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ferrel_hadley t1_je0ev4c wrote

How long will it take to get the same amount of energy back to Earth from 1 tonne of solar arrays as it costs to get that 1 tonne to the relevant orbit?

If the answer is a year, then yes. If its 20 years then unlikely.

Energy cost will be your hard floor, if it takes too long to get the energy back then you are wasting your time. Above that comes the economics, how much can you get from consumers for 1 tonne on orbit vs the cost of getting it there. This is a bit more flexible as you can work on the non fuel costs.

Space does offer advantages, you can almost always be at 90^(0) to the Sun and you can have less atmosphere to get through. Its also almost always very sunny. It has disadvantages like the current insane cost to orbit and the difficulties getting energy once you move beyond the tropics and into more oblique angles.

The current answer is a very loud no with current technology. The point where no becomes yes is one of engineering and economics and an open question if you consider current costs to orbit easy to cut.

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larsschellhas OP t1_je0hg54 wrote

Well, starship is aiming to bring launch costs down to as low as 10 $/kg.

At that price SBSP would still be slightly more expensive than solar and wind, but much cheaper than storage, backup & peak load technologies which we will be needing in a purely renewable system anyway.

SBSP has the big advantage that it can deliver power to many markets, simply by switching to another base station. Thanks to this, it can capture much higher wholesale prices for electricity than wind and solar.

Essentially, it could capture 24/7 peak power prices, putting it at a better position than ground-based wind and solar even though it has higher levelised cost of energy.

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EnigoMontoya t1_je0mila wrote

Bunch of questions here, but starting with a couple...

What's your assumption on the cost of the distributed ground based plants accepting SBSP on a $/MW basis?

What's the breakdown of percent loss from SBSP for the transmission down to ground and conversion into usable AC?

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larsschellhas OP t1_je0yd9s wrote

It's around 50% at the moment, but has no physical limit really. The advantage of microwaves (like Radar) is that they are much less impacted by clouds and weather than visible light.

The receiver stations are also simple antennas which can be manufactured much cheaper than solar PV, therefore making up only a small share of the total CAPEX. I don't have the number off the top of my head, but they can be found in the Roland Berger and Frazer Nash studies.

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EnigoMontoya t1_je11jm3 wrote

Right so the conversion is 50% but the transmission over distance is a distinct loss correct? Yes, microwaves can penetrate the atmosphere, but there is still a cost.

https://ars.els-cdn.com/content/image/1-s2.0-S2352484720317273-gr9.jpg

This diagram from a 2021 study touting a 45% conversion efficiency but notes a huge drop from the transmission... 400 KW -> 10 KW over just 10 KM.

When you consider geosynchronous orbit is all the way out at 35,000 KM. This seems like a major issue. What am I missing?

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larsschellhas OP t1_je11s3v wrote

That there are only around 10-50 km of atmosphere is the way and that accuracy is the primary driver of losses. :)

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larsschellhas OP t1_je1rz1o wrote

Or rather, according to EMROD, the main loss driver is the conversion to microwaves. Reconversion and transmission appear to be relatively efficient.

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Brain_Hawk t1_je16al7 wrote

That $10 per kilogram is an extremely optimistic estimate cited by a person who was well known to exaggerate in order to drive interest and investment.

Personally I suspect it's going to be quite a bit more than that, not that I'm an expert on launch cost. But I think we need to be a bit more skeptical of the claims being made at this time.

To the bigger question, I think any technology may be feasible in the future, but as far as I can see there's still a lot of challenges with orbital-based power. In particular the cost of sending it up and maintaining it, and the amount of power we can get generated back down on earth, and distributing that to a wide area.

But, if we don't come up with a better solution, it's definitely something I can see being in place in the next 50 or 100 years.

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