How Can Efficiency be Improved in Wind Power Systems?

"How will the Betz law affect wind power's future adoption prospects?"

It will limit the maximum power derived from the wind at about 60%.

QED

"As one of the most promising alternative energy resources..."

This is an assumption that needs to be re-evaluated...

Another note, Betz' law has nothing to do with what I understand is the most common failure point for wind turbines- the reduction gearing. Even if you reach the magic number of 30% capacity availability for your wind farm, it is going to do you no good if you are replacing your reduction gears every 18 months or so...

Maybe somebody should develop a generator that doesn't require a reduction gear. Perhaps a multi-pole, low RPM generator.

Or a large volume high pressure hydraulic pump directly coupled. I'm thinking something like a giant Hagglunds or something... Run your hose to the bottom where you put it through a high efficency bent axis motor which transfers the power to a generator. No gears at all, hydraulic braking, little or no need to climb up to the top of the turbine. I envision a higher initial cost, but increased efficiency & safety and less maintenance. This is how I would design a turbine... all hydraulic.

$0.02

Actually, that is the approach being taken by some tidal energy approaches. Seems to work at low speeds. The Pelamis wave energy machine off the coast of Portugal uses hydraulics as well, to convert linear motion (up and down of the waves) to rotary motion (for the generator)...Pretty much the same capacity as a typical wind generator...I don't know much about the maintenance issues with these schemes, though.

As a rough rule of thumb for pumped liquids, KW ≈ psi x gpm ÷ 1500 (depending on efficiency). For a 10-MW turbine, psi x gpm ≈ 15,000,000. One combination might be 5000 gpm at 3000 psi; but I don't know of any hydraulic pumps that big.

Ptooey on "green arithmetic."

That reminds me; we haven't heard from joe.fordham for a while. By now he was supposed to have his turbine prototype tested....

Hey.... I checked the weather... now there is rain all over my parade!

I guess we'll just have to not shoot for a single turbine to produce 10MW, which is pretty ridiculous in the first place...

10MW is currently the biggest wind turbine in the world...

How about those numbers again with a 1MW... or maybe a 500KW... or something I could easily build in my backyard... I'll shoot for 300KW

It would be really, really nice if someone would come up with alternative systems in the 300 kW range- I work with a lot of off-grid systems in that range, and when one looks at alternatives, one has the choice of a few kW or a few MW, nothing in a "practical" range...This is true of solar, wind, ocean energy (although some of the tidal systems I have seen are sized around 700 kW)...

No worries mate! I'm sure some well meaning politician will try to "repeal" Betz law, in order to get the wind power back on track!_{Sorry, just couldn't resist!}

I'm envisioning a change of wind directions that progressively twist a pair of hydraulic hoses into a Maypole...

Maybe the maintenance issues could be less, but what about leaks?

Rotary union... very common, no hose twisting.

It you don't want a hydraulic system to leak, don't use NPT of any kind. (I hate NPT) I'm thinking that you probably get less leakage from a properly designed hydraulic system than you would a gear drive train with all those rod seals holding the lube oil in. I know that the #1 most costly aspect of running a wind farm (other than the initial cost or parts/installation wiring etc) is the maintenence... Those things need constant attention or they become unsafe in a hurry. New grease, regular oil changes (I saw a special on the TV about the difficulties of maintenence... and they spilled a lot of lube oil every time they changed filters or did maintenance) plus the need to send people up the shaft to the top.... If you could change the oil/filters at ground level with a service truck I think the whole operation would be much more efficient.

Who wants to lug a bunch of parts/tools/oil up the shaft... what do you do when you drop that end wrench down to the ground??

Now that I found some folks interested in the wind power theory and 'mechanics' I think it's time to ask my dumb question about Betz limit. OK you can't go over this limit meaning you can't collect more than some 59% of it. I say it is bull. Why? Well here's my answer. Where the darn rest 41% goes? Is it not gone with the wind that flows in the back of the wind turbine that has the same mass as the one going in, just lower speed so lower energy? Well what's stopping us to put another suitable turbine there to collect the 59% of the 41% left and then the same again and so on? Maby I'm getting something wrong being off-my-field so waiting any corrections on flaws in my thinking (not in general please, just on this topic)

"Well what's stopping us to put another suitable turbine there to collect the 59%..."

Turbulence.

Sure. I was talking about the Betz theoretical limit. Turbulance and other problems won't even let you get close. Any thoughts on limit? i.e. turbines in series are subject to it? S.M.

The turbulence of concern is caused by the wake of the blades. It may be possible, wee you to totally enclose the blades and insert stationary blades between stages (similar to how a steam turbine is built) that you might squeak a little more power out of them, but I doubt this scheme would be economically feasible on a grand scale. The latest discussions in the industry suggest moving the turbines even further apart, which increases the amount of land required for a given capacity, and is likely to be a non-starter, expcept maybe for a few places in the world where the population density is too low to create much of a demand anyway...Then you have to worry about buying up rights of way for your transmission lines, since you can't run them across public lands without upsetting some environmental group or indigenous tribe trying to protect their sacred lands...

