A global competition is intensifying to develop technology for transmitting solar power collected in space to Earth, with a Japanese public-private partnership planning to conduct a trial around fiscal 2025.
The concept of space-based solar power was proposed by an American physicist in 1968. It involves launching solar panels into space to generate electricity at an altitude of 36,000 kilometers.
The solar power is converted into microwaves – the same as the electromagnetic radiation used in microwave ovens – and then transmitted down to ground-based receiving stations for conversion into electrical energy.
Microwaves can pass through clouds, providing a stable supply of power from space to the ground regardless of the time of day or weather conditions.
Hiroshi Matsumoto, the former president of Kyoto University, was in charge of the research group that has been leading the research. His team successfully transmitted power through microwaves in space in the 1980s, the first in the world.
The research efforts continued after Kyoto University professor Naoki Shinohara took over. In 2009, the group used an airship to transmit power from an altitude of 30 meters to a mobile phone on the ground. The team is working to refine the core technology for wireless power supply.
The Ministry of Economy, Trade and Industry launched an industry-government-academia project in 2009 with Shinohara as head of the technology committee.
The project successfully conducted microwave power transmission experiments horizontally in 2015 and vertically in 2018 over a distance of 50 meters. The team will run experiments on vertical transmission with distances between 1 km and 5 km in the future.
Looking ahead, "If we can demonstrate our technology ahead of the rest of the world, it will also be a bargaining tool for space development with other countries," Shinohara said.
The group plans to run an experiment around fiscal 2025 to see if power can be transmitted from outer space to the ground. It will use small satellites to transmit power to ground-based receiving stations from a distance of hundreds of kilometers.
Competitors are also working toward commercialization. The U.S. Air Force Research Laboratory and the California Institute of Technology are conducting large-scale projects. In China, Chongqing University is developing the technology while the European Space Agency is also working on its own projects.
As more governments and businesses strive to achieve net-zero emissions, space-based solar has drawn renewed attention in recent years.
However, cost remains a significant challenge. To generate approximately 1 GW of power – equivalent to the output of a nuclear reactor – it would require space-based solar covering an area equivalent to a square measuring 2 km on each side. Even with advanced technology, the installation of such a capacity is expected to incur costs exceeding 1 trillion yen ($7.1 billion).
