Made in orbit: Solar energy

Nothing, of course, can be manufactured in space without power. For sustained space flight, we have to start capturing energy on a space craft, rather than using stores sent up from Earth. But generating electricity from space is more difficult: there is no wind, no waves, no coal, oil or gas. But there is, of course, the Sun. Frequencies of light blocked by the atmosphere are free to access the space stations that sit above, meaning the light is more powerful and will generate more electricity than it will on the planet’s surface. Could this be the key to space-power? Martin Soltau, CEO of Space Solar, joins me to discuss how we can harness the Sun’s energy from space…

Martin - Energy demand is going to quadruple over the next 25 years with demographics, rising living standards, and in particular, technology. I mean, AI data centers is already consuming twice the whole energy demand of Japan, and it's growing exponentially. And this provides gigawatt scale, 24-7, all-weather energy. And it can really democratize energy for all nations. So it's hugely exciting new technology that we absolutely need if we're going to transition to clean energy by the mid-century and also meet this huge energy demand.

Chris - In practical terms, what does it involve?

Martin - These are large satellites, very large, talking kilometer scale. Lightweight solar panels, they harvest the solar energy, typically in a geostationary or geosynchronous orbit, which is about 36,000 kilometers above the Earth. And you turn the electricity into high-frequency radio waves, and then you beam it down to Earth. And it forms this narrow beam, quite low intensity, safe, and the right frequency, we pick a frequency of 5.8 gigahertz, and that goes through the atmosphere and weather with next to no loss. They are large, so they need to be assembled in orbit. So they're made of hundreds of thousands of identical modules. And this modularity gives great resilience, low unit production costs, because you've got the sort of volume of iPhones, really. And then it gives you a clear way to scale up.

Chris - Is it just one craft this would comprise then? Or would it be almost like a fleet of these enormous solar collecting systems in space, and they're all interconnected?

Martin - Think of each one as a large power station, just like a gas-fired power station or a nuclear power station. Each of these satellites produces about 600 megawatts to a gigawatt, so city-scale power. So yes, there would be a fleet of them. So you could potentially see 20 to 50 percent of our future energy demand coming from space-based solar power. And that'll be hundreds of these satellites.

Chris - You say they're going to sit at about 36,000 kilometres. That's the geostationary orbit, where they go round at the same rate that the planet's turning. So they're always in roughly the same position over the Earth's surface. That presumably is because you want to beam the power down to a collecting point on Earth. Does that mean, though, that some of the time they're going to see darkness, so they're not going to work? Or will they be in such a position they'll always see the sun, so it is 24-7 on?

Martin - Because the Earth's axis is tilted, a satellite in a geostationary orbit actually is in the sun all the time, even when the point below it on Earth is at night-time, the satellite is still in the sun.

Chris - And you're going to beam the power down to a collecting point on Earth. You say it's safe. So how big is the beam that's coming down? Is it like a death ray, James Bond-style, that's coming in from space? Or is this a fairly dispersed, that you'll need a massive collector to pick the radio waves back up and then convert them back into electricity on the Earth's surface?

Martin - It's the latter. So even at the peak of the beam, which is in the centre, it's about 230 watts per square metre. It's about a quarter of the intensity of sunlight. That's well below the certification limits for civil and military aircraft. It's benign for flora and fauna.

Chris - What's the reason for doing this in space other than the distribution? Do you get more bang for your buck because there's much more solar power there? You haven't got the effect of the atmosphere.

Martin - That's exactly right. So if you put a solar panel in space, you get 13 times the amount of energy that that same panel on Earth would, because there's no night or weather or atmosphere. And you've got 40% more solar intensity than you have even in the desert at midday on Earth.

Chris - And you mentioned economics. At the end of the day, that is where the buck stops. So how much is this going to cost? How long is this going to take to build? And therefore, ultimately, how practical is it?

Martin - Our economics for the mature systems are $30 a megawatt hour. It's about £25 a megawatt hour, which is incredibly cheap if you think that the current price of wind in the latest auctions is well over £100 a megawatt hour. We've got a very deliverable plan to have a pilot plant in orbit within five years. By 2035, we'll have our first system in geosynchronous orbit beaming about 100 megawatts and then scaling up very quickly to the gigawatt-scale systems. And so by the mid-2040s, we'll have 15 gigawatts of power. That's about 30% of the UK's total demand.