OK since I see you stick to real world deficiencies I will overcome this and add bit theoretical views on this for others also to discuss. For one Betz's law is based in the erroneous assumption that the flow into and out of the axial rotor is axial. Now if anyone can explain to me how on earth flow can be axial since a:you have a standard input diameter and air speed in input and b:you have the same diameter and less speed in output. (This speed difference is what we exploit to steal power from the wind) So either matter dissapears or Betz law for real world axial turbines (whose flow starts cylindrical and ends widening conical in the output) don't apply much. For all I know limit could go eitherway -up or down- and you don't expect me to calculate how. Maby some reader can shed some light here.

This would be a very good job for some professor at a university. Perhaps you could approach someone that teaches fluid dynamics.

However, don't do this lightly. You have better done your home work before you do or they will politely throw you out the door.

I would start with framing my claim against Bet's Law and draft as much of a proof as I can and the supporting theory.

Be very detailed in your draft if you expect anyone to take you seriously. You are trying to disprove a theory (actually a Law) that has existed for nearly a 100 years and has been supported by modern computer analysis as well as past peer review.

Not trying to disproove the law. My point is that it is possibly not realistically applicable as absolutely as we usally take as granted. This is not an uncommon error in applications. Now on something being accepted for 100 years shouln't say much to an engineer if he feels not totally convinced. And I'm not totally convinced about it. Why? For example at the same assumptions it should be also applicable to hydro-turbines which clearly overcome it. S.M.

Well, if it is your claim that it does not work, you need to back that up. If you have enough evidence that it does not apply, then the route I suggested is an excellent mechanism.

If, on the other hand, you are not clear with understanding the nuts and bolts that support the law, then that's another matter. Perhaps that same professor could help you enroll in the right course. ;-)

Tearing down a century long law is no trivial matter and it has been done in the past, but be prepared to have an immutable proof if you expect to be taken seriously.

I'm not apllying a pat to have to do that. I'm just giving out some thoughts on this topic. Actually first time i was involved was when challenged by rhkramer's first post. Even though of course I'm not the OP. So. Do you think what I've posted is bull? I'm not talking prepetual motion here. I'm talking possible bad theory application in practice. And demonstrated exactly where I see the flaw. It's 1.0.1 . You could argue of course the flow I see has no significance, or that it makes things worse. Possibly. We can discuss about that. But I f you can't see the flaw at all, there seems to be nothing to discuss, is it? Friendly. S.M.

An because I could be missunderstood again, I clarify: Bad application of a PERFECTLY good theoretical law. S.M.

You wrote, "Do you think what I've posted is bull?"

I am honestly not qualified to answer that. It is outside my field of expertise. However, I do know that if someone makes a claim (such as SimpleMind did in post #10) it is their responsibility to back up that claim.

Do you think matters like that should be discussed in closed chambers and us mortals not mess with them, just interprete manuals? Anyway topic is not in my field of expertise either. I thought you could tell I am S.M.

No, I don't think these matters should be discussed behind closed doors. However, if one does not have an informed opinion on a subject, it is probably a good idea not to simply call something BS without some arrows in their quiver to back up the claim.

That was my point.

Also, as long as someone posts anonymously, I have no way to to say who they are with certainty, so I do not rush to judgement as to their identity.

A key different assumption might be that air is compressible, whereas liquids are generally not (or not very).

Hi Tornado. One of the (unfulfilled) assumptions for Betz law to fit as-is is that the fluid is incompressible. So according to that it should apply more accurately in liquids than in gases. My (uneducated) view is that the opposite aplies since hydros have gone above it. Not having axial flow of course. Is the 'axial' configuratin the limiting factor? S.M.

OK maby everybody would rush to answer if I asked a question about 'busbar calculations' or something as lame. Thanks anyway. S.M.

Good luck beating Betzs Law - first I suggest you study it to understand it. He is stating that above the 59% limit the air begins to back up in front of the turbine causing it to slow and eventually slow greatly.

There are about a thousand small turbine manufacturers out there that can't (or don't want to) understand Betzs Law either. It would totally screw up their business.

Not going to be defeated in the engineering world we know today.

Are you saying there are "about a thousand small turbine manufacturers" who are getting better than 59% efficiency out of their turbines?

...or claiming better than 59% efficiency?

...or hoping for it?

Claiming it - look at the power curves for many small turbines.

Hi thanks you took the time to reply. If you read my posts from the beginning, you'll undestand I have enough sense not to define the law itself. Also have nothing to gain doing it. I don't manufacture or sell turbines. But I do hate seing the dumb simplifications we're doing when we try to inteprete it. Hell ther's nothing axial in the air flow of an axial turbine if you look at it from less than a mile away. Air is not incompressible as we must take as granted for law to apply as-is. Also "No account is taken of angular momentum imparted to either the rotor or the air flow behind the rotor" (Wiki). Do you still think this is fineprint? S.M.

I think that point in the Wiki was added by a 'wisher' - some green type.