Building solar farms above the clouds | Hacker News Reader

Building solar farms above the clouds

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66 pointsrmason37 comments

I just did the math, it works out!

What we need to do is move the aluminum reduction cells into floating solar powered processing units which drift around the world receiving aluminum oxide from drone craft and deliver refined aluminum back to them.

It will take 59 kilojoules per kilogram to raise the ore to 6km, times the inefficiency of the craft, lets say a number less than 10. Plus, aluminum oxide is only about half aluminum so another 2, lets call it 1 megajoule per kilogram of aluminum in round numbers.

Refining aluminum oxide into aluminum takes 54 megajoules per kilogram of aluminum! (according to a number I found on the internet and most probably read correctly).

That makes the energy to raise the aluminum negligible. So forget about how to transmit electricity down from the solar pelagic behemoths drifting lazily around the planet, just use them to refine aluminum.

Ships of aluminum oxide will cruise out to the behemoth orbitals and track them while they exchange their cargo for refined aluminum.

Presumably a sufficiently clever person will find areas in the Pacific ocean where the behemoths can lazily circle by gently pushing themselves from eastward to westward currents using altitude variation which is easy by controlling how much inventory is onboard, but also by how much waste heat you put into your gas bags. Sure, once in a while they will be blown away on longer excursions, that will take them offline until they can get back over another drone supply ship.

This is the future science fiction has been promising me!

Solar in space is only about 2x more effective per unit area of solar panel than solar on the ground, after you deduct transmission losses. The costs, of course, are much higher. The enthusiasm for hydrogen as energy storage is misplaced. Electricity to hydrogen to electricity is maybe 40% efficient. Lithium batteries are 80% - 90% round trip.

In any place that needs air conditioning, solar power is very effective. Peak load and peak solar panel output line up nicely, and little storage is needed. Keep it simple.

Some countries don't get much sunshine though, e.g. the UK only gets sun around 30% of the daytime according to https://en.wikipedia.org/wiki/Climate_of_the_United_Kingdom .

It also doesn't need much air conditioning. And when it does, it's because the sun is out.

Spain isn't that much farther away than outer space.

We can't beam energy from Spain to elsewhere via microwaves, though. And it still gets dark at night in Spain.

It gets dark in the stratosphere too, and the UK already has a power grid connecting it with the Spanish power grid which doesn't rely on 20km cables into the sky...

The parent post was about outer space, not the stratosphere. And that method uses microwave transmission, not cables.

Outer space gets dark too you not sure which orbit will get you 100 sun time solar synced orbits still get 50% night time. Maybe some geosync high polar orbit but then you have issues with transmition. Space solar makes very little sense you only get twice the solar power at 50% efficiency rate at best.

Hydrogen could be handy for heating. The efficiency would be higher too, since what you want is heat & you get all of it by simply burning it.

You could collect it in North Africa and distribute to Europe in the winter.

Lithium batteries are not portable, hydrogen can be. With sufficient solar power generation that forty odd percent efficiency would become a non issue.

How are these things supposed to stay aloft? They need to lift:

1) Themselves

2) The solar panels

3) Fuel cells

4) 20km of tether and cable

The idea seems really neat, but I'm an engineer and I want to see the math.

Edit: And how about that tether? What's the wind load going to be like? How is it moored? What is it made of?

They are energy collectors, I would assume you use some of that energy to heat the air in their balloons.

I'm more interested in how you optimally position the solar cells, would a sphere really be the best or would a pontoon dragging in the wind give a better chance for the solar panels to receive optimal light? You probably don't want that 20km tether to be twisted too many times either.

Interesting point about placement --- seems like a dense array of these would be at risk of getting tangled. And then there's the risk of the tether / cabling becoming a conduit for electrostatic discharge. Of all the engineering issues here, I think tethering is the most problematic.

I can't imagine many people wanting to live near 20km electrically charged cables, never mind pilots flying between them in a high wind.

Having to build a long way from urban areas rather reduces the advantages of such a system over solar farms in the desert.

> I can't imagine many people wanting to live near 20km electrically charged cables, never mind pilots flying between them in a high wind.

Not being able to imagine something, and other people not being able to do it, are not functionally equivalent.

Lots of people live within 20km of much more dangerous structures already. But there are plenty of places that people live > 20km away from because they're considered a high risk. So, take your pick on that one.

Pilots already have experience at not flying in certain places - environmental reserves, war zones, hurricanes, mountains, etc - they're pretty good at reading maps.

> Having to build a long way from urban areas rather reduces the advantages of such a system over solar farms in the desert.

I'd suggest you refer to the article again for the proposed benefits of having these things above cloud level, rather than on the ground.

Currently (npi) most power generation occurs much more than 20km from the primary urban areas that they provide power to.

Put some propellers on the balloons, and a computer to control them.

If we can get drones to avoid trees while flying through a forest at high speed, we can make balloons maintain a safe distance from one another at an altitude way above most storms.

