Essay by Eric Worrall
University of Glasgow academic Onur Çelik has proposed huge space mirrors could allow solar panels to satisfy electricity demand in the morning and after sundown.
Reflectors in space could make solar farms on Earth work for longer every day
Published: January 12, 2024 4.24am AEDT
Onur Çelik
Postdoctoral Research Associate in Space Technology, University of GlasgowIf you happened to be looking at the sky in Europe on a cold night on February 5 1993, there is a chance you could have seen a dim flash of light. That flash came from a Russian space mirror experiment called Znamya-2.
Znamya-2 was a 20-metre reflective structure much like aluminium foil (Znamya means “banner” in Russian), unfurled from a spacecraft which had just undocked from the Russian Mir space station. Its goal was to demonstrate solar energy could be reflected from space to Earth.
This was the first and only time that a mirror had ever been launched into space for that purpose. But, three decades on, colleagues and I believe it’s time to revisit this technology.
Unlike proposals to build solar power stations in space and transmit energy down to earth, all the generation would still happen down here. Crucially, these reflectors could help solar farms generate electricity even when direct sunlight is not available, especially during evening and early morning hours when demand for clean energy is greatest. Colleagues and I call this concept “orbiting solar reflectors”.
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Read more: https://theconversation.com/reflectors-in-space-could-make-solar-farms-on-earth-work-for-longer-every-day-220554
The following is a video of the concept;
Technically this seems feasible – but at what cost? Solar energy is already absurdly expensive. Adding large space structures might reduce battery backup requirements, but it still seems hideously expensive.
There is also a crucial difference between orbital solar panels and orbital mirrors – orbital panels could still transmit power to the ground when the weather is overcast.
Microwaves from an orbital solar power station can penetrate cloud cover, reflected sunlight not so much – unless there is enough concentrated sunlight to burn away the cloud cover.
Duh, is there an award for being the dumbest greenie in the land? It’s the sun that heats the earth. So if you put a bunch of mirrors in orbit to essentially lengthen the time the sun’s photons impact the ground every day – again duh, you are going to add more solar heating to the damned planet, dumba$$!
Does this idiot not recall why it’s cold in winter and hot in summer regards length of daylight? This idea is almost as stupid as putting particulates into the upper atmosphere to block the sun in an attempt to mitigate so called runaway global warming. At least this dumb idea can be turned off, whereas particulates into the upper atmosphere is not so easy to reverse.
Well, there wouldn’t be a need for street lighting.
Absurdly expensive solar energy? Come on. In last year prices of solar panels and batteries went substantially down.
Price of decent solar system for average household is currently around 3800$.
I’m one and half year using solar system on my house, 3.4kWh panels, 5kWh battery, 3kWh inverter. Saving me around 70% of my 4.6MWh yearly energy needs. I built it for around 4500E ( 5000$).
With current prices I could have 5kW system with 16kWh battery and 5kWh inverter for 3700E(4000$)
Those are prices close to some heat pump or some gas heater.
What is the color of the sky in your world?
I’m really not sure what you mean.
Currently my sky is grey and my solar is making almost nothing. But that is expected during european winter.
But regarding panels and batteries. Almost 3 years ago I bought 300W panels for 125E each. Now I can buy 550W panels for 120E.
I bought my LFP battery 1.5 year ago for 750E, 2.5kWh. Now I could buy 14.3kWh for 1120E.
I’m now retired but one of my coworkers had solar installed on his house’s roof.
He said, as long as he could still sell excess to the grid, it would take 16 years to pay it off.
(But he had more of a “survivalist” point of view.)
Yes it needs thorough counting if you want early pay off and it is very easy to just be victim of expensive solar installation company.
If you focus on independency, your pay off date is going out of sight, like you mentioned 16 years or so.
But if you focus on return, you can get to around 5 years.
My price of electricity is on lower side, currently 0.16E/kWh, what is around 0.14$/kWh
And I’m able to design system with around 5-6 years return.
With prices of electricity around 0.30E/kwh like in Germany, or tiered system PG&E in California, it shouldn’t be problem to get to 3 years return.
And I’m not fan of On Grid systems, I prefer physical battery, which is giving your production back to you for full kWh price, not into grid for some small price.
Clouds, precipitation.
How will they keep them focused, even a 1° misalignment will means miles off target at the surface?
I suppose they can be installed and serviced by those technically feasible orbital elevators tethered to the surface, powered by technically feasible fusion reactors.
Beam me up Scotty – out of this asylum.
Perhaps this is just a case of the University telling him, “Hey, you haven’t produced anything in a while, get something published or you are gone.”
