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Clean Power Basing their work on decades of wind energy research and experience, Sandia engineers are creating several concept designs, running those designs through modern modeling software and narrowing those design options down to a single, most-workable design for a VAWT turbine-blade. Results aren’t in, but the early favorite for further testing is the Darrieus design. (Illustration by Josh Paquette and Matt Barone).

Published on August 2nd, 2012 | by Glenn Meyers

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Offshore Use of Vertical-Axis Wind Turbines Gets Closer Look by Sandia Labs

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August 2nd, 2012 by  

 

Do the best offshore wind turbines operate with a horizontal or vertical-axis mechanism? That question is being reexamined by Sandia National Laboratories’ wind energy researchers who are now re-evaluating vertical-axis wind turbines (VAWTs) to help solve some of the problems of generating energy from offshore breezes using horizontal-axis wind turbines (HAWTs).

Basing their work on decades of wind energy research and experience, Sandia engineers are creating several concept designs, running those designs through modern modeling software and narrowing those design options down to a single, most-workable design for a VAWT turbine-blade. Results aren’t in, but the early favorite for further testing is the Darrieus design. (Illustration by Josh Paquette and Matt Barone).

The economics of offshore wind power are different from land-based turbines, due to installation and operational challenges, Sandia Labs noted in a recent press announcement. Sandia contends that VAWTs can offer three significant advantages that can reduce the cost of wind energy:

  • lower turbine center of gravity, meaning improved stability and lower gravitational fatigue loads;
  • reduced machine complexity with fewer parts, which makes maintenance easier and less time-consuming;
  • better scalability to very large sizes.

Sandia is conducting its research under a Department of Energy solicitation for advanced rotor technologies for U.S. offshore windpower generation. The five-year, $4.1-million project began in January of this year.

Wind Energy Technologies manager Dave Minster said Sandia’s wind energy program is aimed at addressing the national energy challenge of increasing the use of low-carbon power generation.

“VAWTs are elegant in terms of their mechanical simplicity,” said Josh Paquette, one of Sandia’s two principal investigators on the project. “They have fewer parts because they don’t need a control system to point them toward the blowing wind to generate power.”

But VAWT blades must overcome problems with cyclic loading on the drive train. Unlike horizontal-axis wind turbines, which maintain a steady torque if the wind remains steady, VAWTs have two “pulses” of torque and power for each blade, based on whether the blade is in the upwind or downwind position. This “torque ripple” results in unsteady loading, which can lead to drive train fatigue. The project will evaluate new rotor designs that smooth out the amplitude of these torque oscillations without significantly increasing rotor cost.

Because first-generation VAWT development ended decades ago, updated designs must incorporate decades of research and development already built into current HAWT designs. Reinvigorating VAWT research means figuring out the models that will help speed up turbine design work.

Another challenge involves braking. Older VAWT designs had no aerodynamic braking system and relied only on a mechanical braking system.

HAWTS use pitchable blades, which stop the turbine within one or two rotations without damage to the turbine and are based on multiple redundant, fail-safe designs. Barone said new VAWT designs will need robust aerodynamic brakes that are reliable and cost-effective, with a secondary mechanical brake much like on modern-day HAWTs. Unlike HAWT brakes, new VAWT brakes won’t have actively pitching blades, which have their own reliability and maintenance issues.

In the 1970s and 1980s, VAWTs were actively developed as windpower generators until being overtaken by HAWTs.

“HAWTs emerged as the predominant technology for land-based wind over the past 15 years primarily due to advantages in rotor costs at the 1 to 5 megawatt scale,” Paquette said.

The first phase of the program will take place over two years and involve creating several concept designs, running those designs through modern modeling software and narrowing those design options down to a single, most-workable design. In the second phase, researchers will build the chosen design over three years, eventually testing it against the extreme conditions that a turbine must endure in an offshore environment. In addition to rotor designs, the project will consider different foundation designs.

“Ultimately it’s all about the cost of energy. All these decisions need to lead to a design that’s efficient and economically viable,” said Paquette.

Source: Sandia National Laboratories

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About the Author

is a writer, producer, and director. Meyers is editor and site director of Green Building Elements, a contributor to CleanTechnica, and founder of Green Streets MediaTrain, a communications connection and eLearning hub. As an independent producer, he's been involved in the development, production and distribution of television and distance learning programs for both the education industry and corporate sector. He also is an avid gardener and loves sustainable innovation.



  • Dave2020

    “Sandia engineers are creating several concept designs.”

