May 10, 2024 05:24 PM
https://spectrum.ieee.org/space-based-so...2667878868
INTRO: The accelerating buildout of solar farms on Earth is already hitting speed bumps, including public pushback against the large tracts of land required and a ballooning backlog of requests for new transmission lines and grid connections. Energy experts have been warning that electricity is likely to get more expensive and less reliable unless renewable power that waxes and wanes under inconstant sunlight and wind is backed up by generators that can run whenever needed. To space enthusiasts, that raises an obvious question: Why not stick solar power plants where the sun always shines?
Space-based solar power is an idea so beautiful, so tantalizing that some argue it is a wish worth fulfilling. A constellation of gigantic satellites in geosynchronous orbit (GEO) nearly 36,000 kilometers above the equator could collect sunlight unfiltered by atmosphere and uninterrupted by night (except for up to 70 minutes a day around the spring and fall equinoxes). Each megasat could then convert gigawatts of power into a microwave beam aimed precisely at a big field of receiving antennas on Earth. These rectennas would then convert the signal to usable DC electricity.
The thousands of rocket launches needed to loft and maintain these space power stations would dump lots of soot, carbon dioxide, and other pollutants into the stratosphere, with uncertain climate impacts. But that might be mitigated, in theory, if space solar displaced fossil fuels and helped the world transition to clean electricity.
The glamorous vision has inspired numerous futuristic proposals. Japan’s space agency has presented a road map to deployment. Space authorities in China aim to put a small test satellite in low Earth orbit (LEO) later this decade. Ideas to put megawatt-scale systems in GEO sometime in the 2030s have been floated but not yet funded.
The U.S. Naval Research Laboratory has already beamed more than a kilowatt of power between two ground antennas about a kilometer apart. It also launched in 2023 a satellite that used a laser to transmit about 1.5 watts, although the beam traveled less than 2 meters and the system had just 11 percent efficiency. A team at Caltech earlier this year wrapped up a mission that used a small satellite in LEO to test thin-film solar cells, flexible microwave-power circuitry, and a small collapsible deployment mechanism. The energy sent Earthward by the craft was too meager to power a lightbulb, but it was progress nonetheless.
The European Space Agency (ESA) debuted in 2022 its space-based solar-power program, called Solaris, with an inspiring (but entirely fantastical) video animation. The program’s director, Sanjay Vijendran, told IEEE Spectrum that the goal of the effort is not to develop a power station for space. Instead, the program aims to spend three years and €60 million (US $65 million) to figure out whether solar cells, DC-to-RF converters, assembly robots, beam-steering antennas, and other must-have technologies will improve drastically enough over the next 10 to 20 years to make orbital solar power feasible and competitive. Low-cost, low-mass, and space-hardy versions of these technologies would be required, but engineers trying to draw up detailed plans for such satellites today find no parts that meet the tough requirements.
A chart showing efficiency of research and commercial solar cells.Not so fast: The real-world efficiency of commercial, space-qualified solar cells has progressed much more slowly than records set in highly controlled research experiments, which often use exotic materials or complex designs that cannot currently be mass-produced. Points plotted here show the highest efficiency reported in five-year intervals.
With the flurry of renewed attention, you might wonder: Has extraterrestrial solar power finally found its moment? As the recently retired head of space power systems at ESA—with more than 30 years of experience working on power generation, energy storage, and electrical systems design for dozens of missions, including evaluation of a power-beaming experiment proposed for the International Space Station—I think the answer is almost certainly no.
Despite mounting buzz around the concept, I and many of my former colleagues at ESA are deeply skeptical that these large and complex power systems could be deployed quickly enough and widely enough to make a meaningful contribution to the global energy transition. Among the many challenges on the long and formidable list of technical and societal obstacles: antennas so big that we cannot even simulate their behavior.
