# Is orbital solar a bust?

BWV
Saw China launched a project to get a system operating by 2050, but at ~2GW that is about the capacity of a single nuclear power station, the Three Gorges Dam, at 22.5 GW has over 10x the capacity.

https://www.bbc.com/future/article/20201126-the-solar-discs-that-could-beam-power-from-space

US solar installed capacity stands at over 100GW (https://www.seia.org/us-solar-market-insight)

From my understanding orbital solar does not present huge scientific or engineering issues, the problems stem from cost of putting the material in orbit and then maintaining it - but that then implies that better launch economics and space infrastructure would potentially make this competitive - but 2GW by 2050 is too late a time horizon to make any difference, might as well invest in fusion?

Mentor
The economics should be pretty straightforward to calculate, but the feasibility dealbreaker for me is the death ray issue.

nsaspook, Rive and berkeman
BWV
The economics should be pretty straightforward to calculate, but the feasibility dealbreaker for me is the death ray issue.
But that's a bonus! Seriously, with the array locked in geosynchronous orbit, don't we only have Canada and Mexico to worry about?

The security risk for me goes the other way - seems it would be rather easy for a bad actor to launch a missle at the array and disrupt your power supply

Staff Emeritus
but the feasibility dealbreaker for me is the death ray issue.
ditto

Rive
Staff Emeritus
Seriously, with the array locked in geosynchronous orbit,
No no no. That's much too far away. You need the orbital parts in the lowest possible orbit.

BWV
No no no. That's much too far away. You need the orbital parts in the lowest possible orbit.
Not according to the Wikipedia article - geostationary makes it much easier to keep on target, with LEO only for testing prototypes

Gold Member
... the feasibility dealbreaker for me is the death ray issue.

Well now, that ship has already sailed, hasn't it?

GOP Congresswoman Blames Wildfires on Jewish Space Lasers

:gets banned for invoking politics *and* racism:

davenn and hutchphd
BWV
And how effective would the ‘death ray’ be at a gigawatt or two? A GW is roughly a kt of tnt, and we already have nukes or enough conventional munitions to deliver this firepower anywhere

anyway, China is building one and we can’t have a death ray gap, can we?

diogenesNY
Staff Emeritus
Not according to the Wikipedia article - geostationary makes it much easier to keep on target, with LEO only for testing prototypes
Really?

https://en.wikipedia.org/wiki/Space-based_solar_power#cite_note-45
Inability to constrain power transmission inside tiny beam angles. For example, a beam of 0.002 degrees (7.2 arc seconds) is required to stay within a one kilometer receiving antenna target from geostationary altitude. The most advanced directional wireless power transfer systems as of 2019 spread their half power beam width across at least 0.9 arc degrees.

phinds
Dullard
"DO NOT cross the streams..."

Benjies, sophiecentaur, Keith_McClary and 3 others
Gold Member
And how effective would the ‘death ray’ be at a gigawatt or two? A GW is roughly a kt of tnt, and we already have nukes or enough conventional munitions to deliver this firepower anywhere
Well... :hmm: I can think of a few huge advantages off the top of my noggin...
• Speed of light = zero delay = no warning.
• Can't be intercepted/blown up.
• Even if it could, you can simply point it elsewhere.
• etc

I mean, Death Ray is the 'magic bullet' of weapons for a reason.

BWV
Really?
Referring to this in the main article:

The main advantage of locating a space power station in geostationary orbit is that the antenna geometry stays constant, and so keeping the antennas lined up is simpler. Another advantage is that nearly continuous power transmission is immediately available as soon as the first space power station is placed in orbit, LEO requires several satellites before they are producing nearly continuous power.

Power beaming from geostationary orbit by microwaves carries the difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS study required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths, although they have increased atmospheric absorption and even potential beam blockage by rain or water droplets. Because of the thinned array curse, it is not possible to make a narrower beam by combining the beams of several smaller satellites. The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic.[original research?]

A collection of LEO (Low Earth Orbit) space power stations has been proposed as a precursor to GEO (Geostationary Orbit) space-based solar power.[64]

And 36K km is geostationary distance when I Google it

Numerous launches of the upcoming Long March 9 rocket would be used to construct space-based solar power facilities 35,786 kilometers above the Earth, according to Long Lehao, chief designer of China’s Long March rocket series, speaking during a presentation Thursday in Hong Kong.

https://spacenews.com/chinas-super-heavy-rocket-to-construct-space-based-solar-power-station/

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Homework Helper
2022 Award
And how effective would the ‘death ray’ be at a gigawatt or two? A GW is roughly a kt of tnt, and we already have nukes or enough conventional munitions to deliver this firepower anywhere
A GW-hr is roughly a kiloton of tnt. I don't know how that changes the nefariousness calculus. Probably easier to don the aluminum foil sombrero in an hour though.

gmax137
Homework Helper
Gold Member
A GW-hr is roughly a kiloton of tnt. I don't know how that changes the nefariousness calculus. Probably easier to don the aluminum foil sombrero in an hour though.
No, put it on NOW, don't you realize space aliens already have this technology?

