Every developed nation looks up to India; here a windmill was built as early as 1730 at Horse Tail Point in Cuddalore. Concrete as a material of construction can play an important role in realising the potential of wind energy. The trend towards increasing generating capacity of windmills makes concrete a competitive material. Concrete as material of construction is durable.
India ranks fifth amongst top ten wind power producers in the world. As on 31 March 2015, the installed capacity of wind power in India was 23,444 MW, mainly spread across Tamil Nadu (7,253 MW), Gujarat (3,093MW), Maharashtra (2,976 MW), Karnataka (2,113 MW), Rajasthan (2,355 MW), Madhya Pradesh (386 MW), Andhra Pradesh (916 MW), Kerala (35.1 MW).
Out of which, Tamil Nadu continues to maintain No.1 position in the country in wind power with 42% of total installed capacity in India. Currently, windmill projects are running in various parts of the country where Schwing Stetter equipment’s are in action.
Schwing at Windmill Projects:
Schwing Stetter has always been on the forefront for concreting Green Energy projects –a place where clean energy is produced with no emission of hazardous waste and no consumption of fossil fuels. Wind Energy is the least expensive form of renewable energy.
The company Enercon is a pioneer in the construction of wind power stations and their integration into the power grid. The focus here is on considerable higher nominal outputs of the generators and thus on greater heights of the rotor hubs. The rated output of the plants has risen in the last few years from 600 kW to 7,500 kW and the height of the rotor hubs from 45 m to 136 m. In order to make the foundations fit for withstanding all the higher static and dynamic loads, their volumes had to be enlarged accordingly. These heavy-duty foundations require nowadays up to four times as much concrete as the foundations 10 years ago.
Concreting the Windmill:
Concreting is the major work in the windmill tower construction. Schwing Stetter equipment’s are used for concreting their windmills across India. The windmill projects consist of various concrete structures and types, which are considered to be a very challenging task. Depending upon the site conditions both in-situ and pre-cast construction methods have been used for the wind tower construction.
The Construction work in these projects consists of precast concrete towers, which are made using specially developed pre-stressed steel reinforcement. The individual tower sections and foundation are fastened together to form an inseparable unit with stay cables running through jacket tubes in the core of the concrete tower wall. Tubular steel tower, Tubular concrete, Lattice tower, Three legged tower, Guy wired tower, Hybrid tower are the different types of the wind tower.
The tower sections are manufactured in a pre-casting plant. The pre-casted segments of tower sections are prepared by casting concrete in reusable molds in a controlled environment. Specially constructed steel moulds assure manufacturing precision for each individual concrete section. This manufacturing process minimizes dimensional tolerances, which assures a high degree of fitting accuracy.
The advantages of pre-stressed concrete towers include stiffness in case of extreme load capacity, better fatigue properties over steel, unlike steel tower there is no risk of buckling and lower material cost. The foundations are circular. The piles, symmetrically arranged, are slightly inclined so that the imagined extended pile centerlines meet at a point above the center of the foundation.
This provides maximum force/load distribution over the entire surface. The post-tensioned segmental concrete tower design consists of a number of arc segments that combine to form circular sections that are stacked on each other and made to act together in a monolithic manner by post-tensioned high strength tendons that pre-compress the concrete so that it is nearly always in compression to applied loads.
The Towers are made from M55 grade concrete. Schwing Stetter’s Batching plants like HN2.25 with Stetter pan mixer and wirvler along with two discharges are used for precasting the tower and the circular foundation.
Windmill towers are constructed using massive amounts of concrete in which our Schwing stetter batching plants, truck mounted boom pumps contributions are enormous. The prolonged service life of concrete and its ability to cope with increasing loading allows possible retrofitting of turbines after their initial 20 year design life. Therefore, longevity from the concrete avoids the financial and environmental costs of construction.