Space-based solar power for Earth
At this week’s U.N. Climate Change Conference in Dubai, there's one climate mitigation strategy that’s not likely to be widely discussed. That’s unfortunate because the idea of harvesting solar energy from orbit and beaming it back to Earth has been around since the late 1960s. That’s when American aerospace engineer Peter Glaser first put forth the notion of harnessing the Sun's radiation from space.
It all makes sense. The average solar flux in space is five times greater than even the sunniest locations on Earth. In 1968, if humanity had taken Glaser’s idea and run with it, climate change would likely be just a blip on the radar, and we would have more energy than we could ever have imagined.
But finally, a major player —- the European Space Agency —- is taking the idea seriously and has funded a feasibility study to put a constellation of space-based solar satellites in orbit by 2040.
Industry leader Thales Alenia Space says it is leading an ESA-funded consortium to study technologies that would enable high-efficiency space-based solar panels, wireless power transmission and robotized assembly in orbit. Space-based solar power has the potential to produce 800 Terawatt hours per year by 2050 which would help Europe achieve net zero carbon emissions.
What's changed in the last decade to make this a reasonable proposition?
The climate change crisis and energy security (the need for reliable and accessible sources of energy) mean that fossil fuels are no longer considered viable, Roger Ward, chief technical officer of Thales Alenia Space U.K., told me via email.
But The Economics Are Still Challenging
To produce one megawatt of power will require 3000 square meters of space-based collecting surface, says Thales Alenia.
From an economic point of view, it’s still quite difficult, because the space systems are quite expensive, Xavier Roser, product line manager for exploration, science and on orbit services at Thales Alenia Space Cannes, told me in his office. But launch costs are likely to decrease with a new European reusable launcher, he says.
The study will also determine what market segments could support the average kilowatt costs associated with the generation of space-based solar energy.
There are two basic architectural concepts being considered for a commercial space-based solar power satellite constellation.
The first would aim to simply facilitate the on-orbit collection of optical solar radiation that would then be reflected to Earth. This is essentially reflected sunlight. This idea works well with satellites in low-Earth orbit. Such reflected sunlight would be directed back to large solar arrays on Earth where it can be converted into electricity and distributed along conventional electric grids.
And If It’s Cloudy?
If it’s cloudy, you will obviously lose collecting efficiency, says Roser. Efficiencies can drop by several tens of percent, but the satellite can still send its reflected solar photons back to ground stations, he says.
Another part of the study is researching how to convert the on orbit collected sunlight into microwaves that can be beamed back to ground-antennas.
To beam solar energy back to the ground in the form of microwaves, satellites must first collect the Sun’s radiation and convert it into electricity. From there, Thales Alenia says this electrical energy is converted into high energy beams of microwaves that are pointed back to ground-based receiving antennas.
Although this seems like a daunting two-step process, the conversion of microwaves into electricity has been successfully tested. In a 2020 paper published in the journal Materials Science and Engineering, the authors note that microwave radiation can be directed to any desired location, can be collected and converted back to electricity, and unlike reflected sunlight can pass unimpeded through clouds and precipitation.
Once the microwaves are absorbed by ground-based collectors made from semiconductors, the microwaves would then be converted into electric current for distribution.
Roser says he expects that given the amount of territory needed for such ground-based collectors they will likely be positioned in more arid regions of Europe, such as Spain which has lots of desert locations. And such ground-based collectors would have diameters of some ten to twenty kilometers, he says.
To get the megawatt-rated energy back to the ground would require a constellation of satellites collecting solar energy in orbit. Such constellations would likely comprise tens to hundreds of individual satellites at a euro cost ranging into the tens of billions.
Microwave beams have lots of advantages; they can be continuous and have low sensitivity to clouds, says Roser. But the cost of microwave infrastructure is also more expensive than reflected sunlight, because instead of just adding reflectors, you've got solar arrays, plus radiofrequency systems on board, so your system is more complex, he says.
The Next Step?
ESA isn’t likely to commit full funding for space-based solar power until 2025 at earliest.
In orbit, we still need to build structures orders of magnitude larger than the International Space Station, says Ward. And on the ground, we need large ground-based receiving rectennas, says Ward. It is also still uncertain what the public perception of such systems will be, he says. As a spacecraft engineer, I obviously think about the space infrastructure and how we will assemble it robotically as well as control such a huge structure, says Ward.
Thus, the technology may first be tested on the Moon, to generate electrical power in situ for use with forthcoming lunar habitats and colonization efforts.
Medium altitude satellites in orbit around the Moon would enable you to supply tens of kilowatts of power to ground infrastructure during long lunar nights, says Roser.
Roser says the first Earth-based customers are likely to be existing large power companies who would also have the means to distribute electricity along their networks.
As for when we might see the first test mission in Earth orbit?
The first Earth-orbital test mission isn’t likely before 2030. The first full space solar satellite constellation in Earth orbit would hopefully see fruition by 2040.
