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M II A II R II K Oct 13, 2009 7:41 PM

Wind Power Thread
How Wind Power Works


It's hard sometimes to imagine air as a fluid. It just seems so ... invisible. But air is a fluid like any other except that its particles are in gas form instead of liquid. And when air moves quickly, in the form of wind, those particles are moving quickly. Motion means kinetic energy, which can be captured, just like the energy in moving water can be captured by the turbine in a hydroelectric dam. In the case of a wind-electric turbine, the turbine blades are designed to capture the kinetic energy in wind. The rest is nearly identical to a hydroelectric setup: When the turbine blades capture wind energy and start moving, they spin a shaft that leads from the hub of the rotor to a generator. The generator turns that rotational energy into electricity. At its essence, generating electricity from the wind is all about transferring energy from one medium to another.

Wind power all starts with the sun. When the sun heats up a certain area of land, the air around that land mass absorbs some of that heat. At a certain temperature, that hotter air begins to rise very quickly because a given volume of hot air is lighter than an equal volume of cooler air. Faster-moving (hotter) air particles exert more pressure than slower-moving particles, so it takes fewer of them to maintain the normal air pressure at a given elevation.

If you place an object like a rotor blade in the path of that wind, the wind will push on it, transferring some of its own energy of motion to the blade. This is how a wind turbine captures energy from the wind. The same thing happens with a sail boat. When moving air pushes on the barrier of the sail, it causes the boat to move. The wind has transferred its own energy of motion to the sailboat.

Parts of a Wind Turbine

The simplest possible wind-energy turbine consists of three crucial parts:
  • Rotor blades - The blades are basically the sails of the system; in their simplest form, they act as barriers to the wind (more modern blade designs go beyond the barrier method). When the wind forces the blades to move, it has transferred some of its energy to the rotor.
  • Shaft - The wind-turbine shaft is connected to the center of the rotor. When the rotor spins, the shaft spins as well. In this way, the rotor transfers its mechanical, rotational energy to the shaft, which enters an electrical generator on the other end.
  • Generator - At its most basic, a generator is a pretty simple device. It uses the properties of electromagnetic induction to produce electrical voltage - a difference in electrical charge. Voltage is essentially electrical pressure - it is the force that moves electricity, or electrical current, from one point to another. So generating voltage is in effect generating current. A simple generator consists of magnets and a conductor. The conductor is typically a coiled wire. Inside the generator, the shaft connects to an assembly of permanent magnets that surrounds the coil of wire. In electromagnetic induction, if you have a conductor surrounded by magnets, and one of those parts is rotating relative to the other, it induces voltage in the conductor. When the rotor spins the shaft, the shaft spins the assembly of magnets, generating voltage in the coil of wire. That voltage drives electrical current (typically alternating current, or AC power) out through power lines for distribution.

M II A II R II K Oct 13, 2009 7:45 PM

Modern Wind-power Technology

When you talk about modern wind turbines, you're looking at two primary designs: horizontal-axis and vertical-axis. Vertical-axis wind turbines (VAWTs) are pretty rare. The only one currently in commercial production is the Darrieus turbine, which looks kind of like an egg beater.

Vertical-axis wind turbines (VAWTs)

In a VAWT, the shaft is mounted on a vertical axis, perpendicular to the ground. VAWTs are always aligned with the wind, unlike their horizontal-axis counterparts, so there's no adjustment necessary when the wind direction changes; but a VAWT can't start moving all by itself -- it needs a boost from its electrical system to get started. Instead of a tower, it typically uses guy wires for support, so the rotor elevation is lower. Lower elevation means slower wind due to ground interference, so VAWTs are generally less efficient than HAWTs. On the upside, all equipment is at ground level for easy installation and servicing; but that means a larger footprint for the turbine, which is a big negative in farming areas.

Horizontal-axis wind turbines (HAWTs)

As implied by the name, the HAWT shaft is mounted horizontally, parallel to the ground. HAWTs need to constantly align themselves with the wind using a yaw-adjustment mechanism. The yaw system typically consists of electric motors and gearboxes that move the entire rotor left or right in small increments. The turbine's electronic controller reads the position of a wind vane device (either mechanical or electronic) and adjusts the position of the rotor to capture the most wind energy available. HAWTs use a tower to lift the turbine components to an optimum elevation for wind speed (and so the blades can clear the ground) and take up very little ground space since almost all of the components are up to 260 feet (80 meters) in the air.

