perform in space. What were the key takeaways?

Hajimiri: My Caltech colleague Harry Atwater led that experiment. What works best on Earth is not necessarily what works best in space. In space there is a lot of radiation damage, and they were able to measure degradation rates over months. On the other hand, there is no water vapor in space, no air oxidation, which is good for materials like perovskites that have problems with those things. So Harry and his team are exploring the trade-offs and developing a lot of new cells that are much cheaper and lighter: Cells made with thin films of perovskites or semiconductors like gallium arsenide, cells that use quantum dots, or use waveguides or other optics to concentrate the light. Many of these cells show very large promise. Very thin layers of gallium arsenide, in particular, seem very conducive to making cells that are lightweight but very high performance and much lower in cost because they need very little semiconductor material.

Many of the design concepts for solar-power satellites, including one your group published in a 2022 preprint, incorporate concentrators to reduce the amount of photovoltaic area and mass needed.

Hajimiri: A challenge with that design is the rather narrow acceptance angle: Things have to be aligned just right so that the focused sunlight hits the cell properly. That’s one of the reasons we’ve pulled away from that approach and moved toward a flat design.

A view from inside MAPLE: On the right is the array of flexible microwave power transmitters, and on the left are receivers they transmit that power to.Caltech

There are some other major differences between the Caltech power satellite design and the other concepts out there. For example, the other designs I’ve seen would use microwaves in the Wi-Fi range, between 2 and 6 gigahertz, because cheap components are available for those frequencies. But yours is at 10 GHz?

Hajimiri: Exactly—and it’s a major advantage because when you double the frequency, the size of the systems in space and on the ground go down by a factor of four. We can do that basically because we build our own microchips and have a lot of capabilities in millimeter-wave circuit design. We’ve actually demonstrated some of these flexible panels that work at 28 GHz.

And your design avoids the need for robots to do major assembly of components in space?

Hajimiri: Our idea is to deploy a fleet of these sail-like structures that then all fly in close formation. They are not attached to each other. That translates to a major cost reduction. Each one of them has little thrusters on the edges, and it contains internal sensors that let it measure its own shape as it flies and then correct the phase of its transmission accordingly. Each would also track its own position relative to the neighbors and its angle to the sun.

From your perspective as an electrical engineer, what are the really hard problems still to be solved?

Hajimiri: Time synchronization between all parts of the transmitter array is incredibly crucial and one of the most interesting challenges for the future.

Because the transmitter is a phased array, each of the million little antennas in the array has to synchronize precisely with the phase of its neighbors in order to steer the beam onto the receiver station on the ground.

Hajimiri: Right. To give you a sense of the level of timing precision that we need across an array like this: We have to reduce phase noise and timing jitter to just a few picoseconds across the entire kilometer-wide transmitter. In the lab, we do that with wires of precise length or optical fibers that feed into CMOS chips with photodiodes built into them. We have some ideas about how to do that wirelessly, but we have no delusions: This is a long journey.

What other challenges loom large?

Hajimiri: The enormous scale of the system and the new manufacturing infrastructure needed to make it is very different from anything humanity has ever built. If I were to rank the challenges, I would put getting the will, resources, and mindshare behind a project of this magnitude as number one.