Agreed, with the codicil “no matter how silly it is.”
From the above article: Znamya-2 . . . “Its goal was to demonstrate solar energy could be reflected from space to Earth.”
Idiots! . . . I guess the science “geniuses” behind this experiment never considered the cause of full moons, nor the waxings and wanings of planets in the night sky.
Using this for solar generation is idiotic. But big mirrors could be used for direct illumination to extend twilight conditions for cities located far north in Canada or Russia where people see little light for months. Not only the light would not need be concentrated, a 250 m diameter mirror could illuminate softly an area about 1 km diameter, enough to cover a city center. Of course, even this would only work in clear sky conditions…
The problem I’ve always seen from this idea is that there’s no functional difference between a microwave / solar mirror array and a space weapon. If you can steer it, you can dump energy on a target.
Steering (aka “pointing”) is only one part of the problem . . . a equally difficult problem is preventing dispersion (aka “focusing”) of the concentrated radiation one wants to direct to a relatively small spot on Earth’s surface (aka “the target”).
Let’s not even go to the point of talking about energy conversion efficiencies (including reflectivity) and transmission losses due to things like Earth’s magnetic field and its atmosphere. Let alone consider things like maintenance of orbital ephemeris in the presence of Sun, Earth and Moon disturbance torques.
focusing isn’t really a thing in this case – the sun subtends 1/2 degree. No matter the size of the reflector it’s basically a pinhole lens, and the sun “image” size at the ground is basically a function of the distance from the reflector to the ground site. That is, 1/2degree in radians times the distance.
Ridiculous!
1) If the in-space reflector was perfectly flat it would reflect a image having essentially parallel rays from the SUN, but if its reflecting surface was convex-shaped (e.g., “ballooned outward”) or even “wavy” it would reflect a image of the Sun having diverging rays, thus greatly reducing the solar power flux it reflects to Earth’s surface.
2) A reflector (even a concave reflector) is not a pinhole lens . . . you have a total misunderstanding of optics. A reflector has a physical surface across which incoming light rays interact with; a pinhole “lens” instead is based on diffraction of light passing freely through an open circular aperture.
3) A pinhole “lens” (tiny open hole) can only be made to a certain absolute physical aperture size, whereas a reflector (convex, planar, or concave) does not have a geometric size limit.
Th answer is .0087 which is the sin of .5. Both the sun and the moon are half a degree in the sky. The sun will be reflected off the mirror and spread out from that point. Travel 100 miles and the receiver will have to be at least .87 miles to recover most of the light. At 20,000 miles it would be 174 miles. You could use a parabolic shape but that would be far more costly than a flat reflector. A segmented reflector would only work if he reflectors are curved to match the parabolic shape. Not really very practical.
I know about this because I have played around with pin hole cameras and taking pictures of the moon which is also half a degree in the sky.
I thought that the answer was 42 . . . although I can’t quite recall what the question was.
Perhaps a sin of the father visited on the son?
Wrong sin.The trig notation for sine. You also have cos for cosine, tan for tangent and all sorts of other good things. I guess I got something out of that class after all.
As for 42, it’s supposed to be the answer to everything however I haven’t had the time to verify it. Maybe I found an exception?
Use radians, for small angles, rise over run.
sin(0.5) = sine of 0.5 (degrees or radians) ≠ sin of 0.5 (degrees or radians)
Oh hey Dena, I’ve been yakking about this above.
A parabolic shape won’t help! This whole thing is dominated by the sun being an extended object, and the pinhole nature of the reflector.
And even if you could get some big reflector, or array of reflectors, there is the insurmountable problem of them tracking the ground target. I talk about this up comments.
Parabolic would work but the precision required to produce a reflector that size would be well beyond what we could do today. They have had solar cookers for years and they work. Because of the short distance they can be round instead of parabolic. If we can send probes to Pluto, I am pretty sure the tracking issue could be solved. This is simply a case of somebody reading through old science fiction and thinking they came up with something new.
Reflector cooker
Maybe I can explain it a bit better. Each point on a parabolic reflector would be a point source of light. Light from that point would still separate at the agreed half a degree rate as they are a pin point source producing an image of the sun at the target. You would still need a large target as I stated in my initial post but as long as the target matched the half a degree rule, loss would be minimal. For normal daylight, you would need a reflector the size of the target. I don’t think our space program is up to it.
Well, we are talking about relatively small optics, relative to the object distance. That means there is basically no difference between a curved and a flat mirror. In the precise, but unrealistic sense, you would have the focal length of the parabolic mirror be 300 miles. What is the curvature? The radius of curvature would be 600 miles! Basically flat. There would be no measurable difference in irradiance.
