Is space-based solar power a costly, risky pipe dream? Or is it a viable way to combat climate change? Although beaming solar power from space to Earth could ultimately involve transmitting gigawatts, the process could be made surprisingly safe and cost-effective, according to experts from Space Solar, the European Space Agency, and the University of Glasgow.
But we’re going to need to move well beyond demonstration hardware and solve a number of engineering challenges if we want to develop that potential.
Designing Space-Based Solar
Beaming solar energy from space is not new; telecommunications satellites have been sending microwave signals generated by solar power back to Earth since the 1960s. But sending useful amounts of power is a different matter entirely.
“The idea [has] been around for just over a century,” said Nicol Caplin, deep space exploration scientist at the ESA, on a Physics World podcast. “The original concepts were indeed sci-fi. It’s sort of rooted in science fiction, but then, since then, there’s been a trend of interest coming and going.”
Researchers are scoping out multiple designs for space-based solar power. Matteo Ceriotti, senior lecturer in space systems engineering at the University of Glasgow, wrote in The Conversation that many designs have been proposed.
The Solaris initiative is exploring two possible technologies, according to Sanjay Vijendran, lead for the Solaris initiative at the ESA: one that involves beaming microwaves from a station in geostationary orbit down to a receiver on Earth and another that involves using immense mirrors in a lower orbit to reflect sunlight down onto solar farms. He said he thinks that both of these solutions are potentially valuable. Microwave technology has drawn wider interest and was the main focus of these interviews. It has enormous potential, although high-frequency radio waves can also be used.
“You really have a source of 24/7 clean power from space,” Vijendran said. The power can be transmitted regardless of weather conditions because of the frequency of the microwaves.
“A 1-gigawatt power plant in space would be comparable to the top five solar farms on earth. A power plant with a capacity of 1 gigawatt could power around 875,000 households for one year,” said Andrew Glester, host of the Physics World podcast.
But we’re not ready to deploy anything like this. “It will be a big engineering challenge,” Caplin said. There are a number of physical hurdles involved in successfully building a solar power station in space.
Using microwave technology, the solar array for an orbiting power station that generates a gigawatt of power would have to be more than 1 square kilometer in size, according to a Nature article by senior reporter Elizabeth Gibney. “That’s more than 100 times the size of the International Space Station, which took a decade to build.” It would also need to be assembled robotically, since the orbiting facility would be uncrewed.
The solar cells would need to be resilient to space radiation and debris. They would also need to be efficient and lightweight, with a power-to-weight ratio 50 times more than the typical silicon solar cell, Gibney wrote. Keeping the cost of these cells down is another factor that engineers have to take into consideration. Reducing the losses during power transmission is another challenge, Gibney wrote. The energy conversion rate needs to be improved to 10 to 15 percent, according to the ESA. This would require technical advances.
Space Solar is working on a satellite design called CASSIOPeiA, which Physics World describes as looking “like a spiral staircase, with the photovoltaic panels being the ‘treads’ and the microwave transmitters—rod-shaped dipoles—being the ‘risers.’” It has a helical shape with no moving parts.
“Our system's comprised of hundreds of thousands of the same dinner-plate-sized power modules. Each module has the PV which converts the sun's energy into DC electricity,” said Sam Adlen, CEO of Space Solar.
“That DC power then drives electronics to transmit the power… down toward Earth from dipole antennas. That power up in space is converted to [microwaves] and beamed down in a coherent beam down to the Earth where it's received by a rectifying antenna, reconverted into electricity, and input to the grid.”
Adlen said that robotics technologies for space applications, such as in-orbit assembly, are advancing rapidly.
Ceriotti wrote that SPS-ALPHA, another design, has a large solar-collector structure that includes many heliostats, which are modular small reflectors that can be moved individually. These concentrate sunlight onto separate power-generating modules, after which it’s transmitted back to Earth by yet another module.
Space-Based Safety
These plans involve large fluxes of microwave or radio radiation. But space-based solar power is relatively safe. For microwave radiation from a space-based solar power installation, “the only known effect of those frequencies on humans or living things is tissue heating,” Vijendran said. “If you were to stand in such a beam at that power level, it would be like standing in the … evening sun.” Still, Caplin said that more research is needed to study the effects of these microwaves on humans, animals, plants, satellites, infrastructure, and the ionosphere.
Getting that across to the public may remain a challenge, however. “There’s still a public perception issue to work through, and it’s going to need strong engagement to bring this to market successfully,” Adlen said.
Military attacks using space-based solar power might also raise concerns. But even if a space-based solar power station were hijacked for military reasons, the hardware would limit the beam to a safe intensity so that it could not be used to harm people or ecosystems on Earth, Ceriotti said.
Beyond the environmental issues, there are additional concerns that will need to be sorted out before deployment. Interference with communications signals is another potential risk, although Gibney wrote that the beam’s frequency would not disrupt aircraft communication. Some other physical risks are important to take into account.
Orbiting debris such as meteorites or space junk could strike the station and damage it, Vijendran said. If the impacts on the solar power station generate debris, that could cause problems as well. Plus the hardware itself will have to be deorbited when it reaches end-of-life. “ESA has a Clean Space Initiative. Anything that we’re sending to space, we have to think about the whole lifecycle, cradle to grave,” Caplin said.
Finally, the project would still have an environmental impact. Putting the solar power station hardware in orbit, constructing it, and controlling it would generate pollution and use a substantial amount of fuel, Ceriotti wrote. Hundreds of launches might be required.
Launch Economics
Beyond their environmental impact, those launches will cost money. Cost has usually been the main barrier to building a space solar power station so far, Caplin said. “As that landscape is changing and things are generally becoming cheaper to send to space, we can put it on the table again. Money talks. We have the advice of two independent studies on cost-benefit analyses, and they both determined that this could be viable.”
The expense of space-based solar power would include manufacturing costs, maintenance costs, and launch costs, Ceriotti said.
“We expect [the] cost to fall in future,” Vijendran said. “We can start with a power that is competitive with what we pay for nuclear today … between $100 and $200 per megawatt-hour … which is higher than intermittent renewables like solar and wind, but has a role to play because it is reliable and available 24/7.”
Vijendran said he expects the cost of space-based solar power will eventually fall to a point where it is competitive with solar and wind power on Earth, which is below $50 per megawatt-hour. According to the Energy Information Administration’s 2022 publication on this subject, both solar power and onshore wind cost around $20 to $45 per megawatt-hour in 2021.
Adlen’s cost estimate is much lower—around a quarter of the cost of nuclear power.
SpaceX and Blue Origin are designing launch vehicles that can handle heavy lifts, Ceriotti wrote. These vehicles’ parts can be reused, and their high capacity and reusability can drop the cost of some aspects of construction by 90 percent.
Looking toward the future, what are the next steps in the development of space-based solar power? The ESA plans to make a decision next year about its goals in developing an uncrewed space station, Vijendran said. The process has been slowed by a shortage of financial support from some European countries.
“The first major decision point would be to implement a … small-scale in-space demo mission for launch sometime around 2030,” Vijendran said.
Outside of the ESA, Caltech has demonstrated a lightweight prototype that converts sunlight to radio-frequency electrical power and transmits it as a beam. The university has been researching modular, foldable, ultralight space-based solar power equipment.
“My view is that much like the world of connectivity went from wired to wireless, so we're going to see the world of power move in a similar direction,” Adlen said. International cooperation will be key to creating space-based solar power stations if projects like these move forward.
This story originally appeared on Ars Technica.
