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Ultimate Reliability: Wind Turbines
12/26/2012

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BLADEcontrol technology from Bosch Rexroth analyzes the natural oscillations of the wind turbine blade. The frequencies of any blade are a unique pattern, like a fingerprint, in the range up to approximately 350Hz.
BLADEcontrol technology from Bosch Rexroth analyzes the natural oscillations of the wind turbine blade. The frequencies of any blade are a unique pattern, like a fingerprint, in the range up to approximately 350Hz.

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Cabe Atwell
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Rated life?
Cabe Atwell   12/26/2012 6:01:32 PM
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If 20 years is the current focus, what was the product lifetime rating in the past? I suspect much lower.

With the Siemens 6MW turbine, the current world's largest (dec 2012), I would want a 20 year life at the very least. The 8MW Vestas, set for 2015, will be even larger. I say bump the life to 30 years, then we'll have something.

C

Jerry dycus
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Re: Rated life?
Jerry dycus   12/27/2012 9:53:39 AM
 

   A few  points.  In the future there will be no gearboxes cutting that expensive part and problem.   They will be replaced by larger diameter  generators with many more poles instead.  GE already is doing it on their new units.

     You can't look at a composite part and know if it's ok as delaminations and other problems have little to no visual effect until near fairlure.  But a simple microphone can in real time at low cost. To actually find the problem Xray, Ultrasound or other tech is needed though tapping with a hammer can by someone who knows how.

   The biggest problem are these huge WT's are really investment vehicles generating loans, commissions,  units profits with generating power as a nessasary byproduct. 

    The real future in WT's are  small home, build size units that make/save retail electric cost instead of wholesale electricity thus 2-3x's more cost effective. 

    WT's scale well into the .5kw size units though studying it a 2kw/16' dia size for most homes can supply their needs in many places.

    Another is smaller local wind farms close to the demand as transmission lines for lrager, distant ones can cost as much as the wind farm does!!

They have always said 20 yr life but that has not proven anywhere near tue mostly because they keep increasing size thus don't have time to optimise designs before they are an 'obsolete size'.

  Yet many small units from the 30's are still going strong!!  A decent WT should have a 30-50 yr life simply to cut maintaince costs.

'

 

Thinking_J
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Re: Rated life .. time will tell
Thinking_J   12/27/2012 5:01:48 PM
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good observations..

On the controls for 2.5 Mw units I designed..

- rate life isn't the primary metric... it's return on investment (ROI). Life span has an impact, but so long as it is not different that expected, it remains just one of several variables impacting ROI.

- already (6 years ago) designed in processing power for monitoring the vibration with active pitch control for minimizing wear on the minimal transmission involved. (4 generators around one large gear - balanced torque on frame, made easier generator swap out inside nacelle - no crane or helicopters involved). Amazing to "listen" to difference in the system with high freq adjustments being made vs without any active control. The basic controls already have the maintenance monitoring , data logging, high level access across networks, etc. to minimize costs.

- Pitch is constantly changing based on location of blade in a single rotation. Why? because on really large diam systems, the speed of wind is significantly different at the top of the arc vs the bottom of the arc.

- smaller systems? Great, but they will always have some significant disadvantages to big systems. a- closer to the ground (slower wind speeds and near birds of prey food source) b- higher blade speeds (noise/bird strike) c- distributed maintenance over larger area (higher maintenance per watt) d- majority of population does not have a reasonable location for installation (limited urban options)  e- most people will not want to take responsibility for their own power source (most don't want to be responsible for their own plumbing!) .

In many locations it can make sense... but for majority of population in US and Europe, it isn't an option. Centralized power (and all of it's weaknesses) is likely to be with us for a long while. And yes, this will waste power in distribution and be a major cost in maintenance of transmission lines.

I wish it wasn't so.,,. (in general, I prefer de-centralized systems)

Regardless, the real changes in this industry will come when all the energy sources operation on a "level" playing field, not because of 50 year product lives. It is amazing to see the gov incentives still being paid out to oil/gas .. while many alternative energy incentives have dried up.

 

 

 

Jerry dycus
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Re: Rated life .. time will tell
Jerry dycus   12/27/2012 5:27:55 PM
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 Sorry but gear trains have already jumped the shark as the most expensive part of a WT over it's life. 