Large HAWT components:

* Rotor blades - capture wind's energy and convert it to rotational energy of shaft

* Shaft- transfers rotational energy into generator

* Nacelle - casing that holds:

o gearbox - increases speed of shaft between rotor hub and generator

o generator - uses rotational energy of shaft to generate electricity using electromagnetism

o electronic control unit (not shown) - monitors system, shuts down turbine in case of malfunction and controls yaw mechanism

o yaw controller (not shown) - moves rotor to align with direction of wind

o brakes - stop rotation of shaft in case of power overload or system failure

* Tower - supports rotor and nacelle and lifts entire setup to higher elevation where blades can safely clear the ground

* Electrical equipment - carries electricity from generator down through tower and controls many safety elements of turbine

M II A II R II K Oct 13, 2009 7:51 PM

Turbine Aerodynamics

Unlike the old-fashioned Dutch windmill design, which relied mostly on the wind's force to push the blades into motion, modern turbines use more sophisticated aerodynamic principles to capture the wind's energy most effectively. The two primary aerodynamic forces at work in wind-turbine rotors are lift, which acts perpendicular to the direction of wind flow; and drag, which acts parallel to the direction of wind flow.

Turbine blades are shaped a lot like airplane wings -- they use an airfoil design. In an airfoil, one surface of the blade is somewhat rounded, while the other is relatively flat. Lift is a pretty complex phenomenon and may in fact require a Ph.D. in math or physics to fully grasp. But in one simplified explanation of lift, when wind travels over the rounded, downwind face of the blade, it has to move faster to reach the end of the blade in time to meet the wind travelling over the flat, upwind face of the blade (facing the direction from which the wind is blowing). Since faster moving air tends to rise in the atmosphere, the downwind, curved surface ends up with a low-pressure pocket just above it. The low-pressure area sucks the blade in the downwind direction, an effect known as "lift." On the upwind side of the blade, the wind is moving slower and creating an area of higher pressure that pushes on the blade, trying to slow it down. Like in the design of an airplane wing, a high lift-to-drag ratio is essential in designing an efficient turbine blade. Turbine blades are twisted so they can always present an angle that takes advantage of the ideal lift-to-drag force ratio. See How Airplanes Work to learn more about lift, drag and the aerodynamics of an airfoil.

Aerodynamics is not the only design consideration at play in creating an effective wind turbine. Size matters -- the longer the turbine blades (and therefore the greater the diameter of the rotor), the more energy a turbine can capture from the wind and the greater the electricity-generating capacity. Generally speaking, doubling the rotor diameter produces a four-fold increase in energy output. In some cases, however, in a lower-wind-speed area, a smaller-diameter rotor can end up producing more energy than a larger rotor because with a smaller setup, it takes less wind power to spin the smaller generator, so the turbine can be running at full capacity almost all the time. Tower height is a major factor in production capacity, as well. The higher the turbine, the more energy it can capture because wind speeds increase with elevation increase -- ground friction and ground-level objects interrupt the flow of the wind. Scientists estimate a 12 percent increase in wind speed with each doubling of elevation.

M II A II R II K Oct 13, 2009 7:56 PM

Calculating Power

To calculate the amount of power a turbine can actually generate from the wind, you need to know the wind speed at the turbine site and the turbine power rating. Most large turbines produce their maximum power at wind speeds around 15 meters per second (33 mph). Considering steady wind speeds, it's the diameter of the rotor that determines how much energy a turbine can generate. Keep in mind that as a rotor diameter increases, the height of the tower increases as well, which means more access to faster winds.

At 33 mph, most large turbines generate their rated power capacity, and at 45 mph (20 meters per second), most large turbines shut down. There are a number of safety systems that can turn off a turbine if wind speeds threaten the structure, including a remarkably simple vibration sensor used in some turbines that basically consists of a metal ball attached to a chain, poised on a tiny pedestal. If the turbine starts vibrating above a certain threshold, the ball falls off the pedestal, pulling on the chain and triggering a shut down.

