Enormous blades could lead to more offshore energy in US

January 28, 2016
Todd Griffith shows a cross-section of a 50-meter blade, which is part of the pathway to the 200-meter exascale turbines being planned under a DOE ARPA-E-funded program. The huge turbines could be the basis for 50-megawatt offshore wind energy installations in the years ahead. Credit: Randy Montoya

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 blade.

The team is led by the University of Virginia and includes Sandia and researchers from the University of Illinois, the University of Colorado, the Colorado School of Mines and the National Renewable Energy Laboratory. Corporate advisory partners include Dominion Resources, General Electric Co., Siemens AG and Vestas Wind Systems.

"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.

Sandia’s 100-meter blade is the basis for the Segmented Ultralight Morphing Rotor (SUMR), a new low-cost offshore 50-MW wind turbine. 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. Credit: TrevorJohnston.com/Popular Science

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 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 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 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.

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18 comments

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WillieWard
1.4 / 5 (11) Jan 28, 2016
Interesting and Eco-friendly, enormous wind blades (longer than two football fields) that spread out to maximize birds' massacre preventing these dangerous nasty birds from breathing out more CO2 into the environment.
Eikka
5 / 5 (8) Jan 28, 2016
Interesting and Eco-friendly, enormous wind blades (longer than two football fields) that spread out to maximize birds' massacre preventing these dangerous nasty birds from breathing out more CO2 into the environment.


The benefit of having a large 50 MW turbine is that you don't need to place them so close together. In fact you can't, because they slow down the wind too much and shade each other. Each turbine creates a kind of bubble of slow moving air that lifts the incoming winds higher up and out of reach for any other turbine down the line.

With a 50 MW capacity and probably 20-25 MW average output, they have to be placed about 5 kilometers apart because there's generally no more than 1 MW per square kilometer available.

Plenty of room for birds to fly in between. Messes up the thermals though.

The second point is that the tip speed of the turbine cannot exceed a certain optimum ratio relative to the wind speed, so a larger turbine necessarily turns slower.
NoStrings
4 / 5 (2) Jan 28, 2016
Eikka, thank you for thoughtful explanation. When these are commercially available, I may get one or two for my wind farm.
Eikka
4.3 / 5 (6) Jan 28, 2016
Generally speaking, off-shore wind power with traditional turbines generates 1.5 times the energy at 2 times the cost because of the need to lay cable and set up foundations for the towers at sea, and then the frequent visits to replace a broken hydraulic pump or some burnt-out controller board which can only be done when the weather is nice - ie. not windy.

Having a smaller number of units dramatically reduces both the cost of setting up and maintaining the turbines.

The ultra-large turbines don't work as well on land because there's already a boundary layer friction effect with trees and buildings and hills etc. which causes a larger difference in wind speeds from low on the ground to high up. That means the turbine gets a large difference in wind speed from the bottom of the turbine to the top; the bottom of the turbine actually brakes while the top tries to turn faster, which makes for poor efficiency and high mechanical stresses. Hence the turbines can't be too big.
Eikka
4.2 / 5 (5) Jan 28, 2016
Eikka, thank you for thoughtful explanation. When these are commercially available, I may get one or two for my wind farm.


In ones or twos, there's less consideration about spacing because most locations get wind from a predominant direction. Placing the turbines sideways to that direction lets you have a whole row of them without them interfering.

The major effect is that the tighter the row you make them, the longer the "tail" they leave behind because the bubble of slow air doesn't disperse as easily with less wind between the turbines, so you may affect other people's wind farms miles and miles downwind from yours.

Or someone else's wind farm miles upwind can affect yours.
Max5000
4.8 / 5 (4) Jan 28, 2016
"Enormous blades could lead to more offshore energy in US"

What? The US has zero offshore wind turbines so it can not deliver "more" if there is nothing. More then 0 is still 0.

95% of the worlds offshore wind turbines are located on the coasts of EU countries. And those largest 8MW are those by EU companies like Siemens and Vesta. Nothing to sneeze at. Sure you would like to go much bigger to reduce costs. The lower the price the better it can compete with coal and gasoline. But the US is rich in plenty of fossil energy where the EU countries don`t and need more renewable energy to further reduce dependence. If 50 MW wind turbines can be build that would surely help out. But you also need a large local industry of specialized boats and companies to install the systems, build the grid, perform maintenance, upgrades, etc. Currently only Europe has this large industry of special ships, etc. It is not just the turbines but economies of scale in support systems as well.
Lord_jag
5 / 5 (1) Jan 28, 2016
A wind turbine isn't going to slow a 100km diameter, 2km tall mass of air that wants to move inland. The pressure difference isn't going to change just because you have a few hundred square feet of obstacle in the way.

It makes a wind speed vacuum directly behind the turbine, but the wind will just accelerate around this slow wind and spread out on the other side.

Just shove a stick into the ocean. Did you just stop the tide or did you make a local effect that didn't really slow the water at all?