  While smaller unit have some slight didadvatages over large units, getting 2-3x's the $ of it's output easily makes up for them.

Plus one instead of paying an electric bill can get a check from the utility instead. For the consumer/customer, which is the better deal?

jmiller
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Re: Rated life .. time will tell
jmiller   12/31/2012 11:45:09 AM
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My understanding is that the utility company will not pay you any money.  they will give you credit for future energy usage.  But they will not actually send you a check.  Therefore, you can only save what you would spend for each month.  You can't actually make any money with an at home windmill.  I don't know if this is still factual but it came from a reliable source at one time.

Jerry dycus
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Re: Rated life .. time will tell
Jerry dycus   1/3/2013 9:15:12 PM
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Whether you can get a check depends on which state you are in for home, building size units.

 

small WT's in the 2-5kw sizes are very cost effective because they can cost less and easily cover the energy needed by an eff home on many cases. A 1500sq' home can easily run on a 2kw WT in average US conditions.

 

Hydrualics are a joke in this as they are not eff at all mostly under 50% eff, killing them vs 95% eff gears or 100% eff direct drive with no gearing. And a 2Mw radiator to get rid of the waste heat farther adds to the cost. 

 

 

Cabe Atwell
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Re: Rated life?
Cabe Atwell   1/3/2013 5:43:57 PM
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A small but large network of turbines is the future? That sounds like a good idea. The question now, can older/smaller/OEM turnbine be upgraded to modern gearless standards? If not, that could be a niche market for expansion.

C

rainmaking
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Re: Rated life?
rainmaking   1/3/2013 6:34:54 PM
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It's a really interesting idea Cabe. The physical size/diameter of the direct drive generators is typically much larger, but perhaps you keep only the tower and rotor (both very expensive) and replace the entire nacelle. It might work out that the tower fatigue life is close to the 20 year turbine design life even though the ultimate strength is the overriding design factor. It's been a few years since I took a tower design class so I'm not certain about that. Either way I'm sure people would be willing to invest in an upgrade (risking a tower fatigue failure) so long as there was a good value proposition. This assuming in 10-15 years we don't have towers collapsing frequently due to fatigue failures.

jmiller
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Re: Rated life?
jmiller   12/31/2012 11:42:21 AM
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I read an article about some different people who put up private windmills on their property for their own personal use and even with the cost savings on energy it was going to take nearly 20 years to pay it off.  I think until energy prices go way up it takes a long life for some of these green ideas to pay off.

William K.
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Gearbox life versus the alternative life
William K.   12/27/2012 10:28:23 PM
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There does exist an alternative for putting the gearbox and the generator up in the nacele where they are very hard to get to and expensive to service. The solution is to have the turbine directly driving a large variable displacement hydraulic pump, and then use a variable displacement hydraulic motor to turn the generator down on the ground. This wold avoid using a gearbox and also allow generation of power at lower wind speeds, with the added advantage of being able to run the generator at whatever speed was desired. The generator and associated support and control equipment would be at ground level, making them cheaper to install, maintain, and repair, and the power would already be at ground level, making the grid connectionssimpler. Moving the weight down to the ground would reduce the required strength for the base and support, so that would add to the savings. One more potential advantage is that hydraulics does offer a way to store energy in an accumulator, which could potentially assist in a method of longer term energy storage.  

What I don't understand is why this approach has not been used very much so far.

ttemple
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Re: Gearbox life versus the alternative life
ttemple   12/28/2012 10:55:48 AM
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I agree with Jerry on this one.  The answer is low speed, high torque generators that don't need a gearbox at all.

William K.
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Re: Gearbox life versus the alternative life
William K.   12/28/2012 4:03:32 PM
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The challenge with low speed alternators and generators is that they need a whole lot of poles to be "low speed". Each time the number of poles doubles the speed iscut in half, and to get to a 600 RPM synchronous speed one is already up to 16 poles. That winds up being a large device. Putting the generator on the ground allows for whatever speed and number of poles is convenient. Plus, the added advantage of being able to adjust the ratio almost instantly is a handy side benefit.

tekochip
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Re: Gearbox life versus the alternative life
tekochip   12/28/2012 4:25:52 PM
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Using ground hydraulics is an interesting approach and I believe the reason it hasn't been tried would be the losses in moving all that fluid such a great distance.  Up top you would still need something to control the blade pitch and positioning, so you may as well have the transmission up there too.


