Space-based solar power is not a thing

Friday, November 25th, 2022

Space-based solar power is not a thing, Casey Handmer argues:

As Elon Musk has concisely pointed out, the fundamental problem with space-based solar power is that it’s obtaining a commodity, power, somewhere where it’s expensive and selling it somewhere where it’s cheap. This is not a good business. Indeed, it might make more sense to beam power from Earth to space stations, if they needed it.


What are the extra costs? Broadly, they fall into the following categories: Transmission losses, thermal losses, logistics costs, and space technology penalty. Individually, any one of these issues cancels out the benefits, and combined they leave space-based solar power at least three orders of magnitude more expensive than the terrestrial equivalents.


For a baseline comparison, consider a GW-scale power station. For terrestrial solar, this consists of standard panels on single axis mounts, covering about 10 square miles. For the space-based solar case, an identical area of land is covered instead with an antenna, a mesh of conductive wire held above the ground, to absorb the transmitted microwaves and convert them to electricity. An identical area implies similar overall energy fluxes, which is correct.


Transmission losses: The process of converting sunlight to electricity is about 20% efficient, depending on the type of panel – and this is a loss common to both systems. In addition, the space-based system has to convert the electrical power back into EM radiation, which is converted back into power on Earth. Proponents think that it should be possible to perform each conversion with 90% efficiency, but even beam-forming that well is not possible without a much larger antenna. My personal opinion is that the end-to-end microwave link efficiency would be lucky to exceed 40% efficiency, which erodes the competitive advantage substantially.

Thermal losses: The conversion efficiency of the high-power microwave transmitter has a nasty side-effect, namely that what isn’t transmitted is wasted as heat, and that heat has to go somewhere. If the transmitter is 80% efficient (which is being very generous), then it will have to radiate 200MW of thermal power. This is a different problem to the thermal losses in the solar panels, which are more like 4GW but spread over a huge area that is in radiative thermal equilibrium with its environment. Instead, the microwave power electronics will need a huge cooling system. If the electronics can operate at 350K, then the radiator power will be 850W/m^2, so the radiator will need a total area of 23ha, comparable to the total size of the solar array and the microwave transmission antenna. In contrast to the usual claims of perfect scaling efficiency with solar arrays in microgravity, a large space-based solar power system will also need a huge antenna and cooling system, which don’t scale quite as nicely.

Logistics costs: Consider transportation cost. Today, SpaceX has crushed the orbital transport market with a price of around $2000/kg. Compare this to the worldwide network of intermodal containers, which can transport anything in 20T units almost anywhere on Earth for about $0.05/kg. Even if all of Elon Musk’s wildest Starship dreams come true, transport costs will dominate the total capex of any space-based solar system, by many orders of magnitude. A factor of 10x improvement in resource does not make up for transport costs which are more than 10,000x higher. If logistics costs are more than 0.1% of current solar farm costs (they’re more like 20%), then increased transport costs completely negate the improved solar resource. It’s not even close.

One further aspect of logistics bears closer examination. In our baseline case, we considered an array of panels strung up on posts, compared to a mesh of wire strung up on posts. It turns out that (as of 2019) a substantial fraction of the overall cost of a solar PV station is the mounting hardware, which is also required by the microwave receiver. So if the mounting hardware costs 20% of the overall deployment cost for terrestrial solar, that places a strong upper bound on total system cost allowable for space-based. In other words, does anyone seriously believe that the microwave receiving antenna could cost 20% of the overall system capex, the other 80% to be used to launch thousands of tonnes of high performance gear into space? Put another way, the most cost-effective way to get a GW of power out of a microwave receiving antenna is obviously to tear down the wire mesh and sling up a bunch of solar panels, which can be ordered with a lead time of weeks from any of dozens of suppliers worldwide with widely available financing.

Finally, the space technology penalty. On Earth, we are living in an extremely exciting time for energy. Hundreds of major companies are competing on development cycles measuring only months to provide solar panels in an industry that’s growing at 20% a year. As a result, costs have fallen by 10% a year, and in the last few years, solar and batteries have neared, equaled, then utterly crushed all other forms of electricity generation. Initially, this process occurred on remote islands with high fuel import costs. Then the sunnier parts of the US. The rampage continues northwards at about 200 miles a year. The industry can sustain 30% deployment growth rate worldwide for another decade at least, before saturation occurs.

Today, I can pick up the phone and any of dozens of contractors in the LA market can fill hundreds of acres with panels, each built to survive 30 years under the harsh sun and sized perfectly for deployment using the latest tech, which is men in orange vests with forklifts.

In contrast, space technology has not benefited from such breakneck levels of growth, demand, and investment. Prohibitive maintenance costs demand perfect performance, and low rates of deployment ensure a slow innovation feedback loop. The result is that none of the current incredibly cheap solar panels could work in space, where thermal and vacuum, not to mention stresses of launch, would destroy their operation in days.

Instead, space operators rely on more traditional supply chains, with the result that building anything for space takes years and costs billions. Right now, a billion dollars invested will buy about 100MW of solar panels on the Earth, or 100kW of solar panels in space. This is a factor of 1000, and it also erases the advantages of more sunlight in space.

These four elements, transmission, thermal, logistics, and space technology, inflate the relative cost of space-based solar power to the point where it simply cannot compete with terrestrial solar. It’s not a matter of 5% here or there. It’s literally thousands of times more expensive. It’s not a thing.


  1. Senile Old Coot says:

    1. Time passes. Memory fades. When the space shuttle program was initially funded the projections were that it would reduce the cost of lifting payloads into orbit tenfold. Was it from 5,000 dollars a pound down to 500 (with even greater savings later on)? Something like that. Mostly BS? Mainly to shift NASA dollars over to companies that were friends of Nixon? Every trip was putting the weight of the shuttle into orbit just to bring it back down again. I seem to remember much of the boosterism for solar powered space satellites beaming microwaves to Earth was premised on the greatly reduced orbital costs. Maybe someone can confirm my memory here about some of the background context for the popularity of the SPSS idea. 2. Why is this an important topic? Similar techno-utopian hype vibe as much that is going on today when what is really going on is mostly shifting government funding to different corporations for not very plausible technologies. Views may differ but just tossing some out there, transhumanism biotech, various global warming countermeasures, SBF crypto meltdown and CBDC movement, etc.

  2. Caleb Camargo says:

    Handmer is probably right, but my impression reading these posts so far is that he is playing fast and loose with his numbers to get to his desired conclusions, and the more I read, the less I trust him. Whether it’s using NYC (?!) subway tunneling (instead of cut-and-scrape…?) numbers for underground construction on Mars, or lopping numbers in half he doesn’t like, or implying that space power would involve the same number of panels necessary on earth…

  3. Altitude Zero says:

    Yes, Caleb, and that’s a best case scenario. This guy reminds me of a guy in 1902 telling us why heavier than air flight is impossible, or in 1958 explaining why we will never reach the Moon. The late Jerry Pournelle thought that space-based solar had potential, and he was at least as smart as this guy. Also, it seems that Handmer has a “Everything Elon Musk believes is wrong” agenda. He may be right, but it pays to keep his predispositions in mind.

  4. Jim says:

    How about space-based nuclear reactors?

  5. Shadeburst says:

    Altitude Zero, if you go to Handmer’s page he is a major Muskrat. He correctly identifies SLS as a POS, then fails to say a single critical word about Starship.

  6. Jim says:

    How can a critical word be said about something perfect?

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