Beaming Down: Capturing Solar Power From Space

When you first hear about space-based solar power, it seems like it must be science fiction. The idea of collecting solar energy in space and then beaming it down as microwaves to collectors on the Earth's surface, where it is converted back into electrical energy to power the grid, would appear well beyond what’s technically possible. Yet, a handful of countries are spending tens of millions to develop the technologies to enable the concept to take shape—and seeing success. 

 

Concept of space-based solar power. Image courtesy of the European Space Agency 

 

The idea that solar energy could be collected and beamed from space was first suggested in 1968 by a U.S. engineer named Peter Glaser, working for consulting firm Arthur D. Little. Glaser envisioned giant 6-kilometer (km) in diameter disc-shaped solar collectors 36,000 km above the Earth in geosynchronous orbit. Photovoltaic (PV) cells would convert sunlight to electricity, which could then be turned into microwaves and beamed to giant 3 km in diameter receiving antennas (called rectennas) on the Earth. By the mid-1970s, NASA’s Jet Propulsion Laboratory had shown that tens of kilowatts of energy could be transmitted from point to point using microwaves. 

 

Overcoming Earth-Bound Problems of Solar Power

Generating significant electrical power using solar panels on the Earth requires a lot of space that solar panels must cover. While there have been experiments in growing food crops in the shade provided by these terrestrial solar farms, land usage is still a significant concern. In addition, solar panels only produce energy when the sun is shining—cloudy days can reduce their output, and they can only operate during daylight hours. Overcoming intermittent generation problems requires large-scale energy storage, and battery energy storage systems are becoming increasingly popular for utilities. 

 

Solar panels on the International Space Station. Image used courtesy of NASA

 

Space-based solar overcomes these problems with huge solar arrays placed in space and positioned so that they would nearly always produce energy. The microwaves that would send that energy to Earth are not absorbed by clouds and could be counted on to provide continuous carbon-free renewable baseline electrical power to the grid. Since the solar array would be located in space, without the blocking effects of the Earth’s atmosphere, it could yield as much as eight times more power than solar panels on Earth's surface.

 

Progress from Public and Private Sectors

For researchers in the 1970s and 1980s working on the idea of sending solar power from space, two problems were immediately clear. The first was the cost of solar panels, and the second was the enormous cost of sending huge solar arrays, giant microwave systems, and antennas off the planet and into space. These stumbling blocks have become less of an obstacle to the concept in recent years. Solar panel prices have dramatically decreased during the past decade, and a renaissance in interest in the commercialization of spaceflight has brought about less expensive ways to get into space. 

Companies like SpaceX are pioneering the path to lower-cost spaceflight. Reusable rockets, modular designs, and constellations of satellites are bringing down the overall costs. The SpaceX Starlink broadband network is launching 40,000 mass-produced satellites over five years to provide worldwide communication capability. Add in progress with robotic assembly in space and improvement in power technology, and the hardware and space launch side of space-based solar power looks less daunting. In fact, China and the US are both building test facilities, Japan has the concept of power from space as a national goal, and the European Space Agency has endorsed and is funding advanced studies. 

 

Looking Closely at PV Efficiency

Nothing is 100 percent efficient, and a space-based solar power system will suffer losses at every step of power conversion. Solar panels are only 20-30 percent efficient at converting sunlight into electric power, and converting the electrical energy to microwaves will also have losses, as will converting the microwaves back into electricity at the receiving end. Still, according to the European Space Agency, as long as the total losses don’t exceed 85 to 90 percent (and 10 to 15 percent of the solar energy hitting the panels makes it to the grid), the concept is economically viable.  

 

Concept of a future spaced-based power orbiter. Image used courtesy of the European Space Agency 

 

Research to Address the Details

Many details and hurdles must be worked out before even test programs can be developed. Some are already underway, like a recent report from the University of Surrey and Swansea University in the U.K. that details a study of how solar panels in space generated power and weathered solar radiation over six years and  30,000 orbits. They found the panels resisted degradation from radiation, harsh temperature fluctuations, and micrometeor impacts, indicating that such panels could be expected to provide power from a space-based solar power array for many years. 

At the China Academy of Space Technology, researchers have gone so far as to create a land-based, full-chain, system-wide ground verification for a space solar power station. Their system is the first to examine all aspects of converting sunlight into electrical energy, transmitting the energy over a distance by microwave, and then recovering it at a receiver station. In the next phase scheduled for 2028, a satellite carrying a solar array will transmit 10 kW from an orbit 400 km above the Earth to a receiving station on the ground. By 2030, the plan is to expand the solar array to generate 100 kW and transmit it from a geosynchronous orbit 36,000 km above the Earth's surface. 

 

Video used courtesy of Caltech

 

In 2023, they already experimented with transmitting microwave energy from a satellite in space to a receiver on the ground. 

Transmitting microwaves from space is not without health concerns. Alignment with the receiving antenna would need to be carefully maintained, while the level of potential exposure to humans and animals would need to be monitored in an area around the receiving site. The highest levels of microwave intensity would be at the center of the receiving antenna and would drop off toward the edges of the antenna. The effects on birds passing through the microwave beam must also be examined. 

 

Power From Space at What Price?

The cost of building, launching, and maintaining a space-based solar power system could easily run up to hundreds of billions of dollars. Moving the necessary materials into space could take 40 launches, and assembling the equipment in orbit would take advanced space robots and/or a team of skilled space technicians. On Earth, the antenna for receiving microwave energy might be between 3 and 10 km in diameter, requiring a major investment in land and labor to install the antenna system. 

 

Astronaut making repairs on the ISS. Image used courtesy of NASA

 

As we move toward zero-emission energy, the cost of other options is also daunting. According to Bloomberg Intelligence, $5.1 trillion has been spent on renewable energy since 2000. Building traditional nuclear power plants costs tens of billions of dollars. It takes up to 20 years, while the prospect of nuclear fusion as a practical energy source is expected to cost as much as $1 trillion, according to Bloomberg. Fusion also has some significant technical hurdles we don’t yet know how to solve. At least space-based solar power uses technology that is presently understood and would require less innovation to become a practical alternative to coal, oil, and gas to generate base-load electrical power for the grid.