Giant solar collectors in space?

[ScienceNostalgia101]

 

This video showed the construction of a modestly large concave mirror using a fairly meticulous process of carefully placed reflective foil.

 

However, I would presume that, the larger the scale on which it's conducted, the less any wrinkles in the structure matter, at least for the purposes of collecting sunlight.

 

I'm wondering now; is there any cost-effective way to have outer space robotics (Canadarm, etc.) assemble a giant amount of reflective material in outer space? Would electrostatic repulsion and/or magnetic attraction serve to force a giant sheet of reflective material into a concave shape? Could this concave mirror then be used to melt the sands of the Sahara into glass for the purposes of the aforementioned water reservoir idea?

 

Alternatively to mirrors, what about lenses? If one could, using some space elevator or other means, carry a mold impermeable to water into space, and pump a giant amount of seawater into it before it freezes, could this then be used as an outer-space converging lens made of ice, to concentrate sunlight into some massive solar collector?

 

"Geostationary" orbits aside, is there any way to position either's orbit such that it's always at the same angular position relative to the sun?

 

This is not to condone either such project, as I'm guessing there are potential side-effects of which I'm not yet aware, I'm just asking out of curiosity.

[Frank]

This might interest you: China May Soon Have a Second (Artificial) Moon:  https://www.space.com/42183-china-artificial-moon.html

Downside:  even from LEO, reflection is about 30 km wide (IIRC) because of Etendue - Wikipedia:  https://en.wikipedia.org/wiki/Etendue  which means to get 1:1 sunlight, the mirror would need to match that size!

Also, rain and clouds means no light.

There are also ideas about solar panels in space with energy beamed to earth using microwaves.

 

[ScienceNostalgia101]

Interesting. All of China? Does that mean I should be able to see it in 2020 if I visit Shanghai?

 

Speaking of the idea of a large concave mirror, here's another thing I was thinking about.

 

The surface area of the Sahara desert is 9.2 x 10^9 square metres. Sunlight's radiant intensity is 1050 watts per square metre. Doesn't that suggest that a solar collector the size of the Sahara could have a power of 9.7 x 10^12 watts? Wouldn't that be several orders of magnitude more power than all the USA's nuclear power plants combined, being that 805 billion kilowatts are 2898000000000000 joules per year, or 91832078 per second? What's the cheapest highly-reflective material with which you could line the Sahara, assuming you could eventually make this pay for itself?

Edited October 26, 2018 by ScienceNostalgia101

[Frank]

One artificial moonlit test city, maybe - it's not a great idea.

Solar panels in deserts can power the world.  Some projects already exist.

 

[ScienceNostalgia101]

So why aren't they being done more, then?

[mistermack]

The energy is there in abundance. But it's in the wrong place. There's little demand in the Sahara. And the cost of moving it to a thriving market is enormous. 

If it was economically viable, they could do it now in Spain and Portugal, but it's only done small scale at the moment. 

I would say that if you could have giant reflectors in space, places in the North like Canada and Russia could use it best, in the middle of winter when days are just a couple of hours long. 

[Frank]

1 hour ago, ScienceNostalgia101 said:

So why aren't they being done more, then?

Sandstorms damage panels, no water to clean the panels, not close to where people live, generally.  Seems like these problems can be overcome, but the $ is probably not there (yet).

 

[mistermack]

Since there's no prospect of a large population moving to the Sahara any time soon, the only way you could make solar energy pay on a gigantic scale would be to lay an enormous cable across the Mediterranean and up through France to central Europe. 

The cost would be phenomenal, and it would only make sense, if there were stable reliable governments in North Africa. None of that is likely to happen. One other way would be to use solar energy in North African countries to produce synthetic fuels, and ship that around the world. I don't think the economics is there for that either, or they would be trialling it in places like Australia.

There are various experiments going on, using bacteria and algae that have been genetically engineered to produce fuels like propane, but they are in their early stages. I think it's stuff like that that is the most promising in the long run. 

