Windmills in the Sky

An Anonymous Coward sent in: "The BBC is reporting on works of an Australian scientist who has been developing flying turbines that use the stable jet stream at 4.5 km altitude to generate electricity and send it back to the ground via cables."

Re:Why?

[HerringFlavoredFowl]

because slashdot double posted the article, check out the other slashdot article [slashdot.org].

Divide and be Conquered, Unite and Take Over the World..

TastesLikeHerringFlavoredChicken

Questions and Comments

[banks]

I don't see anywhere in the article how much power they expect this to generate. It will have to be a good amount per unit, though. This looks to be a rather large investment, I'd like to see some cost/return data. Is Australia really so thirstry for electricity that they need to resort to this?

Also, what happens when the wind cuts out? Winds are rather unpredicable... The sight of a whole flight of these things plummetting to the ground before their rotors can shift from generate mode to motor mode would be rather amusing, but not very profitable. There's some possibility that they could use autorotation to do a controlled descent, like helicopters, but I think the ground-connection cable might hinder that.

It's kinda funny that the world is so desperate for power that schemes like this get cooked up on a monthly basis, but we're still terrified of nice, cheap, clean nuclear fission power.

Re:Problems

[Yazeran]

The cables would have to be awfully thick (hence heavy) to transmit a decent amount of power 3 miles. Then you're wasting power just keeping them up in the sky.

Well only if you use low voltage. Remember that P = U * I, and that resistance losses scale like I^2 * R.
Thus if you transform the power to high voltage, then you can drastically reduce the powerloss in the transmission lines. (This is the reason for the use of high voltage transmission lines on the ground). Modern high voltage cables (100kV+) dont have to be air-born (as in wires suspended between towers) but can be dug into the ground. theseare somewhat heawy, bur that is only due to the external insulation.
In the case of the cables discussed here, the external insulation is not nescesserry, as the power in the cable could be cut off in case of a kite dropping out of the sky.

Plan: to go to Mars one day with a hammer.

Re:Problems

[jessemckinney]

Put enough of them up there, though, and you're going to change weather patterns.

You have got to be kidding. It would take a lot more that a couple of dozen of these to change weather patterns. I think that the asphalt that we use in roads and paving large parts of the world have a lot more influence on weather patterns. I remember reading a long time ago about the city of Los Angeles' weather patterns being really hot in comparison to surrounding areas because of all the paved areas collecting heat.

Whoa

[adrianzhong]

Well that sounds interesting but will it work on a large scale? I imagine a forest of tangly cables and turbines crashing into each other.. just like kites in a park.

Why?

[Shotgun]

this is one of the coolest ideas I've heard of.

Why the hell ain't it on the front page? It's is much more 'new for nerds' that a 0.0.X release of a kernal PC kernel that refuses to include PC features (like swsup).

Expect

[SpanishInquisition]

UFO reporting to go up in that region....
--

Re:Problems

[krlynch]

There is something that confuses me that this article doesn't address: the jet stream's location is not stable. Over the US, for instance, it can move between the Great Lakes in the North to the Florida Keys in the south, something like 1500 miles, in the course of a day or two. Is that not the case over Australia?

Bunch of crock

[Placido]

What happens when you're bringing a turbine down? It's going to pass through winds which will be blowing in a different direction. There will have to be a huge gap between each turbine to be safe and that's just not practical or cost-effective.



Pinky: What are we going to do tomorrow night Brain?

Speculations and comments

[Spamalamadingdong]

I don't see anywhere in the article how much power they expect this to generate.

You can guesstimate this. If the rotors are 50 meters in diameter and they intercept 30% of the air going through a circle equal to that diameter, that's 590 square meters (to 2 significant figures). Best power output of a standard wind turbine is about 0.295 * rho * A * v^3; if you assume a figure of 0.2 because of the generation of lift, density of 0.65 kg/m^3 and a wind speed of 25 knots, you'd expect about 160 kw out of the machine. For a 100 meter rotor you'd expect about 650 kw.

Also, what happens when the wind cuts out?

You fly the machine down as far as you can like a gyro-glider, then you power the rotors like a helicopter to land it. They said just about as much in the article. People have been flying gyro-gliders for decades; this is not a new problem and it has been solved.

The sight of a whole flight of these things plummetting to the ground before their rotors can shift from generate mode to motor mode would be rather amusing...

Because you'd never see it. Hint, both synchronous and induction generators are always ready to become motors with a slight change in phase or speed, respectively. The only thing that would change is the direction in which power flows along the cable.

Is Australia really so thirstry for electricity that they need to resort to this?

Is Australia enlightened enough that they're ready to loft airborne power stations instead of digging up black fossil crud and releasing all kinds of toxic crap, including heavy metals like mercury, just for electricity? That's the practical alternative, since the nuclear paranoia shows no signs of going away.
--
Give a man a fish and he eats for a day.

You don't necessarily need the jet stream

[Spamalamadingdong]

Jet stream winds would be a real energy bonanza (IIRC they go up to 200 MPH) but I'm not sure if an autogyro would handle winds that high (retreating blade stall seems like a problem, and noise from the advancing blade going supersonic at the tip might be an environmental issue).

Even if you weren't in the jet stream, high-altitude winds often cruise right along. Take a look at this page [unisys.com]; at the time I clicked on it, a healthy fraction of the upper-air wind speeds were 40 knots or above, and the majority appeared to be 30 knots or better. A 30 knot wind, even at half of sea-level pressure (500 millibars), still packs a whale of a lot of power.
--
Give a man a fish and he eats for a day.

Transmission isn't a problem

[Spamalamadingdong]

The cables would have to be awfully thick (hence heavy) to transmit a decent amount of power 3 miles. Then you're wasting power just keeping them up in the sky.

Not really.

1. Transmitting power 3 miles, even over lossy cables, doesn't lose much compared to the losses in transmitting power several hundred miles even over low-loss cables.
2. Keeping the machine in the sky is easy; the rotors develop lift by themselves due to their angle against the wind. You can consider this "wasted power", but it's power that comes from the wind (it's free) and you more than make up for it with the higher wind speeds at the upper altitudes (you get more power from the same size rotor than you would near the ground).

If the winds aren't high enough to keep the machine in the air and still develop excess power, you just reel it down to the ground and park it. You might use a little power to land it and then to help it take off again, but you make up for that with the power it generates when it's on station. You use external power to run the pumps and fans to get a fuel-burning powerplant started up, so I don't see any big difference between the two.

I think this is a very clever idea, and I hope that someone can find a way around the air-traffic and bird-strike issues that are bound to arise and make this practical.
--
Give a man a fish and he eats for a day.

Problems

[Anoriymous Coward]

The cables would have to be awfully thick (hence heavy) to transmit a decent amount of power 3 miles. Then you're wasting power just keeping them up in the sky.

I imagine Australians don't worry too much about stuff falling out of the sky - Skylab & Mir both missed - but I think other, more populated, countries would have a hard time implementing this. Regardless, you have yet more transmission costs once you get to the ground (although obviously this is a problem with well known solutions).

The jet stream is stable because it is uninterrupted. One wind farm isn't going to change that. Put enough of them up there, though, and you're going to change weather patterns.

It's a nice idea, but I don't see it being terribly practical.

--