The Plan to Build a Great Wall of Solar Power on the Moon Is Mostly Ridiculous

If you ignore the whole off-world thing, the Moon is a great place to generate solar power. Lunar days last two Earth weeks, and there’s no atmosphere for the Sun’s light to pass through on its way to a solar panel. But again, it's the Moon, which isn't exactly nearby. But what if we could actually harness that power? One Japanese company says yes, and they have a plan for how to do it.

The idea comes from the Shimizu Corporation, and it details a plan to shift the world from “economical use of limited resources to the unlimited use of clean energy.” This, the company’s website says, “is the ultimate dream of all mankind. The LUNA RING, our lunar solar power generation concept, translates this dream into reality.” Yes, it's kind of ambitious.

The LUNA RING (Shimizu's use of all caps seems warranted for an idea like this) itself would be a strip of solar cells stretching the full 11,000 mile length of the Moon’s equator. It will range in width from a few miles to 250 miles. For a sense of scale, the great wall of China measures 13,170 miles, but of course it's not nearly as wide.

Shimizu’s plan calls for the bulk of the ring to be built on the Moon using materials mined from lunar soil. Minerals, ceramics, glass, and concrete would be transported from our planet to the satellite, while the necessary water would be mined from available resources in the lunar soil using hydrogen also shipped from Earth.

To be clear, this remains far removed from reality. NASA hopes to get the price of sending a pound of payload to space down to around $100 by 2025—costs of getting things to the Moon would be higher, of course—but even then, sending the mining and construction equipment needed to refine lunar materials into working solar panels in an as-yet unbuilt Moon factory would be incomprehensibly expensive.

Even then, the ring Shimizu is proposing is far more complicated than just a solar array because the power these solar cells gather has to make it back to Earth so it can fulfill the goal of powering the planet. To beam the power back to Earth, Shimizu’s plan calls for transmission facilities on the Moon and receiving stations on Earth.

As Shimizu describes it, solar energy will be harvested on whichever side of the Moon is facing the Sun at a given time. Then electrical cables will transport that energy to the near side of the Moon, the side that’s tidally locked to and always facing the Earth. From there, transmitting stations will beam the power to Earth using microwaves and lasers.

The energy will be received by giant conversion facilities located at strategic points around the planet. At these receiving stations, semiconductors and inverters will convert that solar energy into clean electricity. That electricity will then power anything from individual households to large businesses and factories, giving the world a clear energy solution straight out of science fiction.

This means Shimizu’s system is far more complex than just a solar array. There are the transmission facilities, including multiple 12.4-mile microwave power transmission antennas to ensure the power is beamed on the right path to Earth and the high-density lasers to actually beam the energy to Earth. There’s also the need for some way to get the necessary construction materials across the Moon’s surface so astronauts and (or) robots can actually build the solar array and the transmission facilities. Finally, Shimizu will have to build some site where solar cells can be produced on the Moon, which comes with its own challenges.

Building something like this on Earth would be hard enough. Doing it on the Moon, Shimizu acknowledges, will be a long-term, multiphase project. From start to finish, establishing the necessary infrastructure and constructing the LUNA RING could take generations. But the payoffs would be well worth the effort. Putting this massive solar cell array on the Moon eliminates problems of bad weather and will see constant power generation, providing the whole planet with clean energy.

But there are some obvious challenges with the idea, too, aside from the logistic and technical difficulties involved in mounting such a large scale project. Shimizu’s brochure doesn’t mention how much of the harvested solar energy will be used to transport it to the transmission sites, beam it to Earth, and convert it to energy that we can use. There’s also the issue of ownership. Existing space treaties have focused on keeping the worlds militaries from establishing outposts off the planet. But what happens when one country takes firm steps to capitalize off resources in space? Building the LUNA RING would probably have to be an international endeavor on some level so nations could divide up the location of receiving stations with the goal of getting the whole world off fossil fuel power.

For now, there’s plenty of time to work out the details of the LUNA RING’s actual construction. Right now, Shimizu’s long range plan calls for experiments and technological demonstrations in this decade, pilot demonstrations on the Earth and the Moon in the 2020s, and preparation for the LUNA RING in the 2030s. Construction will ideally begin in 2035.

We’re not quite ready to become a clean energy global society, but we might be on the right track with this science-fiction-worthy LUNA RING proposal.