Edit: Some links :

https://www.imperial.ac.uk/news/157026/scientists-create-renewable-fossil-fuel-alternative/ 

https://www.sciencedaily.com/releases/2013/03/130313112211.htm  

https://energyfactor.exxonmobil.eu/news/algae-timeline/   

 

Edited October 27, 2018 by mistermack

[ScienceNostalgia101]

6 hours ago, mistermack said:

Since there's no prospect of a large population moving to the Sahara any time soon, the only way you could make solar energy pay on a gigantic scale would be to lay an enormous cable across the Mediterranean and up through France to central Europe. 

The cost would be phenomenal, and it would only make sense, if there were stable reliable governments in North Africa. None of that is likely to happen.

You can't pay them to accept the presence of armed guards protecting the cable?

 

Ok, so maybe North Africa is not the best place. What about other massive deserts, like the aforementioned central Australia? If you constructed a concave mirror there, whether by conventional means or electric repulsion shaping a sheet of metal, and used the electricity to pump seawater out of the ocean and into the concave mirror, would the water then double as a convex lens, increasing its converging power, increasing the amount of water pumped into the concave mirror? Could the excess water then be desalinized and pumped toward neighbouring countries?

 

I ask because for the prior rainwater collection thread I calculated that the estimated sea level rise is by 310 thousand cubic kilometres... however, a half-sphere with a radius of 53 kilometres wide could accommodate all of that without overflowing.

[mistermack]

There's no advantage in making one mirror, when you can cover the same area with thousands of smaller ones, making maintenance easier. And water gives no advantage at all, and huge disadvantages. You don't need a lens if you have a curved reflector. And still water would probably go green in the sun, making things worse. 

Your ideas seem a bit fantastical. I would have a look at what IS being done successfully with Solar, and read up on the problems that have to be got past in real life.

[Frank]

Built in a mining pit, collects water too.  Not for deserts I guess.

Solar power tower - Wikipedia:  https://en.wikipedia.org/wiki/Solar_power_tower#Novel_applications

 

[ScienceNostalgia101]

Would the seawater be just as likely to turn green if it were filtered or no? Is it a function of the microbes, the salinity, or just being left out in the open long enough?

 

Interesting concept on Bingham Canyon; would drawing attention to that idea make it more likely to get implemented or less so?

[mistermack]

13 hours ago, ScienceNostalgia101 said:

Would the seawater be just as likely to turn green if it were filtered or no? Is it a function of the microbes, the salinity, or just being left out in the open long enough?

I don't know. I was guessing, as I've never done it with sea water. I have had de-ionised water go green in the past though, when left in the sunlight, so I'm guessing that sea water would do the same. 

[ScienceNostalgia101]

Well, being that particles dissolved in water are known to cause turbidity, I would guess either they collected particulates from the air or bacteria/viruses added impurities. Not sure if saltwater could prevent that... probably not. And being that "convex lens increases converging power focusing light on smaller area" was the point of my idea of using a concave mirror in the first place, I think I might as well abandon that idea.

 

Still though, why can't they make more solar collectors in Australia? There's vast amounts of unused desert out there, and even if they can't use all of the electricity themselves, could they use it to generate hydrogen gas they can then sell to other countries? Surely a boat carrying the gas should be reasonably easy to keep afloat. (Assuming at-sea hydrogen pipelines aren't an option.)

[Ken Fabian]

7 hours ago, ScienceNostalgia101 said:

Still though, why can't they make more solar collectors in Australia? There's vast amounts of unused desert out there, and even if they can't use all of the electricity themselves, could they use it to generate hydrogen gas they can then sell to other countries? Surely a boat carrying the gas should be reasonably easy to keep afloat. (Assuming at-sea hydrogen pipelines aren't an option.)

