The idea of building a ring of solar panels around the Moon It has been circulating in the offices of the space industry for years, but recently it has returned with force to the global energy debate. Far from being just a science fiction exercise, this concept is being presented as a possible answer to the growing demand for clean and stable electricity on a planet that wants to leave fossil fuels behind.
The most developed project in this area is the Luna Ring from the Japanese company Shimizu CorporationThis proposal aims to harness the continuous sunlight received by the lunar equator to generate uninterrupted energy and transmit it to Earth via wireless systems. The initiative has been presented as a very long-term vision, without firm deadlines, but it aligns with the renewed international interest in space-based solar power, an area in which the European Space Agency is also active.
What is the Lunar Ring: a solar belt around the lunar equator
The Luna Ring proposal suggests installing a virtually continuous belt of photovoltaic cells along the Moon's equatorwith an estimated length of 10.900 or 11.000 kilometers (approximately 6.800 miles) and a width that could reach up to 400 kilometers according to some preliminary designs. The main objective is to ensure that a portion of this megastructure always receives direct sunlight.
Upon finding themselves in outer space, The panels would not suffer the losses caused by the Earth's atmosphere.Clouds or day-night cycles. In fact, various estimates by Shimizu and other researchers suggest that solar panels located off-Earth could generate between five and twenty times more energy than those installed on the surface, as they operate under much more stable conditions.
The ring would extend only along the equator, but the idea is to continuously cover that lunar band. This would allow, throughout the satellite's rotation, a section of the belt is always illuminated, facilitating 24/7 production that is currently impossible to replicate with terrestrial solar plants, even with large storage systems.
The structure is envisioned as a gigantic lunar power plant, capable, at least on paper, of supplying terawatts of power. Some studies mention the theoretical possibility of reaching generation figures close to 220 terawatts on the lunar surface to deliver about 8,8 terawatts of usable power on Earth, and there has even been speculation about potentials of up to 13.000 terawatts if the system were expanded on a large scale.
How would energy be sent from the Moon to Earth?
Generating electricity on the Moon is only the first part of the challenge; the real crux of the matter lies in how to transfer that energy to EarthThe basic design of the Luna Ring includes a wireless transmission system in two main modes: using microwaves and using high-density laser beams.
In this scheme, the energy captured by the panels would be transformed into electricity and travel through cables to large stations located in the visible face of the Moon, the one that always looks towards our planet. From those facilities, the electricity would be converted into electromagnetic radiation that would be directed to receiving stations on Earth.
In the case of microwaves, ground stations would use rectifying or rectenna antennasThese devices are capable of transforming microwaves into usable electrical current. This technology has already been explored by NASA, JAXA, and several research centers, and the California Institute of Technology has even conducted recent demonstrations of energy transmission from space.
Laser transmission, on the other hand, would allow more power to be concentrated into a narrow beam, but requires a extreme level of precision It is more sensitive to the effects of the Earth's atmosphere, such as absorption, scattering, or the presence of clouds. This complicates its continuous and safe use on a large scale.
Performance studies convey a cautious image: The microwave system would have an overall efficiency of around 5,82%.Whereas a scheme based entirely on lasers would barely reach around 2,20%. That is, most of the energy generated would be lost during the conversion and transmission steps, which necessitates oversizing production on the Moon if significant usable power is to be obtained on Earth.
Project scope and main technical challenges
Beyond the power figures, the Luna Ring faces a list of unprecedented engineering challengesWe are talking about building an infrastructure thousands of kilometers long in an airless environment, with strong temperature contrasts and subjected to a constant bombardment of radiation and micrometeorites.
One of the elements that most concerns aerospace engineers is the lunar dustRegolith is extremely fine and abrasive, a fact already observed during the Apollo missions, where it damaged suits and equipment. This dust can adhere to solar panels, reducing their performance and complicating maintenance, thus requiring long-lasting cleaning and protection solutions.
Cosmic radiation and high-energy particles pose another risk. Panels and power electronics would need to be designed to withstand a highly hostile environment for decades, with little chance of mass replacement. All of this necessitates the development of much more durable materials and designs than those employed in terrestrial photovoltaic plants.
Nor is the challenge of energy transmission itself any less significant. Directing high-density microwaves or lasers to specific stations on the Earth's surface requires highly precise guidance systems, likely supported by beacons and advanced geolocation systemsFurthermore, it would be essential to establish clear international security standards to prevent interference with aircraft, satellites, or other communications.
Meanwhile, the logistics of assembly are colossal. It would require developing fleets of robots capable of operating autonomously on the Moon, building infrastructure, deploying panels, performing maintenance, and, in many cases, working with materials obtained from the lunar soil itself to reduce the mass to be launched from Earth. All of this is coordinated with remote support from control centers and with the occasional participation of astronauts.
Who is behind it and how does it fit into Japan's energy strategy?
The Luna Ring is a proposal from shimizu corporationA major Japanese construction company has been promoting this concept since 2011 as part of its vision for the engineering of the future. The company doesn't see it so much as a project with an opening date, but rather as a roadmap to guide its research in space energy and robotics.
The initiative has some institutional support in Japan. Japan Aerospace Exploration Agency (JAXA) It has spent decades analyzing solar energy from space and has supported studies on wireless transmission and orbital architecture. Furthermore, the national context is driving the exploration of radical options: Japan imports nearly 90% of its primary energy and has little land available for large-scale renewable energy plants.
