Three years ago, Sanjay Vijendran's colleague told him about a scheme that seemed straight out of science fiction: beaming energy from solar panels in space down to the Earth. "The whole idea was new to me," says Vijendran, a scientist at the European Space Agency (ESA). "It sounded like something you'd laugh at."
No one's laughing now, least of all Vijendran. He's heading ESA's Solaris project, which is working toward launching satellites that by the mid-2030s could be beaming down a sizable fraction of all the energy Europe needs. And that's just one of several major pushes around the globe to tap sunlight from space to help reduce dependence on fossil fuel. "The pieces are coming together right now to make this a reality," says Vijendran.
Earth-bound solar panels provide the world with about five percent of its electricity, and that number has been growing at a torrid 25 percent a year. But even by 2050 it isn't expected to meet half the planet's electricity needs. That's partly because there are only so many rooftops and empty lots available for solar panels. But it's also because solar panels sit uselessly in the dark or under clouds most of the time, often when daily energy demand peaks.
Overcoming those drawbacks would require staggering investments in solar farms, batteries and electric grid upgrades to capture, store and transfer enough solar power to the places and times it's needed. Not so with solar panels orbiting the Earth, where they'd rarely leave sunlight. "Power storage and transfer are the true bottlenecks in moving to renewable energy," says Fabien Royer, an assistant professor of aerospace and mechanical engineering at Cornell University, who has researched space-based solar technology. "Solar power from space gets around all that by constantly generating power, and delivering it locally."
Vijendran and many other scientists and engineers believe that energy beamed from space will eventually beat out nuclear, wind and Earth-bound solar panels to become the planet's cheapest and most widespread form of green energy.
Plunging Costs
As hopelessly futuristic as the whole enterprise may sound, it's actually an old, well-explored idea, and even one that's been technically feasible for decades. NASA, for one, has been studying the approach closely since the 1970s. Even back then, the U.S. probably had the launch, solar-panel and wireless power transmission capabilities to pull off a first orbiting solar plant. NASA had even considered embarking on a mission to give it a try. But only meager levels of electricity would have made it to the ground, at a cost of about a trillion dollars, thanks mostly to the massive cost of rocket launches at the time. "You need thousands of tons of hardware to build a power-generating satellite," says Vijendran. The space agency eventually abandoned the plan, especially given that fossil fuel prices remained low.
Now, largely because of SpaceX, launch costs have plunged from about $8,500 per pound of cargo in 2000 to less than a tenth that today, and they are expected to continue to sharply decrease. At the same time, new carbon fiber materials and thin-film electronics have led to solar panels that are larger, lighter, more efficient and flexible enough to be rolled into a compact tube for launching. What's more, new designs do away with giant solar panels in favor of modular panels comprising many small ones. "These modular structures can be affordably launched in pieces with the rockets we have right now," says Cornell's Royer.
These cost breakthroughs, combined with a skyrocketing demand for green energy, have triggered a global race to field the first space-based solar-power generating stations. In addition to ESA's push, China, Japan and the U.K. all have active programs aiming to launch their first demonstration power-generating satellites before the end of the decade. "It looks feasible to have space-based solar power contributing to green energy goals within 10 to 15 years," says Vijendran.
NASA and the Department of Energy haven't announced any significant commitments, but the U.S. isn't taking a backseat. The California Institute of Technology (Caltech) has taken an early lead over everyone by launching a demonstration solar satellite that has already beamed down a tiny bit of power, and military contractor Northrop Grumman is close behind in a partnership with the U.S. Air Force. Several startups are gearing up, too, including Virtus Solis in Troy, Michigan, and others in the U.K. and Australia. "This is going to be one of our major sources of power," says Ali Hajimiri, a professor of electrical engineering at Caltech.
Hajimiri should know. He's co-director of Caltech's Space Solar Power Project, the current world pacesetter in the field. That lead owes in large part to the project's early start nearly a decade ago, with more than $100 million in funding from the Donald Bren Foundation. Northrop Grumman was an early Caltech backer, too, chipping in more than $12 million.
Like most of the solar space projects around the world, Caltech's is built around the idea of wringing energy not from a few giant solar panels, but rather from as many as thousands of small ones tightly linked to make a bigger structure. In Caltech's case, each mini-panel would consist of 16 "tiles," each of which contain all the circuitry needed to convert the sunlight hitting one side of the tile to microwave energy that is beamed out the other side to the Earth's surface.
Microwave radiation—which is just a type of radio energy—is the beam of choice of space-based solar projects. That's because unlike most other forms of energy, such as lasers, microwave beams can pass right through clouds, moisture and other spoilers in the Earth's atmosphere, ensuring that most of the energy reaches the ground. In addition, microwave beams can carry the needed power at safe levels—the beams would be far less intense than what's in a home microwave oven, equivalent to about a quarter of the typical intensity of the sunlight that hits the ground. "There's no risk of anything getting fried by it," notes Royer.
