The energy beamed from space won’t be enough to run more than a coffee maker—but if all goes to plan, Japan will soon make history by transmitting solar power wirelessly from orbit to Earth.
This year, a 400-pound satellite will launch into low Earth orbit and attempt something that once seemed confined to science fiction. Using solar panels and microwave transmission, the satellite will send about one kilowatt of power—roughly enough to run a dishwasher for an hour—down to a ground antenna
“It will be a small satellite, about 180 kilograms [400 pounds], that will transmit about 1 kilowatt of power from an altitude of 400 kilometers,” Koichi Ijichi, one of the researchers and an advisor at Japan Space Systems (JSS), told Space.com.
The project, called OHISAMA—Japanese for “sun”—is part of a growing international push to harness solar power from space as a means to reduce dependence on fossil fuels and help curb climate change.
A step towards unlimited wireless solar power
The idea of collecting solar power in space and beaming it to Earth was first floated in 1968 by Peter Glaser, a scientist working on the Apollo program. At the time, it seemed outlandish. The costs were too high. The required structures, too massive. The engineering challenges, too daunting.
But things have changed. Advances in robotics, wireless transmission, and orbital logistics—particularly the promise of SpaceX’s Starship rocket—are starting to make the once-impossible look feasible.
The JSS satellite will be equipped with a 22-square-foot (2 square meters) solar panel. This photovoltaic panel will collect sunlight and charge an onboard battery. The crucial part is how this stored energy will be sent back down to us.
In the case of a regular solar panel, the collected energy is turned into electricity and is transmitted via wires. However, supplying solar energy from space to Earth through wires is not feasible. So the satellite will convert the electricity into microwaves and send it wirelessly in the form of an energy beam to a specially designed receiving antenna on the ground.
Moreover, since the satellite will be traveling at an incredible speed of about 17,400 miles per hour (28,000 kilometers per hour, the typical speed of satellites in low Earth orbit), the receiving antenna on Earth will need to be quite large, potentially stretching across several kilometers.
However, for now, such large antennas are not required because the satellite will currently serve as proof of concept. Thirteen receivers spread over a 600-square-meter area in Suwa (a city in Japan) will capture microwaves sent from its energy panels and convert them into electricity.
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If this demonstration is successful, the Japanese agencies will launch bigger satellites capable of transmitting much more solar energy.
Not the first attempt at space-based solar power
Japan isn’t alone in exploring the potential of space-based solar power. The United States has also been actively researching this area. For instance, in May 2020, the US Naval Research Laboratory (NRL) conducted a significant experiment called the Photovoltaic Radiofrequency Antenna Module (PRAM).
This experiment resulted in the launch of the X-37B Orbital Test Vehicle, which, for the first time, successfully demonstrated the key technology of converting sunlight into microwave energy in space and wirelessly transmitting it back to Earth.
Then, in March 2023, researchers at Caltech launched a space-based prototype called MAPLE (Microwave Array for Power-transfer Low-orbit Experiment). It offers a lightweight and low-cost approach to supply solar energy from space to a desired location on Earth.
Not everyone is convinced the dream can become reality. In January, NASA released a report casting doubt on the feasibility of space-based solar power.
The agency estimated that such systems could cost as much as 61 cents per kilowatt-hour. That’s over ten times more expensive than the cheapest Earth-based solar or wind energy, which can cost as little as 5 cents per kilowatt-hour.
And yet, the momentum is building.
Whether the mission will successfully achieve this goal remains to be seen. JSS and its partners haven’t yet announced an exact launch date, but in their latest statements, they confirmed the mission is scheduled for sometime after April 2025.
