Blade Design

From Wind wiki

Wind turbine blades have developed a great deal since 1900. If in the past wood was widely used in making European windmills, now other materials such as metal and fiberglass have been utilized by wind turbine makers. However, the material used in designing blades depends on the size and purpose of the wind technology.

There are factors that contribute to the optimal efficiency of the blades. Some of these are the kind of material used, the shape and the number.

Material Used

Wood

Wood is often the material used for small turbines. Wooden blades are made from wood planks or wood laminates formed into the desired shape and finished with a weather-resistant coating. Its leading edge is covered by polyurethane tape, a tape similar to the one used on helicopter blades, for protection from erosion or hail damage. Wood planks are good for machines with a diameter of 5 meters (16 ft) or less while laminated wood is more preferred for bigger turbines. The latter has less tendencies of shrinking and warping and gives more control over the strength and stiffness of the blades.

The laminated wood proves stronger than a single plank because it’s composed of slabs of wood joined together by a resin then shaped into your desired shape.

Metal

Wooden blades were replaced by different metals in the late 19th century. The first one is galvanized steel, which is considered strong so it is used in bigger wind energy projects.

On the contrary, aluminum is lighter and stronger. Possible of being extruded, aluminum poses two drawbacks: it costs too much and experiences metal fatigue. Metal fatigue is like breaking a piece of wire by flexing it back and forth. Aluminum is a good material though there hasn’t been any documented successful use of it yet.

Fiberglass

Fiberglass is the dominant material used in wind turbine blade construction. A wind turbine using a fiberglass blade] Also called glass-reinforced polyester, fiberglass is strong, sold at a relatively reasonable price, and possesses good fatigue characteristics. One thing that makes it in demand is that it can be made through different processes. For example, aside from being extruded, it can also be pultruded where instead of pushing the material to a die, fiberglass cloth is pulled through a vat of resin then through a die.

Shape

As for the shape, wind turbines can either have tail vanes or fan tails. Fan tails mechanically turn the rotor to the wind’s direction. The simple tail vane, as opposed to fan tails, helps the rotor keep directed to the wind even though it changes direction.

Both fan tails and tail vanes, with the wind force, orient the rotor to flow upwind. But when the rotor is placed downwind of the tower, tail vanes or fan tails are not necessary anymore. What it needs instead is a set of blades swept slightly downwind, which forms a coning shape on the rotor. Because downwind machines look sleeker than tail-vaned or fan-tailed turbines, many people consider them modern.

Number

A single blade is not enough to capture the energy of the wind. It may be possible to operate yet it will need a much higher rotor speed than a two-blade turbine. This means that the gear ratio required for the transmission will be reduced as well as the cost of the gearbox. Because of this, a single long blade is considered to be delivering optimal efficiency.