Or do you mean to quote Joe Barton when he said that wind turbines slow the wind and wind cools you so that's why the globe is warming?
WillieWard
1.8 / 5 (5) Jan 29, 2016
Interesting and Eco-friendly, enormous wind blades (longer than two football fields) that spread out to maximize birds' massacre preventing these dangerous nasty birds from breathing out more CO2 into the environment.
Another advantage of such Eco-friendly technology is that the pressure generated by larger wind blades is enough to cause birds' air sacs to explode.
"blades not only strike the animals mid-flight, but the turbine also lowers air pressure, causing birds' air sacs to explode, dooming them to horrific death."
http://harvardmag...-bavaria
"bats are killedby barotrauma caused by rapidair- pressure reduction near moving turbine blades"
http://www.academ...turbines
"Bats are struck by blades .. "barotrauma," sudden air pressure changes that explode their lungs"
https://www.maste...tandard/
Eikka
4 / 5 (4) Jan 29, 2016
A wind turbine isn't going to slow a 100km diameter, 2km tall mass of air that wants to move inland. The pressure difference isn't going to change just because you have a few hundred square feet of obstacle in the way.


Well, it isn't, but you fail to understand the physics of wind turbines.

In order to extract energy out of wind, you need to slow it down - that's what you're doing by extracting the kinetic energy. That large mass of slow-moving air is what's affecting the rest of the air mass coming your way. The flow of wind lifs higher up from the ground, out of reach of your turbines.

The wind turbines cause a boundary layer effect, which is beatifully illustrated in this age-old video: https://www.youtu...WxEUXIoM

Boundary layer effects mean that a small object, by the friction and turbulence it causes in the flow of fluid - in this case air - make the object's effect vastly bigger than its physical size.
Eikka
3.7 / 5 (3) Jan 29, 2016
"bats are killedby barotrauma caused by rapidair- pressure reduction near moving turbine blades"

"Bats are struck by blades .. "barotrauma," sudden air pressure changes that explode their lungs"


They keyword is "rapid". Larger and slower turbines cause shallower pressure gradients though the absolute pressure differential may be large.

The larger turbines make larger vortices, which in turn are easier for small animals to pass through.
Eikka
3.7 / 5 (3) Jan 29, 2016
Or this video:

https://www.youtu...1PkpiXwI

Notice how the yellow-green-blue slow layers lift upwards from the starting condition of mostly laminar flow. That's the bubble effect. The wind turbine causes resistance and eddies in the flow, which increases the effective viscosity of the fluid (air) in the turbulent region and the laminar flow of the wind starts to rise up above the obstruction.

This is the main reason why wind power is limited to an average of 1 MW per square kilometer. The more energy you try to extract per area, the more you slow the winds down and the more the remaining winds lift up out of your reach. The turbine makes a very large "shadow".

It's the same reason why you can't extract all the power of a flowing river - if you did, the river would stop flowing and flood its banks - obviously.
Eikka
3.7 / 5 (3) Jan 29, 2016
It makes a wind speed vacuum directly behind the turbine, but the wind will just accelerate around this slow wind and spread out on the other side.


There's no "vacuum" left behind the turbine that the wind wants to fill - and the wind doesn't accelerate around it. On the contrary.

What you're describing is similiar to the bernoulli effect, which only works if the wind was going through a tube where it has nowhere else to go - as if there was a glass ceiling above and to the sides of the wind turbine that constricts the flow and forces it to speed up.

In reality there's no such thing - there's a hundred kilometers of free space above your turbine for the wind to flow quite freely, so it does exactly that. It doesn't accelerate around your turbine - it doesn't even go there.
Eikka
3.7 / 5 (3) Jan 29, 2016
Here's yet another simulation video: https://www.youtu...Z3q3509w

The distance between the turbines is 7 times the diameter. If those were 100 meter blades, they would be 1.4 kilometers apart. At that distance, the turbines are swimming in each others' wakes. That's way too close for a wind farm.

If the wind over the ocean was compared to water flowing over a dinnerplate, the turbulent wake of the turbine is like a bead of maple syrup sticking to the surface of the plate - it flows along, but much slower than the prevailing flow, and it dissapates slowly over distance by dissolving into the water.
manifespo
3 / 5 (2) Jan 29, 2016
I imagine huge sea-domes embroidered with helical Turbines...
that extract energy from sea level up to the jet stream.

Swarming Drones will construct these things out of silk.

One MW might be available per square kilometer at sea level,
but when you extract the entire 5 KM column of air, you are looking at much more.
tblakely1357
not rated yet Jan 31, 2016
Except in areas where there is enough political pull to not ruin their view.
24volts
5 / 5 (1) Jan 31, 2016
I just want to see one of these things survive though one of the hurricanes we get on the east coast fairly regularly.
kochevnik
not rated yet Feb 01, 2016
@WillieWard Unlike you, birds can evolve
WillieWard
1 / 5 (2) Feb 01, 2016
birds can evolve
'green' hypocrisy evolves too, ever more ecologically hypocritical.

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