Solar Power from Space to Overcome Limitations of Earth-Based Solar Plants
Japanese researchers have achieved a significant milestone in developing space-based solar power plants for Earth’s energy needs. In December, they successfully tested microwave power transmission from an aeroplane to the ground, covering a distance of seven kilometres. This achievement is part of Japan’s “Ohisama Project” by the Japan Space System Organisation, aiming to lead the world in wireless power transmission technology.
The project’s name, which translates to “Honourable Sun,” cleverly abbreviates its long official title: On-orbit Experiment of High-Precision Beam Control Using Small Satellites for Microwave Power Transmission. The next step involves launching satellites to demonstrate the technological feasibility of this ambitious vision.
Space-Based Solar Power: Overcoming Earth’s Limitations
The concept of space-based solar power was first proposed in 1968 by American scientist Peter Glaser. He suggested solving two key drawbacks of Earth-based solar power: no energy production at night and reduced output during cloudy weather. Solar plants in geostationary orbit could operate 24/7, unaffected by weather conditions, and transmit energy to Earth through microwaves or lasers with higher efficiency.
For decades, the high costs of launching the required solar modules made the idea seem impractical. However, declining rocket launch costs now inspire hope for its eventual commercialisation.
Nations worldwide are competing to develop space solar power, with significant investments from the USA, China, and others. Iceland, in collaboration with Transition Labs and Space Solar, aims to become the first country to utilise space-based solar power extensively by 2030.
Feasibility and Challenges
NASA’s 2024 study highlighted the challenges of making space-based solar plants competitive with terrestrial energy sources. Under baseline scenarios, orbital solar power was found to be 12 to 80 times more expensive than conventional energy. However, cost reductions in manufacturing and launch operations could make it viable.
Japan leverages its expertise in wireless power transmission to remain competitive. Unlike the USA and China, which dominate rocket launches, Japan leads in microwave transmission technology.
Japan’s Progress in Wireless Power Transmission
Japan has been diligently advancing wireless energy transfer technology, incorporating it into space exploration policies over the past 15 years. In 2019, Japanese researchers achieved the world’s first wireless energy transfer using a phased-array antenna. This technology is not limited to space but also has potential applications on Earth, such as powering drones and industrial robots.
Since 2020, Japan has been the first country to establish regulations for wireless power transfer in specific frequency bands: 920 MHz, 2.4 GHz, and 5.7 GHz. A 2024 test confirmed the feasibility of transferring energy over longer distances, with 13 sensors successfully receiving microwaves from an aeroplane.
Ambitious Goals for 2050
The Japanese government envisions transmitting power from space-based solar plants to Earth by 2050. Japan Space System’s presentation depicts a two-square-kilometre solar array in orbit paired with a four-kilometre receiver on Earth.
Further testing of lightweight, foldable receiver membranes (Rectennas) and satellite-to-satellite energy transfer is planned. While commercial readiness may take decades, Japan’s efforts mark a critical step towards making space-based solar power a reality.