Skip to content

Is space-based solar ready for liftoff?

Caltech plans to advance a solar-from-space concept that was first proposed by science fiction writer Isaac Asimov in the 1940s.

Jason Deign
4 min read
Is space-based solar ready for liftoff?

The future that science fiction authors wrote about in the 1940s has so far failed to deliver alien civilizations and long-term space travel to other planets.

But one sci-fi concept could get a step closer to reality in December, as the California Institute of Technology (Caltech) launches a space-based solar energy system into orbit.

Using solar energy in space is nothing new, of course — it’s a standard power source for satellites.

What makes Caltech’s SSPD-1 space-based solar power demonstrator unusual is that the array isn’t designed to drive a spacecraft but rather to test the idea of harvesting energy that can be beamed back to Earth as microwaves.

These microwaves would be captured via rectifying antennas, or rectennas, measuring more than half a square mile. The rectennas, likely made of dipole antennas connected via diodes, would convert the electromagnetic microwaves to direct-current electricity.

The idea of powering a planet with solar energy collected in space was first advanced by science fiction maestro Isaac Asimov in a 1941 short story entitled "Reason." The concept isn’t as crazy as it sounds.

Because it is not affected by the Earth’s inclination, atmospheric attenuation, day-night cycles, seasons and weather patterns, space-based solar could capture eight times more power than PV on Earth.

Experimental versions of rectenna technology have shown they’re capable of converting into electricity 80 to 90 percent of the energy contained in the microwaves beamed at them, a relatively high efficiency when one considers that roughly half of the energy of sunlight is reflected back to space or captured in the atmosphere and never reaches the ground, according to NASA.

Plus, a space-based solar array could potentially beam energy down to anywhere on the planet, making it theoretically dispatchable, according to a 2018 speech by Sergio Pellegrino of Caltech.

Solar arrays in space would not be subject to weathering, so they would not require regular maintenance. And the microwave beams sending energy back to collectors on Earth would be so diffuse they would not, in theory, pose a threat to health or ecosystems.

Possible with today’s technology

Last but not least, while space-based solar power may sound like a stretch, it could potentially be commercialized using technology available today — unlike other energy "big bets," such as nuclear fusion.

Pellegrino and his team have calculated that the most cost-effective way of deploying space-based solar energy would be to put a fleet of five ultralight modular power stations into medium Earth orbit.

Each station would measure about 5.5 square miles and would be made up of modules measuring 197 square feet apiece.

The modules would be made of 3.9-inch-square solar tiles with one side doubling up as a microwave transmitter, steered electronically through phase control.

In his 2018 presentation, Pellegrino said the levelized cost of electricity from such an array would be in the range of $1 to $2 per kilowatt-hour. This was based on a 15-year lifespan and the use of an Atlas V 551 rocket to get the systems into space.

“Obviously, [this] is a renewable energy source that is more expensive than the average type of energy production that we currently have in the U.S.,” Pellegrino said.

The main challenge for space-based solar is cost reduction

Most of the cost of space-based solar comes down to what it takes to get the panels into orbit.

“The cost of production, launch and assembly — which would most likely have to happen in space — currently make it commercially unviable,” said Alice Cordo Gallucci, a thematic analyst at GlobalData, in a written response to questions from Canary Media.

“Launching into low orbit costs about $2,720 per kilogram,” she added. “To compete with available sources of renewable energy, the cost would have to drop to around $400.”

There may be only one company on Earth that can achieve that kind of cost reduction at present. And coincidentally, it’s run by someone who is a fan of solar energy.

The Falcon Heavy from SpaceX, the rocket company helmed by Tesla CEO Elon Musk, is already more than 80 percent cheaper than any other low-Earth-orbit launcher and is aiming to achieve a launch cost of $1,100 per kilogram.

Jeremy Wainscott, executive vice president of the U.S.-based National Space Society, said former NASA physicist John Mankins had calculated that “using the Falcon Heavy, a cost of 5 to 7 cents per kilowatt-hour can be obtained for some concepts.”

These costs could come down further with the entry into service of a new SpaceX launch vehicle, the Starship, which underwent a test flight in May, Wainscott said in a written statement.

“The main issue holding back space-based solar power has been launch costs,” he said. “With the advent of the Falcon 9 and Falcon Heavy, space-based solar power becomes economical for niche applications, including islands, northern latitudes and military bases.

“A much broader economic feasibility for space-based solar power will grow out of the anticipated success of the SpaceX Starship rocket and other low-cost launchers.”

Interest in space-based solar is growing worldwide

Unsurprisingly, Caltech is relying on a SpaceX Falcon Heavy to get the SSPD-1 into orbit at the end of this year. The project aims to demonstrate how a solar panel could self-deploy in space and then transmit power wirelessly.

SSPD-1 builds on a U.S. Naval Research Laboratory initiative called the Photovoltaic Radiofrequency Antenna Module Flight Experiment (PRAM-FX), a 12-inch-square tile that converts solar energy into microwaves.

PRAM-FX was launched into space in May 2020 aboard the X-37B, a crewless launcher owned by the U.S. Air Force and usually used for clandestine missions.

The U.S. military has long been interested in developing space-based solar power, with defense technology firm Northrop Grumman collaborating on the work at Caltech. And the U.S. is not the only market looking to develop solar energy in space.

Wainscott said China is investing up to $40 million a year in a research and development program. Japan recently conducted two tests of microwave power transmission, he added, and has “ongoing modest but meaningful efforts in space-based solar power research and development at the level of several millions of dollars per year, focused on component technologies to improve efficiency and performance.”

Finally, the European Space Agency launched a campaign last year to support space-based solar research projects.

“But that is really where we are at the moment — early-stage research,” said Josefin Berg, solar PV market analysis manager at IHS Markit, in an email. “As with any space-related research, it takes time to go from concept to reality.”

“Exactly how fast will depend on how keen national, international, public and private space programs are to fund the research,” Berg said. “There are still uncountable possibilities and challenges to investigate before proving the concept.”

(Article image courtesy of NASA)

solar powerspace-based solarsatellitesclean energysolar PV