William K.
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Re: Gearbox life versus the alternative life
William K.   12/28/2012 4:40:15 PM
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The trasmission is a high-wear and quite heavy device, and presently it is the one item that has a definite lifetime. In addition, it takes up a fair amount of space and the connection to both prop and generator must be quite precisely aligned. REplacing the gearbox in the upper assembly is a very big deal task. The generator, generator controls, gearbox, and gearbox cooling hardware comprise more than half the weight of the upper end, and so moving all of them to ground level would produce quite a savings in space and weight. An added advantage of the hydraulic approach is that all of the cooling could be located on the ground, since cooled oil would also cool the topside pump assembly. The piping losses can be minimized using techniques that have been well known in the hydraulics industry for many years. The somewhat reduced efficiency of using hydraulics would certainly be offset by the increased reliability and the reduced servicing costs associated with having much of the system at ground level.

Scott Orlosky
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Re: Gearbox life versus the alternative life
Scott Orlosky   12/30/2012 11:27:05 PM
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I haven't studied wind turbine design in any depth, but the idea of a hydraulic transmission sounds brilliant to me.  Sort of analagous to the automatic transmissions in cars instead of manual, I suppose.  Efficiency should be good, but the maintenance, nacelle design, etc. should all be greatly simplified.  It would be interesting to have someone in the industry comment on why this path hasn't been taken.

rainmaking
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Re: Gearbox life versus the alternative life
rainmaking   1/3/2013 3:36:02 PM
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I am in the industry and there are hydraulic drivetrain concepts and prototype turbines out there. Another touted advantage is putting the electrical generator on the ground. The reason this is not mainstream is the mechanical efficiency losses. A hydraulic drivetrain can peak in the 80's (%) while a gearbox operates above 95% efficiency. There is a lot of talk about gearboxes and failures because there are a lot of geared machines out there, but the industry is moving away from them. Both Siemens and GE (and others) are shipping >3MW direct drive machines these days. Purpose built low speed PM generators are now the most reliable and efficient way to convert wind to electricity.

Oh, and comment about residential turbines: Smaller turbines are more difficult to get a good return on because of their scale but there are midsize turbines (~50kW-500kW) that can provide good ROI in areas that have a decent wind resource coupled with high electricity costs. You can sell power to utilities if your state has a net metering law. google 'net metering' or look on 'windpoweringamerica.gov' to research using wind in your area. These turbines are too large still for the average home/property.

jmiller
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Re: Gearbox life versus the alternative life
jmiller   12/31/2012 11:47:42 AM
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Interesting thought to use hydraulics.  I wonder if hydraulics can be used at the center of the windmill to do all of those functions at one time.

William K.
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Re: Gearbox life versus the alternative life
William K.   1/1/2013 6:47:06 PM
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It is quite likely that a small portion of the hydraulic fluid from the power transfer lop could indeed be utilized for the other functions of blade pitch control and nacelle rotation. Of course it does come to mind that there are two typs of conditions where that may not work, which are during a shutdown (to avoid storm winds) period of no rotation, and when the wind was so slow that it would not turn the turbine blade. Of course, there could be hydraulic accumulators to provide backup for a while, and there could also be a backup pump running from auxilliary power. Other than that, there is no immeadiately obvious reason why not.

Now that the concept is published, perhaps some organization could run with it.

apresher
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Hydraulic vs. Electromechanical Solutions
apresher   1/3/2013 10:11:55 AM
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The suppliers are split between offering hydraulic and electromechanical solutions with some companies like Moog offering both. The high power density and simplicity of fluid power keeps it in the game.

apresher
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Hydraulics vs. EM Systems for Blade Pitch Control
apresher   1/3/2013 10:17:36 AM
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Below is link to web page that illustrates the advantages and approach to using either hydraulics or electromechanical systems for blade pitch control. http://www.moog.com.cn/english/markets/energy/wind-turbines/blade-pitch-control/comparison-of-electric-hydraulic-blade-pitch-control/

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