Launch a solar power station into space
CLOUDS may be a source of inspiration for poets and romantics, but for solar power engineers, they are nothing but a nuisance. No matter how efficient the solar panel, when the sky clouds over, power output drops to nearly nothing. Move that solar panel into space, however, and this problem disappears. In orbit, a satellite can bask in the perpetual glow of sunlight and generate electricity at maximum capacity nearly all the time.
Engineers have been talking up the idea of a solar power station in space for decades, and when you look at how much energy it could produce, you can see why. A 10-kilometre-wide solar panel in geostationary orbit could produce 570 terawatt-years of energy, according to Ian Cash at International Electric Company. That would be enough to supply 10 billion people at six times the current US levels of energy consumption per capita. (For comparison, the UK’s total electricity demand in 2022 was 320 terawatt-hours.)
So, why haven’t we done it? For a long time, the answer was cost. A spacecraft with solar panels extending for kilometres would be heavy, and launching all the required equipment into space would be horrendously expensive. But with the arrival of reusable rockets built by companies such as SpaceX, that price has tumbled. Estimates suggest that it could cost just $5000 per kilogram to send materials into geostationary orbit, where space solar power stations would need to sit, with SpaceX’s upcoming Starship launch system. That is about half of what it costs with our most economical rocket technology today. “The advent of reusable launch vehicles completely changed the economics,” says Martin Soltau, co-CEO of Space Solar, a UK company dedicated to the commercial delivery of space-based solar power.
Assuming that we can build a huge solar power station in space, we would then have to get the power back down to us. Fortunately, we know how to do this: microwaves beamed to a ground-based receiver called a rectenna. Researchers at the California Institute of Technology in Pasadena demonstrated this was feasible for the first time in February, as part of their Space Solar Power Project.
That was an important milestone. But if we had a truly huge solar plant in space (or lots of quite big ones), the rectennae would no doubt prove contentious. There would have to be roughly the same number of them as solar power satellites, and each would need a collecting area of around 20 square kilometres for each gigawatt that it was designed to receive. At that size, the best solution would be placing them offshore. Imagine a giant floating net of antennae, sitting above the highest waves. “In terms of offshore engineering, they’re going to be much more straightforward than making offshore wind turbines reliably work for 25 years,” says Soltau.
Perhaps the biggest uncertainty is whether the carbon emitted while making the solar panels and getting them into space would outweigh the benefits of space-based solar power. A study by Andrew Wilson at Metasat UK, a space sustainability start‑up, looked at the effects of manufacturing and launching the infrastructure for 25 solar power satellites, each capable of generating 2 gigawatts of power on the ground (collectively, about as much as 620 wind turbines). He found that this would produce about 80 per cent as much carbon as the UK does in a year. However, that would be paid back in carbon savings within six years and the system could operate for as long as 60 years.
Whatever the impact, interest in space-based solar power is growing. As well as the Caltech project, Japan and China have plans to build and test prototype solar power satellites in the next few years. At the European Space Agency, the Solaris programme is also investigating the concept’s feasibility. If the UK puts its shoulder behind this, it might realistically aim to get about 30 per cent of its electricity from space by the early 2040s, says Soltau
