FAQ
Wind is air in motion. Wind is mainly formed due to the Earth’s rotation and the uneven heating of Earth’s surface by sunrays. The sunrays cover a much greater area at the equator than at the poles. The hot air rises from the equator and expands toward the poles that cause wind.
Air has a mass and mass in motion has a momentum.
Momentum is a form of energy that can be harvested.
Where:
- Pwind = Power in the wind (W/m²)
- ρ = Air density (kg/m³)
- A = Projected area (m²) (wind turbine rotor area)
- V = Average wind speed (m/s)
The power increases with the cube of wind speed.
A wind turbine is a system which transforms the kinetic energy available in the wind into mechanical or electrical energy that can be harnessed for any required applications. Mechanical energy is most commonly used for pumping water. Wind electric turbines generate electricity that can be utilized locally or transported to the desired location through grid.
There are two basic configurations of Wind Turbines. One is Vertical axis wind turbine and the other is Horizontal axis wind turbine. The horizontal axis turbine has seen technological and economical growth and it has become the commonly used commercial turbines on large scale and the vertical axis turbines are still in the demonstration purpose and small scale applications.
Rotor
The blades and the hub together are called the rotor. It is the rotating component which converts kinetic energy available in the wind to mechanical energy.
The rotor hub connects the rotor blades to the rotor shaft. It is also the place where the power of the turbine is controlled physically by pitching (a method of controlling the speed of a wind turbine by varying the orientation of the blades).
Hub is one of the critical components of the rotor requiring high strength qualities.
Blades
Blade is a rotating component designed aerodynamically to work on the principle of lift and drag to convert kinetic energy of wind into mechanical energy.
Most turbines have either two or three blades. Mechanical applications like pumping water require more blades as it needs more torque.
Blade length is a key factor determining the power generation capacity of a wind turbine.
Nacelle
The nacelle is an enclosure that sits atop the tower and contains the gearbox, shafts, generator, controller, and brake.
It protects turbine components from weather conditions and reduces noise.
Low-speed Shaft
The low-speed shaft transfers torque from the rotor to the drivetrain and supports the weight of the rotor. It connects to the gearbox to increase RPM.
Gear Box
The gearbox increases rotational speed from about 30–60 rpm to 1000–1800 rpm required by generators.
It is one of the costliest components. Some turbines use direct-drive systems that do not require gearboxes.
Types: Planetary Gear Boxes, Parallel Shaft Gear
High-speed Shaft
Transmits speed and torque from the gearbox to the generator.
Brake
Brakes are used to stop the turbine during high winds or maintenance.
Types:
- Mechanical Brake (Disc brake, clutch brake)
- Aerodynamic Brake (Tip brake, spoilers)
Generator
Converts mechanical energy into electrical energy, usually producing 50-cycle AC electricity.
Types:
- Synchronous Generator (Electrically excited, Permanent magnet)
- Asynchronous Generator (Squirrel cage, Slip ring)
Controller
The controller starts the turbine at cut-in wind speed (~3 m/s) and stops it at cut-out wind speed (~25 m/s).
It monitors and controls parameters like voltage, current, frequency, temperature, wind speed, direction, vibration, pressure, and safety systems.
Anemometer
A sensor used to measure wind speed. It provides input to the controller for power regulation and braking.
Pitch
Blades are pitched to control rotor speed and protect the turbine during extreme wind conditions.
Tower
The tower elevates the turbine to higher altitudes for better wind energy capture and transfers structural loads to the ground.
Types: Lattice, Tubular, Guyed, Hybrid
Foundation
Supports and absorbs loads from the turbine. The type depends on soil and site conditions.
Onshore Types:
- Slab Foundation
- Pile Foundation
Offshore Types:
- Monopile
- Gravity Base
- Tripod
Wind Vane
Measures wind direction and communicates with the controller for proper turbine alignment.
Yaw Drive
Rotates the nacelle to face the wind using a gear system.
Yaw Motor
Powers the yaw drive mechanism.
Axis orientation: Horizontal/Vertical
Power control: Stall / Variable Pitch / Controllable Aerodynamic Surfaces / Yaw Control
Yaw Orientation: Driven Yaw / Free Yaw / Fixed Yaw
Rotor Position: Upwind / Downwind
Transmission: with gear / without gear
Type of Hub: Rigid / Teetered / Hinged blades / Gimbaled
Generator Speed: Constant / Variable
Number of Blades: One, Two, Three, multi-bladed.
