Wind Energy

What are the Advantagess?

• Cost effective (land-based utility-scale wind is one of the lowest-priced sources that costs approximately 1 - 2 cents per kilowatt-hour after production tax credit) [6]
• Creates jobs
• Enables industry growth
• Clean fuel source
• Domestic energy source
• Sustainable
• Can be built on existing farms or ranches (best wind locations are on rural areas)

What are the Disadvantages?

• Wind power must still compete with conventional generation sources on a cost basis [6]
• Good land-based wind sites are often located in remote locations far away from cities where electricity is needed which requires transmission lines to be built
• Might not be the most profitable use of the land
• Turbines cause noise and aesthetic pollution
• Wind plants negatively impact local wildlife

Parts of a Turbine

Generator

The driving force to create the electrical current is created by using the difference in electrical charge to create a change in voltage. The current is then passed through power lines for distribution in the grid [4]. At commercial production level, all electricity generation is in the three-phase alternative current. Therefore, the choice of generators consist of a synchronous generator, which turns at a tightly controlled constant speed to maintain a constant frequency, and an asynchronous generator (also known as an induction generator), which means that the waveform generated is not synchronized to the rotational speed. For wind turbines, the generator commonly used is an induction generator due to the generator having to be rotated at a speed corresponding to the frequency of the electric network, it must be rotated faster than the turbine rotor. Pitch control is when the blade’s angle can be adjusted so that the power output from a turbine is always maximized without overloading the generator and mechanical structures of the blades, tower, and the rotor shaft. The power curve is the performance curve that shows the ratio of power to wind speed carried out from each turbine [3].

Nacelle

The nacelle houses a wind turbine’s generator and is commonly manufactured as either gear-driven or direct drive. Gear-driven can comprise a case as heavy as 150 tonnes whereas direct drive comprises a rotor hub which directly drives the generator without having a gear trim arrangement [4]. Yaw-motion is when the nacelle and the rotor revolve about the tower axis [3].

Tower

Wind turbine towers all have different heights depending on the purpose. Average height of a tower is 50 m and the tallest one is greater than 200 m. The towers are coated with zinc-based finish and epoxy and urethane layers to provide ultraviolet resistance. The average weight of a tower is greater than 40 tonnes and depending on the type of tower, it can account for more than 10% of the total cost of the turbine [4]. To determine the turbine height, the rule of thumb is that the height is the same as the diameter of the circle the rotor blades create while in operation [3].

Rotor Blades

The blades on a turbine can reach speeds of 160 mph when in operation which require robust construction [4]. Normally there are three blades as that has the best efficiency and other advantages but it is possible to have a turbine with two, four or another number of blades. The blade itself is not solid. They are hollow and are made of composite material (e.g. wood, fiberglass, resin, carbon, etc.) so they can be light and strong. The main objective is to make the blade as big as possible while maintaining strength and lightweight. The blades are formed with an airfoil (wings of an airplane) with a twist between their root and tip to be aerodynamic. Blade pitch is when a blade can rotate up to 90^o about their axes [3].

Hub

The purpose of the hub is to hold the blades and make it possible for them to rotate with respect to the rest of the turbine body [3].

Foundation

For onshore turbines, the foundation is under the ground as it is covered by soil. For offshore turbines, the base is under the water and cannot be seen either. The foundation is composed of concrete as it must be able to hold the entire turbine and the forces exerted on it [3].

How is the Energy Harnessed?

The wind turns the propeller-like blades of a turbine around a rotor which spins a generator, creating electricity. Wind is a form of solar energy that is created by the heating of the atmosphere by the sun, the rotation of the Earth, and the Earth’s surface irregularities. Wind flow patterns are modified by large bodies of water, vegetation, and differences in terrain [2]. “A wind turbine turns wind energy into electricity using the aerodynamic force from the rotor blades, which work like an airplane wing or helicopter rotor blade. When wind flows across the blade, the air pressure on one side of the blade decreases. The difference in air pressure across the two sides of the blade creates both lift and drag. The force of the lift is stronger than the drag and this causes the rotor to spin. The rotor connects to the generator, either directly (if it’s a direct drive turbine) or through a shaft and a series of gears (a gearbox) that speed up the rotation and allow for a physically smaller generator. This translation of aerodynamic force to rotation of a generator creates electricity.” [2].