The project is also related to the so-called “hydrogen society”The vision is for an energy system in which hydrogen acts as the primary energy carrier instead of fossil fuels. Some of the electricity generated by the lunar ring could be used to produce green hydrogen, which would then be transported and stored as a clean fuel for industry, heavy transport, or backup power generation.
On the political and social level, the nuclear disaster of Fukushima Daiichi in 2011 It marked a turning point in Japan's energy strategy. From that moment on, the country intensified its commitment to renewables and advanced technological solutions that reduce dependence on both nuclear energy and imported coal and oil.
Today Japan has positioned itself as third largest producer of solar energy in the world And it is working on alternatives such as floating solar panels, offshore wind power, and wave energy, trying to compensate for the scarcity of available land. The Luna Ring fits into this dynamic as an extreme proposal, but one consistent with the country's technological ambition.
Costs, economic viability and international debate
If the project is already technically complex, the economic challenges are even greater. Experts such as Masanori Komori, from the Institute for Energy Economics in JapanThey point out that the concept is attractive on paper, but prohibitively expensive in practice given current costs. There is no official figure, but there is talk of multi-million dollar investments sustained over decades.
So far, the Luna Ring has not secured solid financial backing It is neither a government initiative nor a project of major space agencies like NASA or JAXA as an operational program. It also lacks a defined timeline of milestones or concrete construction phases; it remains a strategic vision rather than an ongoing project.
NASA already evaluated the idea of space-based solar power plants in the 1970s and concluded that the costs made it unfeasible at the time. Subsequent studies have refined that perspective, especially with the reduction in launch costs thanks to new private operators and improvements in electronics, but the consensus remains that A very intense additional cost reduction is needed for a lunar-scale system to be cost-effective.
Despite everything, international interest has grown. China is planning demonstrations of energy transmission from low Earth orbit in this decade and subsequent tests in geostationary orbit. The UK has also been pursuing feasibility studies for space-based solar power plants since 2021, seeking to bolster its security of supply and reduce emissions.
In Europe, the European Space Agency (ESA) Europe has launched the Solaris program, focused precisely on studying the potential of space-based solar energy for the continent. The goal is to determine whether, in the medium term, it can become an additional pillar of the European energy mix, complementing the expansion of ground-based solar and wind power. Although the Luna Ring is a Japanese project, its philosophy aligns with the lines of research also being explored in Europe.
Implications for Spain and Europe in the energy transition
For countries like Spain, with a high solar potential and a clear decarbonization strategySpace-based solar energy would not replace surface-based photovoltaic plants, but it could become an interesting complement in scenarios of high demand and massive electrification of the economy.
An infrastructure like the lunar ring, if it were ever to materialize, would allow receive energy during the night or during periods of low renewable energy production, reducing the need for fossil fuel backup power plants or massive battery storage. In practice, Spain and other European countries could acquire some of that electricity through international agreements, just as they currently import gas or electricity from neighboring countries.
However, integrating a constant flow of lunar energy into the European electricity system would require adapting the transmission and distribution networks, managing new supply and demand profiles and redesign wholesale markets to incorporate this source. Coordination at the European Union level would be key to avoiding imbalances between member states.
In geopolitical terms, such a system could reduce European dependence on imported fossil fuels of unstable regions, although in return it would generate new technological and commercial dependencies with the countries and companies that controlled the lunar infrastructure and transmission stations.
Meanwhile, the priority in Spain and the EU remains the accelerated deployment of conventional renewables and the improvement of internal and international electricity interconnections. In this context, the Luna Ring is perceived more as a a very long-term bet as an immediate solution to the current challenges of the European energy mix.
Between science fiction and the technological roadmap
The ring of solar panels around the Moon has become a symbol of how far the imagination can go when discussing energy and space exploration. Although for now it remains in the realm of concepts, its recurring presence in conferences, reports, and specialized debates indicates that it is not a mere anecdote.
The reduction in launch costs, the advance in autonomous robotics, the improvement of photovoltaic materials, and the development of systems for wireless power transmission They are gradually eroding the barriers that made a project of this kind unthinkable just a few decades ago. That doesn't mean it will be built exactly as planned, but it does open the door to more modest or hybrid versions.
The first real-world application of space-based solar power may not be a belt encircling the Moon, but platforms in Earth orbit that supply electricity to specific regions or critical infrastructure, with lower initial costs and much more manageable logistical complexity. From there, the leap to lunar installations would be an additional step, not the starting point.
In any case, the Luna Ring serves to raise an uncomfortable but necessary question: are we willing to look beyond our planet to guarantee future energy supplies? The answer, for now, is cautious. No one has a fixed timeline or budget, but almost no one rules out the possibility that, within a horizon of several decades, energy generated outside of Earth form part of the global energy mix.
The Japanese proposal for a ring of solar panels around the Moon encapsulates many of the tensions facing the current energy system: ever-increasing demand, the climate emergency, the search for security of supply, and the rapid advancement of space technology. Whether it will ever be built remains to be seen, but the mere fact that it is being seriously considered indicates that the debate about where and how we will generate the energy of the future has clearly crossed the boundaries of our planet.
