Enormous blades could lead to more offshore energy in US

Posted: February 5, 2016 by oldbrew in Energy, turbines, wind
Tags: ,

How big can wind turbine blades get? [image credit: scancomark.com]

How big can wind turbine blades get? [image credit: scancomark.com]

Monster ‘SUMR’ wind turbines are on the US drawing board, says ScienceDaily. SUMO more like?

A new design for gigantic blades longer than two football fields could help bring offshore 50-megawatt (MW) wind turbines to the United States and the world. Sandia National Laboratories’ research on the extreme-scale Segmented Ultralight Morphing Rotor (SUMR) is funded by the Department of Energy’s (DOE) Advanced Research Projects Agency-Energy program.

The challenge: Design a low-cost offshore 50-MW turbine requiring a rotor blade more than 650 feet (200 meters) long, two and a half times longer than any existing wind blade.

“Exascale turbines take advantage of economies of scale,” said Todd Griffith, lead blade designer on the project and technical lead for Sandia’s Offshore Wind Energy Program. Sandia’s previous work on 13-MW systems uses 100-meter blades (328 feet) on which the initial SUMR designs are based.

While a 50-MW horizontal wind turbine is well beyond the size of any current design, studies show that load alignment can dramatically reduce peak stresses and fatigue on the rotor blades. This reduces costs and allows construction of blades big enough for a 50-MW system.

Most current U.S. wind turbines produce power in the 1- to 2-MW range, with blades about 165 feet (50 meters) long, while the largest commercially available turbine is rated at 8 MW with blades 262 feet (80 meters) long. “The U.S. has great offshore wind energy potential, but offshore installations are expensive, so larger turbines are needed to capture that energy at an affordable cost,” Griffith said.

Barriers remain before designers can scale up to a 50-MW turbine — more than six times the power output of the largest current turbines. “Conventional upwind blades are expensive to manufacture, deploy and maintain beyond 10-15 MW. They must be stiff, to avoid fatigue and eliminate the risk of tower strikes in strong gusts. Those stiff blades are heavy, and their mass, which is directly related to cost, becomes even more problematic at the extreme scale due to gravity loads and other changes,” Griffith said.

He said the new blades could be more easily and cost-effectively manufactured in segments, avoiding the unprecedented-scale equipment needed for transport and assembly of blades built as single units. The exascale turbines would be sited downwind, unlike conventional turbines that are configured with the rotor blades upwind of the tower.

SUMR’s load-alignment is bio-inspired by the way palm trees move in storms. The lightweight, segmented trunk approximates a series of cylindrical shells that bend in the wind while retaining segment stiffness. This alignment radically reduces the mass required for blade stiffening by reducing the forces on the blades using the palm-tree inspired load-alignment approach.

Segmented turbine blades have a significant advantage in parts of the world at risk for severe storms, such as hurricanes, where offshore turbines must withstand tremendous wind speeds over 200 mph. The blades align themselves to reduce cantilever forces on the blade through a trunnion hinge near the hub that responds to changes in wind speed. “At dangerous wind speeds, the blades are stowed and aligned with the wind direction, reducing the risk of damage. At lower wind speeds, the blades spread out more to maximize energy production.” Griffith said.

Moving toward exascale turbines could be an important way to meet DOE’s goal of providing 20 percent of the nation’s energy from wind by 2030, as detailed in its recent Wind Vision Report.

The above post is reprinted from materials provided by DOE/Sandia National Laboratories.

Source: Enormous blades could lead to more offshore energy in US — ScienceDaily

  1. oldbrew says:

    The fall-off in power when it’s not windy will be even more dramatic than with existing turbines.

  2. USteiner says:

    I like it!

    Combined with the problem of rust from a harsh sea environment, it will speed up the demise of the wind nonsense, as detailed here http://notrickszone.com/2016/02/02/offshore-offshore-wind-turbine-maintenance-costs-100-times-more-expensive-than-new-turbine-itself/#sthash.DpBXMcOf.dpbs

  3. MishaBurnett says:

    Do they have bird kill estimates for this design?

  4. Graeme No.3 says:

    These blades are essentially thick aerofoils (for strength purposes). As the diameter goes up the speed of rotation has to drop otherwise the blade tip moves into the turbulent flow zone with extra drag and blade damage, but the blade also has to loosely match the wind speed to extract power. This mean that the longer the blade the slower it can rotate and the less power is available in the wind.
    Also, the centrifugal forces go up as the blade diameter increases. Requires higher strength = thicker blade with more drag or thinner blade with more exotic, hence costly, materials.

  5. oldbrew says:

    Graeme: exactly.

  6. p.g.sharrow says:

    . Sandia National Laboratories is in the business of spending Government money on research projects. Generally the larger the better. At least they build real things and test them to failure. Actually expanding the general knowledge base…pg

  7. Jerry says:

    As these three-bladed designs do not seem to take full advantage of the energy in the air stream that passes through their rotation arc, they might be improved significantly with more blades. One option is to just add three more blades to the hub. Another option is two, three blade designs operating in counter-rotation, with one three-blade set immediately behind the other. Design complexity increases, but blade radius would be smaller for a given power extraction from the air stream.