In Space and Operational
The biggest challenge to the endeavor is producing a narrow enough beam in space so that as it travels down and spreads out, it doesn't require a receiving antenna on the ground that's hundreds of miles wide. That turns out to be another advantage of the modular-panel approach: By perfectly synchronizing the beams formed by each tile, the beams can be made to "interfere" with each other—that is, to cancel each other out in some directions and combine in others. It's a trick that physicists have been using since the late 18th century to shape beams of light into specific patterns. Even many AM radio stations enlist the technique to aim their broadcast signals.
In the case of solar-power satellites, the interference between the many small microwave beams can be fine-tuned to produce a single, focused beam that might only be inches wide when it starts its journey, spreading out to a mile or so by the time it reaches the Earth. A two-mile-wide receiving antenna might seem like a tall order—but it would be a fraction of the area needed for enough Earth-bound solar panels to produce as much power as a beam from space panels could.
In January, Caltech put just one of its panels into orbit about 300 miles up—a bit higher than the International Space Station—and by June it was shooting out a microwave beam that generated a miniscule but detectable electrical current in a three-foot-wide receiving antenna on the roof of the school's engineering building. "We've built and launched hardware that's in space and operational," says Caltech's Hajimiri. "There are still challenges to work out, but we're closer to space-based solar power than we've ever been."
Caltech doesn't currently have firm plans to send up more panels. Instead, the project is aiming to refine the technology in part based on the results from the demonstration project. But in theory more modules could be sent up to join alongside the first one, increasing the total amount of solar energy captured. More modules would also produce a more powerful, better focused microwave beam, because the more separate mini-beams there are from multiple panels, the more interference there is between them to narrow and intensify the resulting combined beam. "As we scale the system up, we'll be able to bring more and more power to a smaller and smaller area," says Hajimiri. "That way most of the power goes where it's needed."
A larger solar satellite made up of thousands of modules orbiting a few hundred miles or so above the Earth could keep a beam of energy focused on a single ground receiving antenna for about eight hours a day before the satellite passed out of sight. Three such satellites spread out in orbit could ensure a constant beam to the antenna—and spreading out three ground antennas around the globe would mean each of the three satellites could constantly be beaming power down to an antenna.
That's the sort of ambitious scheme that ESA is shooting for in its Solaris project, which includes aircraft maker Airbus as a partner. Plans call for launching a demonstration satellite in 2030, followed about five years later by a working space-based power plant. If that goes well, the agency says it will put up multiple large plants that together will produce a petawatt of power—that is, a million gigawatts, or about a seventh of Europe's current energy consumption. Each satellite's modular solar panels would likely span more than half a mile, says Vijendran, beaming down to ground receiving antennas that are each about four miles wide.
But Northrop Grumman could beat everyone in sending up a working power plant, thanks to the deep pockets of the Air Force Research Laboratory. The AFRL has so far kicked in $100 million toward a 2025 launch of a prototype, as part of the Space Solar Power Incremental Demonstrations and Research (SSPIDR) project. Because the military's goal is to get electricity to troops, vehicles and weapons on the frontlines of a conflict, it doesn't necessarily need to beam down the many gigawatts required of a practical commercial station. That means it could get by with smaller, more easily achievable power stations and receiving antennas
"In times of war, the costs and dangers of getting fuel to forward operating bases increases exponentially," says Tara Theret, SSPIDR program director at Northrop Grumman. "We've already solved all the technical problems we needed to solve to achieve our first mission." Theret adds that the platform could also help get energy to remote villages hit by environmental catastrophe.
The China Question
China, meanwhile, remains a wild card. Officials there have made a number of statements in recent years promising various timetables for launching large power stations over the coming decade, and there are reports of the existence of a massive lab dedicated to the effort. But details and credible verification remain elusive.
Although the projected costs of developing and setting up space-based solar-power stations have plummeted, they won't be cheap anytime soon. That means space solar power from the first orbiting power stations will likely far exceed the costs of Earth-based solar power, not to mention fossil fuel. But Vijendran notes that launch costs will continue to sharply drop with the availability of the sorts of reusable launch vehicles that SpaceX has been developing, as well as with the growing capability to assemble solar panel components in orbit with robots instead of having to rely on vastly more costly astronaut labor. "When you put these savings together, the cost of electricity from space will become comparable to other clean-energy solutions," he says. "Longer-term it won't just be competitive with existing renewables, it will be the cheapest form of any energy."
By then, a funny science-fiction idea will be helping to save the planet.
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