Japan’s OHISAMA: Beaming Solar Power from Space

Japan is on the verge of turning science-fiction into reality. Through its OHISAMA (On-orbit experiment of HIgh-precision beam control using small SAtellite for MicrowAve power transmission) initiative, Japan Space Systems (JSS) plans to launch a compact satellite that collects sunlight in orbit, converts it into microwaves, and beams roughly 1 kilowatt of power to a ground station on Earth.

How OHISAMA Works

The satellite, weighing about 180 kg, will operate in low Earth orbit, approximately 400 km above the planet.
It carries a solar panel of around 2 square meters (22 ft²) to harvest solar energy constantly — a key advantage over earthly solar farms, which are hampered by night and clouds.
Energy is stored in an onboard battery and then converted into microwaves. These microwaves are precisely directed toward a ground-based “rectenna” (receiver antenna) that turns them back into usable electricity.
The receiving station in Suwa, Japan, consists of an array of antennas roughly 600 m² in total, carefully spaced to capture the microwave beam.
Because the satellite travels extremely fast (about 17,400 mph / 28,000 km/h), the system needs very fine beam-control: even tiny errors could misalign the microwave transmission.

Why It Matters

If OHISAMA succeeds, it will prove that continuous, weather-independent solar power can be harvested from space — even above cloud cover, dusk, or nighttime.
Though 1 kW is a modest output (roughly enough to power a household appliance for an hour), the mission is fundamentally a proof-of-concept, not a commercial power plant — but it could pave the way for much larger orbital solar farms in the future.
An essential technical breakthrough is the rectenna, a device combining antenna and rectifier to convert microwaves back into electricity. Researchers from Kanazawa Institute of Technology have worked with JAXA to build a lightweight, deployable version for the OHISAMA mission.
On the power-transmission side, beam precision is critical: OHISAMA’s technology aims for angular precision better than 0.001 degrees, a remarkable feat to ensure the microwaves hit the ground receiver safely.

Challenges — and the Big Picture

Scaling up: To become commercially viable, future systems would need much bigger satellites and receiving fields — possibly kilometers wide — to deliver gigawatts of power.
Efficiency and safety: While the technology is promising, engineers must balance conversion efficiency, beam strength, and health/safety risks of microwave transmission.
Cost: Launching, building, and operating orbital solar-power infrastructure remains expensive.

Still, if OHISAMA works, it could mark a paradigm shift: rather than relying only on Earth-bound grids, the future of renewable energy could be in orbit, with clean solar power streamed down from space, day and night, rain or shine.