In fact solar energy is proving very popular in Australia. About 1/5th of suitable rooftops already have solar panels on them (I think that is by number of buildings, not their total available area) and the rate of installations has surged. A lot of larger scale solar farms are both coming on-line and under construction. Solar and wind are delivering the lowest cost new electricity generation options in the Australian electricity market and even long established, mostly coal and gas reliant electricity producers are investing in them - even with strong expectations that subsidy support will be withdrawn.

There are some serious proposals for Hydrogen production including for export, but this is still in it's infancy. Proposals to add Hydrogen into gas supply lines are also being considered - taking advantage of existing infrastructure. However, use of pure Hydrogen will require it's own infrastructure. My own view is that Hydrogen will be most valuable for industrial purposes - smelting steel for example. On the subject of steel, the new owner of Whyalla's steel works, Sanjeev Gupta, is investing in wind, solar and storage in a big way, because he sees those as providing the least cost power for the facility - although not yet for steel smelting.

[Frank]

One problem with hydrogen is it is cheaper to strip carbon from methane than to do water electrolysis!   Not a problem (for profits) until there is a carbon tax.

I just read that a nuclear plant in California isn't renewing their license, not because there is a push against nuclear there, but because they can't make money.  Renewables are cheaper and there is a dip in demand between 9 and 5 which is bad for base-load power.  They could produce hydrogen in the lull, but I guess it's not profitable either, or maybe within the lifetime of the plant, renewables will start producing the hydrogen more cheaply - who knows.

 

[mistermack]

In Australia and other hot sunny countries, there is a bonus, in that the times that you want most energy for air conditioning coincides with the times that you can generate electricity from solar panels. You don't get the same bonus in more mixed climates, when you want power for heating, but the Sun isn't giving much. Wind can help to a certain extent to cover some of the gaps, but you still need nuclear or gas or the like to cover all of the gaps. 

Efficient economic storage is still the holy grail. 

I don't really understand the resistance to land-based wind turbines by residents. I like them. I like the look, and the noise is negligible. I think people in the UK automatically object because they are obsessed with their house prices. Even if THEY don't mind them, they think it will reduce the value of their property to others. 

[Ken Fabian]

The majority of the world's population live in climates that can make good use of solar energy. I think Hydrolysis will supplant Hydrogen from fossil fuels; even with pro-fossil fuels government support, Hydrogen from Australian brown coal, for example, has not been very successful. Meanwhile a half megawatt electrolyser is going to be trialled in Sydney. Being cynical, I do think the gas suppliers supporting it are more interested in being able to add "green" and "renewable" into their ongoing marketings of fossil fuel gas than in actually displacing the gas - but it is a start.

I do understand some of the resistance to wind turbines - nice views are highly prized. I just don't prize them so highly that preserving the views are good justification for failing to commit to low emissions. It may turn out they are a transitory technology that will not be replaced at the end of their working life - I hesitate to predict how the end game of a transition to low emissions will play out; solar will improve, tidal and wave power will improve, storage will improve, long distance power transmission will improve.

I don't expect space based solar - at multi-millions US$ per ton to launch to LEO - to become a real thing, although I still do wonder if the transmission elements of space based solar proposals might somehow be turned to a global energy transmission network. Beam up from summer daytime Australia, around the world and back down to winter night in Russia or Scandinavia. Nothing really happening in that area, but we are going to end up with things we didn't expect - like we have with low cost solar.

Nuclear has serious issues beyond the mess of partisan politics (that I think doesn't reflect the reality), but it will improve also - and be popular in those climates and regions that have poor solar resources and limited transmission links to RE rich regions.

Efficient storage is going to be vital - and if, a decade ago I thought the R&D commitment to storage was inadequate, not any more. If a household of the future requires the equivalent of one new car's worth of technology in the form of batteries, to complement the solar on their roof, I don't think that will impoverish anyone. The large scales for any new technologies to make a difference don't daunt me; whatever we do, right or wrong, is going to be at unprecedented scales.