  8. oldbrew says:

    Jerry says: ‘One option is to just add three more blades to the hub’

    But the post says…’The challenge: Design a low-cost offshore 50-MW turbine’ 😉

  9. oldmanK says:

    Jerry says: ‘One option is to just add three more blades to the hub’

    There is only so much you can get from the energy of the wind. Three blade is enough for optimal energy take.

  10. lapogus says:

    Putting a 6MW generator and gearbox c.150m up in the air is an engineering possibility but economically questionable. Attempting to build a 50MW generator and gearbox c. 250m up in the air is just economic and engineering madness. I doubt one of these proposed SUMR windmills would last a week on this side of the Atlantic. Scottish Power abandoned the proposed 1GW Tiree Array (which would have used 6MW or 10MW turbines) because they could find no practical engineering solution to fix the foundations of the platforms to the sea floor. (The depth of the Tiree reef ranges from 10-50m, so parts of it are less than the amplitude of winter waves – so the reef floor is routinely scrubbed clean by rocks after winter storms). The stresses from waves and wind are enormous – after calculating the forces from 100ft high waves and 120mph winds, Stevenson built his lighthouse from enormous interlocking granite blocks, which unlike steel are also impervious to salt spray. When will this delusion with wind power end?

  11. oldbrew says:

    Iapogus asks: ‘When will this delusion with wind power end?’

    As soon as the river of taxpayers’ money dries up.

  12. ntesdorf says:

    When you have something that is costly and inefficient, the answer is always to make it bigger, more costly and more inefficient. You do not need to reflect for a moment.

  13. Graeme No.3 says:

    the Betz limit indicates there is little improvement to make.
    A 2 bladed turbine is slightly more efficient but more likely to become unbalanced. Multiple blades would be affected by the turbulence generated by other blades and that caused by the tower, hence suggested ‘downstream’ blade location.
    For effect of turbulence try

  14. Choey says:

    I’ll bet you’ll be able to hear that thing for 50 miles.

  15. Wind turbines remain ugly bird killers , spoiling views even if out in the sea and producing unacceptable low frequency noise which can be sensed kms away
    Money spent on research could be much more productive researching nuclear technology. If a space vehicle designed over 40 years ago can have a nuclear reactor operating without maintenance for at least 35 years think what might be now if money and effort had been applied for improvements and new technology.
    There should be no government money going into wind or solar (or any so-called renewable). Let private enterprise do it if they think something will be viable.

  16. catweazle666 says:

    studies show that load alignment can dramatically reduce peak stresses and fatigue on the rotor blades

    I believe that the biggest engineering problems are with bearings, which are already at or beyond our existing knowledge. It’s that good old square/cube problem rearing its ugly head again.

    Further, as the tip speed increases, it will come close to Mach the buffet regime, which will feed all sorts of interesting harmonics back into the rotor pitch control mechanism and then into the gearbox.

    Then, after all that, there is the really fun part, clambering up a tower several hundred metres high to unship the rotors and remove the gearboxes. Good luck finding maintenance engineers to do that, there already problems finding anyone willing to work on the North Sea rigs, very few of the oil rig engineers will touch them with a barge pole.

  17. ivan says:

    These things are supposed to run down wind and FOLD when the wind gets too strong. Just think about what the salt spray can do to the hinges in that situation and how long they will last.

    As p.g.sharrow says Sandia has the reputation of doing actual testing but no amount of testing on land is going to find out what will happen at sea.

    If the blades don’t fold and reopen the same amount there will be very large unbalance forces that will play havoc with the bearings and gear box which will already be pushing their limits.

  18. Graeme No.3 says:

    The switch blade turbine?

  19. pochas94 says:

    Of course without subsidies none of these monsters would be built. This means more graft for the rent seekers, more pain for the taxpayers and utility consumers and more “political contributions” for the politicians.

  20. oldmanK says:

    A different perspective.

    choey said “I’ll bet you’ll be able to hear that thing for 50 miles.” I’ve only been once near a wind farm. I noticed the constant hum in the air. Reminded me of long ago, a similar hum and just as loud, that fascinated me. Bees everywhere. That’s all gone now.

    cementafriend said ” spoiling views even if out in the sea”. There was a time I used to count more than 80 ‘chicago air motors’ on the horizon, none more than six miles away. They were necessary then and no one complained. We only worried in high winds when the night clanking meant damage and trouble and great expense both to the unit and what relied on the water they pumped.

    Times change. pendulum like?

  21. p.g.sharrow says:

    The last time Sandia operated a Very Large Turbine here in California, they discovered a serous problem. The air flow around the Pylon caused whipping of the fan blade tips as they passed the pylon that in time caused failure of the blades and bearings. The use of up steam fans and then down stream ones had much the same problem with the whipping as the blades passed through the pylon induced changes in the air flow. Not sure how they plan to avoid this problem this time.

    Far too much of today’s modern science seems to be reinventing the mistakes and discoveries of the previous generation…pg

  22. oldmanK says:

    Qoute : Far too much of today’s modern science seems to be reinventing the mistakes and discoveries of the previous generation…pg

    Yes, the economical design is the one that has done away with the preliminary studies. It happens so often that it has become the rule.