Space-Based Solar Power Is a Possible Alternative Energy Source

This article is part of our special section on the Climate Forward event that will include policy and climate leaders from around the world.


Ali Hajimiri thinks there’s a better way to power the planet — one that’s not getting the attention it deserves. The Caltech professor of electrical engineering envisages thousands of solar panels floating in space, unobstructed by clouds and unhindered by day-night cycles, wirelessly transmitting massive amounts of energy to receivers on Earth.

This year, that vision moved closer to reality when Mr. Hajimiri, together with a team of Caltech researchers, proved that wireless power transfer in space was possible: Solar panels they had attached to a Caltech prototype in space successfully converted electricity into microwaves and beamed those microwaves to receivers about a foot away, lighting up two LEDs.

The prototype also beamed a tiny but detectable amount of energy to a receiver on top of their lab’s building in Pasadena, Calif. The demonstration marks a first step in the wireless transfer of usable power from space to Earth — a power source that Mr. Hajimiri believes will be safer than direct sun rays. “The beam intensity is to be kept less than solar intensity on earth,” he said.

Finding alternative energy sources is one of the topics that will be discussed by leaders in business, science and public policy during The New York Times Climate Forward event on Thursday. The Caltech demonstration was a significant moment in the quest to realize space-based solar power — a clean energy technology that has long been overshadowed by other long-shot clean energy ideas, such as nuclear fusion and low-cost clean hydrogen.

If space-based solar can be made to work on a commercial scale, said Nikolai Joseph, a NASA Goddard Space Flight Center senior technology analyst, such stations could contribute as much as 10 percent of global power by 2050.

The idea of space-based solar energy has been around since at least 1941, when the science-fiction writer Isaac Asimov set one of his short stories, “Reason,” on a solar station that beamed energy by microwaves to Earth and other planets.

In the 1970s, when a fivefold increase in oil prices sparked interest in alternative energy, NASA and the Department of Energy conducted the first significant study on the topic. In 1995, under the direction of the physicist John C. Mankins, NASA took another look and concluded that investments in space-launch technology were needed to lower the cost before space-based solar power could be realized.

“There was never any doubt about it being technically feasible,” said Mr. Mankins, now president of Artemis Innovation Management Solutions, a technology consulting group. “The cost was too prohibitive.”

Today, however, the calculus may be changing.

The advent of Elon Musk’s SpaceX has brought a steep decline in the cost of rocket launches. From 1970 to 2000, the average low-earth-orbit rocket launch cost was around $18,500 for a kilogram, or 2.2 pounds, of weight; today, the cost has plummeted to as low as $1,500 a kilogram. That reduction has helped drastically reduce estimates for building power stations beyond Earth’s atmosphere.

A 1980 review by NASA concluded that the first gigawatt of space-based solar power (enough energy to power 100 million LED bulbs) would cost more than $20 billion ($100 billion today). By 1997, NASA estimated that that number had dropped to about $7 billion ($15 billion today); now, it is estimated to be closer to $5 billion, according to a study conducted for the European Space Agency in 2022.

“I used to be a critic of space-based solar power,” said Ramez Naam, a climate and clean energy investor. Mr. Naam is now actively seeking space-based solar companies to invest in. “The dramatically changing cost of space launches has changed everything,” he said.

Space-based solar power requires wirelessly transmitting electrical energy across space using microwave or laser power beaming. Unlike laser beams, microwaves can penetrate clouds and rainfall, making them the prime candidate for maximizing solar capacity.

Still, there are engineering hurdles. Though Mr. Hajimiri’s team at Caltech proved that the wireless energy transfer of microwaves in space was possible — and even beamed a detectable amount of energy to Earth — they did not beam enough power to Earth to convert it into a usable form.

“No one has demonstrated power beaming more than a few kilometers,” said Paul Jaffe, a U.S. Naval Research Laboratory engineer specializing in power-beaming technology. Mr. Hajimiri thinks it can be done. The Caltech engineer says he is working on technologies that would enable a large array of lightweight, sail-like spacecraft, using billions of small transmitting antennas, to create a focused beam that could travel thousands of kilometers to Earth and carry megawatts worth of energy.

The scale of space-based solar power structures is also daunting. The most prominent building in space today is the International Space Station, which measures 357 feet end to end. Space-based solar power systems would be several thousand feet wide, and an army of robots would be needed to autonomously assemble the structures while in orbit.

In addition to overcoming technical challenges, researchers must also ensure the safety of wirelessly beaming power to Earth. Microwave and laser beams pose a known risk to human health when operated at certain power densities. Researchers say the power density of space-based solar would be designed to operate within limits set by international governing bodies. Still, no studies have focused on the effect of space-based beaming on human health, the environment or the atmosphere — a critical step for public acceptance of the technology.

Then, inevitably, there will be regulatory challenges. The transmission of radio waves from orbit — including telecommunication, GPS and weather satellites — requires licensing to prevent interference from different users. Solar-power satellites would likely need the approval of the International Telecommunications Union, a United Nations agency, to protect and license their operating frequencies.

The complexity of these challenges places the expected arrival of most space-based solar power projects in the 2030s or 2040s, should they ever get to that point. That’s not stopping researchers from pressing forward with the dream of harnessing an uninterrupted, inexhaustible supply of energy from space.

Sanjay Vijendran, an engineer at the European Space Agency, spent much of his life’s work on Mars exploration projects, but climate change brought his focus back to Earth. “Is there more that space could be doing to directly help with the climate crisis?” Mr. Vijendran recalled asking himself and his colleagues in 2020. The result was Solaris, a program he leads that will release a report by 2025 on space-based solar power’s technical and economic feasibility.

Virtus Solis, based in Michigan, and Space Solar in the United Kingdom are among several start-ups working on space-based solar power. Government agencies — including NASA, the U.S. Air Force, the Japan Aerospace Exploration Agency, the European Space Agency and the China Academy of Space Technology — plan to share reports on space-based solar power within the decade. Since 2019, the U.S. Naval Research Lab has launched several demonstrations of power beaming.

Mr. Jaffe thinks there is no certainty that space-based solar power will work or even be necessary. “It could be that we are going to create a portfolio of alternatives that are good enough for our projected energy, and that makes space-based solar unnecessary,” he said.

Mr. Vijendran is also ready to concede that space-based solar power might not work without proper funding. But he sees an absolute need to explore the option, particularly given how little money has been invested in the technology relative to other solutions.

“We’re putting billions into nuclear fusion research each year,” Mr. Vijendran said. “If you put a billion a year into space-based solar power, we will have this ready in 10 years.”