An idea is to use rotating cylinders as balloons which generate lift (Magnus effect). It helps a little.

why tether? why not let the balloon charge a battery, and have drones carry the battery back to earth when full, and vice versa...

Good question. The winds up there are really strong.

Tethering also lets you wind the appliance back to the ground even when (especially when) it's faulty.

Tethering also lets you obtain power throughout the 12+ hours of power generation per day.

Maybe the balloons could be autonomous as well, rising/falling depending on conditions, and also falling to an acceptable elevation for the drones to reach them efficiently :)

Batteries are heavy, lifting them with aircraft is significantly inefficient.

It seems easier to put solar power in deserts Mojave desert, Sahara and transport the power via high voltage direct current which has low tranmission loss.

https://en.wikipedia.org/wiki/High-voltage_direct_current

It should also be possible to put solar power high on mountains in areas where they place observatories that is no cloud cover.

The fuel cell part is a bit dodgy. It would make more sense to include a little hydrogen bottle on the tether if extra H2 is needed to top of the balloon.

And there's no point to storing power in the air like that - it's better fed to the grid when the sun is shining to be stored at the grid level. Generating hydrogen just isn't a very efficient way to store power.

If you're going to use huge tethered balloons, why use PV? You've got the benefit of strong predictable winds up there, 24 hours a day, so once you've bought into the cost of tethered aerial power, wind seems a better bet.

More junk science designed by artists?

Wind I can see making sense since at high altitudes, it's more constant.

Creating and storing the hydrogen in the balloon triggers a strong, this is just fluff. We can't really even do this on the ground.

They are inventing two new technologies we yet don't have?

I going to go with, it'll be better covering the other 98% of roof space with solar first. And get wind powered balloons going for night time use if you're going down this route.

I live in the mountains just a few hundred meters above sea level. It's often clear here when it's cloudy in the valley. There must be other places like this where you could put the panels, without having to resort to balloons?

Although it has always been a good idea for something like this. I'd be surprised if the FAA allowed such a thing to happen. It would have to be a permanent NOTAM, and in an already existing no-fly zone for personal aircraft.

Save you folks a google:

A Notice to Airmen (NOTAM or NoTAM) is a notice filed with an aviation authority to alert aircraft pilots of potential hazards along a flight route or at a location that could affect the safety of the flight.

NOTAM - Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/NOTAMWikipedia

Oh, yeah, and give me shadows in the land.

I hate the idea because it has the potential for abuse: If it works it means blocking the sky for those under. Like making clouds to artificially rain on your land, while not raining where it used to rain.

Sun is one of those fantastic things that is free. Free until someone has the idea to appropriate it.

Problems to aircraft makes this idea non practical near population centers, where energy is consumed. It is possible in the ocean.

The shadow from a balloon six kilometres up is basically non-existent. When was the last time you noticed a shadow from an overflying jetliner cruising at that height?

Isn't it easier to modify the weather in an area populated with PV?

Modify it how? We have some fairly blunt instruments like seeding clouds to modify weather, but those wouldn't be of much use here. Of course, it seems a lot more straightforward to build solar farms in Arizona or Algeria, though transmission is still a problem. Possibly they could be used to generate hydrogen for synthesizing fuels...

True, seem to be harder to go the opposite way.

Something noteworthy: China plans to halt rain for Olympics - http://www.latimes.com/world/la-fg-rain31jan31-story.html

That would mitigate the loss through shadow, but not the apparently much larger loss through diffusion in the atmosphere.

What kind of danger would this kind of thing pose to airplanes?

I was making this argument in another thread yesterday.

The fact that aviation currently assumes it has exclusive right to all airspace does not mean things have to be (or even should be) that way.

The vast majority of commercial air traffic file flight plans and flys along well know routes.

There's currently outcry about drone pilots "flying in dangerous manner for airplanes/helicopters", but it seems to me that nobody ever agreed that the occasional police or news helicopter flying over my local park was automatically reason to ban flying drones/kites/rc-aircraft there _ever_.

Same here, just because general aviation has had un-contested access to the sky and the freedom to assume they're entitled to unimpeded safety _everywhere_, is not something we've ever chosen - it's just "the way things have always been", which isn't necessarily "the way things should stay".

If someone comes up with a technical way to make tethered balloons work as a reliable and cost-effective renewable energy source - I personally don't think that "but it might impose a safety risk to airplanes who want to fly there" is a good enough reason to not allow them to try.

There's is (I suspect) a great "safety risk" to flying your Cessna or gyrocopter over, say, Area 51 or Groom Lake or The Whitehouse, why shouldn't pilots have the responsibility to avoid tethered-balloon electricity plants as well? Surely the net benefit to society of a few GW of renewable energy is way more than the ability of civilian pilots or news choppers to have unlimited access to all airspace at all times for no reason?

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