Stats for nerds
1recommend
19mentions
2people
2018–2023years
26% recommend74% neutral
Mentions per year
What Hacker News says
- NASA completed another study in 2012, with a vastly cheaper and more practical design enabled by new technologies. Here's a description: https://space.nss.org/sps-alpha-a-novel-approach-to-space-so...
and the study itself: https://www.nasa.gov/directorates/spacetech/niac/2011_Practi...
A book-length treatment of modern SPS designs is The Case for Space Solar Power. It has detailed cost figures but was written before SpaceX had accomplished much, estimating a cost at gigawatt scale of 15 cents/kWh. I plugged in Starship launch costs and it came to 4 cents/kWh, which is not bad for 24/7 clean power without storage.
- Solar power satellites without all that tedious beaming of microwaves back to Earth. It might actually work.
The book The Case for Space Solar Power runs through detailed engineering costs for modern solar power sats, and came up with a cost of $15/kWh at scale. That was before SpaceX. I plugged in Starship costs and it came to 4 cents/kWh.
Of that, the ground station was 0.7 cents/kWh, and of course another big chunk was the microwave emitter. Remove both and you're at least down to 3 cents/kWh for 24/7 power, which is pretty competitive with anything on Earth.
However, if Bitcoin ASICs continue to improve, this wouldn't work, since you'd have to keep replacing the sats' mining equipment.
Also, while it might be possible for SpaceX to make money this way, just being competitive wouldn't make Bitcoin clean; they'd have to decisively outcompete all the other miners, and if Bitcoin is all run by a single miner then we might as well replace it with a SQL database and be done with it.
- And that makes solar power satellites more feasible, especially with the BFR.
Musk has expressed skepticism, famously asking "what's the conversion rate?" The answer is that microwave transmission is 40% efficient with today's technology. This isn't bad considering that average daily sunlight in geosynch is five times higher than on the ground,[1] and you don't need much storage or backup.
The early SPS designs were hugely expensive monolithic beasts, but current designs use lots of identical parts (of several varieties) that self-assemble in orbit, so you get economies of scale with factory production.
A year ago I read the book The Case for Space Solar Power [2], which broke down the costs in detail. With pre-SpaceX launch costs they got 15 cents/kWh, including manufacturing and ground stations. I plugged in the BFR cost Musk was claiming (I think I used $50/lb) and got about 4 cents/kWh.
[1] https://en.wikipedia.org/wiki/Solar_irradiance#Irradiance_on...
[2] https://www.amazon.com/Case-Space-Solar-Power-ebook/dp/B00HN...
- A year ago I read the book The Case for Space Solar Power, which goes into the engineering in detail.
The old SPS designs from the '70s were monolithic beasts that would have been ridiculously expensive. Current designs would use a large number of identical parts, of about eight types, which would self-assemble in space. That way they can be mass produced in factories.
The basic design was PV with microwave transmission, which has already been tested over distances of ten kilometers or so. (Iirc it was between a couple Hawaiian islands.) The receiving station sends a sort of homing signal for a phased array transmitter, which makes it difficult to redirect to somewhere without the homing signal and keep a reasonably focused beam, though you could switch between multiple receiving stations (which are fairly cheap). The station would be in GEO.
The book did some detailed cost analysis and found that with pre-SpaceX launch costs, the SPS could provide power at 15 cents/kWh retail.
Elon Musk has said that at scale the BFR could ultimately get to a $50/lb launch cost, so for grins I plugged that number into the book's calculation and got 4 cents/kWh.
Since this type of solar would work through the night, with little or no need for storage, it could be pretty competitive.
book: https://www.amazon.com/Case-Space-Solar-Power-ebook/dp/B00HN...
- The sun throws its energy at us all the time, but half the time there's a planet intercepting the catch.
Cheap storage that scales far enough to run civilization isn't really a solved problem. We may solve it, but it's a research problem just like fusion is.
Another possibility is to get the planet out of the way by putting our solar power stations in geosynchronous orbit. If SpaceX delivers on the extremely low launch cost they're promising for the BFR, this looks surprisingly economical with current solar power satellite designs; a good book about this is The Case for Space Solar Power: https://www.amazon.com/Case-Space-Solar-Power-ebook/dp/B00HN...
- People sure put a lot of weight on an off-the-cuff comment Musk made in 2012, before Starship was even a gleam in his eye. That was the same year NASA published their SPS-ALPHA study[1] on modern SPS design, so Musk may not have been aware of it.
Modern designs use a phased-array transmitter, and a reference signal from the ground for targeting. Overall energy loss is 40 to 60% according to the book The Case for Space Solar Power.
[1] https://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_Alp...
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