Location: on-shore / Off-shore
Asynchronous generator (constant / variable speed / preferably high speed generators)
Synchronous generator (variable speed / slow speed)
Doubly fed induction generator
1. Tubular steel tower
Area of contact is more – hence more loading but evenly distribution– attractive – cost is more.2. Tubular concrete
Area of contact is more – high elasticity – loading high but even distribution – cost slightly less.3. Lattice tower
Area of contact is less – less loading – load distribution is uneven – transportation / fabrication easy.4. Three legged tower
Area of contact is less – less loading – load distribution is uneven – transportation / fabrication easy.5. Guy wired tower
Area of contact is less – less loading – load distribution even – transportation / fabrication easy and not suitable for huge wind turbines.6. Hybrid tower
A combination of tubular and lattice- Less obstruction- Strong FSpecified wind speed at which a wind turbine’s rated power is achieved. Relationship between wind speed (x) and power (y) (source: powernaturally.org)
The survival wind speed is the maximum wind speed that a wind turbine is designed to withstand
The ability of a turbine to generate electric power is measured in Watts (The rate of energy transfer equivalent to 1 Ampere of electric current flowing under a pressure of 1 Volt at unity power factor). Watts being a small unit of power, kilowatts (kW = 1000 Watts) and Mega Watts (MW = 1 million Watts) are the most commonly used units to describe the generating capacity of wind turbines and any power generating unit in general. Electricity production and consumption are most commonly measured in kilowatthours (kWh). A kilowatt-hour means one kilowatt (1,000 Watts) of electricity produced or utilized in an hour (To light up a 100 Watts bulb for 10 hours requires 1 Kilowatt-hour of electricity). Watt-hour is the electrical energy unit of measure equal to 1 Watt of power supplied to, or taken from, an electric circuit steadily for 1 hour. The power produced by a wind turbine depends on the turbine’s size and the wind speed through the rotor. In India, we have the commercial large wind turbines from 225 kW to 2.5 MW. In the global market, 6 MW wind turbines are operating and turbines of 10 MW are in laboratory stage. Wind speed and a wind turbine size are the factors that determine the power generation capacity of a wind turbine installation. Usually, wind resource assessment is done prior to a wind system’s construction. The power (energy/second) available in the wind will be given by the formula Power = 0.5 x rotor swept area (m2 ) x density (kg/m3 ) x velocity3 (m/s) It can be noted that the power generated is cube of the wind velocity and because of this, even a small difference in wind speed will bring about a large difference in available energy and in electricity produced and therefore, a large difference in the cost of electricity generated.
A 100 kW wind turbine produces 100 kWh or units of electricity after running for an hour, at its rated wind speed of about 12 – 14 m/s. Likewise, a 250kW turbine at its rated wind speed of about 12m/s produces 250 kWh after 1 hour of operation.
Alignment of rotor surface area facing the wind direction is called yawing. In detail, rotation of the rotor axis about a vertical axis (for horizontal axis wind turbine only) is called yawing.
Yes, to achieve more power generation, the turbine should require more wind speeds with velocity, which will be available in a good elevation. If the rotor is placed at a height where the flow is least obstructed by obstacles and as the height increases the wind faces less friction from its nearest surface.
Yes, but the generation will be less when the air is humid and has larger percentage of water molecules. if the air is dry and has no water molecules, a wind turbine will produce more power.
Generally, the present wind turbines are designed to last for a period of 20 years. It can also be designed for more than 20 years, only thing is the machine will be far more bulky and costlier than what is available now and would be prohibitive as a alternative to explore economically.
When the wind speed is high beyond cut-out speed, the turbine stops producing power and goes into an inert state to avoid components’ stress and damages. Normally the machines are manufactured with safety incorporation to cater to most of the conceivable emergencies.
Yes, small wind turbines are mountable on roof top for domestic applications. Right now, in India, mostly small wind turbines are stand alone which stores power in battery and in some of the western countries even small wind turbines are connected to the local grid. Small wind turbine with capacity ranging from 300 W to 25 kW are now available in Indian market and gaining popularity.
The most economical application of wind turbines is in groups of large machines. They are called ‘Wind farms’ or’ wind power plants’. Wind plants can vary in size from a few Mega Watts to hundreds of Mega Watts in capacity.
Normally, the powers produced by large wind turbines are connected to the state / central electricity grid whereas smaller wind turbines normally charged into a battery. Now a day lots of encouragement steps are being initiated to couple small wind turbine into grid. The power concentrated to the grid can be sold to the state utility / any private party / can also be used for captive use by paying wheeling charges alone.