Here I offer a road map of the potential chasms and dead ends that could doom a premature space solar project to failure. Such a misadventure would undermine the credibility of the responsible space agency and waste capital that could be better spent improving less risky ways to shore up renewable energy, such as batteries, hydrogen, and grid improvements. Champions of space solar power could look at this road map as a wish list that must be fulfilled before orbital solar power can become truly appealing to electrical utilities... (MORE - details)
INTRO: The accelerating buildout of solar farms on Earth is already hitting speed bumps, including public pushback against the large tracts of land required and a ballooning backlog of requests for new transmission lines and grid connections. Energy experts have been warning that electricity is likely to get more expensive and less reliable unless renewable power that waxes and wanes under inconstant sunlight and wind is backed up by generators that can run whenever needed. To space enthusiasts, that raises an obvious question: Why not stick solar power plants where the sun always shines?
Space-based solar power is an idea so beautiful, so tantalizing that some argue it is a wish worth fulfilling. A constellation of gigantic satellites in geosynchronous orbit (GEO) nearly 36,000 kilometers above the equator could collect sunlight unfiltered by atmosphere and uninterrupted by night (except for up to 70 minutes a day around the spring and fall equinoxes). Each megasat could then convert gigawatts of power into a microwave beam aimed precisely at a big field of receiving antennas on Earth. These rectennas would then convert the signal to usable DC electricity.
The thousands of rocket launches needed to loft and maintain these space power stations would dump lots of soot, carbon dioxide, and other pollutants into the stratosphere, with uncertain climate impacts. But that might be mitigated, in theory, if space solar displaced fossil fuels and helped the world transition to clean electricity.
The glamorous vision has inspired numerous futuristic proposals. Japan’s space agency has presented a road map to deployment. Space authorities in China aim to put a small test satellite in low Earth orbit (LEO) later this decade. Ideas to put megawatt-scale systems in GEO sometime in the 2030s have been floated but not yet funded.
The U.S. Naval Research Laboratory has already beamed more than a kilowatt of power between two ground antennas about a kilometer apart. It also launched in 2023 a satellite that used a laser to transmit about 1.5 watts, although the beam traveled less than 2 meters and the system had just 11 percent efficiency. A team at Caltech earlier this year wrapped up a mission that used a small satellite in LEO to test thin-film solar cells, flexible microwave-power circuitry, and a small collapsible deployment mechanism. The energy sent Earthward by the craft was too meager to power a lightbulb, but it was progress nonetheless.
The European Space Agency (ESA) debuted in 2022 its space-based solar-power program, called Solaris, with an inspiring (but entirely fantastical) video animation. The program’s director, Sanjay Vijendran, told IEEE Spectrum that the goal of the effort is not to develop a power station for space. Instead, the program aims to spend three years and €60 million (US $65 million) to figure out whether solar cells, DC-to-RF converters, assembly robots, beam-steering antennas, and other must-have technologies will improve drastically enough over the next 10 to 20 years to make orbital solar power feasible and competitive. Low-cost, low-mass, and space-hardy versions of these technologies would be required, but engineers trying to draw up detailed plans for such satellites today find no parts that meet the tough requirements.
A chart showing efficiency of research and commercial solar cells.Not so fast: The real-world efficiency of commercial, space-qualified solar cells has progressed much more slowly than records set in highly controlled research experiments, which often use exotic materials or complex designs that cannot currently be mass-produced. Points plotted here show the highest efficiency reported in five-year intervals.
With the flurry of renewed attention, you might wonder: Has extraterrestrial solar power finally found its moment? As the recently retired head of space power systems at ESA—with more than 30 years of experience working on power generation, energy storage, and electrical systems design for dozens of missions, including evaluation of a power-beaming experiment proposed for the International Space Station—I think the answer is almost certainly no.
Despite mounting buzz around the concept, I and many of my former colleagues at ESA are deeply skeptical that these large and complex power systems could be deployed quickly enough and widely enough to make a meaningful contribution to the global energy transition. Among the many challenges on the long and formidable list of technical and societal obstacles: antennas so big that we cannot even simulate their behavior.
Here I offer a road map of the potential chasms and dead ends that could doom a premature space solar project to failure. Such a misadventure would undermine the credibility of the responsible space agency and waste capital that could be better spent improving less risky ways to shore up renewable energy, such as batteries, hydrogen, and grid improvements. Champions of space solar power could look at this road map as a wish list that must be fulfilled before orbital solar power can become truly appealing to electrical utilities... (MORE - details)