The Main Components of Wind Turbines

To help you select a wind turbine that’s built to last, let’s take a closer look at the main components of modern wind turbines, starting with blades and generators.

Blades

Blades are a vital component of a wind turbine. Manufacturers make blades from several different types of materials. Although wood was once commonly used to make blades for small wind turbines, we’re not aware of any companies that manufacture blades exclusively from wood. It’s just too expensive and time consuming. The blades of modern wind turbines are typically made of extremely durable and relatively inexpensive synthetic materials, various types of plastic or composites — plastic reinforced with fiberglass or carbon fibers, for example. These synthetic blades typically last between 10 and 20 years. And, unlike the metal blades
once used in small wind turbines, plastic blades don’t interfere with television, satellite TV or wireless Internet signals. Table 5.1 lists some examples of blade materials commonly used today.

Most modern residential wind machines — both upwind and downwind models — have three blades. Although certain manufacturers produce two- and six-blade turbines (for sailboats),
three-blade wind turbines are the industry standard. They provide the best overall performance. They are quieter and suffer less wear and tear than one- and two-blade models.

Generators

Most residential wind machines on the market contain permanent magnet alternators, described earlier, although larger turbines in the small turbine range, like the remanufactured Jacobs 31-20, incorporate electromagnets (magnets created by running electricity through wire coils in the alternator). most wind turbines produce wild three-phase AC, initially. The wild AC output is converted (rectified) to DC electricity by a rectifier. The rectifier may be located in the wind turbine itself or in the controller. Controllers are typically mounted next to the inverter or may be incorporated in the inverter. DC electricity is then sent to the battery bank.

At least one manufacturer (Endurance) is now producing a small turbine that contains an induction generator. This wind turbine produces grid-compatible AC power without the use of an
inverter. An induction generator looks a lot like electric induction motors used in modern society. When spun faster than its normal operating speed, an induction generator produces AC electricity. Because an induction generator synchronizes with the grid — that is, produces electricity at the same frequency and voltage — no inverter is required. But what features should you look for?

Wind Turbines

Most wind turbines in use today are horizontal axis units, or HAWTs, (explained shortly) with three blades attached to a central hub. Together, the blades and the hub form the rotor. In many wind turbines, the rotor is connected to a shaft that runs horizontal to the ground, hence the name. It is connected to an electrical generator. When the winds blow, the rotor turns and the generator produces alternating current (AC) electricity. (See the accompanying box for an explanation of AC electricity.)

One of the key components of a successful wind generator is the blades. They capture the wind’s kinetic energy and convert it into mechanical energy (rotation). It is then converted into electrical energy by the generator.

The generators of wind turbines are often protected from the elements by a durable housing made from fiberglass or aluminum (Figure 3.1a). However, in many modern small wind turbines, the generators are exposed to the elements (Figure 3.1b).

Most wind turbines in use today have tails that keep them pointed into the wind to ensure maximum production. However,

Fig. 3.1a and 3.1b: Wind Turbine Design. (a) The generators in many small wind turbines are housed in a protective case made from aluminum or fiberglass. (b) Others, like this one, are not.

some very successful turbines like those made by the Scottish company Proven (pronounced PRO-vin) are designed to orient themselves to the wind without tails.

AC vs. DC Electricity

Electricity comes in two basic forms: direct current and alternating current. Direct current (DC) electricity consists of electrons that flow in one direction through the electrical circuit. DC electricity is the kind produced by flashlight batteries or the batteries in cell phones, laptop computers, or portable devices such as iPods.

Most wind turbines produce alternating current electricity. In alternating current, the electrons flow back and forth. That is, they switch, or alternate, direction in very
rapid succession, hence the name. Each change in the direction of flow (from left to right and back again) is called a cycle.

In North America, electric utilities produce electricity that cycles back and forth 60 times per second. It’s referred to as 60-cycle-per-second — or 60 hertz (Hz) — AC. The hertz unit commemorates Heinrich Hertz, the German physicist whose research on electromagnetic radiation served as a foundation for radio, television and wireless transmission. In Europe and Asia, the utilities produce 50-cycle-per-second AC.

AC electricity is also produced by electrical generators in hydroelectric and power plants that run on fossil fuels or nuclear fuels. No matter what form of energy is used to turn a generator, all of them operate on the principle of magnetic induction — they move coils of copper wire through a magnetic field (or vice versa). This causes electrons to flow through the coils, producing electricity.