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Comment by IshKebab | Hacker News Reader

Ah I was wondering how something like this could go ahead when it's pretty obviously a terrible idea to engineers.

> SSPP got its start in 2011 after philanthropist Donald Bren, chairman of Irvine Company and a lifetime member of the Caltech Board of Trustees, learned about the potential for space-based solar energy manufacturing in an article in the magazine Popular Science. Intrigued by the potential for space solar power, Bren approached Caltech's then-president Jean-Lou Chameau to discuss the creation of a space-based solar power research project. In 2013, Bren and his wife, Brigitte Bren, a Caltech trustee, agreed to make the donation to fund the project. The first of the donations to Caltech (which will eventually exceed $100 million in support for the project and endowed professorships) was made that year through the Donald Bren Foundation, and the research began.

"Ok nobody tell him it's a bad idea and we get like 50 PhDs and 5 professors!"

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You forgot to explain why this is "pretty obviously a terrible idea".

Some ideas about what makes it challenging:

- A satellite will have to transmit power through the entire atmosphere from space, which will have substantial losses even in perfect conditions

- A satellite constellation in orbit would need many ground stations to transmit power to from space

- Weather will get in the way of transmission to the ground, just like it does with ordinary solar

- The cost of getting a PV array into orbit is very expensive relative to the amount of power it can generate and transmit

> satellite will have to transmit power through the entire atmosphere from space, which will have substantial losses even in perfect conditions

Balancing this is at least a half an order of magnitude difference in collection efficiency.

> Weather will get in the way of transmission to the ground, just like it does with ordinary solar

True. But there are extraterrestrial atmospheres where water vapor and ozone aren’t a problem. (I’ve only seen this proposed with microwave.)

> cost of getting a PV array into orbit is very expensive relative to the amount of power it can generate and transmit

This is the killer. That said, this is a long-term research endeavour. If we contemplate such an array around the Moon or on Mars, or in a world with in-space resource extraction and manufacturing, the economics shift.

> If we contemplate such an array around the Moon or on Mars, or in a world with in-space resource extraction and manufacturing, the economics shift.

The economics of anything on Mars or the Moon amounts to 'try to convince a government to throw tons of money at you.' A technology which only makes sense in that economic context is very limited.

> technology which only makes sense in that economic context is very limited

If this were a start-up I’d be roundly criticising it. It’s not. It’s a research project. And each of its sub-projects—testing new PVs in space, a novel deployment mechanism, power transmission—has clear value outside a space-based solar context.

As a focussing mechanism, SBSP is neat because each problem needing to be solved to make it economically viable is immediately valuable on the ground. (Save for power transmission. That’s still niche.)

> Save for power transmission

Isn't that the entire point? Putting solar panels in space has been done regularly the 1950s.

I meant that I don't see a near-term use terrestrial use case for better microwave power transmission.

Maybe you could use microwave power transmission (from the ground) to power atmospheric pseudo-satellites, but practical applications seem dubious.

Drones. Electric aircraft in general, recharging continuously in-flight.

Might be ill-advised for a whole mass of reasons that I, as a software engineer, know naught of; but it would be a use case.

> cost of getting a PV array into orbit is very expensive

Musk will find a way. Another stepping stone to Mars.

It would be great on Mars. Mars has planet-wide dust storms.

But for Earth, even if it was free to put the PV in Earth orbit, the ground stations need to have an incredibly low total cost to make sense.

I can't remember how low exactly.

The ground stations are basically just antenna wire. For a large plant they would contribute just 0.7 cents/kWh to the total cost, according to the book The Case for Space Solar Power.

Also needs a microwave frequency rectifier, plus installation costs are non-trivial as evidenced by the difference between the cost/W of a PV cell and a PV farm.

Also, cheapest ground-based PV in the world is 1.04¢/kWh (Saudi Arabia), and the cheapest in the USA is 1.50¢/kWh (New Mexico), so 0.7¢/kWh is already a large percentage.

https://commercialsolarguy.com/lowest-solar-power-prices-in-...

Just to clarify, the 0.7 cents is total ground station cost, according to my source.

At ideal locations, ground solar is super cheap, but the microwave receiver works anywhere. Not needing storage is a big difference, too.

That seems a bit optimistic, but I don't have the book, so OK.

(I really should get around to blogging what I think is wrong with this whole approach to space solar, where it works despite that, and how to improve on it for Earth usage; it comes up here every so often, and linking to my blog is easier than disjointed comments without images).

He's talked about the idea, how much the two aspects - solar power and space - are things that excite him, and how it just is not a viable idea.

He made one comment, a decade ago, well before he started talking about $35/kg to orbit with Starship.

In response to his famous question "what's the conversion rate," the answer is about 50%, according to the book The Case for Space Solar Power. That's not bad considering a panel in geostationary collects five times as much energy in 24 hours as a panel on Earth.

