You may have noticed that the Sun, that star we orbit, is rather bright and energetic. In fact, the voluminous power that the Sun radiates out in a single second could meet the energy needs of the global human population hundreds of thousands of times over.
While the solar industry is constantly finding new ways to tap into this energy from Earth’s surface, some visionaries have their eyes on an even bigger stellar prize: space-based solar power (SSP).
This potential power source would involve launching sophisticated machinery into space to harvest sunlight in an environment where the Sun never sets. The energy would then be wirelessly beamed back down to Earth in the form of microwave or laser emissions that can be converted to electricity at ground stations.
Theoretically, space-based solar power could provide a constant source of green, sustainable energy to the entire planet, day or night, which has made it an attractive option in discussions about how to decarbonize the global energy system in the future. It also has the advantage of easily capturing the imagination, and has inspired futuristic visions of gigantic solar-generating webs, towers, or disks circling our planet.
Scientists have taken small steps toward SSP—for instance, the US military deployed a solar-harvesting test module into space in May—but the concept remains out of reach for a variety of technological, logistical, and economic reasons. Here’s what you need about the promise of space solar power, where we are in our efforts to develop it, and whether it will ever emerge as a viable source of energy for the 21st century and beyond.
What is space-based solar power and how close are we?
The concept of space-based solar power dates back over a century, to the Russian polymath Konstantin Tsiolkovsky, and it has taken on many permutations as both a science fiction trope and technical vision in the decades since.
SSP expert John Mankins envisioned a concept called SPS-ALPHA, constructed from tens of thousands of mirrors that channel solar energy through a gigantic curved satellite, which was funded in 2014 as part of NASA’s Innovative Advanced Concepts program. The European Sail Tower concept, proposed in 2001, is a nine-mile-long structure made of solar sails, which are thin reflective sheets with space applications, embossed with photovoltaic cells.
Designs of this scale would require advanced technologies that could take decades, or longer, to develop. China is currently working on a plan to achieve its goal of building the first operational solar power plant in orbit sometime during the 2030s, but not much is known about this project yet.
Such lofty dreams of space solar power are certainly tantalizing, but we are still in the very early days of testing out this technology and we need a lot of additional work to get the concept up and running, assuming there’s a market for it. But that work is happening.
“I am convinced that we need valid demonstrations to convince the energy sector to take this option into serious consideration,” said Leopold Summerer, head of the Advanced Concepts and Studies Office at the European Space Agency, in an email.
A few months ago, in May, scientists launched the first solar cells into space with the express purpose of testing out some of the fundamentals of SSP. The prototype, called the Photovoltaic Radio-frequency Antenna Module (PRAM), was developed by the U.S. Naval Research Laboratory and carried to orbit by the Air Force X-37B spaceplane.
PRAM is designed to capture sunlight with its solar cells and convert it into microwave transmissions, one of the key mechanisms in a hypothetical space solar power system. The module represents an exciting advance into the testing phase of these concepts in outer space, but countless other missions will be required to figure out whether it is technologically or economically feasible to invest in SSP.
“PRAM is a really early stage test of producing solar electricity in space,” said Peter Maniloff, an assistant professor of economics at Colorado School of Mines, in an email. “It's an important test, particularly of efficiency and heat management.”
“But actually producing at commercial scale will require scaling this up by orders of magnitude, and then beaming the power to Earth,” he added. “We do lots and lots of things at the research and prototype scale. That's an important step! But it doesn't imply that they're close to commercial deployment.”
What will it take to make space-based solar power work?
Space solar power is one of many ambitious off-Earth technologies that are bottlenecked by the sheer cost of getting to orbit. Access to space has become more affordable, in part due to the rise of commercial space vehicles, but it is still incredibly expensive to launch infrastructure off the planet, especially on the scale envisioned by some of the most grandiose SSP proposals.
Even if these technological and cost hurdles were to be cleared, space solar power is simply not competitive against Earth-based energy sources in the near term.
“Part of the challenge for SSP is that energy is cheap,” said Maniloff. “Fracking drove down electricity prices in the early 2010s by providing lots of low-cost natural gas. Now wind and solar are providing more and more electricity, driving prices down further. And wind and solar make electricity for free! That's hard to compete with.”
For Maniloff and his colleagues, the question is not so much whether SSP can one day be scaled-up to meet global energy demands, but whether it is even capable of turning a profit for niche markets. In a paper submitted to NASA’s Economic Research for Space Development program, the team suggested one potential application that might make sense for SSP: mining operations in remote locations on Earth. It’s a similar logic to SpaceX’s Starlink satellite constellation, which aims to deliver internet service to remote areas where broadband is expensive or non-existent.
“We looked for where people use lots of very expensive power,” Maniloff explained. “That's the best business case because SSP then only has to be cheaper than something really expensive.”
“We came up with remote mine sites which have to ship in large quantities of diesel fuel,” he continued. “This is much more expensive than just connecting to the electricity grid that gets its power from the cheapest available source.”
Even in this highly specialized case, the researchers concluded that the manufacturing and transportation costs would have to decrease tenfold for SSP to be viable.
“SSP is still too expensive by an order of magnitude,” Maniloff said. “Perhaps SSP costs will be lower than expected, perhaps oil prices will go up, and perhaps there is a better site for SSP than the one we analyzed.”
While it may be inspiring to picture vast solar power plants above our skies, providing continuous clean energy to the entire world, SSP is largely dependent on far more earthly trends in the energy market.
“While technically it might be possible to generate one day enough power via SSP to meet the global electricity demand, it seems to me that it is neither likely nor advisable,” said Summerer.
Still, he said, concern over the climate crisis has made space-based solar an attractive topic of discussion for years, and even more so now.
“The better understanding and public awareness of climate change has certainly helped put the concept back onto the agenda, though this aspect has already played a major role in the discussions on the rationale to mature the concept in discussions dating back well over 20 years when climate change was not yet a political topic,” he added. “Public interest has always been relatively high.”
Of course, it’s good news that terrestrial sources of green renewable energy are improving all the time, even though it limits the role that SSP may play in the development of a low-carbon economy.
“Decarbonizing energy systems is going to take a lot of different technologies all working together,” Maniloff said. “There may be a niche role for SSP, but it's hard to see it supplanting other non-emitting technologies at large scale.”
Even if the science fiction dream of power beamed-down to Earth from space never pans out, SSP could still play a big part in helping humans expand our presence beyond our planet. Without the complications that come with competing sources of electricity, SSP could finally find its moment in the Sun as a power source for future Moon bases, for instance.
“I am convinced that it will first serve to advance space exploration goals,” Summerer said. Any path to space-to-Earth SSP, he added, will stem from the performance of these off-Earth endeavors.