Tech Insights

Out of This World: Space-Based Solar Not So Far-Fetched

May 24, 2024 by Kevin Clemens

Collecting solar power from a giant satellite in space and transmitting the energy back to Earth is not as sci-fi as it sounds. 

Someday, we will need to develop new ways to produce and distribute electric power. We are already moving away from more than 100 years of thermal coal toward renewables like wind and solar and from massive power grids to smaller, more agile distributed power systems. 

Geothermal power is promising but limited in locations that make it practical, and hydroelectric power is already suffering from droughts caused by the changing climate. Nuclear fusion has been on the horizon for more than 70 years, and although promising, it remains a steady but distrusted option.

Could space-based power be the next energy frontier?

 

Satellite network in space.

Satellite network in space. Image used courtesy of Adobe Stock

 

Space-Based Solar Power

Earth-based solar power is the fastest-growing renewable energy source. Solar has two obvious limitations: it only works during the daytime when the sun is shining, and it takes up huge amounts of space. But what if, instead of installing solar panels on the ground, we could launch them into orbit and deploy them in space? The energy they collect could be beamed to Earth via an array of ground receivers. That’s the idea behind space-based solar power (SBSP).

It's not a new idea. In 1923, Soviet aerospace engineer Konstantin Tsiolkovsky suggested space-based mirrors could beam sunlight to the ground. Science fiction writer Isaac Asimov’s 1941 short story “Reason” was set on a space-based solar power satellite that beamed energy back to Earth and around the solar system. By the late 1960s, proposals were made to beam energy collected in space to the ground via microwaves. 

 

Space Power Advantages

Collecting solar power using an orbiting satellite and beaming the energy to Earth has some advantages. Unlike Earth-based solar arrays, which don’t produce power at night, a solar array in a geostationary orbit (about 22,000 miles or 36,000 kilometers above Earth) would allow energy to be collected continuously. 

In addition, because the Earth’s atmosphere blocks some parts of the solar radiation spectrum, ground-based systems can’t take advantage of all of the sun’s energy. Collecting solar energy outside the atmosphere lessens the problem. Without the blocking effects of Earth’s atmosphere, an SBSP could produce as much as eight times more power than solar panels on Earth. 

Space also has a lot of space. Instead of taking up valuable real estate on the planet, huge solar arrays can be deployed in space without worrying about displacing farmland or other useful land. Power could also be beamed directly where needed, reducing the need for long-distance power transmission lines and the energy losses they experience. 

 

Space Solar Disadvantages

It isn’t hard to think of several difficulties in collecting and beaming solar energy from space. The solar arrays could measure more than a kilometer across, and placing huge solar arrays into space would require hundreds of launches and an army of autonomous robots to assemble the solar array once it reaches orbit. 

The costs of launching payloads into orbit are coming down, thanks to the reusable SpaceX Falcon rocket. The SpaceX Starship promises to reduce costs to as little as $200 per kilogram. Theoretically, no technological hurdles exist in placing a huge solar array into space.

 

Transmitting the Power

The trick will be transmitting energy from space to ground. The most likely way to do this is to convert the electrical energy into microwaves to carry energy through the Earth’s atmosphere, where it will be received on the ground by a rectifying antenna, or rectenna. This microwave beam would need to be wide to transmit sufficient power to the rectennas, requiring a focusing antenna in space that could be more than several kilometers wide. 

 

Satellite-based solar power 

Satellite-based solar power. Image used courtesy of the Department of Energy

 

The rectenna would have to be very large—probably between 3 and 10 kilometers in diameter. It would likely be constructed from a thin metal mesh material held a few meters above the ground on poles. This would allow the ground underneath the rectennas to be used for agriculture, as light would easily pass through the mesh. 

Orbiting SBSP satellites can be positioned in several ways. A geostationary orbit would place the satellite over a specific place on the Earth, where it can target the rectenna more easily. The downside is during some parts of the year, the satellite would experience a short night and would not provide power 24 hours a day throughout the year. The SBSP satellite could also be placed in a polar orbit with a string of rectenna locations on the ground along its orbital path. The satellite would transmit power to each rectenna twice daily as it passed overhead. While this satellite position wouldn’t provide 24 hours a day of power at a single location, the distributed nature of the rectennas along the orbital path would reduce the need for long-distance power transmission. Lastly, the SBSP satellite could be placed a long enough distance from the Earth so that sunlight never gets blocked, and energy could be sent to a series of rectennas on the ground. This would require an accurate targeting system.

 

A possible design for SBSP

A possible design for SBSP. Image used courtesy of NASA

 

Transmitting microwaves from space does have health concerns for both humans and wildlife. The satellite's targeting and alignment with the rectennas would need to be precisely maintained to avoid excess exposure to potentially harmful microwave radiation. The highest levels of microwave radiation would be nearest the center of the rectenna, dropping off toward the edges. Researchers must also examine the effects on birds or aircraft passing through the microwave beam coming from space.

 

Space Solar Efficiency

Solar panels are only 20-30 percent efficient in converting sunlight into electric power, and conversion of the electrical energy to microwaves will also have losses. On the receiving end, converting the microwaves back into electrical energy will also have inefficiencies. At present, transmitting energy via microwaves has around a 5 percent total efficiency. While this doesn’t sound like much, according to the European Space Agency, a 10 to 20 percent efficiency will make the SBSP concept economically feasible. 

 

On the Space Solar Bandwagon

Several nations and organizations worldwide are testing various concepts for SBSP. China, Japan, the European Space Agency, and the US are all funding and building test programs and facilities.  

For example, the China Academy of Space Technology has created a land-based verification system for a space solar power station. Their system converts sunlight into electrical energy, transmits it over a distance by microwave, and recovers it at a receiver station. In 2028, a Chinese satellite 400 kilometers (km) above the Earth, carrying a solar array, will transmit 10 kilowatts (kW) to a receiving station on the ground. By 2030, that will expand to a solar array that generates 100 kW, transmitting the energy from a geosynchronous orbit 36,000 km above the Earth's surface. 

The U.S. space agency NASA is less enthusiastic about space-based power, issuing a report questioning the feasibility of the technology. NASA cites the amount of energy and carbon emissions created by hundreds of launches required to place the necessary components into orbit and the cost of the project when compared to building Earth-based solar and wind energy facilities.  

On the other hand, according to Bloomberg Intelligence, nuclear fusion as a practical energy source will potentially cost as much as $1 trillion, and that assumes some vexing fundamental problems with the technology can be solved. SBSP uses existing technology, and although the costs could rival those of developing fusion, the process would require much less innovation and could provide megawatts of power from space by 2040-2050. Unfortunately, SBSP also would require significant amounts of international cooperation, something which our species does not always do very well.