Space-Based Solar Power (Patreon)

[This is a transcript with references.]

Solar power is a nice idea. Except for the issue with the clouds. And the nights. So, how about we instead put solar panels up in space and then beam the energy down? This futuristic idea is known as “Space Based Solar Power”. It’s been around since the 1960s, but in recent years several nations have launched projects to make it reality. I think they’re not kidding. Space-Based Solar Power is about to become a real thing. But how is it supposed to work? Is it a good idea to beam energy down from space? What are the pros and cons? That’s what we’ll talk about today.

Why’d you want to put a solar power plant into space, when you could as well put it right here down on earth where we need it? Said no British person ever. Solar power might be great if you live in the Australian outback, but not every part of the planet gets sunshine that reliably.

It’s therefore maybe not so surprising that the British are on the forefront of this race. In 2021, the UK Department of Business, Energy, and Industrial Strategy asked the consulting agency Frazer Nash for a feasibility-assessment of space based solar power.

The agency pointed out that both space launches and solar panels have become dramatically cheaper, and that we now have the technology to assemble large facilities in space from small modules. The combination of those three factors has brought down the cost of space based solar power so much that it’s now an option to seriously consider.

The analysis concludes that “it is feasible to realise a constellation of solar power satellites delivering a substantial percentage of the UK’s energy needs by the early 2040s”. They titled their report “De-risking the pathway to Net Zero”. I hope the Oxford Dictionary called to have a word with them.

Once the report was done, they didn’t hesitate. Last year, the Brits founded the UK Space Energy Initiative to get solar power to space. It’s a collaboration of nearly fifty companies and research institutions, including Airbus, Cambridge University, and Lockheed Martin.

But the Brits aren’t the only ones who are pushing forward with the idea. China has an ambitious initiative for space based solar power. Indeed, they announced last year in June that they hope to complete it two years ahead of schedule.

In 2028, they want to do the first experiment to demonstrate power-transmission from a satellite to earth, and by 2030, they want to have a power station in orbit. The Japanese Company Japan Space Systems wants to get it done even earlier, by 2025.

Just in November 2022, the European Space Agency launched a project called SOLARIS with the somewhat passive-aggressive tagline “towards a clean and secure energy future for European citizens.” Its purpose is to explore the economic, political, and technological feasibility of developing a Space Based Solar Power program within the next decade. But only for European citizens. If you can’t present your passport at the wall socket, you’ll have to launch your own satellite, dammit.

They want to come to a decision on whether to proceed by 2025, which hopefully explains why the Brits left the European Union. But leaving aside the EU, the field has been moving incredibly quickly.

The Americans decided last year that if the UK, the European Union, China, and Japan are in the game they have to play it too. So basically, everyone’s doing it because they think everyone else is doing it, which about sums up my recollection of high school.NASA announced in May 2022 that they are working on a report that will re-examine space based solar power, and the American Foreign Policy council recently stressed the military applications. A space-based solar power station could be used, for example, to remotely recharge drones.

A 2021 analysis valued the global market for space-based solar power at about 450 million dollars, and projected it to reach 850 million by 2029. I think seeing how much happened last year this is likely to be an underestimate.

But how does it work? Here’s the basic idea. You launch the power station piecewise into space and assemble the pieces in a geostationary orbit. That’s an orbit around the equator at about 36 thousand kilometres !altitude. An object on such an orbit remains in a fixed position relative to the surface without requiring propulsion, and it’ll be in the sunlight more than 99 percent of the time.

You collect the solar energy up there, convert into electromagnetic waves, and send a beam of that to your ground station. The ground station is basically an array of receiving antennas, or “rectennas” for short. To make sure that the beam doesn’t go astray, the ground station emits a target signal that the space-station can aim at.

The options that have been proposed for the beam are either a laser or microwaves. The benefit of a laser would be that it spreads less during transmission. However, the problem with lasers is that they are expensive and inefficient. This is why at the moment pretty much all designs use microwave beams instead.

The frequency of the microwave beam is typically a few GigaHertz, that’s similar to what your microwave or wireless router works with. It’s a good frequency range because the atmosphere of Earth is almost transparent in this range.

The intensity in the centre of the beam is typically around some hundred watts per square meter. For comparison, the sunlight intensity on the equator can be as high as 1000 Watts per square meter, whereas a cloudy winter day in the UK makes it to maybe 100. So beaming that power down from space is probably not going to make the pigeons fall out of the sky deep fried.

However, the comparison with sunlight is somewhat misleading because in the beam all this energy is in microwaves, and microwaves interact with objects differently than sunlight. Depending on the exact wavelength, microwaves can enter living tissue up to some centimetres of depth. So a better comparison than sunlight may be your wireless router. At a distance of about 1 meter, it emits typically a few tens to a few hundred microwatts per square meter. The beam from those stations delivers a million times more.

The major design challenge for those solar arrays in space is that the panels need to be oriented towards the sun, whereas the beam needs to be oriented towards earth. And also, you don’t want one part of the thing to cast a shadow on another part. There are several ways that scientists and engineers have come up to get this done.