Although as I understand it the beam from a geostationary orbit will have a cross-section at the Earth's surface of about 10km2. At 2GW that's 200Wm-2, about 15% of solar irradiance.

Homework Helper
2022 Award
Oh I always wear it during waking hours...

pbuk
Although as I understand it the beam from a geostationary orbit will have a cross-section at the Earth's surface of about 10km2. At 2GW that's 200Wm-2, about 15% of solar irradiance.
Just on average. As station- and direction-keeping goes, what you get is a far denser 'death spot' wandering around within that 10km2.

hutchphd
Homework Helper
Gold Member
Just on average. As station- and direction-keeping goes, what you get is a far denser 'death spot' wandering around within that 10km2.
Isn't this a dispersion pattern with sinusoidal density so the peak is only ## \sqrt 2 ## times the mean?

If the whole 10km2 is just about that then I think the situation may be considerably worse.
I just can't even assess what would be needed to keep an antenna of the required size in the good shape/direction during aiming and station keeping.

Homework Helper
Gold Member
I believe the solution is an array of many small 'rectennas' (rectennae?)

Homework Helper
Gold Member
Oh I always wear it during waking hours...
Only waking hours? You mean you are letting them beam into your dreams?

hutchphd
Homework Helper
2022 Award
Faraday netting at night...I'm no fool...

pbuk
Gold Member
All I can think about here:

Keith_McClary

### Where the sun always shines: Putting solar in space​

Thanks to a big donation, Caltech has funded a sci-fi-sounding project.
8/18/2021
... the plan is to make the receiving station about the same size as a large utility-scale solar farm.
...
"I want to take something off the table that you haven't asked me about, which is the safety question, " he said. "How do you do this in a way that you haven't created a death ray?"

The answer is in the physics that governs the focusing of photons. It says that a combination of aperture and wavelength dictates the smallest area of focus. There's just no way to focus the output of the in-space portion down to an area where it would be dangerous. The total energy flux at microwave frequencies ends up being the same as you get from sunlight. "You could walk under it," Atwater said.

Staff Emeritus
The total energy flux at microwave frequencies ends up being the same as you get from sunlight. "You could walk under it," Atwater said.

If that's true, why bother? Just put up a PV solar farm with the same area as the microwave receivers, and skip all that expensive space-based stuff to make about the same amount of electric power.

Of course, PV is not 100% efficient, but neither is microwave to electricity 100% efficient.

Have any of these space-based proposals estimated the total cost per kWh produced?

BWV

### Where the sun always shines: Putting solar in space​

Thanks to a big donation, Caltech has funded a sci-fi-sounding project.
8/18/2021
so looks like a bust, because no way will this ever be less than ~2x the cost of ground-based solar:

How this works out in energy-production terms is a little complicated. In space, you would get 30 percent more photons to work with than on the ground, and they're available 24/7. At the same time, the generating system would sometimes have to be at a less-than-optimal angle in order to remain capable of transmitting to the target station. Then you would lose significant fractions of that power during conversion and transmission.

How does it all balance out? It depends on the assumptions you make, but Atwater provided a rough estimate: "The net power generated is a little more than you would get if the Sun were overhead at noon 24 hours a day."

Staff Emeritus
Compare the most optimistic performance of this space-based idea with a real life solar PV project already in operation producing electricity at $0.03/kWh sophiecentaur, berkeman and BWV BWV Compare the most optimistic performance of this space-based idea with a real life solar PV project already in operation producing electricity at$0.03/kWh

View attachment 288040
Cool, that is currently the worlds largest solar installation, not quite as cheap as 3 cents, as it was built in phases and the older installs reflect solar costs during the 2016-2018 installation

There is a 5000 MW project underway, and in total India has plans for 17.5GW across 15 'Ultra Mega Solar Parks' (the gov name for the program)

https://en.wikipedia.org/wiki/Ultra_Mega_Solar_Power_Projects

sophiecentaur, anorlunda and berkeman
Gold Member
If that's true, why bother? Just put up a PV solar farm with the same area as the microwave receivers, and skip all that expensive space-based stuff to make about the same amount of electric power.

Of course, PV is not 100% efficient, but neither is microwave to electricity 100% efficient.

Have any of these space-based proposals estimated the total cost per kWh produced?
I was waiting for someone to make this comment. The fact that the sun don't shine all day every day seems a small point against ground based PV. Everything else seems to be in its favour.

Homework Helper
Gold Member
Do we really want to collect more energy from the sun and inject it under the blanket of our atmosphere?

Should we be trying to do the reverse? Set up transmitters to beam energy into space to get rid of it and cool the planet?

I'm only half serious.

OmCheeto and Keith_McClary
Mentor
I'm only half serious
Whew!

Keith_McClary
CCatalyst
Well personally I feel it highly depends upon the application. It may be an unnecessary application for here on Earth due to logistical issues, but what if you are one day going to create a space-based economy and you need to transmit power from one location to another?

Also, if the satellite can orbit the Earth multiple times a day and it charges up, it can even power a location at night.

Staff Emeritus
geosynchronous orbit

the satellite can orbit the Earth multiple times a day
Got to pick one or the other.

Keith_McClary and Bystander