Probably the most commonly activated safety system in a turbine is the "braking" system, which is triggered by above-threshold wind speeds. These setups use a power-control system that essentially hits the brakes when wind speeds get too high and then "release the brakes" when the wind is back below 45 mph. Modern large-turbine designs use several different types of braking systems:
  • Pitch control - The turbine's electronic controller monitors the turbine's power output. At wind speeds over 45 mph, the power output will be too high, at which point the controller tells the blades to alter their pitch so that they become unaligned with the wind. This slows the blades' rotation. Pitch-controlled systems require the blades' mounting angle (on the rotor) to be adjustable.
  • Passive stall control - The blades are mounted to the rotor at a fixed angle but are designed so that the twists in the blades themselves will apply the brakes once the wind becomes too fast. The blades are angled so that winds above a certain speed will cause turbulence on the upwind side of the blade, inducing stall. Simply stated, aerodynamic stall occurs when the blade's angle facing the oncoming wind becomes so steep that it starts to eliminate the force of lift, decreasing the speed of the blades.
  • Active stall control - The blades in this type of power-control system are pitchable, like the blades in a pitch-controlled system. An active stall system reads the power output the way a pitch-controlled system does, but instead of pitching the blades out of alignment with the wind, it pitches them to produce stall.

vid Oct 13, 2009 10:46 PM

You should do a post about the claimed negative health affects caused by wind turbines in close proximity to homes.

M II A II R II K Oct 13, 2009 10:53 PM


Regulars can post and post threads, you post that!

vid Oct 13, 2009 11:47 PM

Well you just seem so much more eager to post things here, I thought it would look better if you did it. I mean, you do format those posts ever so well.

M II A II R II K Oct 14, 2009 1:45 AM

Video Link

Krases Oct 14, 2009 4:49 AM


I whipped out google sketchup real fast and made this. I basically took the same design and added lights. Wouldn't these make good streetlights?

Pictures courtesy of ME!

vid Oct 14, 2009 5:09 AM

I think the moving shadows would drive people insane, and I am willing to bet that so little energy would be produced (small turbine and low wind speeds) that it wouldn't be of much benefit to society. That's not even considering the cost of such a thing. In many places, regular street lights with solar panels on top (but still connected to the grid just in case) are probably sufficient, especially suburban areas where the street lights don't have to be so bright.

Try designing something that could be put onto a person's home though. I'd like to see things like that and solar panels become standard in single-family housing in the future.

Krases Oct 14, 2009 5:40 AM


Originally Posted by vid (Post 4504332)
I think the moving shadows would drive people insane, and I am willing to bet that so little energy would be produced (small turbine and low wind speeds) that it wouldn't be of much benefit to society. That's not even considering the cost of such a thing. In many places, regular street lights with solar panels on top (but still connected to the grid just in case) are probably sufficient, especially suburban areas where the street lights don't have to be so bright.

Try designing something that could be put onto a person's home though. I'd like to see things like that and solar panels become standard in single-family housing in the future.

Well the guy said the large sized model would produce 3 kilowatts which is twice as wide (same height) as the one in the video. A LED streetlight uses between a quarter or a half kilowatt. Four of them (or three) on top of one of a wind tower would be around a single kilowatt, meaning that the turbine generates an extra two kilowatts under good conditions.

I guess the light could be directed so as not to make people go crazy like you said. No light has to actually illuminate the blades and the blindspot underneath could be illuminated by a small set of LED's wrapped around the pole.

Plus it would be hooked into the grid so its extra power could be harvested and just in case it can't generate enough on a stagnant day. Plus it's not like we can't add solar panels on top of it all.

Actually, it wouldn't even need to be street lighting. I was thinking something more on the scale of athletic field lighting. We also have huge highway lights here in Vegas.

vid Oct 14, 2009 12:55 PM

You still have to consider how a strobe effect would affect drivers and athletes in those situations. You might not be able to avoid the flicker, especially with highway lights since those point pretty much straight down.

M.K. Oct 14, 2009 8:24 PM

every residential and office building should have one of those on top of it. We need more independence from power companies.

Doady Oct 14, 2009 11:21 PM

The problem with wind power is that is that large turbines are usually isolated and far from areas of demand. And the electricity generated fluctuates because of fluctuations in wind speed. So for both of these reasons, a lot of extra transmission capacity is needed to deal with the higher volumes of electricity. Plus, electricity is wasted during transmission, so longer distances just means more wasted electricity.

vid Oct 15, 2009 12:22 AM

But that isn't as much of a problem when it is small scale, home use wind turbines, or if they're in a parking lot or something.

Doady Oct 15, 2009 5:28 AM

Yeah, since they can be located right where the demand is, then they would be even more efficient than conventional power.

Nowhereman1280 Oct 15, 2009 2:43 PM

What kind of wind projects have been constructed near everyone? About 30 min north of my hometown in Wisconsin almost 300 MW of Wind Turbines have been constructed.