> half an order of magnitude

Completely off-topic, but would "half an order of magnitude" be sqrt(10)? I've just never heard someone refer to a factor of ~3 as "half an order of magnitude".

Sqrt(10) is approximately 3.162278, that's close enough to 3.

> just never heard someone refer to a factor of ~3 as "half an order of magnitude"

Last time I looked, the estimates ranged from 270% to 50x. Seeing the latter, my brain went into astronomer mode and then I guess just ran with it.

None of these seem like obvious show stoppers.

https://caseyhandmer.wordpress.com/2019/08/20/space-based-so...

Even ignoring the power transmission challenges, putting stuff in orbit is really really expensive. Surely you knew that?

For now. But if SpaceX succeeds in getting launch costs below $50/kg with Starship, space solar starts looking a lot more attractive.

Advertised price on Falcon Heavy is already just $600/kg to LEO. A big part of that is the throwaway upper stage, which Starship eliminates.

Falcon Heavy is around $2300/kg to LEO. Not sure where you got $600 from.

I'm sure Starship will be better, but 40 times cheaper? I doubt it.

Just checked and the answer splits the difference. $97M for a Heavy launch, divided by 63,800 kg payload to LEO gives $1520/kg. I think my $600 must have been per pound (though that's still a bit off, at the current price).

https://www.spacex.com/media/Capabilities&Services.pdf

The biggest cost is throwing away hardware. If you're not doing that, you can amortize your entire hardware cost over the number of launches. At Falcon's launch cadence that's still going to be significant. But Starship is designed to do hundreds of launches per year, and if they manage it then hardware cost per launch is almost nothing. Then you're mainly paying for fuel and ground services, which are about a million dollars each. 100 tonnes to LEO for $2M gives just $20/kg, leaving plenty of margin for SpaceX at $50.

It might seem hard to envision putting that much cargo into space every year, but if we did solar power satellites at scale, that's exactly what we'd need.

> $97M for a Heavy launch, divided by 63,800 kg payload to LEO

No, $97M is for a launch with reused boosters. 63,800 kg to LEO is when the boosters are dispended.

That sounds plausible but do you have a source? The SpaceX document only gives the one price and payload.

That's what it says on the Falcon Heavy Wikipedia page.

The payload is definitely for expended boosters (check the footnotes). I agree it's not very clear about the price. Wikipedia could be out of date I guess and they're not giving a discount for booster reuse? But then why would anyone ask for reuse?

https://dothemath.ucsd.edu/2012/03/space-based-solar-power/

Pretty funny how often when one brings up engineering challenges to solar, the challenges are ignored or handwaved. There's not even a back of the envelope calculation to prove the solution is scalable, maintainable, or cost effective the solution, it's all just feel good, "cool" factor, "saving the world" factor that's used to argue for investigation.

You mean solar in space specifically right?

Because solar back on earth makes a lot of sense, whereas solar back in space to beam down on earth make no sense.

Solar on earth makes sense in some contexts, but there's questions of how it's not scalable, clean up methods, local climate effects, is intermittent and causes the power grid instability. These are fair questions that should be looked at and solar on earth is not some solution to the problem of gas without tradeoffs, but these questions and concerns are usually ignored.

https://www.nrel.gov/news/features/2020/renewables-rescue-st...

These concerns are not really brought up by the media.

I don't think they're ignored exactly. They're just not really significant problems compared to the greenhouse emissions of gas or coal power.

It's like how virtual keyboards on smartphones are not as good as a full physical keyboard (arguably) but nobody really talks about it anymore because the disadvantages of physical keyboards are so overwhelming that it doesn't matter.

I don't think that comparison is fair at all. You're comparing concerns of a technology and how it scales, to how no one talks about physical keyboards and smart phones? That's not even remotely the same and is pretty dishonest to make that comparison.

The problems of solar as a scalable renewable are very fair to talk about, considering that Africa and India NEED energy to grow their societies. The only solutions that scale are oil or nuclear. The idea you can just hand wave any concerns about renewables doesn't seem very rationale if you genuinely care about the problem.

I'm not sure what you mean about them "not scaling". Do you mean that they don't work at night? What are you expecting people to say about that?

I linked an article above, I suggest you read it before asserting that my issues with solar are simply irrelevant. Here are others:

https://www.greentechmedia.com/articles/read/germanys-stress... https://fee.org/articles/solar-panels-produce-tons-of-toxic-... https://www.science.org/doi/10.1126/sciadv.abj6734

You cannot simply ignore and hand wave off "inconvenient facts" because you have a strong dislike for "climate deniers".

Again, nobody is ignoring these issues. They just aren't using them as reasons not to do solar power.

>Because solar back on earth makes a lot of sense

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