Japan is preparing to transmit solar energy from space to Earth next year in the form of microwaves.
Japan is set to transmit solar energy from space to Earth next year, two years after American engineers achieved a similar milestone. This development marks a significant step towards a solar power station in space, which could help the world reduce fossil fuel reliance in the fight against climate change, Space reported on April 19.
Simulation of a solar power generation system in space. (Photo: AFRL).
Speaking at the International Conference on Space Energy held this week, Koichi Ijichi, an advisor at the Japan Space Systems research institute, outlined a roadmap for testing a small solar power plant in space that will wirelessly transmit energy from low Earth orbit to Earth. According to him, this will involve a small satellite, weighing about 180 kg, transmitting approximately one kilowatt of electricity from an altitude of 400 km. One kilowatt is equivalent to the electricity needed to operate small household appliances like a dishwasher for about an hour, depending on the size. Thus, this experiment is not yet on a scale suitable for commercial use.
The spacecraft will utilize a solar panel measuring 2 m² to charge its battery. The accumulated energy will then be converted into microwaves and transmitted to receiving antennas on Earth. Since the spacecraft travels at a speed of about 28,000 km/h, the antennas need to be spread over 40 km, with each antenna spaced 5 km apart, to successfully transmit enough energy. According to Ijichi, the transmission takes only a few minutes, but when the battery runs low, it requires several days to recharge fully.
This mission is part of the OHISAMA project (meaning ‘Sun’ in Japanese), which is scheduled for launch in 2025. Researchers have previously tested wireless solar energy transmission on the ground from fixed sources. They plan to conduct transmission tests from aircraft in December this year. The aircraft will be equipped with solar panels similar to those used on the spacecraft and will transmit electricity over a distance of 5 – 7 km.
The concept of generating solar power in space was first proposed in 1968 by former Apollo engineer Peter Glaser. Unlike most renewable energy technologies on Earth, solar energy in space is consistently available as it is not affected by weather conditions or the time of day. Currently, nuclear power plants and fossil fuel-fired power plants are used to meet demand when the wind stops blowing or the sun sets. Recent technological advancements may help address part of this issue in the future. However, researchers have yet to find a way to ensure continuous power supply without carbon emissions by the mid-21st century.
The development of automation and wireless electricity transmission technology, especially with the advent of the colossal Starship rocket, could make solar power in space a reality. Last year, a satellite developed by Caltech engineers in the Space Solar Power Demonstrator mission successfully transmitted solar energy from space for the first time. The mission concluded in January 2024. However, according to a NASA report, the energy required to manufacture, launch, and assemble a power station in orbit makes the cost of electricity produced exorbitantly high, more than 12 times that of wind and solar power on Earth.
