Wind Turbine Blades 2

[msquared48]

Anyone experience in available wind turbine blade shapes out there? I'm not.

I saw some being transported on the freeway this afternoon, and the "sail area", if you will, of the blade appeared to be much less than what I commonly have seen. I am wondering if these are intended for higher average wind areas? Is there a variation in the blade sizes as well as pitch?

Just being inquisitive...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[racookpe1978]

Yes - The wing design for those things is just about as easy and simple as designing a 737 or 767 wing. (No flaps and no fuel tanks does simply the actual fabrication somewhat.)

The way one wind-turbine engineer described it to me was: Decide where (in general) the site is going to be and get the wind data at as many points as possible at as many elevations as possible (heights above ground.) (Especially important are summer and spring storms, general (average) winds and peak winds, times of slow or no winds, and "average" winter storms. Apparently, storm winds (heavier than normal) vary by the season and region.)

Subsidies are critical - local government money and availability of land will eliminate many sites that are actually more productive than what is finally chosen. In general, no tax or billing subsidies = no reason to build.

With this data, they evaluate whether any should be built, and where (what location and what height above ground.)

From that, they determine what power can be generated under ideal conditions (assumed ideal wind speeds and direction.) For one wind farm (group of turbines) they always try to use only one make and model to make repair easier and cheaper and to make installation practical on a repeated basis.

It's only now, after they can predict ("sell" to the customer/state/polticians) what could be installed can they decide what blades and style will be best.

Longer blades are almost always more efficient - that's why you never seen newer designs getting smaller. Taller towers are almost always more efficient. The fewer the blades, the less tip-to-tip and blade-blade interferences that cause fatigue failure. A few years ago, they even tried single-blade counter weight balanced design but now almost all are 3-bladed styles.

Low winds that are very constant require fatter, broader blades for best efficiency. Sort of like the older piston plane blades of WWII. Or a helicopter blade compared to a high-speed turboprop blade. High wind speed requires a thinner blade with greater "twist" from tip to root.

Highly variable winds - the most common condition - force compromises.

Power delivered goes up by the cube of the wind speed -> so a thin long blade than is inefficient at low wind speeds can often make up for that losses by being able to produce more power at the higher wind speeds that occur less often. If the fabricator can make a variable pitch blade, the base unit becomes more flexible (literally) and generate power under more conditions, but more complex, expensive, and likely to be broken.

(Theoretically - the blasted things still only have a 18-23% power delivery ratio. You have to build 5 to get the average nameplate power of one. And the whole wind farm is frequently unable to produce any power at all because they must be shut down when ever the wind exceeds their rated speed anyway. So just when they could deliver more powewr, you lose the whole farm and have to run your backup reserve power.)

 

[rb1957]

personally, i look at those blades and think "that's the optimum shape ?"

but what do i know ...

 

[msquared48]

Very interesting. Thanks. I initially thought the useage was for something different, but I couldn't imagine what. Good to know that I am not crazy... yet.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[dhengr]

Mike:
You’re not TOO crazy... yet.
I heard they were building a reallly big helicopter out there, to lift and move whole buildings.