Wind turbine on a boat efficient?

[kokophysics]

I recently read this http://www.earthtechling.com/2011/0...ng+(EarthTechling)&utm_content=Google+Reader" and it's really bugging me.

They claim that by putting wind turbines on the prow of the ship they'll harvest energy from the wind but also, that the air resistance will decrease and so the fuel consumption will be lowered.

No doubt that the air hitting the boat will be less strong (because the wind turbines "trap" its energy) but what about the air hitting the windturbines? Aren't they just claiming this?:

[PLAIN]http://input-image.info/physics-troll/1285635805554.jpg

My assumption had always been "if you put a wind turbine on a moving vehicle, the energy delivered by the wind turbine will always be less than the extra energy you need to move the vehicle bacause of the drag produced by the wind turbine". Am I wrong?

All this leaving aside the fact that the air resistance is not that important in these vehicles I guess. It's the water resistance which matters, hence, the shape of the boat under and above the sea.

 

[Naty1]

Turbosails have been under study for some time...here is a Wikipedia article:

http://en.wikipedia.org/wiki/Turbosail

"that the air resistance will decrease and so the fuel consumption will be lowered."

I'm pretty sure that's an inaccurate description: when I believe they mean to say is that the wind turbine provides a bit of a power boost (analogous to a sail) to move the boat forward. Obviously a small contraption on top of a boat isn't going to reduce the air resistance of the superstructure below.

I believe there is one large privately owned megayacht that uses them for "sail power".

I'm guessing that like so many "green energy" ideas, the economics is not yet favorable. If these were efficient and economical, they'd be on every vessel imaginable. So government subsidies MAY make this practical for the ship operator...but likely not for taxpayers who subsidize them.

 

[kokophysics]

Hi Naty1! Thanks for your early reply.

I have definitely heard about those sails and also have read about cars moving faster than the wind... using the wind as their only source of energy. That's pretty impressive and I have to admit aerodynamics are complicated but I'm not an expert in that field. I do know a bit about it though, as I've studied aerodynamics on a wind turbine course.

Anyway, the article is quite clear and I quote literally:

"The turbines will be located on 4 meter high masts on the front of the ship and not only produce 23,000 kWh per year, but also reduce air resistance. The electricity will be used, among other things, to light up the car deck. The reduction in air resistance will lead to reduced fuel consumption of about 80-90 tons a year."​

I don't really know about VAWT (vertical-axis wind turbine) but I do know that the axial forces on a HAWT (horizontal-axis wind turbine) are much bigger than those moving the blades. One just have to look at a wind turbine blade to notice how do they bend. However, the WT's on this ship are HAWT and I don't really know the aerodynamics involved on this type of turbines.

I have to clarify though, that I'm not saying they're wrong. I understand that there's a team of much more experienced engineers than me behind that project. I'm just looking for an explanantion.

 

[russ_watters]

koko, in general you are correct that putting a wind turbine on a moving vehicle generally increases wind resistance. However, there are potentialy limited cases where it may reduce it. The ferry has a big flat front to its superstructure that is about as bad as you can get, while the turbines are smaller and may have the effect of directing air around the superstructure. I'm skeptical that it would be worth the money to put them there, but this sort of thing is very tough to predict without a wind tunnel.

We talk about this all the time when it comes to wind turbines on cars - it comes up a couple of times a month. While it should be obvious to most that a wind turbine on a car hurts instead of helping, the potentially surprising thing is that when it comes to airflow through the engine compartment, adding a blockage helps too. One company is putting moveable shutters on the front grille to control airflow to balance cooling against wind resistance.

Also, with that troll physics pic - there's nothing trollish about that. It works just fine, it's just that when you're slipstreaming in a car, the car in front also has an engine of its own. Take it another way: trucks sometimes hang a structure on the back to make them more aerodynamic.

 

[kokophysics]

Thanks for the reply russ.

I see your point about the massive flat front of the boat. I thought the same but still doesn't make 100% sense to me. As you said, i would need to see it in a wind tunnel. Anyway, aerodynamics never make sense to me ever since I first learn the Venturi effect. It's just faith! ;)

Now seriously, I like your points, and I'd love to read more about those car air intakes you're talking about.

Just one thing about the cartoon. It is totally troll I think. Whereas in the first drawing you're taking advantage of the other's car engine, in the second one is your engine which is wasting energy in deflecting the air around the car. And note that both cars are equally streamlined. But I don't really want to spend time on the cartoon really. It's all about the ferry.

 

[Twigsoffury]

why can't you take a turbine that looks like this...

And make it like this.

[PLAIN]http://www.rclambert.com/supra/blower/blower%20squirrel%20cage.JPG


works for homes,industrial machines,window air conditioners, central HVAC, tower exhaust vents and well a host of other things where a regular "fan" just doesn't push the amount of air you need.

and i'd wager to say, if it can push more air with less resistance and turbulence, then it can probably "Catch" more air with less turbulence and resistance.

 

[russ_watters]

...and I'd love to read more about those car air intakes you're talking about.

Using various sensors that monitor speed, temperature and wind, the on-board computer will automatically close these shutters which, once closed, are said to improve fuel economy by as much as 100ml per 100km. It doesn’t sound like much, because it isn’t much. But still, this technology is something all manufacturers should be thinking about; adjustable aerodynamics.

http://www.caradvice.com.au/77863/chevrolet-cruze-eco-fuel-saving-adjustable-shutter-grille/

 

[kokophysics]

Very interesting. Thanks russ!

 

[russ_watters]

FYI, at commercial rates around where I live, those turbines produce about $2700 worth of power a year. So hopefully they didn't cost more than $15,000 or so.