How a Wind Turbine Works: Page 5 of 5

Beginner

Inside this Article

Wind Turbine
Wind Turbine Up Close
An anemometer for measuring wind speed
An anemometer is a drag device that can’t spin any faster than the wind is moving. The upwind cup hinders it even further. Only through calibration does it register accurate wind speed. Drag devices are inefficient collectors of wind energy.
A three-bladed, permanent-magnet wind turbine
After reading this article, you’d be able to identify this as a three-bladed, upwind, direct-drive, permanent-magnet, side-furling wind turbine if you saw it in action.
A gearbox
In some cases, a gearbox is necessary to optimize blade/rotor rpm with alternator rpm (also note this turbine’s large disk brake).
An old Jacobs field-wound alternator
This old Jacobs field-wound alternator requires brushes to supply energy to the electromagnetic field on the spinning rotor.
Permanent magnets on the outer rotor allow a simple brushless design.
Permanent magnets on the outer rotor allow a simple brushless design. The windings are mounted on the inner immobile stator.
An axial PM alternator
This axial PM alternator has magnets on its rotor that spin past stationary coils face to face.
Brushes transmit electricity from a yawing turbine down a stationary tower
Brushes transmit electricity from a yawing turbine down a stationary tower without twisting wires.
Passive Upwind Yawing
Passive Upwind Yawing
Passive Downwind Yawing
Passive Downwind Yawing
Active Upwind Yawing
Active Upwind Yawing
Centrifugal force on the blades works a linkage to change blade pitch
Centrifugal force on the blades works a linkage to change blade pitch on an old Jacobs generator. This complex but highly effective governor precisely regulates rpm.
A side-furling governor uses the force of the wind to pivot the blades
A side-furling governor uses the force of the wind on an off-center joint to pivot the blades out of the wind. In this case, mechanical furling is used to brake the machine during maintenance.
Dynamic braking works by shorting all three wires together
Dynamic braking uses the alternator’s electromagnetism against itself by shorting all three wires together.
Wind Turbine
An anemometer for measuring wind speed
A three-bladed, permanent-magnet wind turbine
A gearbox
An old Jacobs field-wound alternator
Permanent magnets on the outer rotor allow a simple brushless design.
An axial PM alternator
Brushes transmit electricity from a yawing turbine down a stationary tower
Passive Upwind Yawing
Passive Downwind Yawing
Active Upwind Yawing
Centrifugal force on the blades works a linkage to change blade pitch
A side-furling governor uses the force of the wind to pivot the blades
Dynamic braking works by shorting all three wires together

Pitch control changes the orientation of each individual blade in high winds, taking them out of their optimum aerodynamic position so they don’t capture (or have to absorb) as much wind energy. This is typically accomplished with an arrangement with weights and springs. Governing happens incrementally as the rotational speed increases, and this strategy can be very precise, so it controls speed accurately and allows good production. This governing system may be more expensive than furling systems and is more prone to wear.

Stall is a speed-control method that relies on the inherent design of the blades, and results in poorer performance at high rotation. Stall regulation works by slowing down the blades in relation to the wind speed. If the rotational speed is constant (induction motor turbines, for example) and the wind speed increases, stall is inevitable—it just needs to be tuned to happen at the right wind speed.

Governing requires a delicate balance, regardless of what method is used, and relies on properly sizing and matching the various angles and offsets of the rotor and tail, the size and weight of blades, and the blade design. If any parameter is changed—making the blades longer or tail heavier, for example—you’ll change the turbine’s governing characteristics. 

Braking

In addition to governing—which needs to happen automatically in high winds—wind generators need the ability to be stopped manually. We do this when we: need to repair them; think there’s some problem; are expecting too-high winds; or when we simply don’t need the energy (for instance, with a seasonal residence or a long vacation).

Mechanical brakes can be drum brakes or disk brakes, and are often activated by a hand winch at the tower base. A few turbines use manual furling with a tower-base winch to swing the rotor out of the wind—this at least slows it, if it doesn’t fully stop the rotation.

Dynamic or electrical braking shorts the DC or wild AC output, stopping the turbine’s rotation. Depending on the alternator design and wire run, this can be very effective. In other cases, it’s iffy, and may not stop a machine in high winds, or hold it once stopped. Neodymium magnets have a more reliable effect for dynamic braking. Make sure you understand the limitations of dynamic braking for your particular machine.

Electronics

A crucial part of a wind generator system is the electronics needed. Each machine will have its own electronic systems, which may include:

  • Rectification to convert AC to DC.
  • Maximum power point tracking (MPPT) to get the most output from the wind generator by matching the charging curve to the wind power curve. This relies on a programmed wind power curve for the particular turbine used.
  • Charge controller to regulate battery charging (if used).
  • Metering and data logging to monitor system performance.
  • Circuit protection (breakers) is often included.

Making a Wise Choice

Understanding how a wind generator functions can help make wise buying and design decisions. Although wind generator specifics are discussed here, what you need is a whole system, which includes tower, transmission wire and conduit, electronics, and more. You need all the appropriate components, they need to be of high quality, and they need to be matched to each other. Usually, it’s best to buy everything as one package to avoid surprises and problems.

Tapping that flow of moving air can be a lot of fun, but I’m here to tell you that it ain’t easy. If you approach it sloppily or with a nickel-and-dime attitude, you’re more likely to get poor and costly results. Investing in a good product and system and installing it with attention to detail will give you dependable renewable energy, now and over the long haul.

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Ian Woofenden has been using, installing, fixing, consulting, and teaching about wind generators for more than 25 years in the Pacific Northwest. He is the author of Wind Power for Dummies, and one of the founders of the Small Wind Conference (www.smallwindconference.com).

Resources:

“Anatomy of a Wind Turbine” by Ian Woofenden & Hugh Piggott in HP116

“Estimating Wind Energy” by Hugh Piggott in HP102

“Wind Power Curves: What’s Wrong, What’s Better” by Ian Woofenden in HP127

“Understanding Wind Speed” by Ian Woofenden in HP143

“Estimating Obstruction Height” by Ian Woofenden in HP141

“Wind Turbine Transmission Wire Sizing” by Hugh Piggott in HP134

“Wind Electric System Basics” by Ian Woofenden in HP110

“Site It Right! An Interview with Wind Energy Consultant & Installer David Blecker” by Ian Woofenden in HP115

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