A wind turbine converts kinetic energy from wind into 'rotary mechanical energy' which is used for doing work. In sophisticated models, rotational energy is converted to electricity with the help of a generator.
People have been using windmills for thousands of years for grinding grain or pumping water. Slender, tall multi-vaned wind turbines made of metal were used in American ranches and homes for pumping water into the plumbing system of the house or into the watering trough of cattle.
Palmer Cosslett Putnam conceived the first large-scale wind turbine in the US. It was capable of supplying electricity to a small town; however, it was later abandoned due to mechanical failure.
In the 1970s, wind turbines used more and more for generating electricity. The model that is currently popular and widely produced commercially includes a horizontal-axis turbine with a 100 kW capacity and three blades not more than 30 m length.
Wind turbines with three blades are better than those with two blades as they spin more smoothly and are easy to balance. Although smaller turbines produce less energy, they can be maintained easily and mechanical failure is less likely.
'Three turbines are better than two' - smooth and easily balanced these types of turbines are better suited to large wind farms. Image Credit: Photos.com
Components of a Wind Turbine
A wind turbine includes the following basic components:
- Tower - Either a steel tubular tower with an inner ladder leading to the nacelle or a steel lattice tower similar to electrical towers. The tower must be built so it absorbs the heavy static loads applied due to wind’s varying power.
- Rotor and rotor blades - The rotor along with the rotor blades converts wind energy into rotary mechanical movement. Presently, the three-blade horizontal axis rotor is the most popular. The rotor blades are mainly made of reinforced carbon-fibre plastics or glass fibre. The blade profile is similar to that of an aeroplane wing.
- Nacelle with drive train - All turbine machinery is held in the nacelle. Since it should be able to rotate in the direction of the wind, it is connected to the tower through bearings. The gearbox is needed for converting the rotor motion of 18-50 rpm to approximately 1500 rpm as required by the generator. For high-power wind turbines asynchronous, double fed generators are used most frequently. Synchronous generators are also used. Due to high torque, the coupling between the transmission and the main shaft is rigid. The brake type is based on the blade control mechanism.
- Electronic equipment - The wind turbine’s electronic equipment comprises of the electricity grid infeed system and a number of sensors. Sensors for measuring wind direction, temperature and wind speed are found around the nacelle and enable turbine monitoring and control.
- Other components - The wind turbine includes components for heating, cooling, following wind direction, lifting gear and fire extinguishing equipment.
'A large operation' - There are several key components needed for construction of wind turbines. Image Credit: Photos.com
Construction Process of Wind Turbines
The following steps are followed for turbine construction:
- First the tower is constructed. The steel sections of the tower may be made offsite in a factory but they are normally assembled on the site. The parts are bolted together and the tower is kept in a horizontal position till it is placed. The tower is lifted into position by a crane, bolts are tightened and on completion, stability is tested.
- The fiberglass nacelle is installed next. The gear box, main drive shaft, yaw controls and blade pitch are assembled and mounted onto a base frame at a factory. The nacelle is bolted enclosing the equipment and at the site, the nacelle is lifted on the completed tower and fixed. The nacelle is usually made of fiber glass and includes the gearbox and the main drive shaft.
- Experimentation with new materials for the blades has taken place. In commercial wind turbines, fiberglass with a hollow core is used for the blades; however, aluminium and lightweight woods are also used. Aluminum blades are made by bolting aluminum sheets together, and wooden blades are carved forming an aerodynamic propeller with a similar cross-section as found on an airplane wing. Fiberglass blade manufacture is comparatively tedious. First a mold in two halves shaped like a blade is made. The inner surfaces of the mold are coated with fiberglass-resin composite mixture. The fiberglass mixture must dry for several hours and an air-filled bladder in the mold helps it to retain its shape. The mold is opened after the fiberglass is dry and the bladder is taken out. The blade is then cleaned, sanding is done, the two halves are sealed and then painted.
- The blades are normally bolted on the nacelle after placing it on the tower. Normally a three-pronged blade has two blades on the nacelle before it is lifted and the third blade is bolted after the nacelle is in place.
- The utility box for the wind turbines and electrical communication system for the windfarm is installed along with placing the blades and the nacelle.
'Bolted in' - in the final stage of the construction process the blades are bolted in - Image Credit: Photos.com
Wind turbines are subjected to regular maintenance to reduce failure. There is an inspection every three months and every six months there is a key maintenance check.
The moving components are lubricated and the oil levels in the gearbox are checked. The electrical system is also checked.
The Future of Wind Turbines
The future is only going to get better for wind energy and turbines. Research is currently being undertaken to improve wind resource knowledge. More areas are being tested for wind farms based on the strength and reliability of wind in that area.
New materials are being tested for increasing the efficiency of the blades, providing improved controls, developing long-lasting drive trains and allowing better grounding and surge protection.
'Where next?' - areas with strong reliable windflow would be suitable for wind farm construction. Image Credit: Photos.com