Thursday, August 2, 2012

Vertical Axis Wind Turbines Get second Look




It appears that vertical blade rotors will get a second look. While they are at it, perhaps it would be useful to consider the three blade configuration. I suspect that would go hugely to ameliorating the pulsing issue while increasing to power output. Even numbers always produces a strong cyclic pulse while odd numbers will partially blend the cycles and smooth out the impact.

I also suspect that these types of blades will turn out to be more bird friendly, but that is just a guess.

The real advantage of course is that the blades never have to reorient, nor need the hardware that makes that possible while producing nothing on its own.

I do not imagine that the tooling will prove any more difficult that has been put in place already. It just takes time and a will. In fact there has little that has been more impressive that the large fabrication tasks that have been taken on during the past decades around the wind turbine industry.



Offshore Use of Vertical-Axis Wind Turbines Gets Closer Look


ScienceDaily (July 30, 2012) — Sandia National Laboratories' wind energy researchers are re-evaluating vertical axis wind turbines (VAWTs) to help solve some of the problems of generating energy from offshore breezes.

Though VAWTs have been around since the earliest days of wind energy research at Sandia and elsewhere, VAWT architecture could transform offshore wind technology.

The economics of offshore windpower are different from land-based turbines, due to installation and operational challenges. VAWTs offer three big advantages that could reduce the cost of wind energy: a lower turbine center of gravity; reduced machine complexity; and better scalability to very large sizes.
A lower center of gravity means improved stability afloat and lower gravitational fatigue loads.

Additionally, the drivetrain on a VAWT is at or near the surface, potentially making maintenance easier and less time-consuming. Fewer parts, lower fatigue loads and simpler maintenance all lead to reduced maintenance costs.
Elegant in their simplicity

Sandia is conducting the research under a 2011 Department of Energy (DOE) 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."

These characteristics fit the design constraints for offshore wind: the high cost of support structures; the need for simple, reliable designs; and economic scales that demand larger machines than current land-based designs.

Large offshore VAWT blades in excess of 300 meters will cost more to produce than blades for onshore wind turbines. But as the machines and their foundations get bigger -- closer to the 10-20 megawatt (MW) scale -- turbines and rotors become a much smaller percentage of the overall system cost for offshore turbines, so other benefits of the VAWT architecture could more than offset the increased rotor cost.

Challenges remain

However, challenges remain before VAWTs can be used for large-scale offshore power generation.

Curved VAWT blades are complex, making manufacture difficult. Producing very long VAWT blades demands innovative engineering solutions. Matt Barone, the project's other principal investigator, said partners Iowa State University and TPI Composites will explore new techniques to enable manufacture of geometrically complex VAWT blade shapes at an unprecedented scale, but at acceptable cost.

VAWT blades must also overcome problems with cyclic loading on the drivetrain. Unlike horizontal axis wind turbines (HAWTs), 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 drivetrain 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.

"Underpinning this research effort will be a tool development effort that will synthesize and enhance existing aerodynamic and structural dynamic codes to create a publicly available aeroelastic design tool for VAWTs," Barone said.

Needed: aerodynamic braking brakes, new VAWT brakes won't have actively pitching blades, which have their own reliability and maintenance issues.

VAWT technology: A long history at Sandia

In the 1970s and 1980s, when wind energy research was in its infancy, VAWTs were actively developed as windpower generators. Although strange looking, they had a lot going for them: They were simpler than their horizontal-axis cousins so they tended to be more reliable. For a while, VAWTs held their own against HAWTs. But then wind turbines scaled up.

"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.

In the 1980s, research focused more heavily on HAWT turbines, and many VAWT manufacturers left the business, consigning VAWTs to an "also ran" in the wind energy museum.

But the winds of change have blown VAWTs' way once more.

Sandia is mining the richness of its wind energy history. Wind researchers who were among the original wind energy engineers are going through decades of Sandia research and compiling the lessons learned, as well as identifying some of the key unknowns described at the end of VAWT research at Sandia in the 1990s.

The first phase of the program will take place over two years and will involve creating several concept designs, running those designs through modern modeling software and narrowing those design options down to a single, most-workable design. During this phase, Paquette, Barone and their colleagues will look at all types of aeroelastic rotor designs, including HVAWTs and V-shaped VAWTs. But the early favorite rotor type is the Darrieus design.

In phase two 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: Early candidates are barge designs, tension-leg platforms and spar buoys.