    All of which come from the last century. Nothing new here.

    There are a number of design false assumptions:-

    “the early favorite for further testing is the Darrieus design.”

    Which variant is best?

    “The project will evaluate new rotor designs that smooth out the amplitude of these torque oscillations without significantly increasing rotor cost.”

    That’s already been done, hasn’t it? Is cost a factor with this design? Looks like it could be replaced at a fraction of the cost of a HAWT turbine repair.

    http://www.rechargenews.com/business_area/innovation/article296513.ece

    “Offshore wind is a different world.” Can’t argue with that.

    “better scalability to very large sizes.”

    Wrong premise. Silly really. A (nominal) 2MW will do nicely – more robust.

    “Barone said new VAWT designs will need robust aerodynamic brakes.”

    No – they won’t need any brakes at all. The (no gearbox) drivetrain should do that job.

    “aimed at addressing the national energy challenge of increasing the use of low-carbon power generation.”

    Aimed in the wrong direction. Dispatchability addresses that challenge best.

    Why capture the wind and not the wave energy? There’s a lot of it out there!

    Draft is a factor in achieving the economies of towing out from port, so sub-sea innovation is the answer.

    “The five-year, $4.1-million project began in January of this year.”

    Too little, too late. But still far better than the UK’s pathetic R&D scene. Anyway, why aren’t the incumbents pushing these boundaries? Too complacent?

  • lakosh

    Torque ripple is smoothed with curved Gorlov
    rotor blades, hence the debate over the increased cost of shaped blades over straight blades. VAWTs can also produce more power per unit area if spaced to induce a schooling effect, (see Caltech FLOWE studies). The low center of gravity and short turbulence wake are very important in erecting the turbines as ganged strings of VAWTs can be erected in port and towed into position at deep water and/or high wind sites that would frustrate erection of HAWTs due to nearly continuous high sea states. This close spacing of ganged turbine spars would also allow mounting of current and wave power generators on the steel cables connecting
    the spar buoys. The combination of multiple power sources would improve power produced per unit area and the capacity factor of the transmission lines if not the power per unit of materials and labor employed.

    • Bob_Wallace

      Floating HAWTs are being built in harbor and towed to position.

      Placing multiple turbines in close proximity could foul the wind.  Ocean is not in short supply.

      I suppose we’ll have some data before too long and can get past the speculating….

       

      • lakosh

        Yes, HAWTs are being floated into position but the idea of ganging spars into long strings is to minimize moorings and time to install the units. If you follow the FLOWE studies, they show a symbiotic effect of close VAWT spacing and these turbines have a shorter/narrower interference and turbulence wake so turbines in the field each have a higher capacity factor. The access to the generator and bearings at sea level is also a big maintenance cost saver.

        • Bob_Wallace

          Do you know of some data that shows that VAWTs ganged produce more power than VAWTs spaced?

          The only thing that I’ve seen says that VAWTs are less degraded than HAWTs when ganged, which is what one would expect. HAWTs don’t
          like turbulence and create some in their wakes.

          That argues that VAWTs might be a better choice when real estate is at a premium, but it doesn’t automatically mean that clustering is better when total area is not an issue.

          I can imagine that turbulence, as long as there isn’t significant energy cancellation, could help VAWTs as it might spread force and somewhat smooth out the loading cycles.

          • lakosh

            http://dabiri.caltech.edu/research/wind-energy.html

            Ocean realestate isn’t as available as you think given shipping channels, fishing grounds and marine mammal habitat

          • Bob_Wallace

            So you don’t know of any data to back up your claim?

            (BTW, I’ve spent a few years as a blue water sailor. I have a pretty good idea how large the ocean is and how much gets used for shipping, etc.)

  • Random passer by

    I think  it was not just cost that caused the Darrieus design to phase out. If I remember correctly, Darrieus rotors need to be kick-started by a motor after stand still,  and there were big fatigue problems caused by the different wind speeds experienced by the lower and higher parts of the blade.

    • Glenn Meyers

      I hope that isn’t an issue this time around!

  • http://daffodilibs.co.za/ Johaar

    Hi
    It seems that smoothing out the torque ripple requires a multiblade design that ensures that the power and torque phases are more frequent.ie more blades mean a continuance of the power and torque phases and therefore should eliminate the drivetrain fatigue phenomena and its implications.More blades please.Have a look at the ventilation blower of the average 90’s sedan.That kind of construction?

    • Glenn Meyers

      Thanks for the input.

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