You were on the right track with the pinhole example.
‘I don’t think our space program is up to it”
I don’t you are considering the dynamic nature of all of this. Whatever the orbit, even geo stationary, the reflector would need to rapidly change orientation to track the ground target. That means an ever changing angle of incidence on the reflector, which it has to compensate. Mind boggling hard for an array of flat mirrors, squared so for a monolithic reflector. IMO, impossible with known materials and technology. But a curved reflector? Like a giant swarm of flat mirrors taking a curved shape? Because the angle of incidence is never 90 degrees, a surface of rotation. e.g. paraboloid, won’t work. An off-axis toroid segment would, but it would have to be continuously changing as the angle of incidence changes. The kinematic demands on a large reflector array are completely stupendously mind boggling.
On a mile diameter disk the center would only be a few feet deep, probably under 4 feet depending on the focal length. It’s not much but it would drastically change the target area.
Inertia would take handle most of the positioning issues but it would probably take additional corrections. Flexing of the reflector would be an issue and resolving that would add even more mass.
The point is theory says it will work but the engineer will say just how much do you want to spend on this? The answer means it isn’t going to get built. We could construct a lot of nuclear reactors for what one of these would cost.
Well, not quite done.
I have to disagree about the curve. This is essentially a paraxial system – aberrations, including focus, are insignificant compared to the image of the extended sun object. The difference in blur is a tiny fraction of the image width.
But those considerations aren’t important compared to the big problem. This is the ridiculously tiny energy and irradiance the proposed 250 meter wide reflector would produce on an array 900-1000km away. On the ground less than one Watt per square meter falling on a hypothetical 50 square kilometer solar farm for 20 minutes. With conversion loss this is about 10MW, or about 3MWH for the 20 minute pass.10MW is the noon output of a 15 acre solar array. We are talking about spending untold billions for that?
Flat would work if the reflector is 4 times the size of the receiver. This would provide uniform light across the full surface of the receiver. If that isn’t a requirement, a smaller reflector would work.
Still, flat could be a better trade off as it would be far simpler to construct than a parabolic reflector and even at 4 times the size would still cost far less. There is the problem that the surrounding area would be illuminated with the wasted light but that could be business or farm land where the light wouldn’t be a problem and might be beneficial.
It took a little while to do ray tracing in my head but I guessed in advance that inverse square would figure into it somewhere and it does. It’ just that the source would be located buried in the earth under the receiver.
With a reflector 4 times larger, 3/4 of the light would go to waste so it’s likely they might be willing to live with a less uniform light distribution and configure the receiver to function with less even distribution of light.
Also note that anything smaller than about a square mile isn’t big enough to handle the light spread of half a degree and that gets larger the higher the orbit.
I went off and read the dumb press release again. There is some disconnect with the author’s grasp of this for sure. The proposed size of the reflector is 250 meters. The orbit height is 900km – say a slant range of 1000km. Using the subtense of the sun – 0.0087 radians – The spot on the earth is about 9km across. The irradiance would be 0.06% of noon insolation, or less than a 1W/m2. For 20 minutes or so, which would still require active tracking by the reflector. What good is that?
Anyway, I’m done with this.
According to them, the world is already too hot, and they want to solve that problem by focusing more sunlight on the planet?
Do these guys have any idea how stupid they sound?
The dude is a postdoc research assistant bs artist. The unknown negative impacts in my mind, are huge!
As I often ask, who is paying these clowns?
Tracking mirror will definitely not work. So only possibility is to do it static. For example use inflatable balls from aluminum foil. Those will be ridiculously cheap, so it is possible to make millions of them, they will reflect light into more than half of space angle. Take them into orbit deflated, with small amount of air inside of them, after exposing to vacuum they will inflate by themselves. No mechanics. 1gram each you can take 1 million of them to orbit in 1 tone. And you need like 100 of them to make 1m2 of reflective surface.
Only problem here is they will reflect sun all the time basically heat up Earth more.
I’m not sure that it will come through green religion.
What space solar power – whether as beamed down photovoltaic, or direct solar reflection – as “fighting global warming” ignores is the fact that each is taking sunlight that would never have reached Earth to begin with, and adding it to the total irradiance. Mirrors reflecting solar to Earth serve the reverse function of the many schemes of geoengineering reflection of incoming sunlight. The schemes for beaming PV-generated microwaves to Earth add somewhat less to the irradiance because of their higher efficiency, but they both involve increasing the solar input to Earth. I don’t know how anyone can say that is an improvement.