Danish Wind Industry Assn: "Price per Square Metre Rotor Area matters"

[phantom power]

This is from a page titled: Pitfalls in Wind Energy Cost Analysis
http://www.windpower.org/en/tour/econ/pitfalls.htm

The price per kW Rated Power is a Very Poor Guide to Investment in Wind Power - the Price per Square Metre Rotor Area matters

Many researchers who are interested in the decline in costs of wind power wish to study the decline in the price of wind turbines. They therefore ask for an apparently simple statistic: The price of a wind turbine per kW installed power. That figure is usually difficult to get hold of, and a very poor guide to cost developments for several reasons.
It is very difficult to give a single figure for price per kW installed power, because the price of a turbine varies much more with its rotor diameter than with the rated power of its generator. The reason is that annual production depends much more on the rotor diameter than the generator size. Studies which compare the average price per kW installed power for different technologies are usually misleading, if they include wind power.


Systematic kW Nonsense - an Example

As an example of why it is misleading to use the price per kW rated power for a wind turbine, compare the annual energy production from two machines from the same manufacturer, both mounted on a 50 m tower. (The first one is a high wind machine, the second one a universal machine). You can use the Wind Turbine Power Calculator to verify the results:

1. Vestas V39, a 600 kW turbine with a 39 m rotor diameter
2. Vestas V47, a 660 kW turbine with a 47 m rotor diameter

The result is that annual energy production from the second machine is 45.2% higher than the first machine, despite the fact that the generator is only 10% larger. If you compare the two rotor areas, however, you may observe that the rotor area of the second machine is exactly 45.2% larger than the first machine.
So, if we assume that the price for the second machine is 33% higher than for the first machine you would get very different results, if you compare

1. The price per kW rated power has increased 21%
2. The price per sq m rotor area has decreased 8.4%
3. The price per kWh energy has decreased 8.4%

New wind turbines are increasingly being built with pitch control rather than stall control. This means that the generator size can be varied more freely in relation to the rotor size. In general, there is a tendency to use larger rotor areas for a given generator size. That means that you will get a completely wrong (overestimated) price development when you compare the price per kW installed power for old turbines with new turbines. The relevant price measure is the price per square metre swept rotor area, not the price per kW installed (rated) power.

[Bread and Circus]

1. Aweosome post, and the physics of wind turbines has me got me thinking...

If you look at most wind turbines you see a huge propeller on a pole. At any given moment the propeller covers a very small percentage of area involved in it's entire sweep. Just by looks it can't be much more than 5% of surface area. Per revolution, the blades are only coming to contact with a small % of wind that actually passes by the circular area it sweeps. Most energy is missed entirely. This makes me wonder why the propellers aren't built in a way to capture more of the available wind in a sweep. I imagine it has to do with the physics of how a propeller system works. Also, anything that "caught too much wind" would probably create a lot of strain on the structure itself, and they are designed this way to keep it from breaking or "blowing over" - so to speak. Thus, in my mind, the current design of wind turbine are probably massively inefficient and a whole new design approach is needed.

All of this lead me to revisiting this website:

http://www.magturbine.com/



The claims of this website are astounding and may very well be fairy tale. However, what's interesting to me is the monstrosity that is supposedly going to be their version of a wind turbine. The key thing about it is that a freeze frame snapshot of it's cross-sectional area shows that essentially half of the wind passing by it will be hitting the power grabbing "propeller" part of the turbine (the other half moves against the grain). It will endure massive cross sectional force and would therefore have the potential to haul in a shitload of energy. If it becomes real and is not just fantasy, it will be made possible by two things (I think).

1.) the main axis is vertical, not horizontal, and therefore it can handle more weight by being balanced radially around it's axis. This is a fundamentally stronger and more stable stucture because the shaft and the generator are larger and integrated.
2.) the design revolves around maglev, so the added weight doesn't necessarily add exorbitant friction. This alone will increase effeciency. However, the maglev's main benefit will be floating the massive drum of wind foils in a near frictionless environment.

To me, the structure looks like the rotary drum of a fan blower that dries wet floors after shampooings or whatnot. However, it seems like it's the size of a building and placed on it's end. Maybe they should put one in Chicago on an empty lot (after all, it is the Windy City - and that's no joke if you've ever been there, the city acts like a wind funnel). It would be quite a tourist attraction and would actually slow wind speeds if it extracted enough energy.

I would really like to see if this thing becomes real and follow it's average yearly power output. I also wonder if these could be built on platforms offshore. I live in Michigan and our best wind is over the eastern half of Lake Michigan.

[phantom power]

2. Two things about the Denmark writeup interested me.

1) their point that (for turbines) the kilowatt-hours per dollar is most correlated with blade-swept area per dollar. Nice.

2) that the important measure for comparing any two turbines, and also for comparing them properly with other energy sources, is kilowatt-hours per dollar. Or, more generally: units of energy delivered per unit of money.

Number 2 is the most important point. It shows how to talk sensibly about differing forms of energy production. It is why you will see people discussing units like "exajoules per billion dollars."

Regarding that enormous vertical axis turbine, you should remember that the other half of the turbine is being pushed against the rotation, by the wind. So, it's not as huge a win over horizontal axis turbines as it looks at first. However, the vertical axis turbines can be mounted with lower-friction systems, which is nice. And they don't require directional aiming.

A turbine that huge seems like it is past the point of diminishing returns on size. Far past. But maybe I'm wrong. At some point, that kind of size starts causing it's own problems, in terms of engineering, safety, etc.

[Bread and Circus]

4. /agree

[skids]

3. VAWTs are a good design...

...this huge one smells fishy to me. Projects of that scale generally just don't get built in the end, even if their design is viable.

VAWTs used to be considered a non-starter, but since then some clever people and their wind tunnels have shown they can be made as efficient as HAWTs, (your normal windmills.)

But as far as the blade "only touching part of the air" on a HAWT, that's actually not the case once the turbine gets up to speed. After each blade is a wake, where there is turbulence and no power to collect. If a blade were there it just wouldn't get much power.

In order to collect power from wind you have to let some of it through -- otherwise you build up a big air cushion in front of you and most of the air just bounces gently around you instead of running headlong into you. That's why you'll never see wind turbine approach 100% of the "theoretical" (wind speed cubed) power -- because if you use a more detailed theory you see you have to have somewhere to put the air molecules you stop, and since you can't pack them very densely your best best is to let them keep some of their speed and pass on through.

[Bread and Circus]

5. I think the VAWT in the picture is possibly a "neo aerodynamic" design of sorts with different...

physics than some of the other VAWT's I've read about.

check out this dude's work:

http://video.google.com/videoplay?docid=3851290548319907747&q=neo-AeroDynamic&total=5&start=0&num=10&so=0&type=search&plindex=1

This is small scale stuff, but if you look at his turbine's, they are alot like the maglev one in the picture.

[NNadir]

8. Would there be something wrong with writing out the words "vertical axis?"

I'm sure that there will be a brazillion of these wonderful wind plants, which will spring up on an exajoule scale, and we'll soon all know what "VA" means as giant maglev windmills solve all of our energy problems.

But for the time being, I think it would be OK to at least once use the words being abbreviated.

[losthills]

6. screw capitalism

Cents per whatever doesn't matter.

Saving our planet matters...

[NNadir]

7. Oh geeze...

Is this an energy comment?

I suspect you couldn't care less about energy.

Economics matters, always will, always did, even in "People's Republics."