Here's a turbine being assembled in Wisconsin:

M II A II R II K Oct 22, 2009 2:58 PM

Windbelts: wind power without the turbine

We’ve covered micro-wind a number of times here, but I think this may be the coolest innovation I’ve seen in a while: inventor Shawn Frayne has come up with a device that harnesses the power of wind without any rotating parts. Instead, his company’s Windbelts capture energy using fluttering fabric.

You can best understand the process by watching this short video, but basically as moving air passes over a taut membrane, it induces a vibration, somewhat akin to a violin bow. Magnets mounted on the membrane bounce back and forth between metal coils, inducing an electric current.

Like solar cells, the technology is modular and can scale up or down to fit numerous applications. At the micro end of the scale, a palm-sized version of the device can act as the equivalent of dozens of AA batteries. Such tiny generators can be used to power remote sensors or other distributed infrastructure that would otherwise require costly wires or regular battery changes.

Scaling up, Frayne’s company has arranged Windbelts into modular arrays that can be deployed like fencing. The technology could find use in urban environments, to capture the energy from air moving past buildings or bridges. Or the systems can be deployed in the developing world, to provide electricity in places that the grid doesn’t yet reach.

Because the materials involved aren’t exotic — the belts themselves are made of mylar-coated taffeta, which is basically kite fabric — the systems can be easily serviced in the field. Best of all, they’re cheap. At a cost of about $1 per watt of capacity, Windbelts are many times cheaper than today’s solar panels.


TexasPlaya Oct 23, 2009 2:41 AM


Originally Posted by vid (Post 4505559)
But that isn't as much of a problem when it is small scale, home use wind turbines, or if they're in a parking lot or something.

They still don't work all the time and there is a reason why wind farms are located far away; there is sufficient amount of wind to generate a decent amount of power. It's a great idea to put small wind generators where economically feasible, but they are a small part of the solution to energy.

BTinSF Oct 23, 2009 3:07 PM


Friday, October 23, 2009
Costs for wind power rise as other energy drops
San Francisco Business Times - by Lindsay Riddell

Wind power developers see dark clouds on the horizon.

Wind power has historically been one of the cheapest forms of renewable power available — in many cases able to compete on cost with wholesale power from fossil fuels. But prices have crept up with the cost of steel needed for towers and turbines, the credit crunch and the decreasing number of available sites near transmission lines. Meanwhile, the price of natural gas has dropped, which may make utilities reconsider adding wind power.

At a recent conference, Peter Darbee, CEO of PG&E Co., said he was paying 10 to 12 cents per kilowatt hour for wind power this year, when in years past he paid 8 to 9 cents. Wind power makes up less than 2 percent of PG&E’s power supply today. While the utility said it’s still pursuing wind opportunities, “if the price of one kind of energy goes up relative to others, other things being equal, we’re likely to shift resources somewhat,” said PG&E spokesman Jonathan Marshall.

The economy isn’t helping speed the development of new wind resources in the state.

It took Pattern Energy six months to find the financing it needed for a 101 megawatt project in a windy region in Shasta County — about three times as long as it took in years past, said CEO Mike Garland. Pattern, based in San Francisco, develops energy projects, including wind, as well as transmission lines.

The cost of wind turbines and the towers that support them has not dropped, Garland said, partly due to pent-up demand for turbines that pushed prices up. Also, steel prices rose dramatically between 2005 and 2008 due to heightened demand, much of that from China, and have not come down.

“Everybody thought because the market went soft and the economy crashed and there wasn’t much building going on, that we should see immediate price reductions,” said Garland. That, he said, hasn’t happened yet.

But what’s really hurting the industry is not the cost of power, but the falling demand for power. When the economy is humming along, demand for power rises, pushing prices up and making renewable power better able to compete on cost.

Meanwhile, Garland said, some of the best sites for wind that are near existing transmission lines have already been developed.

A new transmission line funded by Southern California Edison in the Tehachapis southeast of Bakersfield could unlock 4,000 megawatts of wind and solar generation. But the first phase won’t be ready until late next year and the rest will come online in 2013 if everything goes according to plan.

“It’s not a surprise that things are slow while waiting for transmission, and as soon as that transmission is in we’re going to see a big jump,” said Nancy Rader, executive director of the California Wind Energy Association.

An American Wind Energy Association report released Oct. 20 highlights a third quarter that saw 1,649 megawatts installed — beating the second quarter as well as the third quarter of 2008. But those statistics might not tell the whole story as they represent projects funded before the recession that only came online recently. The report says manufacturing of wind turbines lags behind 2008 levels in production and new contracts. / (415) 288-4968

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