Flying Wind Turbines

[Mike Holmes]

Don't they already have devices that can do that from the heat you give off from your body and/or from kinetics. Like the wristwatches that charge from the swinging of your arms when you walk? http://www.gizmag.com/go/8237/

Why do we have to complicate things... the backup to the wristwatch is winding it. How large would a windup mechanism be for a cell-phone? Army field phones always had, in addition to batteries to run them while speaking, a hand-crank for generatting a ring signal on the other end... I can tell you from practical experience that you had best not be holding on to the ends of the wire connecting the phones when somebody cranks on their end.

What's easier, fly a kite, or crank a machine? Heck, put it on your bike, and with slight extra drag, you'll power the thing just riding around.

So... sure, kite might work as proof of concept for the larger concept. But, again, it already seems reasonable overall. The questions are economic ones (which include the cost of restricted airspace and potential accidents).


If I'm not mistaken, the majority of the mass of one of these devices is going to be in the cable itself, no? If it's 10K long?

Mike

[OneWayTraffic]

The cable will certainly be a big part of the weight.

Kevlar has 3GPa and 1.44 grams per cc.

At 10MW for the turbine and a windspeed of 30m/s (guesstimated by going backwards from the energy density measurements on the site.) You'd need a force of 300KN just for turbine drag. This is minimum.

A Kelvar tether would need to be at least 0.001 sqm to withstand this. Tripling for a fudge factor and we have 0.003*10000*1.44=43 tons.

Of course this is all back of the envelope stuff.

[OneWayTraffic]

I'm not sure that the idea will work out myself, but one could fund all of the fringe wind ideas out there with less money than the US spends on oil every hour.

That may be so. But the oil gets you some where.

For how much longer?

[TallDave]

Till the sun stops shining and we can't grow stuff anymore.

[OneWayTraffic]

Till the sun stops shining and we can't grow stuff anymore.

I guess you're talking about biofuel? Some biofuel has promise, especially algae, but most of the current biofuels are pure boondoggle.

I'm a big fan of bioreactor algae though. Now to get the costs down and ramp production up. Just a matter of engineering surely?



The reason I think that high energy wind is worth looking into is that it's the highest intensity natural source of energy on the planet, with the possible exception of geothermal. Solar isn't going to go above 1.5KW per square meter no matter what you do. And ways of extracting it are lower efficiency than wind.

If Polywell works and can be brought out in the next 10years then this is all academic of course. But if it can't we need to have our fingers in as many pies as possible.

[Helius]

Till the sun stops shining and we can't grow stuff anymore.

I guess you're talking about biofuel? Some biofuel has promise, especially algae, but most of the current biofuels are pure boondoggle.

I'm a big fan of bioreactor algae though. Now to get the costs down and ramp production up. Just a matter of engineering surely?



The reason I think that high energy wind is worth looking into is that it's the highest intensity natural source of energy on the planet, with the possible exception of geothermal. Solar isn't going to go above 1.5KW per square meter no matter what you do. And ways of extracting it are lower efficiency than wind.

If Polywell works and can be brought out in the next 10years then this is all academic of course. But if it can't we need to have our fingers in as many pies as possible.

I gotta agree with Dr. Carlson; Desert Solar, Geothermal, FRCs have the highest marginal expected value, and are well deserving of a share of our next investment dollar to be put toward "alternate" sources of energy.
Dr. Carlson and I disagree (at least outwardly) about polywell getting a share too. I really suspect.... ah, nevermind.

I disagree with your view of Desert Solar, OneWayTraffic, we could develop methods that would use Molten salt (but not NaCl, usng lower melt point salts), to store "solar power" for night time use. We have a lot of "square meters" out there, that could be used, and transported with a DC power transport structure to many large cities....

Power from "electric kites" would not be as easy to store.

[TallDave]

but most of the current biofuels are pure boondoggle.

This was true when gas was <$2 gal, but at current prices even the least efficient conversions (like corn) make economic sense. Cellulosic ethanol is a no-brainer if they can ramp up production; there are several large facilities being built even as we speak.

The problem isn't so much economics as regulation at this point. Once most cars are mandated flexfuel-capable, ethanol will be able to compete for market share with that ever-scarcer petroleum.