The Chinese researcher Hou Xinbin put forward what’s called the Multi-Rotary Joints SPS. That’s basically a line of solar panels that can rotate independently. That way, the panels can be oriented towards the sun while the transmitter points at the ground station. This system would weigh about ten thousand tons and be twelve kilometres long.

The American John Mankins proposed a design called SPS ALPHA that keeps the solar panel and the transmitter in a fixed place, but has several thousand adjustable mirrors that focus the light on the solar panel. The mirrors surround the panels in concentric rings that take on the shape of a cocktail glass. And no, this isn’t just my association – I wonder why you’d think that. This is how it was called in the scientific literature. The thing would have a diameter of almost two kilometres and weigh approximately 8000 tons.

And the British Ian Cash has proposed a design called CASSIOpeia which stands for Constant Aperture, Solid-State, Integrated, Orbital Phased Array. Can we all agree that trying to be smart with acronyms has gone too far? Cassiopeia has the shape of a helix with a solar collector on each end. Its diameter would be almost two kilometres, and it’d weigh about 2000 tons. Cash says the benefit of his design is that there are no parts that have to be adjusted, which means there are fewer bits that can break.

That’s the part that sits in space. The size of the receiver array depends on how much you want to beam down from space, but it’s typically a few square kilometres up to 100 square kilometres, so it ain’t small. The British plan for example estimates 87 square kilometers, that’s roughly the size of Manhattan. This power station could generate two Giga Watts, which is about as much as the power delivered by one nuclear power plant.

Then let’s look at the pros and cons, starting with the pros.

The most obvious benefits are that, besides the production process, this technology doesn’t emit carbon dioxide or any other pollution. There’s also that space-based solar power can operate 24/7. I wouldn’t exactly call this a benefit, it’s rather the absence of a disadvantage, but your mileage may vary.

Another benefit is that it diversifies energy sources which decreases dependence on any one of them.  As we’ve previously seen, it could have military applications.  It could also generally be beneficial for space exploration and commercialization, and it could have unexpected spin offs. Apparently, that’s an argument which isn’t only popular among particle physicists.

And finally if you park your solar panels in space, you don’t need to worry about theft or vandalism, at least not until the man in the moon finds out what we’ve been up to.

Let’s then talk about the cons. Yes, as you’ve guessed, the idea has a few problems.

First of all there’s the costs. It costs a lot of money to shoot all that stuff into space and that makes space based solar power expensive. The previously mentioned report from Frazer-Nash consulting put the costs of such a space-based power plant at about 16 billion British pound. You may think that’s a lot but it’s still far less than the cost for the new particle collider that they want to build at CERN.

Of course the total cost isn’t all that relevant if the thing just runs long enough. In the end you care about the costs per power. The report estimates that if you build several of those things, and the systems are maintained and run for 100 years, the costs would ideally go down to about 50 pound per Mega Watt hour. That’d be only mildly more expensive than ground based solar power and less expensive than nuclear, or gas with carbon capture. *If the thing runs for 100 years. That seems a pretty big if to me.

A study commissioned by ESA found a comparable number of 69 Euro per Mega Watt hour for the first system, but that in the long run the costs could go down to 49 Euro. So that’s quite similar to the British estimate.

The costs don’t just come from the launch, they also come from the maintenance. The issue is there’s stuff flying around in space, space debris and micrometeorites, that are going to damage the solar panels. This question isn’t *if it will happen but just how often.

Besides that, there’s radiation from outer space that’ll degrade the material, dust that you need to somehow get off, and huge temperature gradients that’ll put stress on the material. And up in space you can’t just send Jack to put some duct tape around the thing.You’ll need some kind of autonomous space robot to get the job done.

Then there is the issue of efficiency. First you need to convert the solar energy into microwaves, then you need to send the microwaves over 36 thousand kilometres, then you need to convert them back into electricity. This process is incredibly lossy and the costs per generated power will crucially depend on this efficiency.

So what does the Frazer Nash report say about this? Well, the short summary with the pretty design says that the “concepts studied have assumed realistic efficiency values”. This statement is decorated with a reference to another report. If you look into that other report, it just says “Further work is needed to confirm that high efficiency and accuracy beam forming is possible over long distances” and they rate the task with difficulty “very high”. In other words, they have assumed some number that they have no way of knowing is even remotely correct.

A final issue that already came up is that the receiver on the ground takes up a lot of space.

In summary. I guess you already noticed that I don’t think this idea’ll go anywhere. There are people protesting against using agricultural area for solar power already, some freak out over 5G, and others believe that wind turbines give them heart arrhythmia. Do you really think they’re going to let you build a 100 square kilometre receiver for a big microwave beam coming down from the sky. Maybe in China, but not here.

Yeah, Sabine’s spitting big words today. But where’s the fun of being on YouTube if we can’t look back in ten years to see whether I was right or wrong. Would you invest into this technology? Let me know in the comments.