Known as the Luna Ring, the proposed infrastructure would span roughly 6,800 miles to capture uninterrupted sunlight. While the initial design generated little traction, the project drew renewed interest following the Fukushima Daiichi nuclear disaster in March 2011.
Shimizu Corporation estimates that space based solar panels can generate around 20 times more energy than an equivalent system on Earth. The Moon lacks an atmosphere to block or scatter sunlight. Because the belt wraps around the entire lunar circumference, one half of the system remains constantly exposed to the sun. This positioning allows for continuous, 24 hour power generation.
Terrestrial solar farms stop producing power at night and lose efficiency during overcast weather. The Luna Ring circumvents these planetary limitations by operating entirely outside Earth’s environment.
The transmission process requires multiple steps:
Shimizu’s blueprints also suggest using this energy to produce hydrogen based fuel on Earth. The long-term objective centers on transitioning away from fossil fuels toward a hydrogen based distribution economy.
 
Solar cells on the lunar equator convert sunlight into electricity. Cables carry the power to the opposite side of Earth. Microwaves and lasers transmit it to ground stations. Image credit: Shimizu Corp
Building infrastructure on the lunar surface presents severe logistical challenges. To minimize human risk, Shimizu plans to rely almost entirely on automated machinery. Operators on Earth would guide these construction robots remotely around the clock. A small team of astronauts would live on-site to provide secondary mechanical support.
The blueprint relies heavily on local manufacturing to avoid the prohibitive costs of transporting materials from Earth. Lunar soil, or regolith, contains abundant oxide compounds. By importing hydrogen from Earth, workers could synthesize water and oxygen directly on the Moon.
The same raw lunar sand can be processed into concrete, ceramics, glass fibers, and basic solar cells. Automated production plants would move along the equator, manufacturing and installing the solar arrays as they travel. The final belt would vary in width, stretching up to 249 meters at its widest sections.

The problem of scale and cost

Despite the clear physics behind space based solar collection, the project faces major economic roadblocks. Energy economists point out that while lunar solar power functions on paper, the development costs are currently unquantified. The underlying technologies are still confined to laboratory research.
Transmitting gigawatts of power across 238,000 miles of space requires unprecedented targeting accuracy. Both the microwave and laser systems require synchronized guidance beacons on Earth to ensure the beams hit their targets safely. This level of wireless power transfer has never been attempted at scale.
Shimizu maintains that the fundamental components already exist. Sunlight is free, photovoltaic technology is mature, and microwave transmission is well understood. The true obstacle lies in scaling these components to a level that dwarfs every infrastructure project in human history.
The Luna Ring remains a conceptual Dream Project on Shimizu’s official corporate portfolio. The company has not secured financial backing, and the project lacks official programming support from space agencies like JAXA or NASA.
The project briefly entered public policy debates after the 2011 earthquake and tsunami disabled 30% of Japan’s nuclear capacity. While the government became more receptive to alternative energy concepts at the time, no public funding moved the Luna Ring toward actual development.
The project group remains focused on long-term baseline research. The engineering team notes that they are working with established physical principles, meaning future breakthroughs in space transport could eventually make the concept viable.

This documentary details the structural layout, specific robotic construction phases, and massive scaling bottlenecks of the Shimizu Luna Ring project.

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