[OneWayTraffic]

but most of the current biofuels are pure boondoggle.

This was true when gas was <$2 gal, but at current prices even the least efficient conversions (like corn) make economic sense. Cellulosic ethanol is a no-brainer if they can ramp up production; there are several large facilities being built even as we speak.

The problem isn't so much economics as regulation at this point. Once most cars are mandated flexfuel-capable, ethanol will be able to compete for market share with that ever-scarcer petroleum.

Corn? Come on. I'm not talking about current price; I'm talking about the ability to grow something that can replace fossil fuel basically forever. Corn fails this due to the high inputs of fertilisers and water required and it's low EROEI. Even cellulosic ethanol is dodgy IMO unless it's grown in a closed system. Our current farming methods are not sustainable as it is: we're losing topsoil and soil fertility and most fertilisers are natural gas based. It's just not going to cut it for the next millenia.

The basic problem that all biofuels must answer is: What's being removed from the field in which it's grown, and how will that be replaced?

Algae grown in bioreactors can pass that question easily.

[OneWayTraffic]

Till the sun stops shining and we can't grow stuff anymore.

I guess you're talking about biofuel? Some biofuel has promise, especially algae, but most of the current biofuels are pure boondoggle.

I'm a big fan of bioreactor algae though. Now to get the costs down and ramp production up. Just a matter of engineering surely?



The reason I think that high energy wind is worth looking into is that it's the highest intensity natural source of energy on the planet, with the possible exception of geothermal. Solar isn't going to go above 1.5KW per square meter no matter what you do. And ways of extracting it are lower efficiency than wind.

If Polywell works and can be brought out in the next 10years then this is all academic of course. But if it can't we need to have our fingers in as many pies as possible.

I gotta agree with Dr. Carlson; Desert Solar, Geothermal, FRCs have the highest marginal expected value, and are well deserving of a share of our next investment dollar to be put toward "alternate" sources of energy.
Dr. Carlson and I disagree (at least outwardly) about polywell getting a share too. I really suspect.... ah, nevermind.

I disagree with your view of Desert Solar, OneWayTraffic, we could develop methods that would use Molten salt (but not NaCl, usng lower melt point salts), to store "solar power" for night time use. We have a lot of "square meters" out there, that could be used, and transported with a DC power transport structure to many large cities....

Power from "electric kites" would not be as easy to store.

Maybe I didn't make myself clear. Desert solar is just fine for those countries that can do it. But not all can. In my home country of NZ, we'd be better off putting our money into high risk high altitude wind than desert solar without the deserts.

I know that modern technology can provide energy through the night and it's more predictable than wind. All good. But solar insolation is 1.5KW per sq m in space. It's an average of 200-400 W/sqm on the earth's surface and that's it. That's the hard limit of what you can get minus inefficiencies of 70-99.5% in extraction*. Wind can go an order of magnitude above this and methods of extraction will be more efficient (if they work.)

Solar thermal electricity is roughly 30% efficient.
PV cells 15-40% efficient (40% in labs only.)
Biological methods 0.5%-> efficient (though the output is liquid fuel.)


That efficiency of biofuel is worth thinking about. Take the biomass of switchgrass roughly 10 tons per acre. This gives you 1000 gallons of ethanol.

I like metrics so that's about 200GJ per hectare. Or 20 TJ per square km per year.

Now solar insolation is in the region of 200 watts per square meter over most farmland. (Obviously varies)

200*1,000,000*3600*24*365=6,300TJ per sq Km per year.

Efficiency=0.3%

Now I'm sure that there has to be a better way of getting liquid fuels.

[esotERIC D]

Ah yes, algae biodiesel, in my opinion the only biofuel worth seriously pursuing. If you havent already seen this it is a worthwhile analysis of algae biodiesel.

http://www.unh.edu/p2/biodiesel/article_alge.html

-Eric

[OneWayTraffic]

Ah yes, algae biodiesel, in my opinion the only biofuel worth seriously pursuing. If you havent already seen this it is a worthwhile analysis of algae biodiesel.

http://www.unh.edu/p2/biodiesel/article_alge.html

-Eric

And note that the yields given are for open ponds, which are largely discredited now in favor of closed systems.