The project partners will work on many elements.

Another partner, the University of Maine, will develop floating VAWT platform dynamics code and subscale prototype wind/wave basin testing. Iowa State University will develop manufacturing techniques for offshore VAWT blades and subscale wind tunnel testing. TPI Composites will design a proof-of-concept subscale blade and develop a commercialization plan. TU-Delft will work on aeroelastic design and optimization tool development and modeling. Texas A&M University will work on aeroelastic design tool development.

"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.

Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin company, for the U.S. Department of Energy's National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies and economic competitiveness.

Another challenge is brakes. Older VAWT designs didn't have an aerodynamic braking system, and relied solely on a mechanical braking system that is more difficult to maintain and less reliable than the aerodynamic brakes used on HAWTs.

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


4 comments:

David McElroy said...

I am glad "Vertical Axis Wind Turbines Get Second Look", as reported. I would favor them. But why is all the effort on huge expensive megawatt units profiting major corporations, rather than small residential or farm units setting people free of monthly bills? All that high cost R&D to dersign gigantic rotors that handle the stresses would not be needed. But of course, people must remain enslaved by metered energy, huh?

Anonymous said...

Andrew Carnegie funded Tesla and Edison. Tesla discovered how to transmit FREE, unmetered, electricity through the air. Edison proposed central electric generation, transmitting over wire hung on telephone poles, metered at every consumeer. Carnegie financially profited from Edison's concept and defunded Tesla. The same profit model continues today, Bruce

Hskiprob said...

The Robinson Turbine is a Vertical Axis wind and water turbine (VAWT), patent pending, that has a number of unique physical properties that contributes to its performance. http://www.youtube.com/watch?v=3NTbAz9GyHw

I will send the detailed instructions and a number of pictures of the wind turbine showing the below noted cabling system for $9.99 with 25% of all proceeds from the sales of the plans going to that individual or group that provides the best system to control the panels and 25% to that individual or group that is able to come up with the best system for dealing with catastrophic winds. This is a great challege for older kids to experiment with several aspects of physics, especially relating to centrifigal force and fluid dynanmics. I built my prototype with mostly stuff from the local hobbie shop. Ball baring are in the main shaft as well as two on each of the hinges of the panels. I still beleive that this system is the most efficent one that I've ever seen as it minimizes the drag as the panels come back against the wind while the other panel gathers greater amounts of the kenetic energy from the stream of air, just like a sail. The transfer of energy from the panel control system to the centrifugal forces seems to aid its efficiency. Just to give you some idea of the power, the panels on the water turbines were 1.4' x 2.5' tall 3.75 SF and the water turbin we tested put out over 300 lbs of pressure at less than a 5 MPH water speed. The barge in the video below was not large enough to fully stop the torque effect of the system.

Unlike most other VAWTs, it doesn’t have a blade but a panel system, much like a sail, that is the essence of its potential superior performance. No one to my knowledge has analyzed the various physics to understand how efficient it might be, since I’ve withheld some crucial information, except to those that have signed NDAs. Even then, I have only given the information to a few of those whom appear to understand the physics and asked the right questions.

What makes the system most unique is the ability to transfer the excess torque generated by the flipping panel in the rear of the system, when the wind is at your back looking at the system, while transferring that energy to the compressing panel in the front and the effects it has on the centrifugal forces of the entire system.

I just know that I couldn’t get the wind turbine to work in a wide wind speed range without using a system that panel control system that transferred the energy. I ended up instead of the employing a hydraulic system, which I think would be more effective but very costly upfront, I created a cabling system that gave me the proof of concept. It can be argued the cabling system is not an adequate proof of concept, but I think, the proof is in the pudding, it worked, first time right out of the box, so to speak, exactly as I had envisioned and how my experimentation had brought me to understand. http://www.youtube.com/watch?v=EDYtS0o3lss, The Challenge: To develop the best energy transfer system that improves the efficiency and performance of the Robinson Turbine. For those interested parties please feel to contact me. hskiprob@gmail.com or call me at 561-596-1004

arclein said...

Hi Skipbob

Has anyone done up a story on your work? Mechanical solutions are naturally frustrating and progress is slow. The vertical axis system is nice by its simplicity, yet leave most of the energy behind. The same is true of the present standards. I also think both the vertical axis design and plausibly yours should try a three blade system for superior spread of the torque.