Blade construction of wind turbine defined.
Wind turbine blades are hollow; otherwise their weight would be tremendous, even with a lightweight material, and their use would be impossible. They might not even start to move the rotor.
It is, however, necessary that they have a sturdy structure to withstand all the stress from various loads, and work for the useful life of a turbine.
The blades of a turbine spinning at 14 rpm must go through 175 million cycles in 25 years. Blade shells are made from composite material that is light and strong.
Inside, they must have structural support for the shell. The internal structure can be made from wood or a similar lightweight material.
The shape of blades, their construction, and the other related subjects are to be determined based on careful and extensive studies, and experiments if needed.
One of the important issues in new blades is the integration of a lightning rod in the blade structure. The lightning rod is a strip of copper along the blade.
At some point at the tip of a blade it is exposed to the outside by a small disk. At the other end, it is connected to a metallic counterpart in the hub. Through a number of metal connectors, the strip in the blade ultimately makes a connection to the ground through the tower.
If a blade becomes damaged in operation, it must be repaired. Normally the broken parts must be cut, replaced by pieces of the same size, and glued together by the proper material. Depending on the severity of damage, this can be done while the blade is in the air, or it may have to be brought down to the ground.
Any repair work on the blades is a costly job and involves loss of production.
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